Method and system for facilitating the refinement of data queries6954750Abstract Refining a current query. Receiving information regarding the relevancy of documents retrieved from a document collection in response to a current query. Ranking the retrieved documents in accordance with the relevancy information. Forming a candidate query based on the rankings and analysis of locations of the retrieved documents in a latent semantic index vector space formed from the retrieved document. Applying the candidate query to the document collection. Ranking the documents retrieved in response to the candidate query in accordance with the received relevancy information. Comparing the ranking of documents retrieved in response to the candidate query and the ranking of documents retrieved in response to the current query with the received relevancy information. Choosing the query that produces the best ranking. Claims 1. In an information retrieval system having a current query, and a search engine that is responsive to a query to retrieve documents relevant to the query from a document collection, a method for refining the current query, the method comprising: Description FIELD OF THE INVENTION
LSI techniques are described in Scott C. Deerwester, et al, Indexing by Latent Semantic Analysis, J LSI techniques operate on a collection of text passages, typically referred to in the literature of the art as "documents." The term "document", however, in this case can includes paragraphs, pages, or other subdivisions of text and not necessarily or only documents in the usual sense (i.e., externally defined logical subdivisions of text). Along these lines, this discussion refers to the text passages of interest as "documents." The use of LSI is illustrated with reference to FIG. 2. As a preliminary step in using the LSI technique, a large sparse matrix (the T×D matrix) is formed. Each row in the T×D matrix corresponds to a term that appears in the documents of interest, and each column corresponds to a document. Each element (m,n) in the matrix corresponds to the number of times that the word m occurs in document n. Referring to FIG. 3, the known technique of singular value decomposition (SVD) can be used to reduce the T×D matrix to a product of three matrices, including a matrix that has non-zero values only on the diagonal. Small values on this diagonal, and their corresponding rows and columns in the other two matrices are then deleted. This truncation process is used to generate a vector space of reduced dimensionality as illustrated in FIG. 4 by recombining the three truncated matrices in to (T×D)′ matrix. Both terms and documents are located at specific positions in this new vector space. The primary application of latent semantic indexing has been in the area of information retrieval. In that application, queries are treated as pseudo-documents. Documents are ranked in terms of similarity to the query based on-a cosine measure between the vector corresponding to the query and the vector corresponding to that document in the LSI vector space. Experiments have shown that closeness of documents in this sense is a good proxy for closeness in terms of information content. See [D SUMMARY OF THE INVENTION The present invention provides significant benefits over existing systems and methods for retrieval of data. According to some embodiments, a document retrieval system receives information regarding the relevancy of documents retrieved in response to a current query. The retrieved documents are ranked in accordance with the relevancy information. A candidate query is formed from the rankings and an analysis of locations of the retrieved documents in a latent semantic index space formed from the retrieved documents. The candidate query is applied the document collection and documents retrieved in response to the candidate query are ranked in accordance with the received relevancy information. The ranking of documents retrieved in response to each query is the compared, the query that produces the best ranking is chosen as the new query. According to other embodiments for refining a strategy for ranking the results of a document retrieval operation, the results of a document retrieval process are indexed into a latent semantic index vector space. Information is received regarding relevancy of the results to an information need. The results are ranked based on the current ranking strategy. The current ranking strategy is modified based on the location of the ranked documents in the latent semantic index vector space and the relevancy information. The results are ranked based on the new ranking strategy. The ranking strategy that produces results that better correspond to the relevancy information is chosen as the refined ranking strategy. According to further embodiments, the invention includes methods for refining a current query. In these methods, a subset of documents retrieved in response to a current query is ranked with respect to relevancy of the retrieved documents to an information need. A subset of the documents retrieved in response to a candidate query is ranked with respect to the same standard. The ranking is a function of the context of the relevancy information and the location of each document in a latent semantic index vector space. The refined query is chosen as the query which produces a ranking indicating that the retrieved documents corresponding to the query more closely matches the relevancy information. In yet other embodiments, the invention includes methods for forming a hypothesis for refining a query. In these embodiments, a document collection is indexed into a latent semantic vector space. Information regarding the relevancy with respect to information needs is received regarding the retrieved documents. At least one hypothesis is formed regarding modifications to a query based on analysis of the context of the relevancy information and the documents corresponding to the relevancy information in the vector space. BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS Preferred embodiments of the present invention are shown by way of example and not limitation in the accompanying drawings. FIG. 1 is an example of large result size associated with known Boolean-query Internet searches. FIG. 2 is a schematic illustration of a large sparse Term×Document matrix constructed as an initial step in Latent Semantic Indexing (LSI) FIG. 3 is a schematic illustration of decomposition of a Term×Document matrix into three component matrices, including a singular value matrix, in accordance with LSI. FIG. 4 is a schematic representation of the overall effect of singular value decomposition (SVD) as applied to a large sparsely populated matrix to result in a vector space of reduced dimensionality, in accordance with the technique of Latent Semantic Indexing (LSI). FIG. 5 is a block diagram illustrating the intermediary role played by preferred embodiments of the present invention. FIG. 6 is a high-level architecture representation of one preferred embodiment of the present invention. FIG. 7 is an illustration of an example of a user interface input form of a preferred embodiment of the present invention. FIG. 8 is a simplified illustration of two dimensions of an LSI space. FIG. 9 is a simplified illustration of two dimensions of an LSI space, showing hypothetical locations of sample documents and terms, including the relevancy of those items. FIG. 10 is a simplified illustration of two dimensions of an LSI space, showing hypothetical locations of candidate synonyms. FIG. 11 is an illustration of an example of a user interface input form of a preferred embodiment of the present invention DETAILED DESCRIPTION OF THE INVENTION Preferred embodiments of the present invention provide a method for refinement of queries used in retrieving information from large full-text databases. This method can be used, for example, in at least two important ways:
In preferred embodiments, the invention provides a method for accepting simple inputs from a user 100 and converting them to a complex query structure. Although various other retrieval mechanisms could be employed, the embodiments discussed below involve the transformation of user inputs into complex Boolean queries. Boolean query systems preferably have the following characteristics:
One drawback to the use of Boolean operators in information retrieval systems is that it can be difficult for humans to deal with the cognitive load of manually creating and managing complex Boolean queries that will result in high recall and precision when applied to a target data collection. The present invention can provide means of facilitating the creation of such queries. A block diagram of an architecture designed to implement preferred embodiments of the present invention is presented in FIG. 6. In the operation of one preferred method of the present invention, the following steps can take place:
Although other vector space representations can be used to index the query and the extracted documents, the technique of Latent Semantic Indexing (LSI) provides a vector space that is optimal in significant respects. It has been demonstrated that the LSI space is an optimal semantic subspace based on maximum likelihood estimation. [D In order to visualize the operation of preferred embodiments of the present invention employing an LSI vector space, it is useful to keep in mind the following dual aspect of the LSI vector space:
In known applications, the LSI approach is used to conduct the overall search operations and to provide a ranking of the results. In preferred embodiments of the present invention, the LSI technique is used to guide retrieval operations that are carried out by, for example, a Boolean text retrieval system. In preferred embodiments of the present invention, the LSI technique is used:
This use of the LSI technique for hypothesis generation and testing represents a novel application of the technique. With the LSI technique, documents that are close together in the LSI space have very similar distributions of words. Generally this also indicates that they are quite similar in meaning. In preferred embodiments of the present invention, this is exploited by use of a query refinement loop 660 in which queries are iteratively refined. Preferably, a second loop, the user feedback loop 670, also is implemented, in which feedback from the user is employed in guiding the query refinement process. These two loops are shown in FIG. 6. While it is desirable to implement both loops in some preferred embodiments of the present invention, other preferred embodiments of the present invention advantageously employ only one of the two loops. In preferred embodiments, the present invention further includes the following steps.
This set of steps can be iterated until, preferably, one of several events interrupts or terminates the loop:
In some preferred embodiments of the present invention, a user feedback loop 670 plays a role in guiding the query refinement process. The user 100, for example, provides feedback in two important ways:
Preferably, the two loops 660, 670 run asynchronously. Typically, the query refinement loop 660 will execute far more often than the user interface loop 670. In embodiment where the present invention is used in a software agent role, the query refinement loop may be carried out many thousands of times relative to each instance of user interaction In some embodiments of the present invention, there is a third loop in which the search engine 300 that indexes the overall target collection 400 is used to retrieve additional documents that are added to the data store of extracted documents 620. This is preferably done in at least two instances, both of which involve increasing the recall of the search:
This third loop can play a useful role. The following discussion focuses on two loops preferably used in embodiments of the present invention. In many applications the target text collection 400 of interest will be the Internet. The search engine 300 used to carry out the searches in this third loop may be any of a number of extant search engines. Other applications will involve retrieval operations conducted against internal databases such as an intranet within an organization. In this case also, there are a large number of text retrieval systems that could be employed to carry out this search engine function. In either case, preferred search engines have the following characteristics:
The iteration processes of preferred embodiments of the present invention are preferably designed to provide the following results:
Of the two results, producing an improved ranking is more difficult to achieve. Obtaining high values of recall using the search engine 300 is relatively straightforward once the query is refined by preferred embodiments of the present invention. The present invention greatly reduces the requirements for precision of the search engine's 300 retrieval operation. The product of the search engine 300 is used as an input to the internal processes, rather than being presented directly to the user 100 via the user interface 690. A wide variety of user interfaces 690 could be employed in providing inputs to a retrieval system embodying the present invention. This includes a number of user interfaces that have been developed for existing information retrieval systems. Preferred embodiments of the present invention implement simple user interfaces 690 to mitigate the cognitive load on the user 100. Therefore, in some preferred embodiments discussed below, a minimal user interface 690 is employed. In preferred embodiments, the user interface 690 can include an input form 691 as illustrated in FIG. 7, wherein the user 100 may type words or phrases that fall into one or more of the following categories:
This illustrative simple input form 691 does not require the user 100 to have an understanding of Boolean operators or of how to formulate logic statements. One feature of preferred embodiments of the present invention is that those embodiments can deal effectively with such simple inputs. An initial query entered through such an interface 690 and input form 691 could consist of a single word. This minimization of the cognitive load on the user is an advantageous factor. One feature included in the preferred embodiment of the user input form 691 described above, and illustrated in FIG. 7, is the provision for inclusion of items that would be of particular importance if they were found in relation to the indicated objects of interest. This feature can be of particular value in optimizing rankings of retrieved documents for users. The following non-limiting example illustrates the operation of a preferred embodiment of the present invention. Let us assume that the user 100 wishes to find information about bears. For simplicity, we will assume that the user 100 inputs the single word bear as a term of interest 692 into a form 691 via the user interface 690. The Query Generator 610 accepts this as the one-term Boolean query consisting of the word bear, and sends this query to the search engine 300. For a target collection 400 of any significant size, this query will yield a result set having a large number of hits. Because of the large size of the result set, in this example of a preferred embodiment of the present invention, no attempt will be made to download all corresponding documents. In this illustrative embodiment, a limit is chosen to yield a reasonably sized set of documents for. an initial set of extracted documents. The LSI Engine 630, using the LSI technique, processes the documents downloaded to the extracted document data store 620. Enough documents are downloaded to create an LSI space that covers the likely relevant vocabulary in some depth. This threshold may be determined empirically or the like. Typical numbers of documents for this initial download can be from about a few hundred to about ten thousand. There will likely be an initial delay in the operation of the system due to the time required to download these documents (as limited by the bandwidth of the communications path between the target collection 400 and the extracted documents data store 620) and/or the time required to process them using the singular value decomposition (SVD) algorithm in creating the LSI space. Although there are some bootstrap methods whereby the query refinement process could begin immediately, it typically will be preferred to present some of these documents to the user 100 for evaluation at the start of the refinement process. Preferably, all that will be required of the user is to examine a few documents and provide some indication of their degree of interest, i.e., how relevant they are to the information need that the user is trying to satisfy. We will assume in this example that, while reviewing each of these documents, he or she clicks on one of three buttons, representing highly relevant, mildly relevant, and irrelevant. For concreteness in this example, we will assume that the system presents 10 documents to the user for review and relevance judgment. Historically, there have been attempts to make use of user feedback in improving the effectiveness of text retrieval systems. However, these existing approaches generally have used this information in ways that tend to average out the feedback. Preferred embodiments of the present invention can explicitly use this information in a discrete fashion. One potential advantage of preferred embodiments of the present invention is that even small amounts of user feedback have great discriminatory power when used in this discrete fashion. In this example, the requirements placed on the user so far have been minimal. The initial query was trivial. The time required to review 10 documents in general would be only a few minutes. The only action required of the user during this review is to indicate which of three relevance categories each falls into (highly relevant, mildly relevant, or irrelevant). Nonetheless, when treated as discrete information items, the combinatorics of this feedback is substantial. For example, in indicating which of three categories 10 items fall into, the user has selected one of 310 possible rankings of these documents. Three raised to the tenth power is 59049. The large size of this number illustrates the discriminatory power contained in even a small amount of user feedback. Prior to obtaining the user feedback, the ability to rank the collection of extracted documents was limited. Basically, the only content-related criterion upon which they could be ranked was the frequency of occurrence of the word bear. This is a typical assumption in text retrieval—that the more frequently a query term appears in a document, the more likely that document is to be relevant to the information needs of the originator of the query. In practice, this number of occurrences typically would be normalized by dividing the number of occurrences in each document by the length of each document. Once the initial user feedback has been obtained, however, preferred embodiments can provide many possibilities for creating more effective rankings of the documents. For example, an LSI space provides us with a very powerful approach to ranking. As noted above, the closer together two documents are in the LSI space, the closer they generally are in content. Thus, the documents that the user has identified as being of high relevancy define "regions of interest" in the space. The documents in the space that are near to these regions are likely to be of much greater interest than those that lie far from these regions. Thus, the closer a given document is to one of the documents rated as being of high relevancy, the more highly ranked that document should be. Similarly, documents that are nearest to those designated by the user as being irrelevant should be given a low ranking. Documents near to those designated by the user as being of mild relevance should be given an intermediate ranking. There are of course, many variants of this basic ranking that could be employed. The distances to pairs, clusters, or each entire set of designated high-relevancy, mild-relevancy, or irrelevant documents could be taken into consideration. In some embodiments, weighted combinations of distances to the nearest high-relevancy, mild-relevancy, and irrelevant documents could be combined. In addition to the direct indication of relevance derived in the above fashion, the LSI space provides much additional information of value in the refinement process. The actual distribution of the documents provides many clues to how the documents in the space may relate to a user's information needs. The positions of specific words in the space also provide much important information. This information preferably is analyzed in two modules of preferred embodiments of the present invention. The universal ranking engine 650 takes this information into account in generating improved rankings. The hypothesis generator 680 uses this information in generating sets of potential improvements in the current Boolean query. Preferred embodiments of the present invention include processes of query and ranking refinement. These processes can be generally compared to what often occurs when a requestor works through an intermediary in obtaining information. The requestor will explain his or her information needs in an initial meeting with the intermediary. The intermediary, often a librarian or research assistant, often subsequently will present intermediate results to the requestor. Upon reviewing these results, the requestor typically will provide some additional information that helps the intermediary to better understand the information requirement. It should be noted that during this iterative process, the understanding of the information need on the part of the requestor might be modified. Review of intermediate results may indicate that some elements of the requirement, as originally conceived, may no longer be of interest. Similarly, new items of interest that are relevant may be identified. Preferred embodiments of the present invention include two features in order to implement a highly automated query and ranking refinement process:
In some preferred embodiments of the present invention, the hypothesis generation function 680 is based on analysis of the locations of objects in the LSI space. For purposes of example, a two-dimensional LSI space is considered. In practice, the LSI spaces employed will have a substantially greater dimensionality. Those in the art would be able to, based on this disclosure, apply the principles herein to higher-dimensional spaces. In addition, distances in LSI spaces are measured in terms of cosines between vectors. Because humans are accustomed to dealing with distances in terms of spatial extent, for illustrative purposes only, the distances between vectors are discussed as if they were spatial distances. This will facilitate understanding. In a strict technical discussion, however, the distances would all be described in terms of cosine measurements or the like. FIG. 8 is an illustrative two-dimensional representation of an LSI space. Let us assume that this space has been generated by an initial query, as described above. Let us further assume that we have at least one round of feedback from the user, in which the user has designated some documents as being of either relevant or irrelevant to the user's information need. FIG. 9 labels some of the documents as relevant (R) 901 and some as irrelevant (I) 902. There are many ways in which clues can be derived from this space that suggest changes that might be made to the current query to improve its performance. For example, an analysis of the clustering of the documents indicates that there is a small cluster of relevant documents in the lower right hand corner of the space, and a cluster of irrelevant documents in the lower left hand corner of the space. In addition, there are some individual distributed relevant and irrelevant documents. Both isolated documents and clusters of documents can be used as the starting point for analysis. As noted above, preferably all of the words in all of the extracted documents have a location in this space. The locations of some common words, such as the, and, of, etc., is not of topical significance and thus will not be considered here. (In fact, these words often are treated as stop words in creating LSI spaces, i.e., they are not processed.) Other words, such as help, are applicable in such a wide variety of contexts that they also will not be discussed here. There may, however, be certain collections of documents where the locations of such words provide useful information. The treatment of these words in such cases is not significantly different from that described in the following and thus will not be treated here. The vast majority of words have some degree of topical relationship, and it is those words that are addressed in this example. For the small cluster of relevant documents in the lower right hand corner of FIG. 9, it is a simple task to determine what words in the LSI space are close to the cluster. Commercial LSI software packages accept as inputs objects that may be words, queries, or documents. Locations in the space also may be specified as a starting point. Commercial LSI software will typically return a list of the words, queries, or documents that are closest to the input object. This list is ranked in order of distance, with the closest object first. In the present example, focusing on the centroid of the cluster of relevant documents, a ranked list of the words nearest to the centroid can be retrieved. A word that is located close to the documents that have been identified as relevant has a high probability of itself expressing a concept that is relevant to the current information need. Thus, a word such as the one identified in the term 903 in the lower right of FIG. 9 is a candidate relevant word. There are a variety of ways in which this information could be used in structuring hypotheses regarding possible improved queries. One simple method will be described below in accordance with one preferred embodiment of the present invention. Designating the current query as QUERYNOW and the candidate relevant word as CRW, we may combine CRW with QUERYNOW using a logical OR operator, as follows: QUERYNOW OR CRW=MODQUERY. In many cases, MODQUERY (the modified query) will be a better representation of the user's information needs than the former one. In other cases, the opposite will be true. Preferred embodiments of the present invention include a means that indicates which of these results is more likely. This can be done, for example, through a three-step process as follows.
In this illustrative case, the logic of the hypothesis testing is preferably as follows. If the incorporation of the CRW into QUERYNOW is a beneficial thing to do, this should be reflected in a better ranking of the documents in the result set generated by the three steps outlined above. The universal ranking engine 650 takes into account the number of occurrences of terms of interest in the documents that are being ranked. The basic assumption is that, all else being equal, documents that contain more terms that are of interest should be more highly ranked than those that contain fewer. There are a number of ways such rules can be applied, as would be understood by those in the art. The newly ranked set of documents is compared to the ranking of documents explicitly produced by the user 100. A general principle that is preferably applied is that the new ranking of documents should not contradict the explicit relevancy identified by the user 100. That is, all documents that were indicated as being highly relevant by the user 100 preferably should be highly ranked in the new ranking. All documents that were identified by the user 100 as being of low relevance preferably should be ranked lower than the designated high-relevance documents in the new ranking. All documents identified by the user 100 as irrelevant preferably should either be absent from the new set of ranked documents or ranked very low. At any given point in the process, the number of documents for which relevancy has been identified by the user 100 will be relatively small in comparison to the total number of documents automatically ranked. Closeness in the LSI space is used to interpolate "proper" positions for documents that have not been explicitly ranked. That is, a document that is very close in the LSI space to one that has been explicitly ranked should be close to that document in the new ranking. In some cases, it will be clear that a new ranked result set is significantly better than the previous one. In those cases, MODQUERY will be re-designated as the new working query, i.e., QUERYNOW. In other cases, the new ranked result set will be noticeably inferior to the existing one, and the modification will not be made. In some cases, the differences will be slight. This will be true more often when there is a relatively small amount of feedback available from the user. Some potential modifications in this class may simply not be made. Others can be held for further analysis. Thresholds can be established to determine which potential modifications may receive further consideration. This may be based on a consideration of predicted impact. For example, consider a word whose inclusion in the query using an OR statement has little effect on the ranking. This word might be very close in the space to one whose inclusion using an OR statement led to a much improved ranking. This apparent contradiction could be cause for saving this word for further analysis. Preferred embodiments of the present invention can include a list of apparent anomalies. Some of these anomalies will be statistical flukes. Many others, however, will reflect an as-yet-not-understood subtlety of the users information need. Apparent anomalies receive subsequent treatment in two ways in preferred embodiments of the present invention. First, they may be held for later consideration for inclusion in the query. The order in which the Boolean logical operations are carried out can be significant. It may be the case that a candidate modification at one point has little beneficial effect. However, that same modification may later may have a much more beneficial effect. Second, the word under consideration may be incorporated into a question that is directly asked of the user. A prioritized list of such questions preferably is kept available at all times. A selected subset of these questions is preferably presented to the user whenever the opportunity is available. In the process described above, it is notable that not all of the automated choices need be correct. However, what is important is that on average the choices should be correct. To the extent that this is true, the iterative query refinement process will converge to a solution—a highly effective query and ranking strategy. The more feedback that is available from the user, the more accurately and rapidly this process will converge. Once it has been determined that a given word in the LSI space should be incorporated into a query in a given manner, other words that are near that one in the space may be considered for incorporation in the same manner. For example, consider the two terms shown in FIG. 10. Assume that the above procedure has indicated that term S 1010 should be incorporated into the current query using an OR operator. The fact that term T 1020 is close to term S 1010 in the space indicates that they have some conceptual similarity. The closer these two terms are in the space, the more they are likely to be synonyms. If the incorporation of OR TERM S 1010 into the query produced favorable results, then the incorporation of OR TERM T 1020 is a good hypothesis to be checked. In addition to the specific example given above, many other candidate hypotheses can be derived from examining the LSI space such as the following, for example.
In general, a word that is close to another word is a good candidate for treatment in any manner that has been found to be beneficial for the first word. In practice, suitable cosine value thresholds for closeness preferably are determined heuristically. In all of the above cases, the operations focusing on individual words also can (and should) be carried out with a focus on phrases. This could be done using a list of common phrases. However, preferred embodiments of the present invention maintain maximum flexibility and require minimum maintenance. In this regard, some preferred embodiments of the present invention consider at least all consecutive pairs and triplets of words as potential phrases. This will encompass most phrases of interest. Longer phrases that actually occur in the documents can be determined by examining the statistics of the occurrence of consecutive runs of more than three words. Such runs that occur multiple times can then be treated as phrases in the above types of analyses. The AND and AND NOT operations reduce the size of the result set and lead to high precision. As OR operations are included, the scope of the query is increased. As such operations are added, it will be desirable from time to time to exercise the external search loop and download any additional documents that the expanded query identifies. It is desirable to download only the newly identified documents and add them to the existing store of extracted documents, rather than downloading an entire new result set. Most practical implementations would preferably allow this. At this point, the impressive combinatorics of the present hypothesis generation and testing technique are evident. In most practical applications, the downloaded set of extracted documents may collectively encompass thousands to tens of thousands of terms. Several thousand of these terms may be analyzed in each of the ways listed above. Thus, even in a single pass, several tens of thousands of candidate hypotheses can be generated. Moreover, every time there is feedback from the user 100, it is desirable to re-test all hypotheses in light of this new information. Feedback from the user 100 is highly advantageous and can be used to the maximum extent practical to further increase the efficiency of the system. In a similar fashion, whenever new documents are downloaded to the data store of extracted documents 620, it may be desirable to re-test the hypotheses. This will be true particularly in cases where a significant number of OR operations have been incorporated into the query. It also will be true in cases where a significant amount of new information is likely to have been added to the target collection 400. In general, it can be anticipated that at least several user feedback sessions will take place. In addition, several downloads of additional documents are likely to take place. Thus, from the view of hypothesis generation and testing, there are likely to be a hundred thousand or more candidate query modifications to be tested. While the LSI space provides many potential clues for query refinement, it also yields many clues to be considered in modifying strategies for ranking result sets. For any given document, the universal ranking engine 650 may take into account all or some of the following information from the LSI space generated by the LSI engine 630:
In addition, once again, all of the above types of analyses can be applied to phrases. In all cases, the treatment can range from consideration of averages of the class of objects to an exhaustive treatment of all relevant term, phrase, and document occurrences. The number of possible ranking strategies will correspondingly vary from, for example, scores to tens of thousands. In a preferred embodiment, the extent to which these many possibilities are explored would be controllable. This could be done by implementing universal ranking engine logic wherein the granularity of the processing could be controlled by an external parameter. Alternatively, the software could incorporate heuristically derived metrics that would terminate the ranking refinement process when it reached some point of diminishing returns. In some preferred embodiments, both the query formulation and result set ranking processes can operate on metadata. For example, key elements of documents, such as date or source, may be of great importance in determining a users interest in those documents. Internet standards such as the resource description framework (RDF) and the extensible markup language (XML) are leading content providers to incorporate more metadata in document and web page headers. Many retrieval systems allow Boolean operations involving such fields to be combined with Boolean operations on the textual content of the documents. In preferred embodiments of the present invention, metadata may be treated on an equivalent basis to words and phrases that appear in text. Although such tags may not appear in the LSI space, they may readily be examined in the query refinement and ranking refinement operations. The fact that such processing may be going on can be completely transparent to the user. Preferred embodiments of the present invention thus allow the widest possible range of relevant data to be taken into account in selecting and ranking documents. Notably, this can be done without requiring the user to consciously address the relative importance of each item that is taken into consideration. In comparison to the number of query modification hypotheses likely to be tested by a user 100, the larger number of query modification hypotheses that can be tested by preferred embodiments of the present invention constitutes an increase in search and retrieval capability. Similarly, the larger number of ranking strategies that can be tested presents major advantages. In many cases, some time will be necessary for the associated processing to take place. In some preferred embodiments of the present invention, the user will refine a query in short interaction sessions (e.g., several minutes to a few tens of minutes), likely spread over a few days. In such embodiments, the processing time will not present a concern. In other embodiments, where the processing time needs to be minimized, the number of possibilities that are examined can be limited. For example, as noted above, characteristics of the distribution of objects in the LSI space can be used to produce an estimate of the likely impact of any given query modification. This estimate can be generated with much reduced effort in comparison to actually carrying out the calculations required to test that hypothesis. In an application where processing time is of importance, a threshold could be established so that only the changes with the highest probability of beneficial effect would be considered. Similarly, in applications where the processing time is a concern, the degree of granularity of the ranking hypotheses could be reduced. One preferred aspect of preferred embodiments of the present invention that incorporate user feedback is that cumulative user feedback is preferably employed to create a "gold standard" document ranking. Typically, a user may be able to determine the relevance or irrelevance of a document in a few tens of seconds of examination. Thus, for example, in a ten-minute interaction session, the user might designate the relevance (or irrelevance) of 20 or so documents. In three such sessions, the user will have selected one of 260 or 360 possible rankings of this set. As this number increases, the discrimination capabilities of the query refinement loop increase greatly. Moreover, the likelihood that an incorrect query modification is made decreases. In another preferred embodiment of the present invention, the user is presented with specific questions to refine the query. This is a means of obtaining more specific feedback than that obtained when whole documents are indicated as relevant or irrelevant. Many candidates for such questions will be developed as the query refinement loop 660 is exercised. These may be presented to the user via another very simple interface, such as the one shown in FIG. 11. It should be recognized that various preferred embodiments and characteristics thereof, which have been described, are merely illustrative of the principles of this invention. Numerous modifications and adaptations thereof will be readily apparent to those skilled in the art without departing from the spirit and scope of the present invention.
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