Object-oriented system, method and article of manufacture for migrating a client-server application (#5)6272556
Abstract
An interprise computing manager in which an application is composed of a client (front end) program which communicates utilizing a network with a server (back end) program. The client and server programs are loosely coupled and exchange information using the network. The client program is composed of a User Interface (UI) and an object-oriented framework (Presentation Engine (PE) framework). The UI exchanges data messages with the framework. The framework is designed to handle two types of messages: (1) from the UI, and (2) from the server (back end) program via the network. The framework includes a component, the mediator which manages messages coming into and going out of the framework. A distributed computer system is presented with software for a client computer, a server computer and a network for connecting the client computer to the server computer which utilizes an execution framework code segment configured to couple the server computer and the client computer via the network. A plurality of client computer code segments are stored on the server. Each client code segment is designed for transmission over the network to a client computer to initiate coupling. A plurality of server computer code segments are also stored on the server. A particular client code segment is selected, installed and executed in response to initiation of coupling via the network with a particular client utilizing the transmitted client computer code segment for communicating via a particular communication protocol to a corresponding server code segment on the server computer. Finally, a framework for migrating existing applications into the execution framework is integrated into the client-server architecture.
Claims
Having thus described our invention, what we claim as new, and desire to secure by Letters Patent is:
1. A server for a distributed system, comprising:
(a) a client computer;
(b) a server computer;
(c) a network connecting the client computer to the server computer, wherein the network operates according to the TCP/IP protocol;
(d) an execution framework code segment configured to couple the server computer and the client computer via the network, comprising:
(1) a plurality of client computer code segments resident on the server computer, each one of the plurality of client computer code segments containing Java code and being associated with a single application program initiated on the client computer, and each for transmission over the network to a client computer to initiate coupling;
(2) a plurality of server computer code segments resident on the server computer, each one of the plurality of server computer code segments being associated with a single application program initiated on the client computer, which execute on the server computer in response to initiation of coupling via the network with a particular client computer utilizing the transmitted client computer code segment for communicating via a particular communication protocol, thereby enabling execution of the single application program in a distributed manner between the client computer and the server computer wherein a single copy of the single application program is distributed between the client computer and server computer;
(e) a plurality of definitions that define the plurality of client computer code segments and each of the plurality of definitions defining how to associate the plurality of client computer code segments and the plurality of server computer code segments into applications in response to a request by the client computer wherein the plurality of client computer code segments and the plurality of server computer code segments contain only executable computer programming instructions;
(f) the client computer code segment including a mediator state machine which receives a plurality of messages, determines which message should be handled by which part of the execution framework, and forwards the message for further processing to the execution framework;
(g) the execution framework dispatches messages and initiates events in response to characteristics of the message transferred by the mediator state machine; and
(h) a framework for migrating existing applications into the execution framework.
2. The server for a distributed system as recited in claim 1, including a template for a client program that includes a client communication library.
3. The server for a distributed system as recited in claim 1, including a template for a client program that includes an user-extensible model.
4. The server for a distributed system as recited in claim 1, including a template for a client program that includes an user-extensible user interface adaptor.
5. The server for a distributed system as recited in claim 1, including application program interfaces for defining message events from a network graphical user interface to the execution framework.
6. The server for a distributed system as recited in claim 1, including application program interfaces for registering graphical user interface message handlers.
7. The server for a distributed system as recited in claim 1, including application program interfaces that register execution framework adaptor handlers.
8. The server for a distributed system as recited in claim 1, including application program interfaces that define message events to the communciation layer.
9. The server for a distributed system as recited in claim 1, including appliacation program interfaces from a server communication library for sending message events from the back end code, and registering at least one handler for at least one message event.
10. A method for distributing computing between a server computer system and a client computer system coupled by a network, comprising the steps of:
(a) responding to a request from a client computer system to a server computer system;
(b) downloading an execution framework code segment configured to couple the server computer and the client computer via the network, wherein the network operates according to the TCP/IP protocol comprising:
(1) a plurality of client computer code segments resident on the server computer, each one of the plurality of client computer code segments containing Java code and being associated with a single application program initiated on the client computer, and each for transmission over the network to a client computer to initiate coupling;
(2) a plurality of server computer code segments resident on the server computer, each one of the plurality of server computer code segments being associated with a single application program initiated on the client computer, which execute on the server computer in response to initiation of coupling via the network with a particular client computer utilizing the transmitted client computer code segment for communicating via the TCP/IP protocol, thereby enabling execution of the single application program in a distributed manner between the client computer and the server computer wherein one copy of the single application program is distributed between the client computer and server computer;
(c) a plurality of definitions that define the plurality of client computer code segments and each of the plurality of definitions defining how to associate the plurality of client computer code segments and the plurality of server computer code segments into applications in response to a request by the client computer wherein the plurality of client computer code segments and the plurality of server computer code segments contain only executable computer progamming instructions;
(d) receiving a plurality of messages in a mediator state machine in the client computer code segment;
(e) determining which messages should be handled by which part of the execution framework;
(f) forwarding the messages for further processing to the execution framework
(g) dispatching messages and initiating events in response to characteristics of the message transferred by the mediator state machine; and
(h) migrating existing applications into the execution framework.
11. The method for distributing computing between a server computer system and a client computer system coupled by a network as recited in claim 10, including facilitating migration of computer applications utilizing a template for a client program that includes a client communication library.
12. The method for distributing computing between a server computer system and a client computer system coupled by a network as recited in claim 11, wherein the template for a client program includes an user-extensible model.
13. The method for distributing computing between a server computer system and a client computer system coupled by a network as recited in claim 10, wherein the template for a client program includes an user-extensible user interface adaptor.
14. The method for distributing computing between a server computer system and a client computer system coupled by a network as recited in claim 10, including the step of defining message events from a network graphical user interface to the execution framework.
15. The method for distributing computing between a server computer system and a client computer system coupled by a network as recited in claim 10, including the step of registering graphical user interface message handlers.
16. The method for distributing computing between a server computer system and a client computer system coupled by a network as recited in claim 10, including the step of registering execution framework adaptor handlers.
17. The method for distributing computing between a server computer system and a client computer system coupled by a network as recited in claim 10, including the step of defining message events to the communciation layer.
18. The method for distributing computing between a server computer system and a client computer system coupled by a network as recited in claim 10, including the step of sending message events from the back end code, and registering at least one handler for at least one message event.
19. A computer program embodied on a computer-readable medium for enabling a distributed computer system, comprising:
(a) a code segment for responding to a request from a client computer system to a server computer system;
(b) an execution framework code segment configured to couple the server computer and the client computer via the network, wherein the network operates according to the TCP/IP protocol, comprising:
(1) a plurality of client computer code segments resident on the server computer, each one of the plurality of client computer code segments containing Java code and being associated with a single application program initiated on the client computer, and each for transmission over the network to a client computer to initiate coupling;
(2) a plurality of server computer code segments resident on the server computer, each one of the plurality of client computer code segments being associated with a single application program initiated on the client computer, which execute on the server in response to initiation of coupling via the network with a particular client utilizing the transmitted client computer code segment for communicating via the TCP/IP protocol, thereby enabling execution of the single application program in a distributed manner between the client computer and the server computer wherein one copy of the single application program is distributed between the client computer and server computer;
(c) a plurality of definitions that define the plurality of client computer code segments and each of the plurality of definitions defining how to associate the plurality of client computer code segments and the plurality of server computer code segments into applications in response to a request by the client computer wherein the plurality of client computer code segments and the plurality of server computer code segments contain only executable computer programming instructions;
(d) the client computer code segment including a mediator state machine which receives a plurality of messages, determines which message should be handled by which part of the execution framework, and forwards the message for further processing to the execution framework;
(e) the execution framework dispatches messages and initiates events in response to characteristics of the message transferred by the mediator state machine; and
(f) a framework for migrating existing applications into the execution framework.
20. The computer program embodied on a computer-readable medium for enabling a distributed computer system as recited in claim 19, including a template for a client program that includes a client communication library.
Description
COPYRIGHT NOTIFICATION
Portions of this patent application contain materials that are subject to copyright protection. The copyright owner has no objection to the facsimile reproduction by anyone of the patent document, or the patent disclosure, as it appears in the Patent and Trademark Office.
FIELD OF THE INVENTION
This invention generally relates to improvements in computer systems and, more particularly, to operating system software for managing Interprise computing in a network user interface.
BACKGROUND OF THE INVENTION
One of the most important aspects of a modern computing system is the interface between the human user and the machine. The earliest and most popular type of interface was text based; a user communicated with the machine by typing text characters on a keyboard and the machine communicated with the user by displaying text characters on a display screen. More recently, graphic user interfaces have become popular where the machine communicates with a user by displaying graphics, including text and pictures, on a display screen and the user communicates with the machine both by typing in textual commands and by manipulating the displayed pictures with a pointing device, such as a mouse.
Many modern computer systems operate with a graphic user interface called a window environment. In a typical window environment, the graphical display portrayed on the display screen is arranged to resemble the surface of an electronic "desktop" and each application program running on the computer is represented as one or more electronic "paper sheets" displayed in rectangular regions of the screen called "windows".
Each window region generally displays information which is generated by the associated application program and there may be several window regions simultaneously present on the desktop, each representing information generated by a different application program. An application program presents information to the user through each window by drawing or "painting" images, graphics or text within the window region. The user, in turn, communicates with the application by "pointing at" objects in the window region with a cursor which is controlled by a pointing device and manipulating or moving the objects and also by typing information into the keyboard. The window regions may also be moved around on the display screen and changed in size and appearance so that the user can arrange the desktop in a convenient manner.
Each of the window regions also typically includes a number of standard graphical objects such as sizing boxes, buttons and scroll bars. These features represent user interface devices that the user can point at with the cursor to select and manipulate. When the devices are selected or manipulated, the underlying application program is informed, via the window system, that the control has been manipulated by the user.
In general, the window environment described above is part of the computer operating system. The operating system also typically includes a collection of utility programs that enable the computer system to perform basic operations, such as storing and retrieving information on a disc memory, communicating with a network and performing file operations including the creation, naming and renaming of files and, in some cases, performing diagnostic operations in order to discover or recover from malfunctions.
The last part of the computing system is the "application program" which interacts with the operating system to provide much higher level functionality, perform a specific task and provide a direct interface with the user. The application program typically makes use of operating system functions by sending out series of task commands to the operating system which then performs a requested task. For example, the application program may request that the operating system store particular information on the computer disc memory or display information on the video display.
FIG. 1 is a schematic illustration of a typical prior art computer system utilizing both an application program and an operating system. The computer system is schematically represented by box 100, the application is represented by box 102 and the operating system by box 106. The previously-described interaction between the application program 102 and the operating system 106 is illustrated schematically by arrow 104. This dual program system is used on many types of computer systems ranging from main frames to personal computers.
The method for handling screen displays varies from computer to computer and, in this regard, FIG. 1 represents a prior art personal computer system. In order to provide screen displays, application program 102 generally stores information to be displayed (the storing operation is shown schematically by arrow 108) into a screen buffer 110. Under control of various hardware and software in the system the contents of the screen buffer 110 are read out of the buffer and provided, as indicated schematically by arrow 114, to a display adapter 112. The display adapter 112 contains hardware and software (sometimes in the form of firmware) which converts the information in screen buffer 110 to a form which can be used to drive the display monitor 118 which is connected to display adapter 112 by cable 116.
The prior art configuration shown in FIG. 1 generally works well in a system where a single application program 102 is running at any given time. This simple system works properly because the single application program 102 can write information into any area of the entire screen buffer area 110 without causing a display problem. However, if the configuration shown in FIG. 1 is used in a computer system where more than one application program 102 can be operational at the same time (for example, a "multi-tasking" computer system) display problems can arise. More particularly, if each application program has access to the entire screen buffer 110, in the absence of some direct communication between applications, one application may overwrite a portion of the screen buffer which is being used by another application, thereby causing the display generated by one application to be overwritten by the display generated by the other application.
Accordingly, mechanisms were developed to coordinate the operation of the application programs to ensure that each application program was confined to only a portion of the screen buffer thereby separating the other displays. This coordination became complicated in systems where windows were allowed to "overlap" on the screen display. When the screen display is arranged so that windows appear to "overlap", a window which appears on the screen in "front" of another window covers and obscures part of the underlying window. Thus, except for the foremost window, only part of the underlying windows may be drawn on the screen and be "visible" at any given time. Further, because the windows can be moved or resized by the user, the portion of each window which is visible changes as other windows are moved or resized. Thus, the portion of the screen buffer which is assigned to each application window also changes as windows from other applications are moved or resized.
In order to efficiently manage the changes to the screen buffer necessary to accommodate rapid screen changes caused by moving or resizing windows, the prior art computer arrangement shown in FIG. 1 was modified as shown in FIG. 2. In this new arrangement computer system 200 is controlled by one or more application programs, of which programs 202 and 216 are shown, which programs may be running simultaneously in the computer system. Each of the programs interfaces with the operating system 204 as illustrated schematically by arrows 206 and 220. However, in order to display information on the display screen, application programs 202 and 216 send display information to a central window manager program 218 located in the operating system 204. The window manager program 218, in turn, interfaces directly with the screen buffer 210 as illustrated schematically by arrow 208. The contents of screen buffer 210 are provided, as indicated by arrow 212, to a display adapter 214 which is connected by a cable 222 to a display monitor 224.
In such a system, the window manager 218 is generally responsible for maintaining all of the window displays that the user views during operation of the application programs. Since the window manager 218 is in communication with all application programs, it can coordinate between applications to insure that window displays do not overlap. Consequently, it is generally the task of the window manager to keep track of the location and size of the window and the window areas which must be drawn and redrawn as windows are moved.
The window manager 218 receives display requests from each of the applications 202 and 216. However, since only the window manager 218 interfaces with the screen buffer 210, it can allocate respective areas of the screen buffer 210 for each application and insure that no application erroneously overwrites the display generated by another application. There are a number of different window environments commercially available which utilize the arrangement illustrated in FIG. 2. These include the X/Window Operating environment, the WINDOWS, graphical user interface developed by the Microsoft Corporation and the OS/2 Presentation Manager, developed by the International Business Machines Corporation, and the Macintosh OS, developed by Apple Computer Corporation.
Each of these window environments has its own internal software architecture, but the architectures can all be classified by using a multi-layer model similar to the multi-layer models used to describe computer network software. A typical multi-layer model includes the following layers:
User Interface
Window Manager
Resource Control and Communication
Component Driver Software
Computer Hardware
where the term "window environment" refers to all of the above layers taken together.
The lowest or computer hardware level includes the basic computer and associated input and output devices including display monitors, keyboards, pointing devices, such as mice or trackballs, and other standard components, including printers and disc drives. The next or "component driver software" level consists of device-dependent software that generates the commands and signals necessary to operate the various hardware components. The resource control and communication layer interfaces with the component drivers and includes software routines which allocate resources, communicate between applications and multiplex communications generated by the higher layers to the underlying layers. The window manager handles the user interface to basic window operations, such as moving and resizing windows, activating or inactivating windows and redrawing and repainting windows. The final user interface layer provides high level facilities that implement the various controls (buttons, sliders, boxes and other controls) that application programs use to develop a complete user interface.
Although the arrangement shown in FIG. 2 solves the display screen interference problem, it suffers from the drawback that the window manager 218 must process the screen display requests generated by all of the application programs. Since the requests can only be processed serially, the requests are queued for presentation to the window manager before each request is processed to generate a display on terminal 224. In a display where many windows are present simultaneously on the screen, the window manager 218 can easily become a "bottleneck" for display information and prevent rapid changes by of the display by the application programs 202 and 216. A delay in the redrawing of the screen when windows are moved or repositioned by the user often manifests itself by the appearance that the windows are being constructed in a piecemeal fashion which becomes annoying and detracts from the operation of the system.
This problem becomes even more accentuated in a client-server environment where many applications are all in contention for very limited resources. The Internet has permeated the workplace as a communication medium of choice. Since the internet is accessible from almost any point in a typical business enterprise a new buzzword has evolved from the form enterprise computer into an "enterprise" computer. Interprise is a concatenation of internet and enterprise.
In today's client server enterprises, applications that exist in current client server enterprises are not really built to be managed since they are architected for distributed system environments. New systems are also required to be evolutionary, not revolutionary. Redesign of current systems that require significant expense need to be avoided.
A system is required that allows a user to create manageable applications, that can be readily deployed, installed on a variety of platforms, and configured to facilitate partitioning them on clients versus servers and administer the applications once they're running. Systems don't always break because of failure, errors, or bugs, they sometimes break because the enterprise itself is complicated and somebody does something unexpected somewhere which will bring the whole system down. When the system does come down, then a system administrator must be able to readily identify the problems, and deal with them in an effective manner so that a business doesn't stop functioning when one of these unforeseen events happens.
The application should be designed based on domain requirements, so it is independent of any platform underneath, and fits more with how commercial developers work. In the commercial world, the development process isn't that important. The regular employees are not applications developers or programmers. Companies usually hire such work out; they get consultants to do that kind of work. Depending on the company and what they want done, it usually hires a consulting firm, individual consultants, or smaller groups of consultants to come in, help it develop an application. Their goal is the end application, which must be maintained. The company configures it, evolves it, and grows it. To allow for modification, the development task must be modular to allow different groups of people working on different parts of an application, without requiring any one group to understand every detail of the whole application of the enterprise.
The second criterion requires minimal extra knowledge, burden or sophistication on the part of the people developing the system. Most companies do not desire to have their business hinge on a single individual. Rather, they desire to have people who are primarily domain experts who can work with well-understood tools to produce a application matching company requirements quickly without making special demands on the company.
SUMMARY OF THE INVENTION
The foregoing problems are overcome in an illustrative embodiment of the invention in which an application is composed of a client (front end) program which communicates utilizing a network with a server (back end) program. The client and server programs are loosely coupled and exchange information using the network. The client program is composed of a User Interface (UI) and an object-oriented framework (Presentation Engine (PE) framework). The UI exchanges data messages with the framework. The framework is designed to handle two types of messages: (1) from the UI, and (2) from the server (back end) program via the network. The framework includes a component, the mediator which manages messages coming into and going out of the framework.
A distributed computer system is disclosed with software for a client computer, a server computer and a network for connecting the client computer to the server computer which utilizes an execution framework code segment configured to couple the server computer and the client computer via the network. A plurality of client computer code segments are stored on the server. Each client code segment is designed for transmission over the network to a client computer to initiate coupling. A plurality of server computer code segments are also stored on the server. A particular client code segment is selected, installed and executed in response to initiation of coupling via the network with a particular client utilizing the transmitted client computer code segment for communicating via a particular communication protocol to a corresponding server code segment on the server computer. Finally, a framework for migrating existing applications into the execution framework is integrated into the client-server architecture.
BRIEF DESCRIPTION OF THE DRAWINGS
The above and further advantages of the invention may be better understood by referring to the following description in conjunction with the accompanying drawings, in which:
FIG. 1 is a schematic block diagram of a prior art computer system showing the relationship of the application program, the operating system, the screen buffer and, the display monitor;
FIG. 2 is a schematic block diagram of a modification of the prior art system shown in FIG. 1 which allows several application programs running simultaneously to generate screen displays;
FIG. 3 is a block schematic diagram of a computer system for example, a personal computer system on which the inventive object oriented window manager operates;
FIG. 4 is a block diagram in accordance with a preferred embodiment;
FIG. 5 illustrates how a preferred embodiment leverages Java to facilitate the establishment and implementation of sever-centric policies;
FIG. 6 illustrates the processing associated with application startup in accordance with a preferred embodiment;
FIG. 7 illustrates the three fundamental components of an application in accordance with a preferred embodiment;
FIG. 8 illustrates the migration of an existing client-server application to one supported by a preferred embodiment;
FIG. 9 is a block diagram illustrating a PE 960 in accordance with a preferred embodiment;
FIG. 10 is a block diagram of a prior art client server architecture in accordance with a preferred embodiment;
FIG. 11 illustrates an application in accordance with an alternate embodiment;
FIG. 12 illustrates a server 1210 establishing contact with a client 1200 in accordance with an alternate embodiment;
FIG. 13 illustrates a loosely coupled client-server application in accordance with an alternate embodiment;
FIG. 14 illustrates the system integration task necessary to develop an application 1430 in accordance with a preferred embodiment;
FIG. 15 is a block diagram illustrating the modular design of a client application in accordance with a preferred embodiment;
FIG. 16 is a block diagram of a framework in accordance with an alternate embodiment;
FIG. 17 illustrates the basic building blocks in accordance with an alternate embodiment;
FIG. 18 is a block diagram highlighting the steps utilized to extend the framework in accordance with a preferred embodiment;
FIG. 19 is an illustration of a PE Object in accordance with a preferred embodiment;
FIG. 20 is an illustration of a PE Event Handler 2000 used by Views to handle incoming messages and UI events in accordance with a preferred embodiment;
FIG. 21 illustrates a PEInfo object 2100 data in accordance with a preferred embodiment;
FIG. 22 illustrates incoming message flow to a model in accordance with a preferred embodiment;
FIG. 23 illustrates incoming messages mapping a UI to a Model in accordance with a preferred embodiment;
FIG. 24 illustrates outgoing messages mapping a model to messages in accordance with a preferred embodiment;
FIG. 25 illustrates outgoing messages mapping a model to a UI in accordance with a preferred embodiment;
FIG. 26 illustrates the steps associated with launching an application URL in accordance with a preferred embodiment;
FIG. 27 describes the forms of a Presentation Engine, as an abstract Java class, a template for development, and an executable component in an application in accordance with a preferred embodiment;
FIG. 28 describes the functions developers must fill in using the server program template in accordance with a preferred embodiment;
FIG. 29 illustrates Server Properties in accordance with a preferred embodiment; and
FIG. 30 is a table of client and server side exceptions in accordance with a preferred embodiment.
DETAILED DESCRIPTION
The invention is preferably practiced in the context of an operating system resident on a computer such as a SUN, IBM, PS/2, or Apple, Macintosh, computer. A representative hardware environment is depicted in FIG. 3, which illustrates a typical hardware configuration of a computer 300 in accordance with the subject invention. The computer 300 is controlled by a central processing unit 302 (which may be a conventional microprocessor) and a number of other units, all interconnected via a system bus 308, are provided to accomplish specific tasks. Although a particular computer may only have some of the units illustrated in FIG. 3, or may have additional components not shown, most computers will include at least the units shown.
Specifically, computer 300 shown in FIG. 3 includes a random access memory (RAM) 306 for temporary storage of information, a read only memory (ROM) 304 for permanent storage of the computer's configuration and basic operating commands and an input/output (I/O) adapter 310 for connecting peripheral devices such as a disk unit 313 and printer 314 to the bus 308, via cables 315 and 312, respectively. A user interface adapter 316 is also provided for connecting input devices, such as a keyboard 320, and other known interface devices including mice, speakers and microphones to the bus 308. Visual output is provided by a display adapter 318 which connects the bus 308 to a display device 322, such as a video monitor. The computer has resident thereon and is controlled and coordinated by operating system software such as the SUN Solaris or JavaOS operating system.
In a preferred embodiment, the invention is implemented in the C++ programming language using object-oriented programming techniques. C++ is a compiled language, that is, programs are written in a human-readable script and this script is then provided to another program called a compiler which generates a machine-readable numeric code that can be loaded into, and directly executed by, a computer. As described below, the C++ language has certain characteristics which allow a software developer to easily use programs written by others while still providing a great deal of control over the reuse of programs to prevent their destruction or improper use. The C++ language is well-known and many articles and texts are available which describe the language in detail. In addition, C++ compilers are commercially available from several vendors including Borland International, Inc. and Microsoft Corporation. Accordingly, for reasons of clarity, the details of the C++ language and the operation of the C++ compiler will not be discussed further in detail herein. As will be understood by those skilled in the art, Object-Oriented Programming (OOP) techniques involve the definition, creation, use and destruction of "objects". These objects are software entities comprising data elements and routines, or functions, which manipulate the data elements. The data and related functions are treated by the software as an entity and can be created, used and deleted as if they were a single item. Together, the data and functions enable objects to model virtually any real-world entity in terms of its characteristics, which can be represented by-the data elements, and its behavior, which can be represented by its data manipulation functions. In this way, objects can model concrete things like people and computers, and they can also model abstract concepts like numbers or geometrical designs.
Objects are defined by creating "classes" which are not objects themselves, but which act as templates that instruct the compiler how to construct the actual object. A class may, for example, specify the number and type of data variables and the steps involved in the functions which manipulate the data. An object is actually created in the program by means of a special function called a constructor which uses the corresponding class definition and additional information, such as arguments provided during object creation, to construct the object. Likewise objects are destroyed by a special function called a destructor. Objects may be used by using their data and invoking their functions.
The principle benefits of object-oriented programming techniques arise out of three basic principles; encapsulation, polymorphism and inheritance. More specifically, objects can be designed to hide, or encapsulate, all, or a portion of, the internal data structure and the internal functions. More particularly, during program design, a program developer can define objects in which all or some of the data variables and all or some of the related functions are considered "private" or for use only by the object itself. Other data or functions can be declared "public" or available for use by other programs. Access to the private variables by other programs can be controlled by defining public functions for an object which access the object's private data. The public functions form a controlled and consistent interface between the private data and the "outside" world. Any attempt to write program code which directly accesses the private variables causes the compiler to generate an error during program compilation which error stops the compilation process and prevents the program from being run.
Polymorphism is a concept which allows objects and functions which have the same overall format, but which work with different data, to function differently in order to produce consistent results. For example, an addition function may be defined as variable A plus variable B (A+B) and this same format can be used whether the A and B are numbers, characters or dollars and cents. However, the actual program code which performs the addition may differ widely depending on the type of variables that comprise A and B. Polymorphism allows three separate function definitions to be written, one for each type of variable (numbers, characters and dollars). After the functions have been defined, a program can later refer to the addition function by its common format (A+B) and, during compilation, the C++ compiler will determine which of the three functions is actually being used by examining the variable types. The compiler will then substitute the proper function code. Polymorphism allows similar functions which produce analogous results to be "grouped" in the program source code to produce a more logical and clear program flow.
The third principle which underlies object-oriented programming is inheritance, which allows program developers to easily reuse pre-existing programs and to avoid creating software from scratch. The principle of inheritance allows a software developer to declare classes (and the objects which are later created from them) as related. Specifically, classes may be designated as subclasses of other base classes. A subclass "inherits" and has access to all of the public functions of its base classes just as if these function appeared in the subclass. Alternatively, a subclass can override some or all of its inherited functions or may modify some or all of its inherited functions merely by defining a new function with the same form (overriding or modification does not alter the function in the base class, but merely modifies the use of the function in the subclass). The creation of a new subclass which has some of the functionality (with selective modification) of another class allows software developers to easily customize existing code to meet their particular needs.
Although object-oriented programming offers significant improvements over other programming concepts, program development still requires significant outlays of time and effort, especially if no pre-existing software programs are available for modification. Consequently, a prior art approach has been to provide a program developer with a set of pre-defined, interconnected classes which create a set of objects and additional miscellaneous routines that are all directed to performing commonly-encountered tasks in a particular environment. Such pre-defined classes and libraries are typically called "frameworks" and essentially provide a pre-fabricated structure for a working application.
For example, a framework for a user interface might provide a set of pre-defined graphic interface objects which create windows, scroll bars, menus, etc. and provide the support and "default" behavior for these graphic interface objects. Since frameworks are based on object-oriented techniques, the pre-defined classes can be used as base classes and the built-in default behavior can be inherited by developer-defined subclasses and either modified or overridden to allow developers to extend the framework and create customized solutions in a particular area of expertise. This object-oriented approach provides a major advantage over traditional programming since the programmer is not changing the original program, but rather extending the capabilities of the original program. In addition, developers are not blindly working through layers of code because the framework provides architectural guidance and modeling and, at the same time, frees the developers to supply specific actions unique to the problem domain.
There are many kinds of frameworks available, depending on the level of the system involved and the kind of problem to be solved. The types of frameworks range from high-level application frameworks that assist in developing a user interface, to lower-level frameworks that provide basic system software services such as communications, printing, file systems support, graphics, etc. Commercial examples of application frameworks include MacApp (Apple), Bedrock (Symantec), OWL (Borland), NeXT Step App Kit (NeXT), and Smalltalk-80 MVC (ParcPlace).
While the framework approach utilizes all the principles of encapsulation, polymorphism, and inheritance in the object layer, and is a substantial improvement over other programming techniques, there are difficulties which arise. Application frameworks generally consist of one or more object "layers" on top of a monolithic operating system and even with the flexibility of the object layer, it is still often necessary to directly interact with the underlying operating system by means of awkward procedural calls.
In the same way that an application framework provides the developer with prefab functionality for an application program, a system framework, such as that included in a preferred embodiment, can provide a prefab functionality for system level services which developers can modify or override to create customized solutions, thereby avoiding the awkward procedural calls necessary with the prior art application frameworks programs. For example, consider a display framework which could provide the foundation for creating, deleting and manipulating windows to display information generated by an application program. An application software developer who needed these capabilities would ordinarily have to write specific routines to provide them. To do this with a framework, the developer only needs to supply the characteristics and behavior of the finished display, while the framework provides the actual routines which perform the tasks.
A preferred embodiment takes the concept of frameworks and applies it throughout the entire system, including the application and the operating system. For the commercial or corporate developer, systems integrator, or OEM, this means all of the advantages that have been illustrated for a framework such as MacApp can be leveraged not only at the application level for such things as text and user interfaces, but also at the system level, for services such as printing, graphics, multi-media, file systems, I/O, testing, etc.
A preferred embodiment is written using JAVA, C, and the C++ language and utilizes object oriented programming methodology. Object oriented programming (OOP) has become increasingly used to develop complex applications. As OOP moves toward the mainstream of software design and development, various software solutions require adaptation to make use of the benefits of OOP. A need exists for these principles of OOP to be applied to a messaging interface of an electronic messaging system such that a set of OOP classes and objects for the messaging interface can be provided.
OOP is a process of developing computer software using objects, including the steps of analyzing the problem, designing the system, and constructing the program. An object is a software package that contains both data and a collection of related structures and procedures. Since it contains both data and a collection of structures and procedures, it can be visualized as a self-sufficient component that does not require other additional structures, procedures or data to perform its specific task. OOP, therefore, views a computer program as a collection of largely autonomous components, called objects, each of which is responsible for a specific task. This concept of packaging data, structures, and procedures together in one component or module is called encapsulation.
In general, OOP components are reusable software modules which present an interface that conforms to an object model and which are accessed at run-time through a component integration architecture. A component integration architecture is a set of architecture mechanisms which allow software modules in different process spaces to utilize each others' capabilities or functions. This is generally done by assuming a common component object model on which to build the architecture.
It is worthwhile to differentiate between an object and a class of objects at this point. An object is a single instance of the class of objects, which is often just called a class. A class of objects can be viewed as a blueprint, from which many objects can be formed. OOP allows the programmer to create an object that is a part of another object. For example, the object representing a piston engine is said to have a composition-relationship with the object representing a piston. In reality, a piston engine comprises a piston, valves and many other components; the fact that a piston is an element of a piston engine can be logically and semantically represented in OOP by two objects. OOP also allows creation of an object that "depends from" another object. If there are two objects, one representing a piston engine and the other representing a piston engine wherein the piston is made of ceramic, then the relationship between the two objects is not that of composition. A ceramic piston engine does not make up a piston engine. Rather it is merely one kind of piston engine that has one more limitation than the piston engine; its piston is made of ceramic. In this case, the object representing the ceramic piston engine is called a derived object, and it inherits all of the aspects of the object representing the piston engine and adds further limitation or detail to it. The object representing the ceramic piston engine "depends from" the object representing the piston engine. The relationship between these objects is called inheritance.
When the object or class representing the ceramic piston engine inherits all of the aspects of the objects representing the piston engine, it inherits the thermal characteristics of a standard piston defined in the piston engine class. However, the ceramic piston engine object overrides these ceramic specific thermal characteristics, which are typically different from those associated with a metal piston. It skips over the original and uses new functions related to ceramic pistons. Different kinds of piston engines have different characteristics, but may have the same underlying functions associated with it (e.g., how many pistons in the engine, ignition sequences, lubrication, etc.). To access each of these functions in any piston engine object, a programmer would call the same functions with the same names, but each type of piston engine may have different/overriding implementations of functions behind the same name. This ability to hide different implementations of a function behind the same name is called polymorphism and it greatly simplifies communication among objects.
With the concepts of composition-relationship, encapsulation, inheritance and polymorphism, an object can represent just about anything in the real world. In fact, our logical perception of the reality is the only limit on determining the kinds of things that can become objects in object-oriented software. Some typical categories are as follows:
Objects can represent physical objects, such as automobiles in a traffic-flow simulation, electrical components in a circuit-design program, countries in an economics model, or aircraft in an air-traffic-control system.
Objects can represent elements of the computer-user environment such as windows, menus or graphics objects.
An object can represent an inventory, such as a personnel file or a table of the latitudes and longitudes of cities.
An object can represent user-defined data types such as time, angles, and complex numbers, or points on the plane.
With this enormous capability of an object to represent just about any logically separable matters, OOP allows the software developer to design and implement a computer program that is a model of some aspects of reality, whether that reality is a physical entity, a process, a system, or a composition of matter. Since the object can represent anything, the software developer can create an object which can be used as a component in a larger software project in the future.
If 90% of a new OOP software program consists of proven, existing components made from preexisting reusable objects, then only the remaining 10% of the new software project has to be written and tested from scratch. Since 90% already came from an inventory of extensively tested reusable objects, the potential domain from which an error could originate is 10% of the program. As a result, OOP enables software developers to build objects out of other, previously built, objects.
This process closely resembles complex machinery being built out of assemblies and sub-assemblies. OOP technology, therefore, makes software engineering more like hardware engineering in that software is built from existing components, which are available to the developer as objects. All this adds up to an improved quality of the software as well as an increased speed of its development.
Programming languages are beginning to fully support the OOP principles, such as encapsulation, inheritance, polymorphism, and composition-relationship. With the advent of the C++ language, many commercial software developers have embraced OOP. C++ is an OOP language that offers a fast, machine-executable code. Furthermore, C++ is suitable for both commercial-application and systems-programming projects. For now, C++ appears to be the most popular choice among many OOP programmers, but there is a host of other OOP languages, such as Smalltalk, common lisp object system (CLOS), and Eiffel. Additionally, OOP capabilities are being added to more traditional popular computer programming languages such as Pascal.
The benefits of object classes can be summarized, as follows:
Objects and their corresponding classes break down complex programming problems into many smaller, simpler problems.
Encapsulation enforces data abstraction through the organization of data into small, independent objects that can communicate with each other. Encapsulation protects the data in an object from accidental damage, but allows other objects to interact with that data by calling the object's member functions and structures.
Subclassing and inheritance make it possible to extend and modify objects through deriving new kinds of objects from the standard classes available in the system. Thus, new capabilities are created without having to start from scratch.
Polymorphism and multiple inheritance make it possible for different programmers to mix and match characteristics of many different classes and create specialized objects that can still work with related objects in predictable ways.
Class hierarchies and containment hierarchies provide a flexible mechanism for modeling real-world objects and the relationships among them.
Libraries of reusable classes are useful in many situations, but they also have some limitations. For example:
Complexity. In a complex system, the class hierarchies for related classes can become extremely confusing, with many dozens or even hundreds of classes.
Flow of control. A program written with the aid of class libraries is still responsible for the flow of control (i.e., it must control the interactions among all the objects created from a particular library). The programmer has to decide which functions to call at what times for which kinds of objects.
Duplication of effort. Although class libraries allow programmers to use and reuse many small pieces of code, each programmer puts those pieces together in a different way. Two different programmers can use the same set of class libraries to write two programs that do exactly the same thing but whose internal structure (i.e., design) may be quite different, depending on hundreds of small decisions each programmer makes along the way. Inevitably, similar pieces of code end up doing similar things in slightly different ways and do not work as well together as they should.
Class libraries are very flexible. As programs grow more complex, more programmers are forced to reinvent basic solutions to basic problems over and over again. A relatively new extension of the class library concept is to have a framework of class libraries. This framework is more complex and consists of significant collections of collaborating classes that capture both the small scale patterns and major mechanisms that implement the common requirements and design in a specific application domain. They were first developed to free application programmers from the chores involved in displaying menus, windows, dialog boxes, and other standard user interface elements for personal computers.
Frameworks also represent a change in the way programmers think about the interaction between the code they write and code written by others. In the early days of procedural programming, the programmer called libraries provided by the operating system to perform certain tasks, but basically the program executed down the page from start to finish, and the programmer was solely responsible for the flow of control. This was appropriate for printing out paychecks, calculating a mathematical table, or solving other problems with a program that executed in just one way.
The development of graphical user interfaces began to turn this procedural programming arrangement inside out. These interfaces allow the user, rather than program logic, to drive the program and decide when certain actions should be performed. Today, most personal computer software accomplishes this by means of an event loop which monitors the mouse, keyboard, and other sources of external events and calls the appropriate parts of the programmer's code according to actions that the user performs. The programmer no longer determines the order in which events occur. Instead, a program is divided into separate pieces that are called at unpredictable times and in an unpredictable order. By relinquishing control in this way to users, the developer creates a program that is much easier to use. Nevertheless, individual pieces of the program written by the developer still call libraries provided by the operating system to accomplish certain tasks, and the programmer must still determine the flow of control within each piece after it's called by the event loop. Application code still "sits on top of" the system.
Even event loop programs require programmers to write a lot of code that should not need to be written separately for every application. The concept of an application framework carries the event loop concept further. Instead of dealing with all the nuts and bolts of constructing basic menus, windows, and dialog boxes and then making these things all work together, programmers using application frameworks start with working application code and basic user interface elements in place. Subsequently, they build from there by replacing some of the generic capabilities of the framework with the specific capabilities of the intended application.
Application frameworks reduce the total amount of code that a programmer has to write from scratch. However, because the framework is really a generic application that displays windows, supports copy and paste, and so on, the programmer can also relinquish control to a greater degree than event loop programs permit. The framework code takes care of almost all event handling and flow of control, and the programmer's code is called only when the framework needs it (e.g., to create or manipulate a proprietary data structure).
A programmer writing a framework program not only relinquishes control to the user (as is also true for event loop programs), but also relinquishes the detailed flow of control within the program to the framework. This approach allows the creation of more complex systems that work together in interesting ways, as opposed to isolated programs, having custom code, being created over and over again for similar problems.
Thus, as is explained above, a framework basically is a collection of cooperating classes that make up a reusable design solution for a given problem domain. It typically includes objects that provide default behavior (e.g., for menus and windows), and programmers use it by inheriting some of that default behavior and overriding other behavior so that the framework calls application code at the appropriate times.
There are three main differences between frameworks and class libraries:
Behavior versus protocol. Class libraries are essentially collections of behaviors that you can call when you want those individual behaviors in your program. A framework, on the other hand, provides not only behavior but also the protocol or set of rules that govern the ways in which behaviors can be combined, including rules for what a programmer is supposed to provide versus what the framework provides.
Call versus override. With a class library, the code the programmer instantiates objects and calls their member functions. It's possible to instantiate and call objects in the same way with a framework (i.e., to treat the framework as a class library), but to take full advantage of a framework's reusable design, a programmer typically writes code that overrides and is called by the framework. The framework manages the flow of control among its objects. Writing a program involves dividing responsibilities among the various pieces of software that are called by the framework rather than specifying how the different pieces should work together.
Implementation versus design. With class libraries, programmers reuse only implementations, whereas with frameworks, they reuse design. A framework embodies the way a family of related programs or pieces of software work. It represents a generic design solution that can be adapted to a variety of specific problems in a given domain. For example, a single framework can embody the way a user interface works, even though two different user interfaces created with the same framework might solve quite different interface problems.
Thus, through the development of frameworks for solutions to various problems and programming tasks, significant reductions in the design and development effort for software can be achieved. A preferred embodiment of the invention utilizes HyperText Markup Language (HTML) to implement documents on the Internet together with a general-purpose secure communication protocol for a transport medium between the client and the merchant. HTTP or other protocols could be readily substituted for HTML without undue experimentation.
Information on these products is available in T. Berners-Lee, D. Connoly, "RFC 1866: Hypertext Markup Language--2.0" (November 1995); and R. Fielding, H, Frystyk, T. Berners-Lee, J. Gettys and J.C. Mogul, "HypertextTransfer Protocol--HTTP/1.1: HTTP Working Group Internet Draft" (May 2, 1996). HTML is a simple data format used to create hypertext documents that are portable from one platform to another. HTML documents are SGML documents with generic semantics that are appropriate for representing information from a wide range of domains. HTML has been in use by the World-Wide Web global information initiative since 1990. HTML is an application of ISO Standard 8879:1986 Information Processing Text and Office Systems; Standard Generalized Markup Language (SGML).
To date, Web development tools have been limited in their ability to create dynamic Web applications which span from client to server and interoperate with existing computing resources. Until recently, HTML has been the dominant technology used in development of Web-based solutions. However, HTML has proven to be inadequate in the following areas:
Poor performance;
Restricted user interface capabilities;
Can only produce static Web pages;
Lack of interoperability with existing applications and data; and
Inability to scale.
Sun Microsystem's Java language solves many of the client-side problems by:
Improving performance on the client side;
Enabling the creation of dynamic, real-time Web applications; and
Providing the ability to create a wide variety of user interface components.
Java is compiled into bytecodes in an intermediate form instead of machine code (like C, C++, Fortran, etc.). The bytecodes execute on any machine with a bytecode interpreter. Thus, Java applets can run on a variety of client machines, and the bytecodes are compact and designed to transmit efficiently over a network which enhances a preferred embodiment with universal clients and server-centric policies.
With Java, developers can create robust User Interface (UI) components. Custom "widgets" (e.g. real-time stock tickers, animated icons, etc.) can be created, and client-side performance is improved. Unlike HTML, Java supports the notion of client-side validation, offloading appropriate processing onto the client for improved performance. Dynamic, real-time Web pages can be created. Using the above-mentioned custom UI components, dynamic Web pages can also be created.
Sun's Java language has emerged as an industry-recognized language for "programming the Internet." Sun defines Java as: "a simple, object-oriented, distributed, interpreted, robust, secure, architecture-neutral, portable, high-performance, multithreaded, dynamic, buzzword-compliant, general-purpose programming language. Java supports programming for the Internet in the form of platform-independent Java applets." Java applets are small, specialized applications that comply with Sun's Java Application Programming Interface (API) allowing developers to add "interactive content" to Web documents (e.g. simple animations, page adornments, basic games, etc.). Applets execute within a Java-compatible browser (e.g. Netscape Navigator) by copying code from the server to client. From a language standpoint, Java's core feature set is based on C++. Sun's Java literature states that Java is basically "C++, with extensions from Objective C for more dynamic method resolution".
Another technology that provides similar function to JAVA is provided by Microsoft and ActiveX Technologies, to give developers and Web designers wherewithal to build dynamic content for the Internet and personal computers. ActiveX includes tools for developing animation, 3-D virtual reality, video and other multimedia content. The tools use Internet standards, work on multiple platforms, and are being supported by over 100 companies. The group's building blocks are called ActiveX Controls, small, fast components that enable developers to embed parts of software in hypertext markup language (HTML) pages. ActiveX Controls work with a variety of programming languages including Microsoft Visual C++, Borland Delphi, Microsoft Visual Basic programming system and, in the future, Microsoft's development tool for Java, code named "Jakarta." ActiveX Technologies also includes ActiveX Server Framework, allowing developers to create server applications. One of ordinary skill in the art readily recognizes that ActiveX could be substituted for JAVA without undue experimentation to practice the invention.
A preferred embodiment provides a system for building manageable applications. The applications can be readily deployed, on to a variety of platforms, and configured so that it's easy to partition them on to clients versus servers and administer the applications. A preferred embodiment is enabled as a client server application that's distributed nodes in a multi-node platform. A single application is divided up into pieces and distributed across nodes in the network. Thus, an application is defined as a distributed system.
Enterprise computing systems often a heterogeneous collection of nodes interconnected by a network. In a typical environment, a server node in the network holds data and programs that interact with the database, and a client node contains a program or programs for accessing the information on the server. The complexity of these environments makes it difficult to create, configure, deploy and administer software applications. However, the advent of Web technologies (browsers, the Java language and HTTP) has enabled enterprises to create and use internal Webs to assist in solving some of these problems. Java enables the Web as a client-server application platform and distribution channel to interact with a preferred embodiment in addressing many of the aforementioned challenges.
A preferred embodiment includes a toolkit for creating client programs that can be downloaded from the Web; interfaces for enabling a server program to function with a client as a single application; tools for connecting both client programs and server programs with a framework for executing the tools; and tools for installing, deploying and administering applications.
An application created in accordance with a preferred embodiment consists of a set of components that cooperate with each other. A server component can be implemented in any source language that can call a C program. A client component is implemented in the Java programming language. The client component consists of a GUI and a Presentation Engine (PE). To complete the application system, a preferred embodiment provides a communication layer that enables the exchange of messages between the client and the server components, an Exception layer for reporting errors, and an Access layer for managing application deployment. The task of an application developer utilizing a preferred embodiment is to assemble the components into an application system.
A preferred embodiment provides Java client access to server applications and can be utilized to create new applications or extend existing applications. Among existing applications, those that are partitioned so that server programs and databases are on the server, and user interfaces are on the client are especially suited for migration to the preferred embodiment. Other applications especially suited to a preferred embodiment require access to departmental or corporate data without changes to databases or the programs that access them. For enterprises already using the web technologies in an Internet, Intranet or other network environment, applications in accordance with a preferred embodiment provide quick access to existing data from anywhere in the organization or the world. Applications in accordance with a preferred embodiment can execute on any processor with the Java interpreter/runtime (Java JDK) or JavaOS installed. Application client programs are developed in Java using a null application template that contains the necessary Java classes and methods for integration with a Graphical User Interface (GUI). The template includes Java classes which will allow the client program to communicate with the server program. Scripts and tools for installing and deploying applications, include a generalized startup applet for application launch from a Web browser or applet viewer.
The primary development task in accordance with a preferred embodiment is to create an application front end referred to as a Presentation Engine, hereinafter (PE), from a provided template. The PE template includes methods (logic in an object) to send messages and their data through a client communication library. Developers modify the template to specify the messages and data required for their application. The communication library handles the passing of messages and data across the network. The PE toolkit supports these tasks. The toolkit is a full set of Java components which can be modified and extended for a particular application's requirements. The server program must also be enabled to communicate with the client by specifying which handler functions are called in response to inbound messages and inserting "send" calls to a server-local communication library when data are sent to a client. The two PE development tasks are to: (1) connect a Java UI to the PE framework, and (2) define/describe the messages to be exchanged between the PE and the server.
All of the components in accordance with a preferred embodiment reside on the server so that the server controls all access to its resources. The server thus controls deployment and administration of its set of applications. The clients use the web to access the server's resources. A template is also provided for creating an applet that enables users at client nodes to start applications from a browser which will be discussed in added detail below.
FIG. 4 is a block diagram in accordance with a preferred embodiment. The client 410 and back end server 400 create and receive data messages communicated via messages at their local communication libraries 420. Messages are events which are encoded in a protocol, "ictp" layered on top of TCP/IP. The. execution framework 430 layer could be implemented on any network protocol as asynchronous, event-driven message passing on top of a communication protocol, such as TCP/IP, avoiding the dependencies of any particular server protocol. An application has a specific set of message events, and each component (front 410 and back 400 ends) includes local handlers for the set of message events. Thus, any two components can be plugged into the execution framework 430 to form an application 440 if they include local handlers for messages in the set of message events defined for the application 440. The components each include a local instance of a communication library 420. A component only interacts with the Application Programming Interface (API) of its local communication library 420 in order to send or receive message events.
Application components in accordance with a preferred embodiment are "loosely coupled" because there is no direct dependence (or communication) between the components. The execution framework 430 provides a consistent connection for all message transfer for the various applications. The execution framework 430 supplies additional services, such as error reporting, for the connection. An application 440 is insulated from the physical properties of the specific distributed platform on which the application is deployed. Thus, the application components and set of message events remain constant while the distributed platform can be scaled and modified.
Since applications 440 are systems containing well defined components as is shown in FIGS. 4 and 5, it is possible to install sets of front ends 530 and back ends 540 plus the definitions of how to associate them into applications 440. The server, therefore, holds all the resources while the client 500 can only request access to the resources. The server 520 is extended to allow it to control access to its resources by enforcing well defined policies.
FIG. 5 illustrates how a preferred embodiment leverages Java to facilitate the establishment and implementation of server-centric policies. The client and server nodes communicate utilizing the web technologies in an Internet, Intranet or other network environment. The client node 500 contacts the server node 520 via HTTP with a request to execute an application. After authenticating the client 500, the server node 520 selects front 502 and back end 510 components based on the application definition list maintained at the server node 520. The server starts its back end process 510 and sends the front end program 502 to the client node via the Web technologies in an Internet, Intranet or other network environment. The client 500 executes the selected front end 502 locally at the client node 500. The front end (client) programs open a TCP/IP connection back to the server to initiate message passing in order to run the applications. The front end program 502 is implemented entirely in Java which facilitates instances of client/server applications which can run concurrently on a set of multi-platform clients. The server 520 is able to send a front end program 502 to any client node 500 which has the Java runtime installed on the computer. Server policies will not involve the clients. The policies will focus on the server's control of its local resources.
FIG. 5 also illustrates the loose coupling between the front end 502 and the back end 510 application components. Each program includes a local communication library 515. The front end library is implemented in Java, the back end library is implemented in C++ with a C API. The programs each utilize their local communication library API to send and receive messages. Thus, the programs do not communicate directly with each other.
Presentation Engine
There are two phases for each application execution. In the first phase, application startup, the client node requests access to the server node's resources and the server acts on this request. The nodes are associated via the Internet or other communication network, and thus do not have a permanent relationship within the enterprise. In the second phase, application execution, the client has received a front end Java program called a Presentation Engine (PE) to facilitate presentation services. The front end and back end are communicating via the execution framework over TCP/IP.
FIG. 6 illustrates the processing associated with application startup in accordance with a preferred embodiment. When an application is started, the client node executes a startup applet 620 which first collects information about the client 600 user and contacts the server node 610 via http 602. The server node 610 has been extended to include a web server 630 for processing requests via HTTP over the Web technologies in an Internet, Intranet or other network environment. The access layer 640 is called via a cgi-bin interface from the web server 630. The access layer 640 provides a framework so that the information about the client user, for example userid and password, can be used to call server-resident authentication services. Should authentication be successful, the access layer 640 uses the application name, which is also supplied by the startup applet, and invokes the app manager 650. The app manager 650 handles the application definitions installed on the server node 610. The app manager 650 selects the application back end 660 and initiates the processing. A listener socket is opened on the server node, and the port number is returned to the app manager 650. The ap manager 650 also selects the application Front End (FE) 670, stored on the server as a set of Java bytecodes, and creates a PE 670 instance which includes the listener socket port number. Application startup ends when the PE 670 instance is downloaded to the client node for execution.
Application Execution
When application execution is initiated, the client node begins to interpret the PE 700 (FIG. 7) it has received from the server node 710. The PE 700 is a framework (which includes an User Interface (UI) which can include a graphical UI (GUI)) and an instance of a communication library 720 implemented in Java. Once it starts up, the PE 700 opens a socket connection to the server node 710 utilizing the server port number it was supplied when the server app manager 650 started the back end process 730. The back end process 730 on the server node 710 may be a distributed system which encapsulates an interface to a Data Base Management System (DBMS) 712. The front end 700 focuses solely on presentation services and its own web access capabilities. The execution framework 724 specifically links the front end component 700 to the back end component 730 using event-driven message passing 735. This design preserves modularity between the front end 700 and the back end 730 of an application.
During application execution, the server node 710 communication library 720 manages the connection to facilitate policies that maximize access to its resources. For example, a server can be configured for a maximum time to await a transaction response. A timer runs, if it exceeds the maximum time before new client messages are received the server will terminate the client connection and recycle the port. The execution framework 724 supplies runtime error reporting services and application execution data which are accessible to system administrators via Web technologies in an Internet, Intranet or other network environment access. When application execution terminates, the relationship between the client node 700 and the server node 710 also terminates. Application startup must occur each time application execution is desired.
A client's presentation engine can be stored on the client node and started dynamically if the presentation engine is cached on the client. The reason for storing the presentation engine in cache is to support mobile (nomadic) computing, performance and to reduce network traffic. This technique would require versioning to assure that the presentation engine is synched with the latest, most current release on the server.
Application Development
The application development process in accordance with a preferred embodiment is a system integration task rather than a third generation language programming task. FIG. 7 illustrates the three fundamental components of an application in accordance with a preferred embodiment. The front end, client side 700, the back end 730 server side 710, and the execution framework 724 which facilitates the connection between the front end and the back end. The application development process consists of a plurality of steps. The first step defines the responsibilities of the front and back end components. A preferred embodiment is designed to facilitate migration of existing client/server applications to function utilizing the Web technologies in an Internet, Intranet or other network environment for communication services. This migration does not require redesigning existing application logic. The process entails the implementation of a new PE front end implemented in the Java language which exchanges message events with the remaining server back end code. FIG. 8 illustrates the migration of an existing client-server application to one supported by a preferred embodiment.
The new Java PE front end 820 is added to the existing application code and will contain the Presentation Layer (UI tier) 800 and some amount of non-database aware logic responsible for manipulating variables. All logic which is aware of the database and its data remains in the back end component. The PE 820 is not limited to logic from the existing application. It is a program implemented in Java, and thus can take direct advantage of additional Internet related services within the enterprise intranet. The complexity of the PE is determined by the developer's choice.
The second step in migrating existing applications to utilize a preferred embodiment is to define the message events exchanged between the PE and the back end. The PE and the back end are loosely coupled and exchange data events. Each event has a unique name and data associated with the event. Message event data items are declared by type, all primitives plus one composite type. Message data types directly map to primitive types in both Java and C. The communication libraries have APIs which can be used by developers to define message events.
The third step is to set up the back end to handle message events. The server resident back end component must handle message events. This processing is enabled by linking in an instance of the communication library with existing server code. The communication library has a C API, so the server code can be implemented in any language which can call C. The existing server code utilizes the communication library API to send and receive messages. The communication library calls handler functions in the server code when message events come in from the front end. The developer will create these handler functions and register them, one handler function per defined message event, using APIs in the communication library.
Once compiled and linked, the back end is a single process which is started by the app manager during application initiation. The interface between the server communication library and the server code is multi-threaded.
The fourth step is to develop a Presentation Engine front end. Java is utilized for this task. Templates and tools are provided to facilitate this task. The detailed tasks associated with facilitating these tasks are described below.
The final step in migrating an existing client server application to a preferred embodiment is to install application components on the server node. Both the front end (client) and back-end components are installed on the server node. A Java startup applet enables clients to access the application on the server. A set of tools for application installation and configuration are provided as applications on server nodes in accordance with a preferred embodiment. A Java startup applet template is also provided to facilitate development of the application's startup applet.
Presentation Engine Development
Presentation engine development is the step of developing a new application front-end in Java. To simplify this task and provide application performance and robustness guarantees, all application front ends are instances of a single class of programs. A basic presentation engine framework implemented in Java is provided as an example in accordance with a preferred embodiment. Developing a specific application presentation engine means extending and customizing the basic presentation engine framework template. A Presentation Engine (PE) is itself a system with two components: (1) a UI implemented in Java, and (2) the PE framework. Developing a PE is a system integration task with the following two steps.
(1) Develop a UI Which is Implemented with Java.
FIG. 9 is a block diagram illustrating a PE 960 in accordance with a preferred embodiment. The UI 900 component is developed according to a developer's particular requirements. Since the front end processing utilizes the Java language, the UI also takes advantage of Java's rich functionality. The UI 900 is connected to the PE 960 framework via an interface to the UI Adaptor 910 component. The interface is a general message-passing interface that facilitates the attachment of any Java implemented UI 900 with the PE 960 framework to exchange data events. An API is provided to the PE 960 framework so that a developer can link the UI 900 to the UI Adaptor 910.
(2) Extend the PE Framework Template (960)
FIG. 9 illustrates how the PE Framework 960 architecture is arranged to facilitate two kinds of external events in accordance with a preferred embodiment. The two kinds of external events are UI events and Message events from the Execution Framework. The framework includes a Java implemented communication library component, the Comm Adaptor 950. The PE framework 960 interfaces to the UI 900 via the UI Adaptor 910 and interfaces to the server TCP/IP connection via the Comm Adaptor 950. The mediator 920 component handles all external events moving into and out of the PE framework 960.
The UI 900, UI Adaptor 910 and the Model 940 are directly extended by the developer supplying application specific information. The communication library and mediator components are not extended by developers. The PE framework 960 has a model 940-view 930-controller architecture. A developer may extend the Model 940 component in order to implement local logic and maintain PE-local state. The view component 930 maps between the Model 940 data representation and the message data representations.
It is possible to create a PE framework without extending the Model 940 component of the PE Framework 960. This model is referred to as a "PE-lite" option and consists of the comm adaptor 950, mediator 920, UI Adaptor 910 and the UI 900. To utilize this option, a developer assembles the components from a UI 900 and a PE framework instance 960. The PE framework 960 makes use of the Mediator 920 to directly map between UI external events and Comm external events.
The execution framework 960 is a communication abstraction that utilizes TCP/IP as a communication backbone, and is analogous to a bus in a computer system. Each component in accordance with a preferred embodiment plugs into the execution framework much as various function cards plug into the bus of a computer system. There is no notion of local versus remote in the components which is unlike a typical distributed computing environment.
In this architecture, there is no distributed domain. Everything is local and the way that a component connects up with this framework is by making local calls to a communication layer which is the framework. It's all embodied in the communication library components. So, the messages that are exchanged between programs are data. Rather than function calls, they are actually data containers. All that can happen in the exchange is that data are packed up and sent as an event, or data are packed up here and sent over there as an event.
Inside of the client and server programs, there are handlers for the data in the message events. So, any front end and any back end has local handlers for a common set of message events. They can be plugged together by the framework to create an application. So, what we call these is, "loosely coupled", which means that there are no dependencies between the programs and they do not communicate directly. This preserves modularity in the application. A program may send data events, and the program also is enabled to handle data events which interrupt its processing.
The framework currently is layered over TCP/IP for a communication vehicle, but other networking protocols can be utilized. The programs always interact with the ICE-T Comm Layer. There is a firewall between the actual, physical distributed platform, underneath and the application above because the application components are interfacing with the abstraction. Thus, applications are independent from the details of the physical structure of the distributed enterprise. The enterprise may be scaled, and/or modified without requiring re-design of the applications.
EXAMPLE IN ACCORDANCE WITH A PREFERRED EMBODIMENT
FIG. 10 is a block diagram of a prior art client server architecture. In the prior art a client computer 1000 would access a network 1030 via a predefined data protocol (datastream) and interact with a predefined server 1001 containing code 1010 and data in the form of a DataBase Management System (DBMS) 1020.
An application in accordance with an alternate embodiment is shown in FIG. 11. The encapsulated DBMS 1102 is conserved, as is the enormous investment in code 1170. However, the server 1180 includes a service API 1160 for communicating to the network support 1150 which is responsible for turning the web node into a loosely coupled client 1120 utilizing a small amount of Java code and conforming to a predefined datastream that is sent by the server 1180 to the client 1120. A web server 1106 is utilized to facilitate access to and transmission of messages over the web from the server 1180 via the access module 1108 and the PE framework 1104 as discussed earlier and reiterated below.
FIG. 12 illustrates a server 1210 establishing contact with a client 1200 in accordance with an alternate embodiment. The code 1240 and DBMS 1230 are as described in FIGS. 10 and 11. However, web contact is established between the nodes by authenticating a user utilizing the Access Layer 1280 to establish client 1200-server 1210 communication. Then, the Java bytecodes 1250 are extracted from the PE Repository 1290 and downloaded to the client 1200 using the Access Layer 1280 and the Web Server 1270.
FIG. 13 illustrates a loosely coupled client-server application in accordance with an alternate embodiment. The Server 1300 communicates via a service API 1360 and Network Support 1340 to a Client 1330 utilizing a predefined data stream 1350 and application code 1320 and a DBMS 1310. The "loosely" coupled nature of the application architecture is enabled through message communication in an asynchronous manner letting the Client 1330 and the Server 1300 maintain state independence and connect via a low bandwidth network 1350. The applications require no function call level API's.
Some of the basic architectural design decisions that form the foundation of a preferred embodiment include the Server 1300 controlling both the Client 1330 and Server 1300 states. The Java language is utilized to communicate via the Web technologies in an Internet, Intranet or other network environment to distribute Client 1330 state information to the Client node. The Server 1300 presents an encapsulated DBMS interface to the network. The Server 1300 node is extended by a framework to support the establishment of a Client 1330-Server 1300 relationship for web nodes.
The Client 1330-Server 1300 relationship for web nodes is established utilizing a secure http process which authenticates the user at the requesting node. Then, the Client 1330 node is established by selecting an appropriate Client 1330 state from stored states at the Server, and the Java client state is downloaded over the network to the particular Client 1330 node. Next, the Client 1330-Server 1300 network communication session is commenced by starting the server process and establishing a socket connection to the Client 1330 node. Once the session is established, then the network must be managed by maintaining event-driven message passing with the PE communication library.
FIG. 14 illustrates the system integration task necessary to develop an application 1430 in accordance with a preferred embodiment. First, the developer defines the message events 1450 that must be exchanged between components. The client program 1410 and server program 1420 are defined as applications 1430 on the Server Node 1420. The back end must be enabled to send and receive messages. The front end (PE) must be developed, then the components are installed in the server node 1420. The goal is to support modular application development and require minimal additional knowledge burden (e.g. sophistication in Java or OOP) from developers.
FIG. 15 is a block diagram illustrating the modular design of a client application (PE) in accordance with a preferred embodiment. The application logic 1530 is written entirely in Java to maximize access to Internet facilities. The application logic runs as a Java program or an applet. An External Interface Library 1520 contains various callable functions for interfacing to the UI or API 1500 through the UI layer 1510. A Message Library 1540 provides messages for use in communicating information through the communication layer 1550 to the Server 1560. The architecture is a client loosely coupled with the server 1560. Data exchange is via event-driven message passing. A flexible UI 1510 and communication layer 1550 facilitates message passing APIs interfacing to a Server or UI designs. Developers are not required to understand network communication or system programming in order to design and implement applications. The client program can be designed to support efficient presentation services. The DBMS interface is encapsulated in the back end (server). Thus, there are no distributed transactions which must be handled in the web connection between client and server.
FIG. 16 is a block diagram of a framework in accordance with an alternate embodiment. Model data 1600 is provided in the form of predefined classes that can be accessed and modified by a user to add additional data or logic to meet the requirements of a particular application and specify appropriate maps for views or UI components. All of the class templates necessary to be extended into a fully functional model are provided. The Model data 1600 is utilized on the external IF View 1622 and additional model data 1620 may be added as necessary to expand the view. Similarly, the message view 1612 can be expanded by adding additional model data 1610 to the message view 1612. A mediator 1630 is responsible for routing messages and granting control to the Communication Adaptor 1640 or the UI Adaptor 1650.
FIG. 17 illustrates the basic building blocks in accordance with an alternate embodiment. A PE object 1700 is an object containing methods (logic) and data (public and private information) that is utilized to facilitate a reusable, extensible function. A PE function 1710 utilizes PE objects 1700 to implement callbacks, observers, event handlers and maps in accordance with a preferred embodiment. PE Info 1720 is a basic unit of data moved between functional components, and a PE Event Handler 1730 is used by views to handle incoming messages and UI events in accordance with a preferred embodiment.
FIG. 18 is a block diagram highlighting the steps utilized to extend the (PE) framework in accordance with a preferred embodiment. A user must modify the UI Adaptor 1800 as shown at 1810. All of the base processing necessary to facilitate the application is incorporated into the basic framework which provides all of the basic classes for instantiating objects necessary to perform user's requirements.
FIG. 19 is an illustration of a PE Object 1900 in accordance with a preferred embodiment. The PE object is a data structure library that is used for building the model and other structured data passed around in messages. There is an associated containment hierarchy with primitive 1910 and composite 1920 objects instantiated from the base PE Object 1900. An object-oriented architecture facilitates polymorphic, encapsulated objects that are fully self-describing and fully enabling for a serialization interface.
FIG. 20 is an illustration of a PE Event Handler 2000 used by Views to handle incoming messages and UI events in accordance with a preferred embodiment. The PE Event Handler 2000 dispatches tasks based on a name field and data defined in objects PEInfo 2010 data which is passed utilizing a message to implement a map to the model. FIG. 21 illustrates a PEInfo object 2100 data in accordance with a preferred embodiment. The data encapsulates event and message signatures and is used in three places for passing between model and XIF View, Model and Msg View and XIF View and the
FIG. 22 illustrates incoming message flow to a model in accordance with a preferred embodiment. A message flows into a communication layer in bytestream format 2200 and passed via a mediator to a message view 2210 to unpack and dispatch the message utilizing a MsgHandler PE Event Handler to transfer the PEInfo 2220 data. The PEInfo 2220 is used to encapsulate the event and message signatures and transform the message into a model map 2230 which is thereafter utilized for setValue and getvalue processing 2240. When a UI Event, such as a key press or other activity occurs at 2260, a callback PE Function 2270 utilizes PEInfo 2280 to pass event and data information to the external view dispatcher 2290 for transformation into information that the Model PEObject 2250 can utilize for further message processing.
FIG. 23 illustrates incoming messages mapping a UI to a Model in accordance with a preferred embodiment in a manner very similar to FIG. 22. FIG. 24 illustrates outgoing messages mapping a model to messages in accordance with a preferred embodiment in a manner similar to FIG. 22 and FIG. 23. FIG. 25 illustrates outgoing messages mapping a model to a UI in accordance with a preferred embodiment in a manner similar to the foregoing Figures. To further clarify processing in accordance with a preferred embodiment, the detailed installation and logic specification for an application in accordance with a preferred embodiment is presented below.
Enterprise computing environments usually consist of many kinds of nodes interconnected by a network. In a typical environment, a server node in the network holds data and programs that interact with the database, and a client node contains a program or programs for accessing the information on the server. The complexity of these environments makes it difficult to create, configure, deploy, and administer software applications. The advent of Web technologies (browsers, the Java language, HTTP) has enabled enterprises to create and use internal Webs to help solve some of these problems.
Java enables the Web as a client-server application platform and distribution channel. The "Interprise" Computing Environment Toolkit (ICE-T) enables building, extending and deploying client-server applications for the Web. ("Interprise" combines the internet and the enterprise.)
The ICE-T application provides:
A toolkit for creating client programs that can be downloaded on the Web
Interfaces for enabling a server program to work with a client as a single application
The tools to connect both client program and server programs to a framework for executing them
Tools for installing, deploying, and administering applications
ICE-T Applications
An application consists of a server program component (implemented in any language that can call C) and a client program component (implemented in Java). The client component consists of a GUI and a Presentation Engine (PE). To complete the application system, ICE-T provides a Communication Layer that enables the exchange of messages between the client and server components, an Exception Layer for error reporting from ICE-T components, and an Access Layer for managing how applications are deployed. The task of the ICE-T application developer is to assemble the components into an application system.
ICE-T provides Java client access to server applications. New applications or existing ones extended utilizing a preferred embodiment. Among existing applications, those that are partitioned so that server programs (business logic) and databases are on the server, and user interfaces are on the client (three-tier client-server applications) are especially suited for migration to ICE-T front ends.
ICE-T is especially suited for enterprise applications that require:
Access to department or corporate data without changes to databases or the programs that access them.
For enterprises already using an enterprise web technologies in an Internet, Intranet or other network environment, ICE-T applications can provide quick access to existing data from anywhere in the organization or the field where there is an internet connection.
Client platform independence.
ICE-T Presentation Engines can run anywhere the Java Virtual Machine is present.
Rapid development.
Clients are developed in Java using a null application template that contains the necessary Java classes and methods for integration with a GUI and a Communication Library.
Easy deployment.
ICE-T provides scripts and tools for installing and deploying applications, include a generalized startup applet for providing application launch from a Web browser or applet viewer.
Centralized authentication of users.
A customizable Access Layer, installed on the server, enables centralized control of access to client programs.
Easy maintenance.
For most enterprises, maintaining existing applications is a tremendous resource burden. ICE-T provides the means to make new application front-ends (clients), or migrate existing ones, without changing the architecture or programs of the back-end (server), or requiring a steep learning curve.
Wide use throughout the enterprise, from the desktop or the laptop. A familiar and pervasive interface.
End-users can name ICE-T applications as applets in a Web browser.
ICE-T Application Development and Deployment
The primary development task in an ICE-T application is to create an application front end, a Java Presentation Engine, from the provided template. The Presentation Engine (PE) template includes methods to send messages and their data through a client Communication Library. Developers modify the template to specify the messages and data required for their application. The Communication Library handles the passing of messages and data across the network. The Presentation Engine Toolkit supports these tasks. The Toolkit is a full set of Java components some of which you must modify or extend.
An additional development task is to modify the server program to specify which function to call in response to inbound messages and make calls to a server Communication Library to send results to the client. All of the components in an ICE-T application system reside on the server. To deploy an application, you install its components and additional ICE-T files and programs that manage applications on the server. ICE-T also provides a template for creating a startup applet that enables users to start applications from a browser. Chapter 3, "Configuring and Deploying ICE-T Applications" describes these tasks and tools.
Event-Driven Message Passing in ICE-T Applications
The components of ICE-T applications create, send, and receive messages in response to external events. An event is a way of communicating that something has happened, such as input from the user (a mouse click) or a change in the system environment (a server shutdown).
The ICE-T Communication Layer enables asynchronous event-driven message passing between client and server program components on TCP/IP. In ICE-T, the messages themselves are events, and each program component includes local handlers for message events.
Client and server program components must each be set up to create, send, and receive messages. Part of the Presentation Engine's functionality is to determine the recipients and deliver the messages to them. For example, the user interface sends a message to the Presentation Engine when a user clicks a button. The Presentation Engine receives the message and then either sends it to the data model or the server program, which then performs an operation and replies with the result.
The server program must also be able to receive messages and must register functions to handle them.
The recipients of messages do not need to know much about each other, they just need to specify what messages they want to receive. This information is registered using the createMessageHandlers ( ) method in the client program and the createMessageHandlers ( ) function in the server program.
Presentation Engines should include handlers for two kinds of application events:
Events from the user interface
Events coming in to the Presentation Engine from the user interface result in messages to the server or the Presentation Engine's data model.
Events from the server
Events coming in to the Presentation Engine from the server result in displaying data in the user interface or putting data in the Presentation Engine's data model.
Server programs should include handlers for messages from the client. Typically, the handler would call application logic and send the resulting message and its data back to the client through the server Communication Library.
ICE-T Application Execution
ICE-T applications are designed to work within existing client-server environments. They differ from familiar client-server applications in some key ways.
Typically client programs are developed, maintained, and distributed periodically, taking long cycles of development time, and requiring time to deploy to client nodes. Users who are not on a node on the distribution route may miss software updates. Development can consume resources because of the difficulty of the language or tools used.
Compiled ICE-T Presentation Engines are installed on the server and downloaded on request through HTTP servers. A pair of Communication Libraries behave as a framework for executing the application. This communication layer handles the marshaling and unmarshalling of the message data transferred between client and server. Both client and server should be prepared to handle shutdown events. ICE-T provides default shutdown handlers for this purpose, and developers can add their own.
How ICE-T Applications Work
Before developing an ICE-T application, you might find it useful to see how ICE-T applications work, from both an end-user's perspective and inside ICE-T.
The User View
ICE-T applications can use a Java-enabled Web browser for client access to application execution. Although developers may choose to have applications launched outside a browser, a Web page presents a familiar and easy to use interface for launching applications.
The user begins by opening a Web page and clicking on the URL for the application she wants to run. The URL is the address for a Web page that includes an ICE-T application startup applet. The Web page with the startup applet is loaded into the browser. The applet collects access information from the user. The applet contains the URL of the server holding the application components and the application name. This information is processed on the server. If the user name, password, and chosen application are authorized, the server downloads a Presentation Engine to the user's node.
The Presentation Engine presents the user with an interface for interacting with the server program and data. It also determines where to pass messages for handling, either to the server program or to its own data model. One example of a client program is one that communicates with a server program that searches a database, for example an employee database. Such a client program might have these user interface elements:
A text field where users enter a first or last name that they wish to find in the employee names database
Buttons for clearing the fields (Clear), exiting the application (Quit), and launching the search (Search)
A scrolling window for viewing the results of the query
The user enters a first or last name and presses Return or clicks a Search button. The client program sends the query to the server, where the server program searches the employee database for a matching name. If a match is found, the server returns the results to the client. The results are displayed in a window on the client.
The ICE-T View
When a user launches an ICE-T application, the client node establishes a Web connection with the server node using HTTP. The server manages this Web connection. ICE-T applications can be launched from a browser, an applet viewer, or as standalone applications. FIG. 26 illustrates the steps associated with launching an application URL in accordance with a preferred embodiment. On the server side, the ICE-T Access Layer (a cgi-bin executable) authenticates the user data. If the authentication succeeds, the Access Layer contacts the ICE-T Application Manager and the Application Manager starts the server program and initiates a network session.
The Application Manager downloads an HTML page with a startup applet for the application. When the user runs the startup applet, the Application Manager selects a compiled Presentation Engine and downloads an HTML page containing the applet tag for it to the client using HTTP. The compiled Presentation Engine includes a GUI and an instance of the client Communication Library and is ready for execution in a Java-enabled browser or anywhere the Java Virtual Machine is installed.
The client node then executes the Presentation Engine locally. The Presentation Engine makes a TCP/IP connection to the server where the server program is running, and the client and server programs cooperate to execute the application.
When a user interface event occurs--for example, when the user enters a first name in the text field and clicks a Search button--the user interface passes a message to the Presentation Engine. The Presentation Engine either sends the message to its data model for processing by the client, or passes the message to the server for processing by the server program. The Presentation Engine determines where on the client a message is handled based on how you have registered message handlers. When the server program sends a message with data to the client, the Presentation Engine displays the result.
The exchange of messages between client and server is handled through the ICE-T Communication Libraries in the ICE-T Communication Layer. When the client program terminates, the Application Manager closes the socket connection to the client and terminates any server processes it started.
ICE-T Task Summary--Building Program Components
ICE-T's modular architecture makes it easy to distribute development tasks to multiple developers. Alternatively, a single developer can complete ICE-T development tasks in stages. Developing a client program requires making a Java Presentation Engine, connecting it to a user interface and to the ICE-T Communication Layer so that it can communicate with a server program The server program could be an existing program or a new one. It must be written in a language that can call C so that it can work with the ICE-T Communication Layer. You don't need to develop new server programs for ICE-T applications, but you must enable the server program to handle messages from the client.
ICE-T Application Building Blocks
An ICE-T application consists of a client program and a server program communicating through a Communication Layer. The client program consists of:
A GUI built with Java
A Java Presentation Engine built using a template
These components, and related classes used by the Presentation Engine, combine to behave as a single client under the control of the Presentation Engine. The Presentation Engine may be presented as an applet launched from an applet viewer or a Web browser, or as a standalone application.
The server program, new or existing, is developed however the developer chooses. It must be in a language that calls C and it must include functions for handling messages from the client. A template with these functions is provided, as is a main routine that makes calls to the provided server Communication Library.
ICE-T provides these templates, tools, and libraries for developing applications:
pe_template java
A template for a working Presentation Engine.
ICE-T packages (supplementary to the standard Java packages)
server-template.c and server_template.cc
Server program templates (one each for C and C++) that define and enable message passing to and from the client. The templates can be used with existing programs or used as a starting point for developing server programs. These templates are analogous to the pe-template used for the client.
ICE-T message data types that work the same on both client and server.
ICE-T also provides a framework that the developer does not modify and in which ICE-T applications can execute. This framework includes:
Communication Layer
Supports network communication between client and server programs. The server Communication Library presents a C API to the server program, which is linked to this library. The client Communication Library is implemented in Java.
ICE-T Exception Layer
Provides exception reporting from the ICE-T application (client and server) in addition to standard system error reporting.
The Presentation Engine
Every Presentation Engine extends (inherits from) a Java class named PresentationEngine. All of the objects that the client program needs are either in the Presentation Engine class or called by it. ICE-T provides a class that extends java, and calls the methods that you need to create a working Presentation Engine.
The filename for the Presentation Engine template is pe_template.java. You can find it in the ICE-T application installation directory under Templates/C or Templates/C++. The file is placed in each of the Template subdirectories for convenience. The pe_template is the same in both files.
FIG. 27 describes the forms of a Presentation Engine, as an abstract Java class, a template for development, and an executable component in an application in accordance with a preferred embodiment.
To create a working Presentation Engine, you copy the pe-template file and make these changes:
Supply your own Presentation Engine name.
Create user interface components or map the ones from a Java GUI builder.
Create a data model (if your application requires client-side processing).
Define messages and their handlers.
Register message handlers.
These steps are described in this chapter.
Presentation Engine Implementation Options
Developers can create Presentation Engines that simply send messages from the user interface to the server and display the data that the server returns on the client. This option for Presentation Engine implementation is called a "PELite." An alternative implementation of Presentation Engine handles some local data storage in what is called the Presentation Engine's data model. For the latter, developers are required to implement a createModel( ) method, described in this chapter. Both options are supported by the pe_template.
ICE-T Classes and Packages
The documentation for the ICE-T Presentation Engine API is presented in HTML form, like the Java API documentation, and is accessible from the following URL:
file:///<ICE-T Installation Directory>/doc/api
where <ICE-T Installation Directory>is the name of the directory on your system where you have installed ICE-T. The C and C++ header files used by the server program are in the ICE-T installation directory under Server.
ICE-T Message Data Types
ICE-T message data types:
Can be used to construct the data model in the Presentation Engine
Are available for use in the server program for use in application logic
Have analogs on both the client (Java) and server (C)
Use basically the same APIs on both the client and server
Can contain only other ICE-T data types
Are used in messages from client to server, and server to client, where they will appear as a local data structure of their analogous type.
The table appearing below describes the primitive ICE-T message data types and their analogous types on client and server. The prefixes Pe and Srv are provided for your convenience in naming things. They are handled as the same type by ICE-T.
ICE-T Message Types (Primitive)
Data Type Client {PE) Server (C)
Petbar, SrvChar char (Unicode) char (C)
16 bits] 8 bits
PeString, SrvString string char*
PeBoolean, SrvBoolean Boolean int
16 bits 1 byte
PeInteger, SrvInteger int int
32 bits 32 bits
PeLong, SrvLong long long
64 bits 64 bits
PeFloat, StyFloat float float
32 bits 32 bits
PeDouble, SrvDouble double double
64 bits 64 bits
1. ICE-T transmits only the ASCII (8 bits).
ICE-T supports a composite data type based on the Java vector class Oava. util.Vector). It differs from the Java vector type in that it provides an implementation that works on both sides of the ICE-T application (Java clients and C or C++ server programs), and it only takes ICE-T primitive data types.
TABLE
ICE-T Vector Type
Data Type Description
PeVector, A collection that implements a variable-length array.
StyVector Add elements sequentially with the add Element ( ) method.
Access an element by its index.
Working with the ICE-T Directory Structure
Before developing applications, copy the provided templates and Makefiles to an application development directory. There are two subdirectories of templates.
<ICE-T Installation Directory>/Templates/C
Contains Example. mk, pe_template. java, and server_template.c.
<ICE-T Installation Directory>/Templates/Cplusplus
Contains Example .mk, pe_template. java, and server_template. cc.
For example, create an application directory for an application named myAppName in which the server program is written in C++, and copy the templates to it:
% mkdir myAppNams
% clo <ICE-T Installation Directory>/Templates/C++/* <ICE-T Installation Directory>/Applications/myAppName/.
The ICE-T installation scripts and MakeHierarchy depend on the newly created application directory being two levels below the ICE-T installation directory. If you choose not to follow the directory setup suggested by the example, you will have to supply options or arguments indicating where the ICE-T installation directory is in relationship to the directory you have created.
Designing the Client Program
Here are some design decisions to make before you develop the client program for an ICE-T application.
Using a graphical user interface (GUI) toolkit, specify and design the user interface.
Determine the events the client and server components of the application should handle. Name each of these events and associate data with it. In this step you answer the question of what messages will be passed between the Presentation Engine and the user interface and between the Presentation Engine and server.
Decide what application logic to put in the client program, if any.
Decide what, if any, data processing you want the client program to handle. This affects whether you create event handling for data updates in the Presentation Engine or just use the Presentation Engine as a mediator between the user interface and the server data (a "PE Lite").
Specify how the user interface should be updated when the Presentation Engine receives messages and data from the server.
Specify how the Presentation Engine receives and decodes data from the server and whether it stores the data for later retrieval or displays the data directly.
If you choose to store data in the Presentation Engine, specify how it is to be stored and updated and what other components in the application depend on that data.
Developing the User Interface
You can create the user interface for the ICE-T application at the same time as, or before, you create the Presentation Engine. Even though they can be separate, the Presentation Engine and user interface work together, so the interactions between them should be planned.
Creating a Presentation Engine
Create a Presentation Engine involves the following basic steps that are described in detail throughout this section:
1. If you have not done so already, copy one of the Templates subdirectories to the Applications directory.
The ICE-T installation directory includes a communication directory for developers to use. To create applications, make a subdirectory under applications for each ICE-T application you develop.
2. Modify and rename the pe_plate file to suit the application. Use the same name for the class and the file.
3. Create a Presentation Engine class.
Create your own Presentation Engine definition using pe-template.java.
4. Integrate the Presentation Engine with the user interface (GUI).
Create a separate user interface class using your chosen Java tool. Integrate the GUI with the Presentation Engine by implementing the createUI ( ) method that is found in pe_template.java.
"Working with the ICE-T Directory Structure" describes how to implement createUI( ).
5. Determine and define the message events to be passed between the Presentation Engine and server program and the Presentation Engine and user interface.
Name each of these events and associate data with it. Specify the type of data that will be passed in response to each message event.
a. Add handlers for events on GUI components.
Implement the operations you want the application to perform in response to user interface events.
b. Write the code for handling incoming message events in the Presentation Engine.
Define handlers in the Presentation Engine for incoming messages from the GUI. Define handlers in the Presentation Engine for incoming messages from the server.
Developers can choose to write a separate class, or classes, in separate files to handle events. This means that a named handler can be modified without modifying the Presentation Engine framework itself.
6. Register which handlers will be sent which messages when events occur (map messages to handlers).
Specify what handler should receive each message.
"Registering Handlers" describes this step.
7. Build the Presentation Engine.
ICE-T provides a makefile to build both server and client programs.
These activities are analogous to the tasks for modifying server programs to work with clients. In both client and server program cases, ICE-T provides templates with methods (Presentation Engine) and functions (server) for registering handlers. Developers provide only the application-specific messages and data.
Creating a Presentation Engine Class
Copy one of the Templates subdirectories to the Applications subdirectory. There are two subdirectories, one for C and one for C++. For example, create a directory for an application named myAppName. If the server program for myAppname is to be written in C, copy all of the files from the Templates/C directory:
% inkair myAppName
% cp <ICE-T Installation Directory>/Templates/C/*
<ICE-T Installation Directory>/Applications/myAppName/.
For each Presentation Engine you create, modify pe_template.java to declare a class that extends the abstract Java class PresentationEngine:
public class myPresentationEngine extends PresentationEngine
{// methods for your application
}
Note--Be sure to give the class and the file the same name. For example, if the Presentation Engine class is named myPresentationEnqine, the file should be named myPresentationEnqine. java.
pe_template. java contains the class and method declarations that you implement to provide the functionality you want.
The methods must include:
createuI ( )
createModel ( )
createMessageHandlers ( )
initializeApplication ( )
Implementing createModel ( ) and initializeApplication ( ) is optional.
You do not have to use initializeApplication ( ) unless your client program requires local initialization before communication is started.
Importing Packages
The pe_template imports the appropriate packages, including these ICE-T packages and standard Java packages:
sunsoft.ice.pe
sunsoft.ice pe
java.net
java.io
java.applet |
