Distributed database management system including logical database constituted by a group of physical databases

Abstract

A distributed database management system includes a communication network, at least a terminal device including an application program execution unit connected to the communication network, a plurality of information processors connected to the communication network, a plurality of physical databases installed in at least one of the information processors, at least a logical database grouping a plurality of the, physical databases, the logical database being defined by logical database information stored in at least one of the terminal device and the plurality of information processors, at least a table stored in at least one of the physical databases, and a table location searching unit installed in at least one of the terminal device and the plurality of information processors, for searching a table stored in at least one of the physical databases based on the logical database information, the table being requested to access on a logical database, from the application program execution unit.

Claims

What is claimed is:

1. A distributed database management system comprising:

a communication network;

at least a terminal device including application program execution means connected to said communication network;

a plurality of information processors connected to said communication network;

a plurality of physical databases installed in at least one of said information processors;

at least a logical database grouping a plurality of said physical databases, said logical database being defined by logical database information is stored in at least one of said terminal device and said plurality of information processors;

at least a table stored in at least one of said physical databases; and

table location searching means installed in at least one of said terminal device and said plurality of information processors, for searching a table stored in at least one of said physical databases, when said table is requested from said application program execution means, by searching a group of physical databases defined in said logical database information.

2. A distributed database management system according to claim 1, wherein said logical database information includes a priority order of each physical database constituting the logical database; and

wherein said table location searching means searches for a database stored in the desired table on the physical database on the basis of the priority order of said logical database information.

3. A distributed database management system according to claim 1, wherein said logical database information includes access privilege information for the logical database; and

wherein said table location searching means checks an access privilege of an application program user instructed from said terminal device prior to access to the logical database.

4. A distributed database management system according to claim 1, wherein said logical database information includes account information for identifying whether to approve said request or not, of the physical database constituting the logical database; and

wherein said table location searching means logs in the physical database constituting the logical database based on the account information of said logical database information for identifying account information issued from an application program in said terminal device.

5. A distributed database management system according to claim 4, wherein said table location searching means checks the account information received from the application program in said terminal device with the account information of said logical database information prior to access to the logical database.

6. A distributed database management system according to claim 1, wherein said logical database information includes account information for identifying whether to approve said request or not, of the physical database constituting the logical database; and

wherein said table location searching means logs in the physical database constituting the logical database using account information corresponding to the physical database of said logical database information on the basis of account information issued from an application program in said terminal device.

7. A distributed database management system according to claim 1, wherein said logical database information includes identification information of a physical database constituting the logical database and a password as account information of the physical database.

8. A distributed database management system according to claim 1, wherein a desired database processor (server) is a processor among said plurality of information processors each having a physical database management system and a physical database.

9. A distributed database management system according to claim 1, wherein one of said plurality of information processors is a gateway server located between a plurality of information processors as database servers having said terminal device, a physical database management system, and a physical database, via said network each having distributed database access management means for managing said plurality of database servers.

10. A distributed database management system comprising:

a communication network;

at least a terminal device including application program execution means connected to said communication network;

a plurality of information processors connected to said communication network;

a plurality of physical databases installed in at least one of said information processors;

at least a logical database grouping a plurality of said physical databases and account information for identifying whether to approve an access to at least one of said physical databases, said logical database and said account information being defined by logical database information stored in at least one of said terminal device and said plurality of information processors; and

account information searching means installed in at least one of said terminal device and said plurality of information processors, for searching account information for logging in a physical database constituting said logical database using the account information held in said logical database information, said account information for said logging in being inputted in an access to a logical database, said access being issued from said application program execution means.

11. A distributed database management system according to claim 10, wherein a desired database processor (server) is a processor among said plurality of information processors each having a physical database management system and a physical database.

12. A distributed database management system according to claim 10, wherein one of said plurality of information processors is a gateway server located between a plurality of information processors as database servers having said terminal device, a physical database management system, and a physical database, via said network each having distributed database access management means for managing said plurality of database servers.

13. A distributed database management system which is an information processor which is connected to at least one physical database holding a table via a physical database management system for managing said physical database, and is connected furthermore to application program execution means for accessing said physical database, receiving an access statement for accessing physical databases which is issued by said application program execution means, selecting one of said physical databases as an access object, and transferring said access statement to the physical database management system for managing said physical database, comprising:

a logical database dictionary for holding information on a logical database in which at least one of said physical databases is grouped;

a logical database defining unit for registering information on said logical database in said logical database dictionary;

a statement buffer for holding said access statement;

a logical database access controller for receiving an access statement from said application program execution means and storing it in said statement buffer; and

a table location searching unit for transferring said access statement held in said statement buffer to the physical database management system for managing said physical database by selecting one of said physical databases as an access object;

wherein said table location searching unit includes means for receiving an access statement for instructing logging in the database, for selecting one of said physical databases belonging to the instructed logical database as an access object of said access statement when the database which is instructed to be connected is registered in said logical database dictionary as said logical database, for selecting another one of said physical databases belonging to the instructed logical database as an access object of said access statement when a response of access refusal is given to the transfer of said access statement, and for transferring said access statement held in said statement buffer once again.

14. A distributed database management system according to claim 13, wherein said information on the logical database includes identification information of the logical database, and a priority order of at least one of said physical databases, wherein each identification information of at least one physical database belonging to said logical database; and

wherein said table location searching unit includes means for deciding an access object of said access statement according to said priority order of at least one of the physical databases included in said information on the logical database held in said logical database dictionary.

15. A distributed database management system according to claim 13, wherein said information on the logical database includes identification information of the logical database, a priority order of said physical databases belonging to the logical database, and identification information of each of said physical databases belonging to the logical database; and

wherein said table location searching unit includes means for selecting a highest priority physical database as an access object of said access statement according to said priority order of at least one of the physical databases included in said information on the logical database held in said logical database dictionary, when said access statement to be transferred is a statement for instructing creation of tables.

16. A distributed database management system according to claim 13, wherein said information on the logical database includes access privilege information for said logical database; and

wherein said table location searching unit includes means for checking an access privilege of said application program execution means which issues said access statement using said access privilege information which is held in said logical database dictionary, prior to transfer of said access statement and for refusing transfer of said access statement when there is no access privilege.

17. A distributed database management system according to claim 13, wherein said information on the logical database includes identification information of the logical database, and identification information of each of said physical databases belonging to the logical database; and

wherein said table location searching unit includes means for rewriting the logical database identification information of said access statement held in the statement buffer, which is to be logged in to decided identification information of the physical database when said access statement to be transferred designates the identification information of the logical database and instructs logging in and for transferring said rewritten access statement to the physical database management system for managing said physical database by selecting said decided physical database as an access object.

18. A distributed database management system according to claim 17, wherein said information of the logical database has at least one logical database account having at least one user identifier and password which are permitted to access said logical database furthermore; and

wherein said table location searching unit includes means for checking whether the logical database account described in said access statement coincides with one of logical database accounts held in said logical database dictionary prior to transfer of said access statement and for refusing transfer of said statement when there is no coincidence.

19. A distributed database management system according to claim 17, wherein said information of the logical database has a physical database account having a user identifier and password which are permitted to access said physical database according to each identification information of said physical database furthermore; and

wherein said table location searching unit includes means for rewriting the logical database account of said access statement held in the statement buffer to said physical database account held in said logical database dictionary prior to transfer of said statement furthermore when said access statement to be transferred instructs logging in the database.

20. A distributed database management system according to claim 19, wherein said logical database dictionary has a logical database control block and a logical account control block as a storage area of information on said logical database, and said logical database control block is installed in each said logical database and holds at least the identification information of said logical database and the identification information of at least one physical database belonging to said logical database, and said logical account control block is installed for each said logical database account and holds a physical database account having at least the identification information of said physical database which is permitted to access by said logical database account and the identifier and password of a user who is permitted to access said physical database; and

wherein said table location searching unit includes means for selecting the physical database indicated by the physical database identification information which is held in said logical database control block holding said logical database identification information and said logical account control block holding said logical account in common as said access object when said logical database identification information and said logical database account are described in said access statement.

21. A distributed database management system according to claim 20, wherein said logical database defining unit includes means for receiving input of said logical database account, encrypting the physical database account included in said information by using said logical database account as a key, and storing it in said logical database dictionary when the information of said logical database is registered in said logical database dictionary; and

wherein the physical database account rewriting means of said table location searching unit includes means for receiving input of said logical database account, decrypting the encrypted physical database account which is held in said logical database dictionary in correspondence with the identification information of the physical database decided as a transfer object by using said inputted logical database account as a key, and using it so as to rewrite said logical database account.

22. A distributed database management system according to claim 21, wherein said table location searching unit includes means for refusing transfer of said access statement when decryption of the physical database account stored in said logical database dictionary fails.

23. A distributed database management system according to claim 20, wherein said logical database dictionary has a logical account control block for holding at least the identification information of said physical database which is permitted to be accessed by said logical database account and the physical database account of said physical database for each said logical database account as a storage area of said physical database account for information on said logical database, and rewriting of said database account is to rewrite the account of said logical database of the access statement held in said statement buffer to an account corresponding to the physical database identification information which is decided as an access object among the physical database accounts held in said logical account control block which holds said described logical database account when said logical database account is described in said access statement.

24. A distributed database management system according to claim 23, wherein said table location searching unit includes means for transferring said logical database account without rewriting it when said logical account control block holding said described logical database account is not in said logical database dictionary.

25. A distributed database management system according to claim 23, wherein said table location searching unit includes means for transferring the access statement without rewriting said logical database account when the account of the physical database which is decided as an access object is not in said logical account control block which holds said described logical database account furthermore.

26. A distributed database management system according to claim 20, wherein said information of the logical database has a physical database account having a user identifier and password which are permitted to access said physical database according to each identification information of said physical database furthermore; and

wherein said table location searching unit includes means for rewriting the logical database account of the logical database of said access statement held in the statement buffer to said physical database account held in said logical database dictionary prior to transfer of said statement furthermore when said access statement to be transferred instructs logging in the database.

27. A distributed database management system according to claim 17, wherein said logical database dictionary has a logical database control block for holding at least the identification information of said logical database and the identification information of at least one physical database belonging to said logical database in each said logical database as a storage area of information on said logical database and said table location searching unit rewrites the identification information of said logical database to the identification information of the physical database which is decided as an access object among the physical database identification information held in said logical database control block which holds the identification information of said designated logical database.

28. A distributed database management system according to claim 27, wherein said table location searching unit includes means for transferring said logical database identification information without rewriting it when said logical database control block holding said described logical database identification information is not in said logical database dictionary.

29. A distributed database management system according to claim 13, wherein said table location searching unit includes means for selecting each of at least one physical database belonging to said logical database as an access object, transferring said access statement to the physical database management system for managing said physical databases, creating a table by combining system catalog information of each physical database which is inputted as a response to said transfer into said physical database management system, and informing said application program execution means which issues said access statement of the contents of said table when said access statement to be transferred designates said logical database and instructs to refer to the system catalog.

30. A distributed database management system according to claim 13, wherein the distributed database management system has a log information storage area for holding the log information on access to said logical database in each said logical database furthermore; and

wherein said table location searching unit includes means for storing the log information on the executed logical database access in said log information storage area, and means for informing of the information held in said log information storage area according to a request from said application program execution means.

31. A distributed database management system according to claim 30, wherein said log information includes at least one of identification information of the logical database, identification information of the physical database, the table identification information, a user identifier of the logical database described in said received access statement, and a user identifier of the physical database described in said transferred access statement which are to be accessed.

32. A distributed database management system according to claim 13, wherein when said access statement includes designation of a table, said table location searching unit includes table location predicting means for predicting said physical database holding said table before transferring said access statement, and selecting said predicted physical database as an access object of said access statement.

33. A distributed database management system according to claim 32, wherein said table location predicting means is means for extracting physical database identification information which is described in said access statement beforehand from said access statement and selecting said physical database indicated by said physical database identification information as an access object.

34. A distributed database management system according to claim 32, wherein the distributed database management system has an access table buffer for associating and holding the identification information of said physical database and the table identification information held in said physical database furthermore; and

wherein said table location predicting means is means for searching for identification information of the designated table in said access table buffer, detecting the physical database corresponding to said table identification information, and selecting said physical database as an access object, and said table location searching unit includes means for storing the identification information of said physical database which is decided as an access object by transferring the access statement which designates said table and the identification information of said designated table in said access table buffer furthermore.

35. A distributed database management system according to claim 32, wherein the distributed database management system has a system catalog buffer for associating and holding identification information of said logical database, identification information of the physical database belonging to said logical database, and table identification information held in said physical database furthermore;

wherein said table location searching unit includes means for selecting each of at least one physical database belonging to said logical database as an access object, transferring said access statement to the physical database management system for managing said physical databases, creating a table having the identification information of the logical database, the identification information of the physical database belonging to said logical database, and the table identification information held in said physical database by combining the system catalog information of each physical database which is inputted as a response to said transfer into said physical database management system, informing said application program execution means which issues said access statement of the contents of said table, and storing the contents of said table in said system catalog buffer furthermore when said access statement to be transferred designates said logical database and instructs to refer to the system catalog; and

wherein said table location predicting means is means for searching for the identification information of said designated table in said system catalog buffer, detecting the physical database corresponding to the table identification information, and selecting said physical database as an access object.

36. A distributed database management system according to claim 35, wherein the distributed database management system has an access table buffer for associating and holding the identification information of said physical database and the table identification information held in said physical database furthermore; and

wherein said table location searching unit includes means for storing the identification information of said physical database which is an access object of transfer when the access statement designating said table is transferred and the identification information of said designated table in said access table buffer furthermore.

37. A distributed database management system according to claim 13, wherein said table location searching unit includes means for creating a new access statement for designating each table designated in said access statement one by one and instructing an operation which is the same as that of said access statement on the basis of said access statement when the access statement to be processed which is held in said statement buffer includes designation of a plurality of tables and for selecting each access statement as a processing object of said transfer and means for creating a table by combining a response corresponding to the transfer of each of said new access statements into said physical database management system, and informing said application program execution means which issues said access statements of the contents of said created tables furthermore.

38. A distributed database management system which is an information processor which is connected to at least one physical database holding a table via a physical database management system for managing said physical database, and is connected furthermore to application program execution means for accessing said physical database, receiving an access statement for accessing physical databases which is issued by said application program execution means, selecting one of said physical databases as an access object, and transferring said access statement to the physical database management system for managing said physical database, comprising:

a logical database dictionary for holding information on a logical database in which at least one of said physical databases is grouped;

a logical database defining unit for registering information on said logical database in said logical database dictionary;

a statement buffer for holding said access statement;

a logical database access controller for receiving an access statement from said application program execution means and storing it in said statement buffer; and

a table location searching unit for transferring said access statement held in said statement buffer to the physical database management system for managing said physical database by selecting one of said physical databases as an access object;

wherein said table location searching unit includes means for receiving an access statement for instructing logging in the database, creating an access statement for designating each table designated in said access statement one by one and instructing an operation which is the same as that of said access statement when the access statement to be processed which is held in said statement buffer includes designation of a plurality of tables, selecting one of said physical databases belonging to the designated logical database as said access object, transferring said created access statements respectively, creating a new table by combining responses to said transfer, and informing said application program execution means which issues said access statement of the contents of said created table.

39. A distributed database management method in a system including

a communication network,

at least a terminal device including application program execution means connected to said communication network,

a plurality of information processors connected to said communication network, and

a plurality of physical databases installed in at least one of said information processors,

said method comprising the steps of:

storing logical database information in at least one of said terminal device and said plurality of information processors, said logical database information defining at least a logical database grouping a plurality of said physical databases;

storing tables in at least one of said physical databases;

receiving a request for one of said tables from said application program execution means; and

searching said table for which said request was received by searching a group of physical databases defined in said logical database information.

40. A distributed database management method in a system including

a communication network,

at least a terminal device including application program execution means connected to said communication network,

a plurality of information processors connected to said communication network, and

a plurality of physical databases installed in at least one of said information processors,

said method comprising the steps of:

storing logical database information in at least one of said terminal device and said plurality of information processors, said logical database information defining at least a logical database grouping a plurality of said physical databases, and account information for identifying whether to approve an access to at least one of said physical databases;

receiving an access to a logical database from said application program execution means, account information for logging in a physical database constituting said logical database being inputted in said access; and

searching said account information for logging in using the account information held in said logical database information.

41. A distributed database management method in a system which is an information processor which is connected to at least one physical database holding a table via a physical database management system for managing said physical database, and is connected furthermore to application program execution means for accessing said physical database, receiving an access statement for accessing physical databases which is issued by said application program execution means, selecting one of said physical databases as an access object, and transferring said access statement to the physical database management system for managing said physical database, said method comprising the steps of:

holding in a logical database dictionary, information on the logical database in which at least one of said physical databases is grouped;

registering by a logical database defining unit, information on said logical database in said logical database dictionary;

holding in a statement buffer, said access statement;

receiving through a logical database access controller, an access statement from said application program execution means and storing it in said statement buffer; and

transferring through a table location searching unit, said access statement held in said statement buffer to the physical database management system for managing said physical database by selecting one of said physical databases as an access object;

wherein said table location searching unit includes means for receiving an access statement for instructing logging in the database, for selecting one of said physical databases belonging to the instructed logical database as an access object of said access statement when the database which is instructed to be connected is registered in said logical database dictionary as said logical database, for selecting another one of said physical databases belonging to the instructed logical database as an access object of said access statement when a response of access refusal is given to the transfer of said access statement, and for transferring said access statement held in said statement buffer once again.

42. A distributed database management method in a system which is an information processor which is connected to at least one physical database holding a table via a physical database management system for managing said physical database, and is connected furthermore to application program execution means for accessing said physical database, receiving an access statement for accessing physical databases which is issued by said application program execution means, selecting one of said physical databases as an access object, and transferring said access statement to the physical database management system for managing said physical database, said method comprising the steps of:

holding in a logical database dictionary, information on the logical database in which at least one of said physical databases is grouped;

registering by a logical database defining unit, information on said logical database in said logical database dictionary;

holding in a statement buffer, said access statement;

receiving through a logical database access controller, an access statement from said application program execution means and storing it in said statement buffer; and

transferring through a table location searching unit, said access statement held in said statement buffer to the physical database management system for managing said physical database by selecting one of said physical databases as an access object;

wherein said table location searching unit includes means for receiving an access statement for instructing logging in the database, creating an access statement for designating each table designated in said access statement one by one and instructing an operation which is the same as that of said access statement when the access statement to be processed which is held in said statement buffer includes designation of a plurality of tables, selecting one of said physical databases belonging to the designated logical database as said access object, transferring said created access statements respectively, creating a new table by combining responses to said transfer, and informing said application program execution means which issues said access statement of the contents of said created table.

Description

BACKGROUND OF THE INVENTION

The present invention relates to a distributed database management system having a plurality of information processors connected to a network.

Recently, database management systems for holding various data in common so as to use it effectively are introduced in many information processing systems.

Among them, a relational database management system for handling data in a related table format has come into wide use rapidly.

Conventional users construct a database on a main frame system and search or update common data. However, there are problems on cost, function, and operability imposed in a database management system of a main frame system.

Therefore, such a database management system of a main frame system is being changed to a client server type database management system using a miniature information processor such as a workstation or personal computer so as to decrease the cost of the system, to expand the function, to improve the operability, and to respond to the diversified information society flexibly. The client server type database management system can construct a highly expandable distributed database environment depending on the business scale.

A user connects an information processor which is a client to each database management system via a network and accesses a table on a relational database using a database access statement, for example, in the SQL (structured query language) which is the standard data manipulation language of the ISO (International Standardization Organization). In this case, it is necessary for the user in the distributed database environment to always recognize the database where the table to be accessed is stored, that is, the table location and to connect himself to an appropriate database before table access. Furthermore, it may be necessary to add the table location to each access statement. However, in a large scale distributed database environment, it is difficult for the user to recognize many table locations one by one and addition of the table location to each access statement requires a very complicated operation.

In the relational database, data in a plurality of related tables is searched by a database access statement and the tables can be joined as a table. This processing which is called a join is generally executed in a single database management system. In the distributed database environment, however, a join (distributed search function) for a plurality of tables stored in different database management systems is also necessary. However, a general client cannot be connected to a plurality of database management systems at the same time. Therefore, there is a product in which the database management system which receives a join request automatically fetches data from another database management system and joins it with the own search data so as to support the distributed search function. When such a distributed search function is used, it is necessary for the user to explicitly describe identification information for another database management system in which the table to be accessed is stored and user certification information at the time of connection in the database access statement.

To solve the above problems, it is important to allow the user in the distributed database environment not to be aware of the database management system where the table is stored, that is, to make the table position transparent.

As a method for realizing such a subject, there is a derivation database processing method which is described in Japanese Patent Application Laid-Open No. 4-112246. This method collects tables on a plurality of distributed database management systems partially and handles them as a derivation database and the user registers the definition information of each database management system and the definition information of the derivation database in a dictionary. The definition information of each database management system consists of identification information of a plurality of tables stored in each database and the definition information of the derivation database consists of identification information of a plurality of database management systems and tables which constitute the derivation database. The database manipulation means receives a derivation database access request from the application program, searches the above dictionary for the table location, and issues a database access statement to the database management system where the table is stored. By this method, the application program can access a plurality of database management systems via a derivation database.

By this derivation database processing method, the user can access a plurality of tables which are registered in the dictionary as a derivation database without being aware of the table location. However, when the user creates a new table after definition of the derivation database, it is necessary for the user to additionally define the created table and the stored identification information of the database management system in the dictionary.

In the distributed database environment, each department of enterprises often operates each database management system independently and accordingly there is a possibility that a duplicated table name exists between a plurality of database management systems. Since the aforementioned derivation database processing method identifies tables of the duplicated name uniquely, it is necessary to define a different name for each table.

In a general database environment, a new table is created frequently. Therefore, in the aforementioned derivation database processing method, it is necessary for the user to redefine the derivation database every time or to define a different name of the table and the operation burden is increased.

The database management system prevents an unqualified person from use of a database under the account control using the independent user ID (identifier: identification) and password (hereafter a combination of the two is called an account). The account control means installed in the database management system checks the password which is inputted by the user at the time of logging-in prior to table access, checks whether the logging-in user is granted a privilege for writing or reading in the table or record to be accessed, and then starts the table access processing.

However, in the distributed database environment where each database management system is operated independently, the accounts registered in the database management systems are not always the same. There is a method available for reregistering the accounts of all the database management systems and constructing a unified database account environment. However, for the reason of an increase in the account reregistration operation and reusing to the existing database application program property, many enterprises use a different account environment for each database management system continuously. Therefore, it is necessary for the user to selectively use the corresponding account for each database management system to be connected. However, in a large scale distributed database environment, in the same way as with the table location, storing and using of accounts to be used by the user for many database management systems require a very complicated operation.

SUMMARY OF THE INVENTION

An object of the present invention is to eliminate the difficulties of the prior arts mentioned above and to provide a distributed database management system which can correspond to a large scale distributed database environment by a simple operation without the table location being added to many access statements by the user.

Another object of the present invention is to provide a distributed database management system which can correspond to a large scale distributed database environment on the basis of single account information without a large amount of account information being stored and used by the user.

Another object of the present invention is to provide a distributed database management system which has a distributed database access management unit in a gateway server or specific database server and can correspond to a large scale distributed database environment with a simple configuration.

To accomplish the above objects, the present invention is a distributed database management system consisting of a terminal device which is connected to a network and has an application program execution means and of a plurality of information processors (servers) connected to the above network, wherein a distributed database access management means including a logical database defining unit for defining a logical database in which at least one database among physical databases covering the above plurality of information processors (servers) is grouped beforehand, a logical database dictionary for registering the definition information of the logical database which is defined in the above logical database defining unit, a logical database access controller for receiving a database access statement which is instructed from the application program execution means of the above terminal device, and a table location searching unit for searching for the database stored in the desired table on the physical database belonging to the logical database via the physical database management system of the above desired information processor (server) with reference to the definition information of the logical database which is registered in the above logical database dictionary on the basis of the database access statement received by the above logical database access controller is installed in the above desired information processor (server). Furthermore, the present invention is a distributed database management system consisting of a terminal device which is connected to a network and has an application program execution means and of a plurality of information processors (servers) connected to the above network, wherein a distributed database management means including a logical database defining unit for defining the identification information of the physical database constituting the logical database in which at least one database among physical databases covering the above plurality of information processors (servers) is grouped beforehand and the account information of the physical database, a logical database dictionary for registering the identification information of the physicl database constituting the logical database and the account information of the physicl database which are defined in the above logical database defining unit, a logical database access controller for receiving a database access statement which consists of the identification information of the logical database and of the account information of the logical database which are instructed from the application program execution means of the above terminal device, and a table location searching unit for logging in the physical database belonging to the logical database via the physical database management system of the above desired information processor (server) with reference to the identification information and the account information of the physical database which is registered in the above logical database dictionary on the basis of the database access statement received by the above logical database access controller and searching for the database stored in the desired table is installed in the above desired information processor (server). Furthermore, the present invention is a desired database server among a plurality of database servers having a physical database management system and a physical database as a desired information processor (server) having the above distributed database access management means in the above distribution database management system.

Furthermore, the present invention is a gateway server for positioning between a plurality of database servers having the above physical database, physical database management system, and terminal device via the above network as a desired information processor (server) having the above distributed database access management means in the above distributed database management system and for managing the above plurality of database servers.

Furthermore, in the above distributed database management system of the present invention, the above definition information which is registered in the logical database dictionary includes the priority order of each physical database constituting the logical database and the above table location searching unit searches for the database stored in the desired table on the physical database on the basis of the priority order registered in the above logical database dictionary.

Furthermore, in the above distributed database management system of the present invention, the above definition information which is registered in the logical database dictionary includes the access privilege information for the logical database and the above table location searching unit checks the access privilege of the application program user which is instructed from the above terminal device prior to access to the logical database.

Furthermore, in the above distributed database management system of the present invention, the above definition information which is registered in the logical database dictionary includes the account information of the physical database constituting the logical database and the above table location searching unit logs in the physical database constituting the logical database using the database account registered in the above logical database dictionary on the basis of the account information of the application program user which is instructed from the above terminal device.

Furthermore, in the above distributed database management system of the present invention, the above table location searching unit checks the account information which is received from the application program which is instructed from the above terminal device with the account of the above logical database prior to access to the logical database.

Furthermore, in the above distributed database management system of the present invention, the above definition information which is registered in the logical database dictionary includes the account information of the physical database constituting the logical database and the above table location searching unit logs in the physical database constituting the logical database using the account corresponding to the physical database registered in the above logical database dictionary on the basis of the account information of the application program user which is instructed from the above terminal device.

Furthermore, in the above distributed database management system of the present invention, the above definition information which is defined in the logical database defining unit consists of the identification information of the physical database constituting the logical database and the account information of the physical database.

On the other hand, the present invention provides a distributed database management system which is an information processor which is connected to at least one database (hereinafter called a physical database so as to distinguish from the logical database which will be described later) holding a table via a database management system (hereinafter called a physical database management system so as to distinguish from the distributed database management system of the present invention), is connected furthermore to the application program execution means for accessing the above physical database, receives an access statement for accessing physical databases which is issued by the above application program execution means, and transfers the above access statement to the physical database management system for managing the above physical database by selecting one of the above physical databases as an access object and which has the following configuration.

Namely, the distributed database management system of the present invention has a logical database dictionary for holding information on the logical database wherein at least one of the above physical databases is grouped, a logical database defining unit for registering information on the above logical database in the above logical database dictionary, a statement buffer for holding the above access statement, a logical database access controller for receiving an access statement from the above application program execution means and storing it in the above statement buffer, and a table location searching unit for transferring the above access statement held in the above statement buffer to the physical database management system for managing the above physical database by selecting one of the above physical databases as an access object.

The above table location searching unit has a means for receiving an access statement for instructing logging in the database, when the database which is instructed to be connected is registered in the above logical database dictionary as the above logical database, selecting one of the above physical databases belonging to the instructed logical database as an access object of the above access statement, when a response of access refusal is given to the transfer of the above access statement, selecting another one of the above physical databases belonging to the instructed logical database as an access object of the above access statement, and transferring the above access statement held in the above statement buffer once again.

According to the distributed database management system of the present invention, the logical database access controller receives a database access statement from the application program and informs the table location searching unit of it. The table location searching unit which is informed automatically logs in the database using the identification information and account information of the physical databases constituting the logical database in the logical database dictionary and issues the database access statement received from the application program. The table location searching unit repeats the aforementioned inquiry processing for at least one database constituting the logical database and decides the database which obtains a response indicating processing completion as a table location.

When the physical database account is stored in the logical database dictionary, the table location searching unit of the present invention logs in each physical database using the stored account. When no physical database account is stored, the table location searching unit logs in the physical database using the account received from the above application program execution means.

As mentioned above, according to the distributed database management system of the present invention, the user can access transparently tables stored in a plurality of physical databases constituting the logical database and tables which will be newly stored hereafter without being aware of the table location and physical database account.

In the distributed database management system of the present invention, by logging in each physical database using the account information stored in the logical database dictionary, tables having duplicated names which are prepared by different users can be excluded from the access objects. By doing this, there is no need to define another names for tables having duplicated names which are prepared by different users and to manage them.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of the distributed database management system in Embodiment 1.

FIGS. 2(a) and 2(b) are illustrations showing the constitution of the logical database dictionary in Embodiment 1.

FIGS. 3(a) and 3(c) are illustrations showing statements used for definition, change, and deletion of the logical database in Embodiment 1.

FIG. 4 is an illustration showing database connection statement conversion processing of the table location searching unit in Embodiment 1.

FIG. 5 is a flow chart showing the processing procedure of the table location searching unit in Embodiment 1.

FIG. 6 is a drawing showing the sequence of the information which is exchanged by the table location searching unit in Embodiment 1.

FIGS. 7(a) and 7(b) are illustrations showing the constitution of the logical database dictionary in Embodiment 2.

FIG. 8 is a drawing for explaining the operation in Embodiment 3.

FIGS. 9(a) and 9(b) are illustrations showing the constitution of the logical database dictionary in Embodiment 4.

FIG. 10 is a drawing for explaining the operation in Embodiment 4.

FIG. 11 is a drawing for explaining the pass word encripting function in Embodiment 6.

FIG. 12 is a drawing for explaining a countermeasure using the distributed database management system in Embodiment 1.

FIG. 13 is a drawing for explaining the distributed system catalog function in Embodiment 9.

FIG. 14 is an illustration showing the constitution of the logical database access log buffer in Embodiment 10.

FIG. 15 is a drawing for explaining the view information and synonym information in Embodiment 12.

FIGS. 16(a) and 16(b) are illustrations showing the constitution of the logical database dictionary in Embodiment 5.

FIG. 17 is a drawing for explaining the operation of the distributed database access management unit in Embodiment 5.

FIGS. 18(a) and 18(g) are illustrations showing statements used for definition, change, and deletion of the logical database and logical account in Embodiment 4.

FIG. 19 is a flow chart showing the procedure of the whole automatic logging-in processing of the table location searching unit in Embodiment 8.

FIG. 20 is a flow chart showing the procedure of the automatic logging-in processing of the table location searching unit in the strict mode in Embodiment 8.

FIG. 21 is a drawing showing the sequence of the information which is exchanged by the table location searching unit by the automatic logging-in processing in the strict mode in Embodiment 8.

FIG. 22 is a flow chart showing the procedure of the automatic logging-in processing of the table location searching unit in the loose mode in Embodiment 8.

FIG. 23 is a drawing showing the sequence of the information which is exchanged by the table location searching unit by the automatic logging-in processing in the loose mode in Embodiment 8.

FIG. 24 a block diagram of the table location searching unit in Embodiment 13.

FIG. 25 is an illustration showing the database connection statement conversion processing by the table location extraction unit in Embodiment 13.

FIG. 26 is a flow chart showing the procedure of the automatic logging-in processing in the strict mode in Embodiment 13.

FIG. 27 is a hardware diagram showing a system configuration example to which the distributed database system of the present invention is applied.

FIG. 28 is a hardware block diagram showing a system configuration example to which the distributed database system of the present invention is applied.

FIG. 29 is a hardware block diagram showing a system configuration example to which the distributed database system of the present invention is applied.

FIG. 30 is a flow chart showing the procedure of the logical database registration processing of the logical database defining unit in Embodiment 4.

FIG. 31 is a flow chart showing the procedure of the logical database registration processing of the logical database defining unit in Embodiment 1.

FIG. 32 is a flow chart showing the procedure of the logical database change processing of the logical database defining unit in Embodiment 4.

FIG. 33 is a flow chart showing the procedure of the logical account control block change processing of the logical database defining unit in Embodiment 4.

FIG. 34 is a flow chart showing the procedure of the automatic logging-in processing in the loose mode in Embodiment 13.

FIG. 35 is a flow chart showing the processing procedure of the table location searching unit in Embodiment 11.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The embodiments of the present invention will be explained hereunder with reference to the accompanying drawings. The same numbers are assigned to the same parts in the drawings.

Embodiment 1

A hardware block diagram of a client server system to which the distributed database management system in this embodiment is applied is shown in FIG. 27. The client server system in this embodiment consists of a network 42, three database servers 41 (41a, 41b, 41c) connected to the network 42, a client 39 connected to the network 42, and a gateway server 40. Each database server 41, the client 39, and the gateway server 40 are information processors having at least a central processing unit (CPU) and a main storage and each means (described later) which is installed in each database server 41, the client 39, and the gateway server 40 is realized when an instruction held in the main storage is executed by the CPU. Each unit is connected to the network 42 such as an LAN in a client server form.

Each database server 41 includes a physical database 1 and a physical database management system 270 for managing the physical database 1. The database server 41a has a physical database DB_a, and the database server 41b has a physical database DB_b, and the database server 41c has a physical database DB_c. Access to each physical database 1 is made via the physical database management system 270. In this embodiment, the three physical databases DB_a, DB_b, and DB_c are installed in different database servers 41 respectively. However, a plurality of physical databases 1 may be installed in a database server. Furthermore, in this embodiment, the three physical databases DB_a, DB_b, and DB_c are managed by different physical database management systems respectively. However, a plurality of physical databases 1 may be managed by a physical database management system.

The client 39 in this embodiment is a miniature information processor (terminal device) such as a personal computer in which an application program 2 is operated. The client 39 has an application program execution means 2 for executing the application program for updating or searching the databases and instructs to update or search each database.

Each database server 41 is an information processor (server) having a secondary storage such as a workstation or main frame in which the physical database 1 is operated.

A distributed database access management unit 3 which is installed in the gateway server 40 is a mechanism which exists between the application program 2 and the physical database 1 and plays a role as a gateway between the client and server so that the application program execution means 2 can handle a plurality of distributed databases 1 in the same way as with a single physical database. In this embodiment, the distributed database access management unit 3 is installed in the gateway server 40. However, it may be installed in the client 39 as shown in FIG. 28 or it may be installed in the database server 41 as shown in FIG. 29. However, when the distributed database access management unit 3 is installed in the client 39 which is an application as shown in FIG. 28, it is undesirably necessary to install it in all the clients 39. Therefore, the embodiment shown in FIG. 29 or FIG. 27 is desirable.

The function constitution of a server client system to which the distributed database management system of this embodiment is applied is shown in FIG. 1. The distributed database management system of this embodiment consists of the distributed database access management unit 3.

In this embodiment, a plurality of physical databases 1 are combined so as to form logical databases 4 (LDB_A, LDB_B). The logical database LDB_A consists of physical databases DB_a and DB_b and the logical database LDB_B consists of physical databases DB_b and DB_c. The physical databases 1 in this embodiment store and manage a plurality of tables 100. The physical database DB_a holds a table al and a table a2. The physical database DB_b holds a table b1 and a table b2. The physical database DB_c holds a table c1 and a table c2.

The client 39 in this embodiment has input/output devices (not shown in the drawing) such as a display (not shown in the drawing), a keyboard (not shown in the drawing), and a mouse as pointing devices. The application program execution means 2 has a user interface 11 for controlling these input/output devices, receiving input on search and update of data held in the physical databases 1 from the user, and displaying the processing result and a statement generating unit 12 for creating an access statement for accessing the physical databases 1 according to the received input and informing the distributed database access management unit 3 of it.

The distributed database access management unit 3 in this embodiment has a logical database dictionary 8 for storing the identification information, account information, and control information of the physical databases 1 constituting the logical databases 4, a statement buffer 6 for temporarily storing at least one database access statement, a logical database access controller 10 for receiving a database access statement from the application program 2 and distributing processing to a logical database defining unit 9 or a table location searching unit 7, the logical database defining unit 9 for registering the definition information on the logical databases 4 in the logical database dictionary 8, the table location searching unit 7 for inquiring as to whether tables 100 exist in at least one physical database 1 constituting the logical databases 4 and deciding stored physical databases 1, and a database interface unit 5 for transferring the database access statement to the physical databases 1 and receiving the result. The database interface unit 5 stores the physical location information (network address, etc.) of each physical database 1, searches for the address corresponding to the physical database name instructed from the table location searching unit 7, and sends the statement held in the statement buffer 6 to physical database management systems 270 for managing the object physical database 1. In this Embodiment 1, access to the physical databases 1 from the table location searching unit 7 is all made via the database interface unit 5 and the physical database management systems 270.

The logical database access function is realized by the distributed database management unit (distributed database management system) in this embodiment.

A. Outline of the Logical Database Access Function

The logical database access function provided by the distributed database management system in this embodiment will be explained hereunder.

The logical databases 4 are virtual databases in which at least one physical database 1 is grouped. In FIG. 1, the physical databases DB_a and DB_b are defined as a logical database LDB_A and the physical databases DB_b and DB_c are defined as a logical database LDB_B. In this embodiment, the user of application program 2 can make location transparent access to the tables a1, a2, b1, and b2 by the logical database LDB_A and to the tables b1, b2, c1, and c2 by the logical database LDB_B.

The distributed database management system of this embodiment can set the priority order for search in a plurality of physical databases 1 constituting the logical databases 4. The table location searching unit 7 inquires about the existence of tables sequentially according to the priority order of each physical database 1 and decides the physical database 1 where the table to be accessed is stored. Namely, according to the distributed database management system in this embodiment, when there are tables with the same name in a plurality of physical databases 1 constituting the logical databases 4, the table 100 on the highest priority physical database 1 is accessed.

(1) Account Control

Next, the account control method of the logical database access function in this embodiment will be explained. The account consists of a user ID for identifying the user and a password.

The distributed database management system in this embodiment prevents the user from being aware of a difference in the account between the physical databases 1, so that it logs automatically in a plurality of physical databases 1 constituting the logical databases 4 using the account information of each physical database 1 which is registered in the logical database dictionary 8 beforehand. To prevent the table 100 having no access privilege which is stored in each physical database 1 from use, it is necessary that the legality of the user is certified. Therefore, prior to logging in each physical database 1, the table location searching unit 7 checks the account for the logical databases 4 (hereinafter called a logical database account). The logical database account consists of a user ID and password the same way as the account of the physical databases 1 and the table location searching unit 7 can grasp a plurality of account informations different for each physical database 1 which are registered in the logical database dictionary 8 as an account for using each physical database 1 without being aware of them.

(2) Access Privilege Management

Next, the access privilege management method of the logical database account function in this embodiment will be explained.

The distributed database management system in this embodiment also has a function for confirming the legality of a database access user as a user of the operating system (hereinafter called an OS user) corresponding to the multi-user environment in addition to the aforementioned logical database account.

When the application program 2 is operated on a general multi-user operating system, the user sets his own processing environment by logging in the operating system beforehand. Furthermore, a plurality of OS users are defined as a group and the same processing environment can be used in common. However, a normal physical database management system has a unique database account environment separately from the user account of the operating system. Therefore, the distributed database management system in this embodiment grasps the definition information on each logical database 4 registered in the logical database dictionary 8 as an object and sets an access privilege to the OS user in each logical database 4 so as to limit users of the logical databases 4.

The access privilege information consists of the ID of an OS user which permits access to the logical databases 4 or the group ID and the privilege kind such as use permission or change permission. In this embodiment, permission of use or change of the logical databases 4 is implicitly given to the OS user (owner of the definition information on the logical databases) who defines the logical databases 4. The owner of the definition information on the logical databases 4 can grant another OS user or group permission of use or change of the logical databases 4.

According to the access privilege management method in this embodiment, the statement generating unit 12 of the application program 2 informs the distributed database access management unit 3 of the ID of the OS user and the ID of the belonging group together with the created database access statement. Before logging in each physical database 1, the table location searching unit 7 of the distributed database access management unit 3 refers to the access privilege which is set in the requested logical database 4 and checks whether use of the logical database 4 is permitted for the informed OS user.

The information which is held by the logical database dictionary 8 is shown in 2(b). The logical database dictionary 8 has at least one logical database control block 13. Each logical database control block 13 holds the definition information on a logical database 4. As shown in FIG. 2(a), each logical database control block 13 has an area 13a for storing the name of each logical database 4, an area 13b for storing the access privilege to the logical databases 4, an area 13c for storing the account (user ID and password) for the logical databases 4, an area 13d for storing the name of each physical database 1 constituting the above logical databases 4, and an area 13e for storing the account (user ID and password) for the above physical database 1.

The logical database dictionary 8 in this embodiment is realized in the main storage of the gateway server 40 as a file which is managed by the operating system of the gateway server 40. However, it may be realized in one of the physical databases 1 as a database table 100.

The access privilege 13b can hold a plurality of OS users or the group ID and the privilege kind. The logical database account 13c can hold a plurality of sets of account. Furthermore, the physical database name 13d and the physical database account 13e have a link indicating the storing order. In this embodiment, the priority order of searching is decided by the order of this link.

In the distributed database management system in this embodiment, two kinds of logical databases 4 such as a public logical database and private logical database can be defined. Therefore, as shown in FIG. 2(b), the logical database dictionary 8 has a storage area 201 of the logical database control block 13 holding the definition information on the logical database 4 which is a public logical database and a storage area 202 of the logical database control block 13 holding the definition information on the logical database 4 which is a private logical database. FIG. 2(b) shows that three logical database control blocks 13 are held in the storage area 201 of public logical database control block. However, the storage area 201 can hold an optional number of logical database control blocks 13 and the number of logical database control blocks 13 is not limited to 3. The same may be said with the storage area 202 of private logical database control block.

The public logical database is a database which can be used by all the OS users. The logical database control blocks 13 relating to the logical database 4 which is defined as public are managed by the system in a batch. Therefore, it is necessary to assign a unique logical database name to each logical database 4.

On the other hand, the private logical database is a database which can be used only by the defined OS user or another OS user who is permitted to use. In this embodiment, the logical database control blocks 13 correspond to user names 50 of usable OS users (they are shown as user_alpha, user_beta, and user_gamma in FIG. 2(b)) and are held in the storage area 202 of private logical database control block. Therefore, in this embodiment, a free logical database name can be assigned without duplication with a registered public logical database name or a private logical database name registered by another OS user being aware of.

When the logical database name to which an access request is given from the user is registered in both the logical database control block 13 which is registered in the storage area 201 of public logical database control block and the logical database control block 13 which is registered in the storage area 202 of private logical database control block in correspondence with the user name of the above OS user, the distributed database access management unit 3 in this embodiment performs processing using the information of the logical database control block 13 registered in the storage area 202 of private logical database control block. Namely, in this embodiment, when a logical database having the same name is registered in both the public logical database and usable private logical database, an access request to the logical database having the above same name of an OS user is handled as an access request to the logical database having the above same name which is registered as a private logical database.

B. Details of the Logical Database Access Function

Next, the logical database access function in this embodiment will be explained in detail.

In this embodiment, an SQL statement is used as a database access statement. In the SQL standard, a data definition language for a CREATE TABLE statement for creating a table 100 newly and a DROP TABLE statement for deleting a table 100 and a data manipulation language for a SELECT statement for searching for data in a table 100, an INSERT statement for adding a new row to a table 100, a DELETE statement for deleting a row from a table 100, and an UPDATE statement for changing data in a table 100 are regulated. In this embodiment, the data definition language and data manipulation language used for the tables 100 are called a table access statement. Each table access statement contains the table name to be accessed. Furthermore, in the SQL standard, a database connection statement such as a CONNECT statement for logging in the database and a DISCONNECT statement for logging out of the database is also regulated. In this embodiment, a table access statement created by the application program execution means 2 is informed to the table location searching unit 7 via the logical database access controller 10. The table location searching unit 7 interprets this table access statement as access to the logical database 4, creates a table access statement to the actual physical database 1, issues the created statement to the physical database 1 via the database interface unit 5, and receives the result.

In this Embodiment 1 (and the embodiments which will be described later), in the processing which is executed when the DROP TABLE statement, SELECT statement, INSERT statement, DELETE statement, or UPDATE statement is received from the application program execution means 2 and uses the table 100 existing in the physical database 1 as an object, the table location searching unit 7 automatically detects the physical database 1 where the table 100 to be processed exists actually and executes the access to the above physical database 1.

On the other hand, when the CREATE TABLE statement is received from the application program execution means 2, the table location searching unit 7 creates a table 100 newly and stores it in a newly reserved storage area. When the table location searching unit 7 receives the CREATE TABLE statement for the logical database 4 from the application program execution means 2, the unit transfers the statement to the highest priority physical database 1 among the physical databases belonging to the above logical database 4. Namely, the table location searching unit 7 attempts to store newly created tables for the logical database 4 all in the highest priority physical database 1.

Storing newly created tables 100 in the highest priority physical database 1 like this allows easy operation and management in the distributed database environment and effectively reduces the processing overhead of the table location searching unit 7. The reason is that in the processing for a table 100 which exists in the physical database 1 already, searching the physical database 1 where the table 100 to be processed exists actually is performed according to the priority order of the physical databases 1, so that when the table 100 to be searched is detected by the first try of access, the searching efficiency is improved.

(1) Definition Function of Logical Databases

Next, the definition function of the logical databases 4 in this embodiment will be explained.

For example, a general-purpose interactive database application program for instructing a table to be accessed or a search condition by an interactive operation and for indicating the search result often includes a function for issuing a database access statement which is inputted directly from the keyboard by the user to the physical database 1 as it is. Therefore, in the distributed database management system in this embodiment, the logical databases 4 can be defined by the database access statement shown in FIGS. 3(a) to 3(c) which is expanded partially. According to the distributed database management system in this embodiment, the user can define a unique logical database environment easily by using an interactive database application program on sale.

The logical database access controller 10 of the distributed database access management unit 3 identifies the definition statement of the logical database 4 which is informed of from the application program execution means 2 and informs the logical database defining unit 9 of it together with the OS user ID of the definition user and the group ID.

An example of a statement used to create the logical databases 4 is shown in FIG. 3(a). This logical database creating statement 14 contains description contents of the logical databases 4, description contents of at least one physical database 1 constituting the above logical databases, descriptors (CREATE, LOGICAL DATABASE, USER_ID, IDENTIFY, and DATABASE), and a continuation symbol (,) and furthermore, may contain a descriptor PUBLIC.

The description contents of the logical databases 4 are the name of each logical database, logical database user ID, and password. The description contents of the physical databases 1 constituting the logical databases are the name of each physical database 1 and the user ID and password of the above physical databases.

The descriptor CREATE and descriptor LOGICAL DATABASE mean a statement for instructing creation of a logical database having the name described behind the descriptor LOGICAL DATABASE. The descriptor PUBLIC means the definition of the public logical database. When the descriptor PUBLIC is omitted, the database is defined as a private logical database.

The descriptor USER_ID means that the name described behind the descriptor USER_ID is the user ID of the user who is permitted to use the logical database 4 or the physical database 1 which is described immediately before the descriptor USER_ID. The descriptor IDENTIFY means that the password of the user having the user ID described immediately before is the pass word described behind the descriptor IDENTIFY. A plurality of user IDs and passwords of the user who is permitted to use the logical databases 4 can be described. When a plurality of user IDs and passwords are described, they are delimited by a continuation symbol of ",".

The descriptor DATABASE means that the name described behind the descriptor DATABASE is a name of the physical databases 1 constituting the logical database to be defined. In the statement 14, the user who is permitted to use the physical database 1 is defined by the aforementioned descriptors USER_ID and IDENTIFY described behind this physical database name. A plurality of physical databases 1 can be described. When a plurality of physical databases are described, they are delimited by a continuation symbol of ",". In this embodiment, the physical databases 1 constituting the logical databases 4 which are described in the upper stages in the statement are given higher priority for searching.

The logical database defining unit 9 analyzes the logical database creating statement 14 which is informed of from the logical database access controller 10, stores the above information in the logical database name storage area 13a, the logical database account storage area 13c, the physical database name storage area 13d, and the physical database account storage area 13e of the logical database control block 13, and stores the ID of the OS user who issues the statement and the use or change permission kind in the access privilege storage area 13b.

The flow of the logical database registration processing of the logical database defining unit 9 is shown in FIG. 31.

When the logical database defining unit 9 receives the logical database creating statement 14 issued from the application program execution means 2 via the logical database access controller 10, the unit checks first whether there is a designation of PUBLIC (Step 311). When PUBLIC is designated immediately after the descriptor CREATE, the logical database defining unit 9 creates a logical database control block 13 newly in the storage area 201 of public logical database control block (Step 312). When PUBLIC is not designated, the logical database defining unit 9 creates a logical database control block 13 newly in the storage area 202 of private logical database control block (Step 313). Next, the logical database defining unit 9 stores the logical database name following LOGICAL DATABASE in the statement in the logical database name storage area 13a of the logical database control block 13 (Step 314) and stores the logical database user name following USER_ID and the logical database password following IDENTIFY sequentially (Step 310) in the logical database account storage area 13c (Step 315). Furthermore, the logical database defining unit 9 stores the physical database name described behind DATABASE sequentially (Step. 319) in the physical database name storage area 13d (Step 316) and stores the user ID of the USER-ID clause following the above physical database name and the password of the IDENTIFY clause in the physical database account storage area 13e corresponding to the above physical database name storage area 13d (Step 317). The logical database defining unit 9 connects the physical database name storage areas 13c with links and stores the above data so that the storage locations on the links are set in the description order. Finally, the logical database defining unit 9 stores the ID of the OS user who issues the statement and the use or change permission kind in the access privilege storage area 13b (Step 318).

Next, an example of a statement used to delete the logical databases 4 is shown in FIG. 3(b). This logical database 4 deleting statement 15 consists of a descriptor DROP LOGICAL DATABASE and a logical database name. The logical database defining unit 9 deletes the logical database control block 13 in which the name described immediately after the descriptor DROP LOGICAL DATABASE is held in the logical database name storage area 13a. The logical database defining unit 9 refers to the access privilege 13b prior to deletion of the logical database control block 13 and checks whether permission of change is given to the OS user who issues the statement. When no permission of change is given, the logical database defining unit 9 refuses deletion of the logical databases 4.

In this embodiment, the owner of the logical databases 4 can grant the access privilege to another user. An example of a statement used to grant the access privilege relating to the logical databases 4 is shown in FIG. 3(c). This access privilege granting statement 16 consists of descriptors GRANT, ON, and TO USE or TO GROUP or TO PUBLIC, the kind of access privilege to be granted (use permission or change permission), the logical database name which is the above access object, and the user ID of the OS user who is an granting object or the group ID.

The descriptor GRANT means a statement for granting the access privilege of the kind described immediately after it.

The descriptor ON means that the access privilege to be granted is the access privilege to the logical database having the logical database name which is described immediately after the descriptor ON. The descriptor TO USER means that the OS user having the user ID which is described immediately after it is a granting object. The descriptor TO GROUP means that the OS user belonging to the group having the group ID which is described immediately after it is a granting object. The descriptor TO PUBLIC means that the granting objects are all the OS users.

The logical database defining unit 9 analyzes the logical database access privilege granting statement 16 which is informed of from the logical database access controller 10 and adds the above information to the access privilege 13b of the logical database control block 13.

Furthermore, in this embodiment, by using another database access statement (for example, SELECT, UPDATE, INSERT, DROP, etc.), the contents of the logical database control block 13 which are registered in the logical database dictionary 8 can be searched or updated and the information relating to the physical databases 1 of the logical database control block 13 can be added or deleted. By doing this, the user can edit a unique logical database environment freely. SELECT means searching, UPDATE updating, INSERT addition, and DROP deletion.

(2) Processing of the Logical Database Access Controller

The logical database access controller 10 receives the CONNECT statement from the application program execution means 2 first, stores it in the statement buffer 6, and then informs the table location searching unit 7 of the above CONNECT statement, the ID of the OS user who issues the CONNECT statement, and the group ID. The logical database access controller 10 also stores a table access statement which is received from the application program execution means 2 after the CONNECT statement is received in the statement buffer 6 and then informs the table location searching unit 7 of it.

(3) Processing of the Table Location Searching Unit

FIG. 4 is an illustration showing the conversion processing of the CONNECT statement by the table location searching unit 7. In the SQL standard, the database name to be connected, the database account consisting of user ID, and password is defined as parameters of the CONNECT statement. However, in this embodiment, the database name of the CONNECT statement is interpreted as a name of the logical database 4 and the database account as an account to the logical database 4. In this embodiment, a specific physical database 1 can be accessed using the name and account of the physical database 1 in the same way as with the conventional method.

In this embodiment, as shown in FIG. 4, a CONNECT statement 45 prepared by the application program execution means 2 is received by the table location searching unit 7 via the logical database access controller 10. The table location searching unit 7 which receives the CONNECT statement 45 interprets the statement 45, replaces the logical database name and logical database account in the CONNECT statement 45 with the physical database name and physical database account for the physical database 1 which are registered in the logical database control block 13, creates a CONNECT statement 46 for actually accessing the physical database 1, and issues it to the physical database 1.

In the CONNECT statement 46 created by the table location searching unit 7, the name of the physical database 1 to be connected is described immediately after the descriptor CONNECT TO, and the user ID of the user to be connected is described immediately after the descriptor USER, and the password of the user to be connected is described immediately after the descriptor USING in the same way as with the SQL standard.

However, when the CONNECT statement 45 is interpreted, the described database is interpreted as a logical database. Namely, the table location searching unit 7 interprets the word (name of the physical database 1 to be connected in the SQL standard) following the descriptor CONNECT TO in the statement 45 as the name of the logical database to be connected, the word (user ID of the user to be connected in the SQL standard) following the descriptor USER as the user ID of the logical database, and the word (password of the user to be connected in the SQL standard) following the descriptor USING as the password of the logical database.

FIG. 5 is a flow chart showing the processing procedure of the table location searching unit 7.

The table location searching unit 7 extracts the logical database name from the CONNECT statement stored in the statement buffer 6 (Step 501) and searches the logical database control block 13 in which the logical database name extracted at Step 501 is held in the logical database name storage area 13a(Step 502). This searching is executed in the storage area 202 of private logical database control block first. When the logical database name is not detected, the searching is executed in the storage area 201 of public logical database control block. The searching in the storage area 202 of private logical database control block is executed for the logical database control block 13 which is registered in correspondence with the OS user who is informed of from the logical database access controller 10 and with the group ID. When the table location searching unit 7 detects the logical database control block 13 in which the logical database name extracted at Step 501 is held in the logical database name storage area 13a, the unit goes to the processing at Step 503. When the logical database control block 13 having the designated name is not detected in both storage areas 201 and 202, the table location searching unit 7 goes to the processing at Step 515.

When the designated logical database control block 13 is detected in the storage area 202 of private logical database control block, the table location searching unit 7 checks whether use permission of the logical database 4 is given to the OS user who requests database access (Step 503). Whether use permission is given or not is judged with reference to the contents of the access privilege storage area 13b of the logical database control block 13 on the basis of the OS user ID and group ID which are informed of from the logical database access controller 10. When the searched logical database control block 13 relates to the public logical database, the table location searching unit 7 will not check the access privilege. When use permission of the private logical database is not given, the table location searching unit 7 informs the application program execution means 2 of refusal of access (Step 514) and ends the processing.

When the use permission of the private logical database is confirmed or the public logical database is a use object, the table location searching unit 7 extracts the logical database account from the CONNECT statement, confirms that it agrees with one of at least one logical database account registered in the logical database account storage area 13c of the detected logical database control block 13 (Step 504), and informs the application program execution means 2 of normal completion of logging in the logical databases 4 (Step 505). By doing this, the next statement is informed of from the application program execution means 2, so that the logical database access controller 10 stores the statement in the statement buffer 6. When the account does not agree with any one at Step 504, the table location searching unit 7 informs the application program execution means 2 of refusal of access (Step 514) and ends the processing.

When the above user confirmation processing ends, the table location searching unit 7 replaces the logical database name and logical database account in the CONNECT statement which are stored in the statement buffer 6 with the physical database name and physical database account for the physical database 1 assigned the highest priority (namely, registered at the top of the link) which is registered in the detected logical database control block 13, creates a CONNECT statement for access to the physical database 1, and then logs in the physical database 1 (Step 506). Next, the table location searching unit 7 reads the table access statement which is issued by the application program execution means 2 and stored in the statement buffer 6 by the logical database access controller 10 which receives it, issues it to the logged-in physical database 1 (Step 507), and waits for a response (Step 508).

The physical database management system 270 of the physical database 1 which receives the CONNECT statement and table access statement checks existence or nonexistence of the table to be accessed and the access privilege to the table to be accessed of the logged-in database user by using, for example, a system catalog which will be described later. When all the conditions are satisfied, the physical database management system 270 for managing the physical database 1 executes the processing corresponding to the received table access statement and returns the result. However, when one of the conditions is not satisfied, the physical database management system 270 returns information indicating refusal of access.

When the table location searching unit 7 receives information indicating refusal of access at Step 508, the unit judges that the table to be accessed is not stored in the physical database 1 which is under logging-in at present, creates and issues a DISCONNECT statement which is logged out of the physical database 1 (Step 509), and then repeats the table location searching processing at Steps 506 to 508 by using the physical database name and physical database account of the physical database 1 assigned the second-highest priority which is registered in the logical database control block 13 (Step 510). When the physical database 1 assigned the second-highest priority is not registered at Step 510, the table location searching unit 7 goes to the processing at Step 514 and informs the application program execution means 2 of refusal of access.

When the table location searching unit 7 receives the processing result from a certain physical database 1 at Step 508, the unit decides the table location as the physical database 1 which is under logging-in at present, returns the processing result to the application program execution means 2 via the logical database access controller 10 (Step 511), and waits for input of the next statement (Step 512). When the statement which is received from the application program execution means 2 next is a table access statement, the table location searching unit 7 repeats the processing at Step 507 and the subsequent steps. When a table access statement for accessing a table stored in the different physical database is received, refusal of access is judged at Step 508. Therefore, the table location searching unit 7 returns to Step 506 and inquires each physical database 1 about existence or nonexistence of the table.

When the received statement is a DISCONNECT statement for instructing logging out of the logical database 4 at Step 512, the table location searching unit 7 issues the DISCONNECT statement to the physical database 1 which is under logging-in at present (Step 513) and ends the processing.

On the other hand, when the database name in the CONNECT statement is different from the logical database name stored in any of the logical database control blocks 13 at Step 502, the table location searching unit 7 judges it as access to a specific physical database 1 and transfers all the statements to the physical database 1 as they are (Step 515) until the DISCONNECT statement is received (Step 516).

(4) Processing Sequence Example

FIG. 6 shows a sequence example of information which is exchanged between the application program execution means 2, the distributed database access management unit 3, and the physical databases 1 by the logical database access function in this embodiment. In the storage area 202 of private logical database control block, the logical database control block 13 relating to the private logical database LDB_A is held. In the physical database name storage area 13d of the logical database control block 13 relating to the logical database LDB_A, the names of the physical databases DB_a and DB_b are stored. In the access privilege storage area 13b of the logical database control block 13, permission of use and change is assigned to user_alpha who is an OS user and permission of use is assigned to group_alpha which is an OS group. Furthermore, in the logical database control block 13, user_a is registered as a physical database account of the physical database DB_a and user_b is registered as a physical database account of the physical database DB_b in the physical database account storage area 13e respectively. As shown in FIG. 1, the physical database DB_a has tables a1 and a2 and the physical database DB_b has tables b1 and b2.

Firstly, the table location searching unit 7 of the distributed database access management unit 3 receives notification of the CONNECT statement (CONNECT (LDB_A, user_A) to the logical database LDB_A from the application program execution means 2. This CONNECT statement means an access request to the logical database LDB_A by the logical database account user_A. Therefore, the table location searching unit 7 checks the access privilege to the OS user (user ID: user_alpha, group ID: group_alpha) who issues the CONNECT statement (S503) and checks the logical database account user_A (Step 504). When the use privilege of the user is confirmed by the above check, the table location searching unit 7 informs the application program execution means 2 of permission of access (Step 505, D62). The application program execution means 2 which receives the notification of permission of access issues a table access statement (SELECT statement (SELECT (b1)) for the table b1 shown in the example in FIG. 6) (D63).

The table location searching unit 7 which receives the SELECT statement creates a CONNECT statement (CONNECT (DB_a, user_a), which is logged in by using the physical database account user_a, in the physical database DB_a assigned the highest priority among the physical databases 1 contained in the logical database LDB_A and logs it in the physical database DB_a (Step 506, D64). When the table location searching unit 7 receives a response of success of logging-in (D65) from the physical database DB_a, the unit issues the SELECT statement for the table b1 which is received from the application program execution means 2 to the physical database DB_a (Step 507, D66).

However, the physical database DB_a in which the table b1 is not stored returns information (D67) indicating refusal of access to this SELECT statement. Therefore, the table location searching unit 7 creates and issues a DISCONNECT statement for breaking the connection to the physical database DB_a (D68). When the table location searching unit 7 confirms breaking of the connection (D69), the unit creates a CONNECT statement (CONNECT (DB_b, user_b), which is logged in by using the physical database account user_b, in the physical database assigned the second-highest priority and logs it in the physical database DB_b (Step 506, D70). When a response of permission of access (D71) is returned to this CONNECT statement from the physical database management system for managing the physical database DB_b, the table location searching unit 7 issues the SELECT statement once again (Step 507, D72).

In accordance with this SELECT statement, the physical database management system for managing the physical database DB_b searches for the stored table b1 and returns the processing result (D73). The table location searching unit 7 which receives the result informs the application program execution means 2 of this response (D74). From this response, the table location searching unit 7 recognizes the physical database DB_b as a physical database 1 in which the table b1 is stored and issues the access statement (UPDATE statement (UPDATE (b1)) for the table b1) (D75) and DISCONNECT statement (D79), which are received from the application program execution means 2 thereafter, to the physical database DB_b (D76, D80). The table location searching unit 7 informs the application program execution means 2 of responses (D77, D81) of the physical database management system for managing the physical database DB_b to it.

C. Effect of Embodiment 1

(1) Realization of Logical Databases

As mentioned above, by using the distributed database management system (distributed database access management unit 3) in this Embodiment 1, at least one physical database 1 can be handled as a logical database 4, which is a virtual database, in a batch.

When the table location searching unit 7 in this Embodiment 1 receives an access instruction to the logical database 4, the unit automatically logs in at least one physical database 1 which is defined to constitute the logical database 4 and decides the table location by inquiring about existence or nonexistence of the table to be accessed by transferring the table access statement. Therefore, even if the table configuration in the physical database 1 is changed such as creation or deletion of tables, a user of the distributed database management system of this Embodiment 1 does not need to change the information relating to the logical database 4 which is stored in the logical database dictionary 8 and can access an optional table 100 transparently regardless of the table configuration in the physical database 1. Furthermore, a user of the distributed database management system of this Embodiment 1 can access the desired table 100 in the distributed database environment without being aware of differences in the account between the physical databases 1 only by knowing a single logical database account.

(2) Double Check of Use Qualification

According to this Embodiment 1 (and the embodiments which will be described later), permission of use of a user for accessing the logical database 4 is doubly checked by the logical database account and the access privilege on the OS user level. Therefore, for example, if the ID and password for logging in the operating system do not leak out though the logical database account is known by another person, illegal use of the logical database 4 can be prevented.

However, one of the check functions can be omitted. For example, when an operating system for a single user is used as an operation environment of the application program execution means 2, logging in the operating system is not necessary. When qualification check as an OS user is not necessary like this, in this Embodiment 1, by registering the logical database to be used as a public logical database, the check of the access privilege at Step 503 can be omitted. Since the legality of the user is confirmed by logging in the operating system, there is a user's need for simplification of account input at the time of logging in the database. When the qualification check as an OS user or the logical database account check is not necessary like this, by correcting the processing flow of the table location searching unit 7 and deleting Step 503 and/or Step 504, one of the double checks or both of them can be omitted. For example, when Step 504 is deleted, the user can access the logical database 4 without inputting the logical database account after logging in the operating system.

(3) Troubleshooting Function

Using the logical database access function in this Embodiment 1, by storing a copy of a table stored in a certain physical database 1 in a different physical database 1 assigned lower priority in the same logical database 4 under the same name beforehand, a user can cope with faults of the physical database 1.

A database troubleshooting function applying the logical database access function in Embodiment 1 will be explained with reference to FIG. 12. In the example shown in FIG. 12, a copy of the table a1 stored in the physical database DB_a is stored in the physical database DB_b contained in the same logical database LDB_A under the same name so as to cope with faults. It is assumed that the physical database DB_a is stopped due to an occurrence of a fault.

The table location searching unit 7 receives an access request to the logical database LDB_A from the application program execution means 2 and tries to log in the physical database DB_a assigned highest priority first (Step 506, D121). The physical database DB_a which is a copy source and stores the table al cannot return a response to logging-in due to the occurrence of the fault. Therefore, the table location searching unit 7 logs in the physical database DB_b assigned the second-highest priority and issues the table access statement received from the application program execution means 2 to the table a1 in the physical database DB_b (D122).

As mentioned above, when a fault occurs in the physical database 1 in which the table to be accessed is stored, the table location searching unit 7 in this Embodiment 1 (and the embodiments which will be described later) automatically searches another physical database 1 constituting the logical database 4 for the above table. By doing this, when the physical database 1 assigned higher priority holding the above table cannot be accessed, the copied table stored in the physical database 1 assigned lower priority is accessed. Therefore, the user can access the desired table data without being aware of a fault in a certain physical database 1 in the distributed database environment.

Embodiment 2

In the case of the logical database access function in Embodiment 1 mentioned above, the logical database account is stored in each logical database control block 13. Namely, the logical database user is managed for each logical database 4. Therefore, when a different logical database 4 is accessed by the same logical database account, it is necessary to register the same account in the logical database account 13c of each logical database control block 13. Therefore, in the distributed database management system of the present invention, a second account management method which is different from the account management method used in Embodiment 1 may be used. According to the account management method in this embodiment, the whole distributed database management system manages the logical database user and assigns use permission of each logical database 4 to the user.

A. Constitution of the Logical Database Dictionary

According to the second account management method, as shown in FIG. 7(b), the storage area 203 of logical account control block is installed in the logical database dictionary 8. In Embodiment 1, all the accounts, that is, the user ID and password are held in the storage area 13c of logical database account of the logical database control block 13. In this Embodiment 2, however, as shown in FIG. 7(a), only the user ID is held in the storage area 17c of logical database account of the logical database control block 17. In this embodiment, all the accounts are stored in the logical account control block 18 which is held in the aforementioned storage area 203 of logical account control block instead of the storage area 17c of the logical database account.

According to the second account management method, the logical account control block 18 which is held in the storage area 203 of logical account control block of the logical database dictionary 8 is an area where the account information (user ID and password) of all the logical database users using the distributed database management system is stored. Furthermore, according to the second account method, the storage area 17c of logical database account of the logical database control block 17 is an area where the user ID of the logical database user who can use the logical database 4 indicated by the logical database control block 17 is held. A plurality of user IDs can be registered in the storage area 17c of logical database account. User IDs stored in the area 17c are a part of the set of user IDs which are stored in the logical account control block 18. In the public logical database which is permitted to be used by all users, "NULL" (a symbol meaning a null value) is registered in the area 17c.

B. Processing of the Logical Database Defining Unit

The logical database deleting processing and logical database access privilege granting processing of the logical database defining unit 9 in this Embodiment 2 and the logical database registering processing excluding Step 315 are the same as those in Embodiment 1. The processing at Step 315 in this Embodiment 2 is as shown below. Firstly, the logical database defining unit 9 stores the designated logical database user ID in the storage area 17c of logical database account. When "PUBLIC" is designated, the logical database defining unit 9 stores "NULL" in the storage area 17c of logical database account. Next, when the logical account control block 18 holding the designated logical database account is not in the storage area 203 of logical account control block, the logical database defining unit 9 reserves an area newly in the logical account control block 18 and stores the designated logical database user ID and logical database password in this area.

When the logical database defining unit 9 receives a logical account deleting statement, for example, as shown in FIG. 18(g), the unit may delete the logical account control block 18 which exists already.

C. Processing of the Table Location Searching Unit

In the logical database account confirmation processing (Step 504), the table location searching unit 7 in this Embodiment 2 extracts the logical database account from the CONNECT statement and confirms that the user ID of the extracted account agrees with one of the user IDs held in the logical database control block 17. However, this processing will not be executed when "NULL" is registered in the logical database account 17c of the logical database control block 17, that is, in the case of the public logical database. Next, the table location searching unit 7 searches the logical account control block 18 holding the logical database account which is extracted from the CONNECT statement in the storage area 203 of the logical account control block 18. When the logical account control block 18 to be desired is detected, the table location searching unit 7 goes to the processing at Step 505 and the subsequent steps. When one of the above conditions is not satisfied, the table location searching unit 7 refuses access to the logical database 4 (Step 514). The other processing of the table location searching unit 7 is the same as that shown in Embodiment 1.

D. Effect of this Embodiment 2

According to this embodiment using the second account management method, when the logical database account is registered in the logical account control block 18 once, there is no need to register the password in the storage area 17c of logical database account of each logical database control block and a plurality of logical databases 4 can be accessed by using a single logical database account.

Embodiment 3

There are physical database management systems on sale, which have an auditing function for acquiring records relating to access to physical databases for each user. If each user uses his unique logical database 4 in Embodiment 1 or 2, there is no problem imposed. However, if a plurality of users share one logical database 4, all the users log in a plurality of physical databases 1 belonging to one logical database 4 using the same account. The reason is that the account to be used for logging in the physical databases 1 is limited to the physical database account 13e or 17e of the logical database control block 13 or 17. Therefore, detailed access records for each physical database user cannot be obtained from the auditing function of the physical databases 1. To correspond to the auditing function of the physical databases 1, it is necessary to change the account for automatic logging in depending on the user. Therefore, in this Embodiment 3, a third account management method which is different from the account management method which is used in Embodiment 1 or 2 is used.

A. Processing of the Table Location Searching Unit

In this Embodiment 3, the account to be used for automatic logging in the physical databases 1 is changed depending on the user, so that the table location searching unit 7 is provided with a function for automatically logging in the physical databases 1 using a different account for each user. In this Embodiment 3, when "NULL" is registered in the physical database account 13e or 17e of the logical database control block 13 or 17, the table location searching unit 7 judges that the third account management method is used. The other processing of the table location searching unit 7 is the same as that of Embodiment 1.

B. Operation Example

The operation of the table location searching unit 7 so as to realize the third account management method will be explained with reference to FIG. 8.

When the logical database defining unit 9 receives the logical database creating statement 14 (shown in FIG. 3(a)) in which "NULL" indicating a null value is described in the locations of the logical database creating statement 14 shown in FIG. 3(a) where the physical database user ID and, e dare described, the defining unit registers "NULL" in the physical database account 13e or 17e of the logical database control block 13 or 17.

When "NULL" is registered in the physical database account 13e or 17e of the logical database control block 13 or 17, the table location searching unit 7 logs the logical database account in the CONNECT statement in each physical database 1 as it is without replacing it at Step 506. Namely, the table location searching unit 7 uses the logical database account user_A or user_B which is inputted by the user at the time of logging in the logical database LDB_A as it is as an account to be logged in the physical database DB_a or DB_b constituting the logical database LDB_A.

C. Effect of this Embodiment 3

According to this Embodiment 3, even in an environment that the logical databases 4 are shared by a plurality of users, the account to be used for logging in the physical databases 1 can be changed depending on the user. Furthermore, in Embodiment 1 or 2, to prevent each physical database account stored in the logical database dictionary 8. from illegal reference, it is desirable to protect these data by encryption. However, according to this Embodiment 3, it is not necessary to store the account in the logical database dictionary 8 and a means of encryption is not necessary.

In this Embodiment 3, the automatic logging-in function by the register account which is shown in Embodiments 1 and 2 can be included by use of one logical database 4. In this case, it is desirable to register "NULL" in the physical database account 13e or 17e of the physical database 1 in which it is necessary to change the account depending on the user and to register the desired account in the physical database account 13e or 17e of the physical database 1 in which it is not necessary to change the account.

Embodiment 4

According to Embodiment 3, the logical database account which is inputted by the user at the time of logging in the logical databases 4 is logged in some databases 1 among the databases 1 constituting the logical databases 4 in which "NULL" is registered as an account. Therefore, it is necessary that an account which is the same as the logical database account is registered in these databases 1. However, in a distributed database environment that each database 1 is uniquely operated in each department of enterprises, all the database accounts are not always standardized.

Therefore, in this Embodiment 4, by using a fourth account management method which is different from the account management methods used in Embodiments 1 to 3, the account at the time of logging in can be changed depending on the user also for a plurality of physical databases 1 in which different accounts are registered.

A. Constitution of the Logical Database Dictionary

According to the fourth account management method, as shown in FIG. 9(b), the storage area 204 of logical account control block is installed in the logical database dictionary 8. The logical database control block 19 in this Embodiment 4 is an area where the logical database constitution information which can be shared by a plurality of users is stored and the logical account control block 20 in this Embodiment 4 is an area where the account information for each user is stored.

In Embodiments 1 to 3, the logical database control block 13 or 17 in the storage area 202 of private logical database control block is held in correspondence with the OS user name. However, in this Embodiment 4, it is held in correspondence with the logical database user name.

However, in Embodiments 1 to 3, it may be held in correspondence with the logical database user name. In this Embodiment 4, it may be held in correspondence with the OS user name.

In this Embodiment 4, as shown in FIG. 9(a), the logical database control block 19 consists of a logical database name storage area 19a, a logical database account storage area 19b, and a physical database name storage area 19c but does not include the access privilege storage area 13b and the physical database account storage area 13e which are installed in the logical database control block 13 in Embodiment 1. The area 19a is an area for storing the name of logical database 4, and the area 19b is an area for storing the logical database user ID for permitting use of the logical database 4, and the area 19c is an area for storing the names of a plurality of physical databases 1 constituting the logical database 4.

In the logical database account storage area 13c in Embodiment 1, the user ID and password are stored. However, in the logical database account storage area 19b in this Embodiment 4, only the user ID is stored and no password is stored. A plurality of user IDs can be stored in the logical database account storage area 19b. However, in the above area of the logical database control block 19 relating to the logical database 4 which is defined as public, "NULL" is registered. In the physical database name storage area 19c, the physical databases 1 belonging to the logical database 4 to which the logical database control block 19 is assigned are stored.

In the aforementioned storage area 204 of logical account control block, the logical database account control block 20 which is created by the logical database defining unit 9 for each logical database account of the logical database is held. The logical database account control block 20 in this Embodiment 4 consists of a logical database account storage area 20a, an access privilege storage area 20b, a physical database name storage area 20c, and a physical database account storage area 20d. In this embodiment, all the physical database accounts are held in the physical database account storage area 20d but not in the logical database control block 19.

The area 20a of the logical account control block 20 is an area for storing the logical database account consisting of the user ID and and the area 20b is an area for storing the access privilege relating to the logical database account, and the area 20c is an area for storing the name of the physical database 1, and the area 20d is an area for storing the account of the physical database 1. In this Embodiment 4, it can be considered that a plurality of physical database accounts are assigned to a logical database account. Therefore, a plurality of sets of physical database name storage areas 20c and physical database account storage areas 20d are provided so that the physical database names and physical database accounts can be held in correspondence with a plurality of physical databases 1. For example, in a logical account control block 20, the logical database account for identifying a certain user uniquely, the names of all the physical databases 1 which can be accessed by the above user, and the account which is used by the user for logging in are registered beforehand. In this Embodiment 4, the storage order of this combination is used as a priority order at the time of searching of the table location.

B. Processing of the Table Location Searching Unit 7

Next, the processing of the table location searching unit 7 in this Embodiment 4 will be explained. The processing other than the one which is described hereunder is the same as that in Embodiment 2.

(1) Confirmation of the Logical Database Account (Step 504)

The table location searching unit 7 in Embodiment 2 confirms the account at Step 504 by searching the logical account control block 18 holding an account which agrees with the logical database account designated by the CONNECT statement in the storage area 203 of logical account control block. On the other hand, the table location searching unit 7 in this Embodiment 4 confirms the account at Step 504 by checking that the account which is held in the logical database account storage area 20a of the logical account control block 20 in the storage area 204 of logical account control block agrees with the logical database account which is designated by the CONNECT statement.

(2) Confirmation of the Access Privilege (Step 503)

The table location searching unit 7 in Embodiment 2 confirms the access privilege at Step 503 by using the contents of the access privilege storage area 13b of the logical database control block 13. On the other hand, the table location searching unit 7 in this Embodiment 4 confirms the access privilege at Step 503 by using the contents of the access privilege storage area 20b of the logical database control block 20 (when the user ID which agrees with the logical database user ID designated by the CONNECT statement is held in the logical database account storage area 20a).

In Embodiment 2, the access privilege as an OS user is not confirmed for the public logical database. However, in Embodiment 4, the access privilege is a privilege for accessing the logical account control block 20 and the access privilege as an OS user is checked regardless of the public and private logical databases. When the access privilege as an OS user is not necessary in the same way as with Embodiment 1, the processing at Step 503 may be deleted.

In this Embodiment 4, Step 504 is executed prior to Step 503. The reason is that in this Embodiment 4, the access privilege storage area 20b which is referred to at Step 504 exists in the logical account control block 20 which is detected at Step 504.

(3) Decision of an Object to be Logged In (Step 506)

When the table location searching unit 7 in this Embodiment 4 decides the physical database 1 to be logged in, the searching unit refers to both the logical database control block 19 and the logical account control block 20. Namely, the table location searching unit 7 logs in the physical database 1 which is registered in the physical database name storage area 19c of the logical database control block 19 and is registered in the physical database name storage area 20c of the