# Patent

## Title
Automatic index term augmentation in document retrieval

## Abstract

Disclosed are methods and systems for automatically assigning index terms to electronic documents such as Web pages or sites in a manner which may be used to facilitate the retrieval of electronic documents of interest. The method involves determining co-occurrences of terms in other documents with the electronic document, and selecting terms as index terms based upon those scores. The method permits the efficient retrieval of electronic documents.

## Background
CROSS-REFERENCE TO RELATED APPLICATIONS
This patent application is a continuation-in-part of the following U.S. patent applications: “Weighted Term Ranking for On-Line Query Tool”, Ser. No. 09/282,730, to Jay Ponte; and “Hybrid Category Mapping for On-Line Query Tool”, Ser. No. 09/283,268, to Jay Ponte, having a common application date of Mar. 31, 1999, having the same inventor and assignee as herein named.


TECHNICAL FIELD
This invention relates to techniques for organizing material on computer networks for retrieval, and more particularly to methods of indexing material of interest to a user.
BACKGROUND OF THE INVENTION
Computer networks have become increasingly important for the storage and retrieval of documents and other material.
The Internet, of which the World Wide Web is a part, includes a series of interlinked computer networks and servers around the world. Users of one server or network connected to the Internet may send information to, or access information on, other networks or servers connected to the Internet by the use of various computer programs which allow such access, such as Web browsers. The information is sent to, or received from, a network or server in the form of packets of data.
The World Wide Web portion of the Internet comprises a subset of interconnected Internet sites which may be characterized as including information in a format suitable for graphical display on a computer screen. Each site may include one or more separate pages. Pages, in turn, may include links to other pages within the site, or to pages in other Web sites, facilitating the user's rapid movement from one page or site to another.
In view of the quantity of information and material available on computer networks such as the Web, and for other reasons as well, automated or semi-automated techniques for retrieving information that is thought to be relevant to a user at a given time may be employed. These techniques may be utilized in response to a specific user request, as when a search query by a user seeks information. These techniques also may be utilized when a user is accessing certain material, in order to make available material that it is thought may be of interest to a user who has accessed the original material. These techniques may also be utilized when a user, given access to particular material, requests other similar material. Other situations when these information retrieval techniques may be employed will also be apparent to one of ordinary skill in the art.
Some information retrieval techniques such as are employed in these circumstances choose documents for retrieval from among documents in a collection based upon the occurrence of specified terms in the documents in the collection. (Hereinafter, for simplicity, “document” shall be used to refer to the items, such as Web pages or Web sites, in the collection being analyzed.) There are a variety of different techniques for specifying the terms to be used. (A “term” may be any word, number, acronym, abbreviation or other collection of letters, numbers and symbols which may be found in a fixed order in a document.) In some methods, a search may be made among the documents in the collection for some or all of the terms in a search query generated by the user. In other methods, a search may be made for some or all of the text of a given document. (In some methods, all terms except certain common words, referred to as stop words, such as “the” or “and”, may be included in the search.) In other methods, a search may be made for index terms which have been associated with that document by various means. Still other methods will use a combination of the above techniques, and further approaches to selecting terms for which a search is to be made will be familiar to one of ordinary skill in the art.
After a list of terms for which a search is to be made has been compiled, many information retrieval techniques then proceed by calculating scores for each document in the collection over which the search is being made, based upon the occurrence of the terms on the list in the documents. These scores which are calculated may be referred to as term frequency scores, insofar as the score assigned to a document depends on the frequency of occurrence of terms in the document.
There are a variety of different formulae which may be used to calculate these term frequency scores, including for example the Robertson's term frequency score (RTF). Term frequency score formulae may assign varying weights to terms found in a document, depending upon such factors as the relative rareness or commonness of the term. Other factors which may be used to vary the weight assigned to a term in calculating a term frequency score will also be apparent to one of ordinary skill in the art.
Documents in a collection which is being searched may be divided into different sections or segments, such as an introduction or summary, a main body, footnotes, captions, and the like. Other divisions of documents will be apparent to one of ordinary skill in the art.
A Web site may permit a user to obtain lists of relevant items of interest, such as Web sites, other documents or names of merchants carrying merchandise in particular categories. The site may be organized so that an item of interest may be considered to be in more than one category. The site may be organized so that the categories presented to the user may vary, depending on a term or terms specified by the user. If this approach is utilized, the user may input terms that relate to the merchandise in which he is interested, such as “automobiles”, and in return he may be presented with several categories, such as “automobiles, manufacturers” or “automobiles, sales” or “automobiles, service.” The categories presented may be chosen by any one of a number of techniques that will be familiar to one of ordinary skill in the art.
It may be desirable present additional material to a user who is searching for items of interest. For example, it may be desirable to present the user with banner advertisements which relate to the item of interest for which he is searching.



BRIEF DESCRIPTION OF DRAWINGS
The above-mentioned and other features of the invention will now become apparent by reference to the following description taken in connection with the accompanying drawings in which:
FIG. 1 is a schematic diagram of a computer system that may be operated according to the present invention.
FIG. 2 illustrates a relationship between terms and documents.
FIG. 3 is a flow chart which illustrates a process, according to the present invention, of automatically assigning index terms to documents.
FIG. 4 illustrates a relationship between terms, documents and index terms when some but not all documents in a collection have had index terms manually assigned to them.
FIG. 5 is a flow chart which illustrates an overall process, according to the present invention, of automatically assigning index terms to documents, where some documents have previously had index terms assigned to them.
FIG. 6 illustrates a relationship between terms, documents and index terms after documents in a collection have had index terms assigned to them automatically.
FIG. 7 illustrates a relationship between items of interest, categories and supercategories when some but not all categories in a collection have been manually assigned to supercategories.
FIG. 8 is a flow chart which illustrates an overall process, according to the present invention, of automatically assigning categories to supercategories, where some categories have previously been assigned to supercategories.
FIG. 9 illustrates a relationship between items of interest, categories and supercategories when categories in a collection have been assigned to supercategories.
FIG. 10 illustrates a relationship between categories and supercategories.
FIG. 11 is a flow chart which illustrates a process, according to the present invention, of assigning a supercategory to a query.



SUMMARY OF THE INVENTION
According to the present invention, a method and device for automatically choosing index terms to be associated with a document D, for purposes of facilitating document retrieval processes, comprises creating a search query Q comprised of terms in document D, applying the search query Q to a collection of documents C0, selecting the N0 documents from the collection of documents C0 which achieve the highest scores upon application of the search query Q, and selecting IT terms for use as index terms for document D from among terms Tn in the N0 documents based upon the co-occurrence of the terms Tn in the N0 documents with the terms Ti in the document D. The IT terms for use as index terms for document D may be selected by calculating, for terms Tn which occur in the N0 documents selected, the co-occurrence of that term Tn with each term Ti in document D, and the co-occurrence of that term Tn with document D, and selecting IT terms for use as index terms for document D from among the terms Tn in the N0 documents based upon the scores achieved by the terms Tn. The documents may be Web pages, Web sites or other collections of material. The search query Q which is applied may comprise all of the terms in document D. Preselected stop terms may be eliminated. The search query Q may be applied to select documents from among the documents in the collection C0 by calculating for each document D in the collection C0 a score SD based upon the occurrence in the document D of terms in the search query Q. In applying the search query Q to the collection of documents C0 the total score SD for a document D in the collection C0 may be calculated using a formula utilizing Robertson's term frequency for the term T in the document D. The number N0 of documents chosen by application of the search query Q may be predetermined. In one embodiment, the number N0 may be 50. All documents whose scores upon application of the search query Q exceed a given cutoff score may be selected. Co-occurrences may be calculated for all terms contained in the N0 documents selected. Preselected stop terms may be eliminated. The number IT of terms chosen as index terms may be predetermined. In one embodiment, the number IT may be 30. All terms whose scores exceed a given cutoff score may be selected for use as index terms.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)
Referring to FIG. 1, a computer system 2001 includes a workstation 2002 having local storage 2003. The workstation may also be connected to a local area network 2004 and may access to the Internet 2005. The Internet 2005 may include or be coupled to remote storage 2006. The workstation 2002 may be any one of a variety of commercially available computers capable of providing the functionality described in more detail below. The local storage 2003 may include ROM, RAM, a hard disk, a CD, and/or any other media capable of containing data and/or programs for the workstation 2002 or other data. The local area network 2004, which is coupled to and exchanges data with the workstation, may also contain data and/or program information for use by the workstation 2002. The Internet 2005 may be accessed in a conventional manner by the workstation 2002. Alternatively, the workstation 2002 may access the Internet 2005 through the local area network 2004, as shown by the dotted line of FIG. 1. The remote storage 2006 may also contain data and/or program information for the workstation 2002 or may contain other information, as will become apparent from the description below.
The system described herein permits a user (utilizing the computer system 2001 which includes the workstation 2002) who has accessed the Internet 2005, either directly or through the local area network 2004, to be given access to material that may be of interest to him. It will be appreciated by one of ordinary skill in the art that the system may be implemented using a variety of computers and programming languages. The system may be accessed by the user through the Internet 2005 from his workstation 2002 using a Web browser of conventional design, as would be familiar to one of ordinary skill in the art.
In the prior art, it is well known that information retrieval techniques may be utilized to identify documents, such as Web pages or sites, or portions of documents which may be of interest to a user. (Hereinafter, for simplicity, “document” shall be used to refer to the items, such as [but not limited to] pages or sites, in the collection being analyzed.) These techniques may be called into play in response to a search query initiated by the user. Alternatively, they may be called into play when a user requests additional documents that are similar to a document to which he has been given access. Alternatively, they may be called into play when a user is accessing a particular document, and it is desired to make available to him other documents that are related to the document being accessed. Other circumstances where it may be desirable to utilize information retrieval techniques to identify documents that may be of interest to a user will be apparent to one of ordinary skill in the art.
Information retrieval techniques may choose documents from among the documents in a collection based upon the occurrence in the documents of specified terms. The terms to be utilized in this process may be selected by a number of methods that will be apparent to one of ordinary skill in the art.
One technique that may be employed to select terms to be utilized in the process is to permit the user to specify terms by defining a search query. Another technique that may be employed is to select some or all of the terms in a document being accessed by the user. Another technique that may be employed is to select some or all of the terms in a document identified by the user as being of interest to him, or as having characteristics he wishes to have found in documents made available to him. (In these techniques, all of the terms may be used, or certain common words, referred to as stop words, such as “the” or “and”, may be omitted.) Another technique that may be employed is to select index terms which have previously been associated with the document being accessed or selected by the user. Still other techniques may use a combination of the above approaches. Other techniques for selecting terms to be utilized will be apparent to one of ordinary skill in the art.
Once a list of terms has been generated, by the above methods or any other, information retrieval techniques may proceed by calculating, for each document in the collection from which documents of potential interest are to be chosen, a score which reflects the occurrence in the document of the terms on the list. Based upon the scores achieved by the documents in the collection, the documents may be ranked, and a predetermined number of documents may be presented to the user, or all documents which achieve scores above a predetermined cutoff may be presented.
These scores which are calculated for documents are sometimes referred to as term frequency scores, in that the scores depend in part upon the frequency of occurrence of terms in the document.
The formula for calculating a total score SD for a document D may be written generally as: 



  
    S
    D
  
  =
  
    
      ∑
      
        T
        =
        1
      
      
        T
        0
      
    
    ⁢
    
      TF
      TD
    
  




where: T0 is the number of terms T which occur in the collection of terms included in the search, and

    
    
        TFTD is the term frequency score for document D based on the frequency of occurrence in document D of term T.
    
    


One particular formula in the prior art which may be used to assign a total score SD to a document D utilizes Robertson's term frequency score: 



  
    
      S
      D
    
    =
    
      
        ∑
        
          T
          =
          1
        
        
          T
          0
        
      
      ⁢
      
        
          TF
          TD
        
        *
        
          IDF
          T
        
      
    
  
  ,




where:

    
    
        T0 is the number of terms which occur in the collection of terms included in the search,
        TFTD is Robertson's term frequency for term T in document D,
        
            =NTD/(NTD+K1+K2*(LD/L0)),

where:

        
        
        NTD is the number of times the term T occurs in document D,
        LD is the length of document D,
        L0 is the average length of a document in the collection being searched, and
        K1 and K2 are constants

and IDFT=log ((N+K3)/NT)/ log (N+K4)

where:

        N is the number of documents in the collection
        NT is the number of documents containing the term T in the collection, and
        K3 and K4 are constants.
    
    


Whatever particular formula is used, documents are ranked in order of their total scores SD, and those which achieve the highest score are presented, typically in order of their scores, to the user.
In order to improve the effectiveness of information retrieval methods, additional terms may be associated with documents before term frequency scores are calculated. For example, index terms or key words may be associated with each document in a collection, and the calculation of term frequency scores may take into account the index terms or key words as well as terms that occur in the documents themselves, or may be based solely on the index terms or key words.
These additional terms may be assigned to a document by means of manual review of the document or by automatic means, or by a combination of manual review and automatic means. Methods for doing so by manual means will be apparent to one of ordinary skill in the art.
The manual assignment of index terms to a document may be time consuming, and this may make it impractical to assign index terms to large collections of documents by this method. In addition, manual assignment of index terms may fail to reveal underlying relationships between documents. It may therefore be useful to utilize automatic techniques to generate appropriate index terms for documents, based upon analysis of the characteristics of the terms which occur in the documents.
In one embodiment of the system described herein, additional index terms are added to a set of documents D in a document collection automatically. In this embodiment, terms are chosen to be added as index terms to a given document Di automatically according to their co-occurrence to a high degree with terms already found in the document Di, according to the method of local context analysis. This method has been described by Xu and Croft, in Improving the Effectiveness of Informational Retrieval with Local Context Analysis, which is incorporated herein by reference.
FIG. 2 illustrates a collection of Documents D 2020 which contain Terms T 2010. As illustrated in FIG. 2, each Term T 2010 may occur in one or more Documents D 2020, and each Document D 2020 contains one or more Terms T 2010.
According to FIG. 3, this method 2050 proceeds first at a step 2060 to select a Document Di which has not yet had index terms assigned to it. At step 2070, a search Query Qi is created, consisting of Terms Tj found in Document Di. In one embodiment of the system, the set of Terms Tj in the Document Di used to create the Query Qi comprises all of the Terms in the Document Di. In another embodiment, the set of Terms Tj comprises all of the Terms in the Document Di except certain common words, referred to as stop words, such as “the” or “and.”
In this embodiment, after the query Qi is prepared at step 2070 it is applied at step 2080 to a chosen collection C0 consisting of N documents. This collection of documents C0 may be the set of documents for which index terms are being generated by automatic means, it may be a larger set of documents including those documents for which index terms are being generated by automatic means as a subset, or it may be another set of documents, such as the set of documents over which searches will be done utilizing the index terms. It is helpful if the collection C0 has the property that the usage of terms in documents in it is characteristic of the usage of terms that will be found in documents over which searches will be carried out using the additional index terms added to the documents.
In applying the query at the step 2080, a total score SD for a document D in the collection of documents C0 searched may be written generally as: 



  
    S
    D
  
  =
  
    
      ∑
      
        T
        =
        1
      
      
        T
        0
      
    
    ⁢
    
      TF
      TD
    
  




where: T0 is the number of terms T which occur in the query Qi, and

    
    
        TFTD is the term frequency score for document D based on the frequency of occurrence in document D of term T.
    
    


While any one of a number of formulas for term frequency and inverted document frequency which will be known to one of ordinary skill in the art may be used without departing from the spirit and scope of the invention, in one embodiment of the system, Robertson's term frequency score is used to assign a total score SD to a document D: 



  
    
      S
      D
    
    =
    
      
        ∑
        
          T
          =
          1
        
        
          T
          0
        
      
      ⁢
      
        
          TF
          TD
        
        *
        
          IDF
          T
        
      
    
  
  ,




where:

    
    
        T0 is the number of terms which occur in the query Qi,
        TFTD is Robertson's term frequency for term T in document D,
        
            =NTD/(NTD+K1+K2*(LD/L0)),

where:

        
        
        NTD is the number of times the term T occurs in document D,
        LD is the length of document D,
        L0 is the average length of a document in the collection C0 being searched, and
        K1 and K2 are constants

and IDFT=log ((N+K3)/NT)/ log (N+K4)

where:

        N is the number of documents in the collection C0 
        NT is the number of documents containing the term T in the collection C0, and
        K3 and K4 are constants.
    
    


After the query is run at step 2080, at a step 2090 a number of documents N0 in C0 which achieve the highest scores under the search query Qi are selected. For example, in various embodiments the number N0 may be between 10 and 300, but it may vary depending on operational considerations which will be apparent to one of ordinary skill in the art. In one embodiment, the number of documents N0 selected is 50. This set of N0 documents has the property that Documents in it contain Terms also found in Document Di, the document which is having index terms assigned to it. The next steps 2100 to 2150 in the process 2050 then attempt to determine which other terms in the N0 documents occur most frequently with the Terms Tj in the Document Di.
After the N0 documents are selected in the step 2090, the system continues at step 2100 by choosing a Term Tk from among the Terms found in the N0 documents. In one embodiment, all terms in the N0 documents are used. In another embodiment, all terms in the N0 documents except certain common words, referred to as stop words, such as “the” or “and,” are used.
At a step 2110, the system then chooses a Term Tj from among the Terms in the Document Di which is having index terms assigned to it.
At a step 2120, the system then proceeds by calculating the co-occurrence Cn(Tj, Tk) of the Term Tk from the N0 documents with the Term Tj from the Document Di. The co-occurrence Cn(Tj, Tk) of a given Term Tk which occurs in the N0 documents, with a Term Tj in Document Di, is determined as follows:


Cn(Tj, Tk)=log10(coki(Tj, Tk)+1)*idf(Tk)/ log10(N0), 



  
    
      where
      ⁢
      
        :
      
      ⁢
      
         
      
      ⁢
      
        
          co
          ki
        
        ⁡
        
          (
          
            
              T
              j
            
            ,
            
              T
              k
            
          
          )
        
      
    
    =
    
      
        ∑
        
          n
          =
          1
        
        
          N
          0
        
      
      ⁢
      
         
      
      ⁢
      
        tf
        ⁢
        
           
        
        ⁢
        
          (
          
            
              T
              k
            
            ,
            n
          
          )
        
        *
        tf
        ⁢
        
           
        
        ⁢
        
          (
          
            
              T
              j
            
            ,
            n
          
          )
        
      
    
  
  ,




    
    
        tf (Tk, n)=number of occurrences of term Tk in Document n in the N0 documents,
        tf (Tj, n)=number of occurrences of term Tj in Document n in the N0 documents,
        idf(Tk)=the inverted document frequency for the term Tk,
        
            =min (1.0, log10(N/NT)/5.0)
        
        
         N=the number of documents in the collection C0 over which the query Qi was run, and
         NT=the number of documents in the collection C0 over which the query Qi was run, which contain the term Tk.
    
    


The system then proceeds to a step 2130. If it is determined at the step 2130 that not all Terms Tj from among the Terms in the Document Di, have had their co-occurrences calculated with the Term Tk from the N0 documents, control returns to step 2110, and the co-occurrence of another Term Tj from among the Terms in the Document Di, is calculated with the Term Tk from the N0 documents.
If it is determined at the step 2130 that all Terms Tj from the Document Di, have had their co-occurrences calculated with the Term Tk from the N0 documents, control passes to a step 2140, at which a score fD (Tk) is calculated for the term Tk with respect to the document Di: 



  
    
      f
      D
    
    ⁡
    
      (
      
        T
        k
      
      )
    
  
  =
  
    
      ∏
      
        j
        =
        1
      
      
        T
        0
      
    
    ⁢
    
       
    
    ⁢
    
      
        (
        
          δ
          +
          
            
              C
              ni
            
            ⁡
            
              (
              
                
                  T
                  k
                
                ,
                
                  T
                  j
                
              
              )
            
          
        
        )
      
      
        idf
        ⁡
        
          (
          
            T
            j
          
          )
        
      
    
  




    
    
        where
        
            Tj= a term in document Di,
            T0= the number of terms in document Di,
        
        
        idf(Tj)=the inverted document frequency for the term Tj,
         =min (1.0, log10 (N/Nj)/5.0),
        
            N= the number of documents in the collection C0 over which the query Qi was run,
            Nj= the number of documents in the collection C0 over which the query Qi was run, which contain the term Tj and
            
                δ= a constant. (In one embodiment, δ may be assigned a value of 0.01, but this value may be varied without departing from the spirit and scope of the invention.)
            
            
        
        
    
    


After fD (Tk) is calculated at the step 2140, control passes to a step 2150. If it is determined at the step 2150 that not all Terms Tk from among the Terms in the N0 documents have had their Scores fD (Tk) calculated for the Document Di, control returns to step 2100, and the process of steps 2100-2140 is carried out for another Term Tk from among the Terms in the N0 documents.
If it is determined at the step 2150 that all Terms Tk from among the Terms in the N0 documents have had their Scores fD (Tk) calculated for the Document Di, control passes to a step 2160, at which index terms are chosen for the Document Di. To do so, in this embodiment the values of fD (Tk) for the Document Di are compared for the terms Tk in the N0 documents, and the terms Tk with the highest values of fD (Tk) for the Document Di are chosen as additional terms to be added as index terms to the Document Di. While the number of terms added may vary without departing from the spirit and scope of the invention, in one embodiment 30 terms are chosen to be added as index terms.
After index terms are assigned to Document Di at the step 2160, control passes to a step 2170. If it is determined at the step 2170 that not all Documents Di have had index terms assigned, control returns to step 2060, and the process of steps 2060-2160 is carried out for another Document Di.
If it is determined at the step 2170 that all Documents Di, have had index terms assigned, this portion of the system is completed.
The system described herein may be employed via a Web site which presents a user with, or permits a user to obtain, specific documents or lists of documents, such as Web sites, names of merchants or stores carrying merchandise in particular categories, or other documents, and which uses index terms assigned to documents to assist in the process of identifying documents for presentation to the user, or for inclusion in a list to be presented to the user.
A further aspect of the system described herein may be employed when some of the documents in the collection from which the selection(s) are to be made have had index terms assigned to them manually (or by other automatic methods), but index terms have not been assigned to all documents, and it is desired to assign index terms to the remaining documents automatically.
According to FIG. 4, in one embodiment of the system described herein, there may be a very large number of Documents D 2420 which contain Terms T 2410.
In this embodiment of the system, it is desired to assign an Index Term 12440 or Index Terms to each Document D.
It may desirable in this embodiment of the system to associate each Document D 2420 with one and only one Index Term I 2440, or it may be desired to associate a plurality of Index Terms with a Document D.
Index Terms may be associated with Documents manually. However, manual association is time consuming and therefore costly, and this is particularly the case if the Documents and/or Index Terms may change frequently. The system described herein therefore permits Documents to be assigned Index Terms automatically, after an initial group of Documents have been assigned manually. FIG. 4 illustrates the relationship of Terms, Documents and Index Terms, when some Documents have been assigned Index Terms manually, and others have not had Index Terms assigned. (It will be understood by one of ordinary skill in the art that the system here described may also be applied where an initial group of documents have had Index Terms assigned by another automatic method, rather than manually.)
According to FIG. 5, the process 2450 of assigning Index Terms 2440 to Documents 2420 begins at a step 2460 in which an (as-yet-unprocessed) Document Di to which no Index Terms have been assigned manually is selected. Control then passes to a step 2470 at which an (as-yet-unanalyzed for the selected unprocessed Document Di) Index Term Ij is selected. (The Index Terms may consist of a set of terms chosen from among the Terms T which occur in the collection of documents, or they may be chosen independently of whether they occur among the Terms in the document collection.) Control then passes to a step 2480 at which a Document Dk which has been manually assigned Index Term Ij is selected.
At a step 2490, the process 2450 then calculates the log likelihood ratio L (Di, Dk): 



  
    
      L
      ⁡
      
        (
        
          
            D
            i
          
          ,
          
            D
            k
          
        
        )
      
    
    =
    
      log
      ⁡
      
        (
        
          
            ∑
            
              m
              =
              1
            
            
              M
              0
            
          
          ⁢
          
             
          
          ⁢
          
            
              ∏
              m
            
            ⁢
            
               
            
            ⁢
            
              
                (
                
                  
                    D
                    i
                  
                  ,
                  
                    D
                    k
                  
                
                )
              
              /
              
                
                  ∑
                  
                    m
                    =
                    1
                  
                  
                    M
                    0
                  
                
                ⁢
                
                   
                
                ⁢
                
                  
                    ∏
                    m
                  
                  ⁢
                  
                     
                  
                  ⁢
                  
                    (
                    
                      D
                      i
                    
                    )
                  
                
              
            
          
        
        )
      
    
  
  ,




where:

    
    
        πm(Di, Dk)=1, if Term m is in Document Di and to Document Dk 
        
            =0 otherwise
        
        
        πm(Di)=1, if Term m is in Document Di 
        
            =0 otherwise
        
        
         M0=the number of Terms which are in Document Di.
    
    


Control then passes to a step 2500, at which it is determined if there remain any further Documents Dk, manually assigned the Index Term Ij being analyzed, for which the log likelihood ratio of that Document Dk to the Document Di being processed has not yet been calculated. If any such Documents Dk remain at the step 2500, control returns to the step 2480 at which a further Document Dk, which has had Index Term Ij manually assigned to it, is chosen for calculation. If no such Documents Dk remain at the step 2500, control instead passes to a step 2510 at which is calculated the total score T (Di, Ij) for the unprocessed Document Di for the Index Term Ij: 



  
    
      T
      ⁡
      
        (
        
          
            D
            i
          
          ,
          
            I
            j
          
        
        )
      
    
    =
    
      
        ∑
        
          k
          =
          1
        
        
          K
          0
        
      
      ⁢
      
         
      
      ⁢
      
        W
        ⁢
        
           
        
        ⁢
        
          (
          
            
              D
              k
            
            ,
            
              I
              j
            
          
          )
        
        *
        
          
            L
            ⁡
            
              (
              
                
                  D
                  i
                
                ,
                
                  D
                  k
                
              
              )
            
          
          /
          
            
              ∑
              
                k
                =
                1
              
              
                K
                0
              
            
            ⁢
            
               
            
            ⁢
            
              W
              ⁢
              
                 
              
              ⁢
              
                (
                
                  
                    D
                    k
                  
                  ,
                  
                    I
                    j
                  
                
                )
              
            
          
        
      
    
  
  ,




where

    
    
        K0=the number of Documents manually assigned Index Term Ij,
        W(Dk, Ij)=the weight assigned to Index Term Ij for Document Dk 
    
    


This system permits varying weights to be assigned to different Index Terms Ij associated with a given Document D. The weights assigned to the index terms associated with a given Document D may be equal, or they may be varied to reflect the degree of importance associated with the Index Term, or they may be varied to reflect the degree of confidence with which the Index Term is believed to represent the characteristics of the document. Other reasons and methods of varying the weight assigned to an Index Term associated with a Document will be apparent to one of ordinary skill in the art.
In the case where each Document D has assigned to it only a single Index Term Ij, then W(Dk, Ij)=1 for the one and only one Index Term Ij assigned to Document Dk, and the formula for the total score T (Di, Ij) is simplified: 



  
    
      T
      ⁡
      
        (
        
          
            D
            i
          
          ,
          
            I
            j
          
        
        )
      
    
    =
    
      
        ∑
        
          k
          =
          1
        
        
          K
          0
        
      
      ⁢
      
        
          L
          ⁡
          
            (
            
              
                D
                i
              
              ,
              
                D
                k
              
            
            )
          
        
        /
        
          K
          0
        
      
    
  
  ,




where

    
    
        K0=the number of Documents manually assigned Index Term Ij,
    
    


Control then passes to a step 2520, at which it is determined if there remain any further Index Terms Ij for which total scores T (Di, Ij) have not yet been calculated for the Document Di being processed. If any such Index Terms Ij remain at the step 2520, control returns to the step 2470 at which a further Index Term Ij is chosen for analysis with the Document Di. If no such Index Terms Ij remain at the step 2520, control instead passes to a step 2530 at which an Index Term or Index Terms are selected to be associated with the Document Di being processed.
In one embodiment of the system, a single Index Term IM, whose total score T (Di, Ij) for the Document Di being processed is the highest, is selected as the index term for Document Di. In another embodiment of the system, a predetermined number R of Index Terms may be selected as index terms for Document Di. In this embodiment, the R Index Terms with the highest total scores T (Di, Ij) are selected. In another embodiment, all Index Terms whose total scores T (Di, Ij) exceed a predetermined cutoff score To are selected as index terms for Document Di. (In any of these embodiments, if no co-occurrences were found between the Document Di being processed and any document which has been manually assigned index terms, then no index terms are assigned to the Document Di.)
Control then passes to a step 2540 at which it is determined if there remain any further Documents Di, which were not assigned index terms manually, which have not yet been processed. If any such unprocessed Documents Di remain at the step 2540, control returns to the step 2460 at which a further as-yet-unprocessed Document Di is chosen for processing. If no such unprocessed Documents Di remain at the step 2540, the process 2450 is concluded, and each Document Di, to which no Index Terms had been assigned manually, either has been assigned Index Terms or has been found not to have co-occurrences with any Document which had index terms manually assigned to it. According to FIG. 6, when the process 2450 has been completed, Index Terms 2440 will have been assigned to Documents 2420 containing Terms 2410, except for Documents 2420 which could not be assigned Index Terms 2440 because they lack any co-occurrences with any Document 2420 which had Index Terms 2440 manually assigned to it.
The system described herein may be utilized in one embodiment in connection with the assignment of categories consisting of items of interest into categories of categories, or supercategories.
In this embodiment, an item of interest may be considered to be a merchant, store or other source for a product or service, or a number of (related or unrelated) products or services. Each variety of product or service may be considered to be a category (such as, for example, “Auto Dealers, Used Cars”). In this embodiment, items of interest (merchants or stores, such as, for example, “Lannan Chevrolet, Oldsmobile”) may be assigned to more than one category (variety of product or service).
In this embodiment, it is desired to present categories to a user in response to his request. The categories presented to the user may vary, depending on a term or terms (such as, for example, “automobiles, used”) specified by the user in the request. The categories presented may be chosen by any one of a number of techniques that will be familiar to one of ordinary skill in the art.
In this embodiment of the system described herein, it is desired to present additional material to a user who is searching for items of interest. For example, it may be desired to present the user with banner advertisements (such as for automobile financing sources) which relate to the item of interest (such as used cars) for which he is searching.
According to FIG. 7, in one embodiment of the system described herein, there may be a very large number of individual items of interest 2810 to be organized into categories 2820 for presentation. While the number may vary without departing from the spirit and scope of the invention, there may be about 20,000 categories.
In this embodiment of the system, it is desired to choose a banner advertisement to present to a user. The banner advertisements in turn may be divided into categories 2840. While the number may vary without departing from the spirit and scope of the invention, there may be about 50 categories 2840 into which the banner advertisements may be divided. (To avoid confusion with the categories into which the items of interest are divided, these banner advertisement categories 2840 are referred to herein as “supercategories,” 2840).
It is desirable in this embodiment of the system to associate each category 2820 of items of interest 2810 with one and only one supercategory 2840 of banner advertisements, such that when a user is accessing that category 2820 of item he is presented with banner advertisements from the corresponding supercategeory 2840. (For example, in one embodiment the category “Auto Dealers, Used Cars” may be assigned to a supercategory also comprising other categories related to automobiles, such as “Automobile Dealers” and/or “Auto Repair & Service.”)
Categories may be associated with supercategories manually. However, manual association is time consuming and therefore costly, and this is particularly the case if the categories and supercategories may change frequently. This embodiment of the system described herein therefore permits categories to be assigned to supercategories automatically, after an initial group of categories have been assigned manually. FIG. 7 illustrates the relationship of items of interest, categories and supercategories, when some categories have been assigned to supercategories, and others remain unassigned. While the number may vary without departing from the spirit and scope of the invention, in one embodiment there may be about 2,000 categories manually assigned to supercategories.
According to FIG. 8, the process 2850 of assigning categories 2820 to supercategories in this embodiment of the system 2840 begins at a step 2860 in which an (as-yet-unprocessed) unassigned category Ci is selected. Control then passes to a step 2870 at which an (as-yet-unanalyzed for the selected unassigned category) supercategory Sj is selected. Control then passes to a step 2880 at which a category Ck, which has been manually assigned to supercategory Sj is selected.
At a step 2890, the process 2850 then calculates the log likelihood ratio L (Ci, Ck): 



  
    
      L
      ⁡
      
        (
        
          
            C
            i
          
          ,
          
            C
            k
          
        
        )
      
    
    =
    
      log
      ⁡
      
        (
        
          
            ∑
            
              m
              =
              1
            
            
              M
              0
            
          
          ⁢
          
             
          
          ⁢
          
            
              ∏
              m
            
            ⁢
            
               
            
            ⁢
            
              
                (
                
                  
                    C
                    i
                  
                  ,
                  
                    C
                    k
                  
                
                )
              
              /
              
                
                  ∑
                  
                    m
                    =
                    1
                  
                  
                    M
                    0
                  
                
                ⁢
                
                   
                
                ⁢
                
                  
                    ∏
                    m
                  
                  ⁢
                  
                     
                  
                  ⁢
                  
                    (
                    
                      C
                      i
                    
                    )
                  
                
              
            
          
        
        )
      
    
  
  ,




where:

    
    
        πm(Ci, Ck)=1, if item of interest m is assigned to category Ci and to category Ck 
        
            =0 otherwise
        
        
        πm(Ci)=1, if item of interest m is assigned to category Ci 
        
            =0 otherwise
        
        
         M0=the number of items of interest which are assigned to category Ci 
    
    


Control then passes to a step 2900, at which it is determined if there remain any further categories Ck, manually assigned to the supercategory Sj being analyzed, for which the log likelihood ratio of that manually assigned category Ck to the category being processed Ci, has not yet been calculated. If any such manually assigned categories Ck remain at the step 2900, control returns to the step 2880 at which a further manually assigned category Ck is chosen for calculation. If no such manually assigned categories Ck remain at the step 2900, control instead passes to a step 2910 at which is calculated the total score T (Ci, Sj) for the unprocessed category Ci for the supercategory Sj: 



  
    
      T
      ⁡
      
        (
        
          
            C
            i
          
          ,
          
            S
            j
          
        
        )
      
    
    =
    
      
        ∑
        
          k
          =
          1
        
        
          K
          0
        
      
      ⁢
      
        
          L
          ⁡
          
            (
            
              
                C
                i
              
              ,
              
                C
                k
              
            
            )
          
        
        /
        
          K
          0
        
      
    
  
  ,




where

    
    
        K0=the number of categories manually assigned to supercategory Sj 
    
    


Control then passes to a step 2920, at which it is determined if there remain any further supercategories Sj for which total scores T (Ci, Sj) have not yet been calculated for the category Ci being processed. If any such supercategories Sj remain at the step 2920, control returns to the step 2870 at which a further supercategory Sj is chosen for analysis with the category Ci. If no such supercategories Sj remain at the step 2920, control instead passes to a step 2930 at which is selected a supercategory SM whose total score T (Ci, Sj) for the category Ci being processed is the highest. The category being processed Ci then is assigned to the supercategory SM. (If no co-occurrences have been found between the category Ci being processed and any category manually assigned to a supercategory, the category Ci being processed is not assigned to any supercategory.)
Control then passes to a step 2940 at which it is determined if there remain any further unassigned categories Ci not yet processed. If any such unprocessed categories Ci remain at the step 2940, control returns to the step 2860 at which a further as-yet-unprocessed category Ci is chosen for processing. If no such unprocessed categories Ci remain at the step 2940, the process 2850 is concluded, and each previously-unassigned category Ci has either been assigned to a supercategory Sj, or it has been determined that it has no co-occurrences with any manually-assigned category, and hence no supercategory Sj assignment has been made for it. According to FIG. 9, all categories 2820 containing items of interest 2810 will have been assigned to supercategories 2840, except for those categories 2820 as to which it has been determined that the category 2820 has no co-occurrences with any manually-assigned category 2820.
When additional terms such as index terms or key words are assigned to a document, such as by the system described herein, the additional terms may be considered as terms along with the terms that occur in the document itself for purposes of calculating term frequency scores. The original terms and the index terms may be used together in searches, or the index terms alone may be used.
It may be thought that the occurrence among the additional terms of a term for which a search is being made may be more or less important as a predictor of the utility of the document than the occurrence of a term found in the document itself. A technique for taking into account whether a term occurs in a document itself or among the additional terms associated with the document, in the calculation of a term frequency score for that document, therefore may be useful.
In addition, documents in a collection which is being searched may consist of various segments or sections. The segments or sections may include a title, an abstract or introduction or summary, captions, and footnotes. Other sections or segments into which a document may be divided will be apparent to one of ordinary skill in the art.
In some circumstances, it may be thought that the occurrence of a term in one segment of a document may be more predictive of the utility of that document than its occurrence in another segment. A technique for taking into account the segment of a document in which a given term occurs, in the course of calculating a term frequency score for that document, therefore may be useful.
According to the system being described herein, a weight WSD may be assigned to each segment Si of a document D containing S0 segments. In one embodiment of the system: 



  
    
      ∑
      
        
          S
          i
        
        =
        1
      
      
        S
        0
      
    
    ⁢
    
      W
      SD
    
  
  =
  1.




In one embodiment of the system, an entire document itself is considered a single segment, and the additional index terms associated with the document, such as by the system described herein, are considered a second segment. In that embodiment, there are a total of two segments in a document, including the new segment containing the index terms.
In a further embodiment of the system, the index terms associated with the document, such as by the system described herein, are considered a segment, and the text of the document itself may be divided into a number of separate segments which may include a title, an abstract or introduction or summary, captions, and footnotes. Other sections or segments into which a document may be divided will be apparent to one of ordinary skill in the art.
In a further embodiment of the system, where additional terms such as index terms have been associated with a document by more than one method, for each method used the additional terms associated with the document by that method may be considered a separate segment of the document.
In a further embodiment of the system, where no additional terms have been associated with the document, the text of the document itself may be divided into a number of separate segments which may include a title, an abstract or introduction or summary, captions, and footnotes.
The weights WSD assigned to the segments of documents may be chosen arbitrarily.
In one embodiment of the system, the weights WSD assigned to the segments Si of a document D may be individually determined in advance, based upon a decision about the relative utility of various segments of the document D in determining the relevance of the document under various criteria.
In an embodiment of the system, a given segment Si may be required to have equal weight WSD in all documents.
In a further embodiment, the weight WSD of a given segment Si of different documents may be different, based upon the relative utility of that segment of each document in predicting whether that document will be of interest to a user.
The weights assigned to the segments S1 of a document containing the additional terms assigned to the document may be varied based upon the method used to assign the additional terms, and the degree to which the additional terms are considered to be highly related to the content of the documents. In an embodiment of the system, a segment S1 may be required to have equal weight WSD in all documents. In a further embodiment, the weights WSD of the segments S1 of different documents may be different, based upon the method used to assign the additional terms, and the degree to which the additional terms are considered to be highly related to the content of each document.
In one embodiment of the system, the weights WSD are varied depending on the results of experiments which vary the weights for test searches and evaluate the utility of the results returned, either in terms of precision (the ability of the search formula to avoid returning documents that are not useful), or of recall (the ability of the search formula to avoid omitting documents that are useful), or of a combination of the two.
When it is determined to calculate a term frequency score under a given search query Q for a document D with S0 segments in the collection of documents C0 being searched under the system, a generalized term frequency score may be calculated as follows: 



  
    S
    D
  
  =
  
    
      ∑
      
        T
        =
        1
      
      
        T
        0
      
    
    ⁢
    
      
        ∑
        
          
            S
            i
          
          =
          1
        
        
          S
          0
        
      
      ⁢
      
        TF
        STD
      
    
  




where: SD is the total score for the document D,

    
    
        T0 is the number of terms which occur in the search query Q, and
        TFSTD is the score for document D based on the occurrence of term T in segment Si of document D.
    
    


In one embodiment of the system, scores are assigned to documents utilizing Robertson's term frequency score, and the generalized term frequency score SD for a document D may be calculated as follows: 



  
    S
    D
  
  =
  
    
      ∑
      
        T
        =
        1
      
      
        T
        0
      
    
    ⁢
    
      
        ∑
        
          
            S
            i
          
          =
          1
        
        
          S
          0
        
      
      ⁢
      
        
          TF
          STD
        
        *
        
          IDF
          ST
        
      
    
  




where:

    
    
        SD is the total score for the document D,
        T0 is the number of terms which occur in the search query Q,
        S0 is the number of segments in the document D,
        TFSTD=Robertson's generalized term frequency score for Term T in Segment Si of Document D
        
            =GSTD/(GSTD+K1+K2*WSD*(HSD/HSO)),

where:

        
        
        GSTD=the generalized term count for Term T in Segment Si of Document D, =WSD*WSTD*NSTD,

where:

        WSD is the weight assigned to segment Si of document D,
        WSTD is the weight assigned to term T in segment Si of document D, and
        NSTD is the number of times the term T occurs in segment Si of document D,
        HSD=the generalized length of segment Si of document D, 



  
    H
    SD
  
  =
  
    
      ∑
      
        T
        =
        1
      
      
        L
        SD
      
    
    ⁢
    
      
        W
        STD
      
      *
      
        N
        STD
      
    
  




where:

        LSD is the number of different terms in segment Si of document D,
        HSO=the generalized average length of segment Si of documents in the collection C0 being searched, 



  
    
      H
      SO
    
    =
    
      
        ∑
        
          N
          =
          1
        
        
          N
          0
        
      
      ⁢
      
        
          (
          
            
              W
              STD
            
            *
            
              H
              SD
            
          
          )
        
        /
        
          
            ∑
            
              N
              =
              1
            
            
              N
              0
            
          
          ⁢
          
            W
            SD
          
        
      
    
  
  ,




where:

        N0 is the number of documents in the collection C0, and
        K1 and K2 are constants (In one embodiment, K1 may be assigned a value of 0.5, and K2 1.5, but these values may be varied without departing from the spirit and scope of the invention.)
    
    


In this system, IDFST=the generalized inverted document frequency for term T,

    
    
        IDFST=log ((N0+K3)/NST)/ log (N0+K4)

where:

        N0 is the number of documents in the collection C0 
        NST is the number of documents in the collection C0 containing the term T in the segment Si,
        K3 and K4 are constants. (In one embodiment, K3 may be assigned a value of 0.5, and K4 1.0, but these values may be varied without departing from the spirit and scope of the invention.)
    
    


In one embodiment of the system, each segment Si of a document D consists of a portion of the text of the document D, and there are no segments containing index terms. In this embodiment, the weights WSTD assigned to terms T in the segments Si of the document D are equal. In this embodiment, the factors WSTD, the weights assigned to terms T in segment Si of document D, may all be considered to be equal to 1.0, and the formula simplifies to: 



  
    S
    D
  
  =
  
    
      ∑
      
        T
        =
        1
      
      
        T
        0
      
    
    ⁢
    
      
        ∑
        
          
            S
            i
          
          =
          1
        
        
          S
          0
        
      
      ⁢
      
        
          TF
          STD
        
        *
        
          IDF
          ST
        
      
    
  




where:

    
    
        TFSTD=Robertson's generalized term frequency score for Term T in Segment Si of Document D
        
            =GSTD/(GSTD+K1+K2*WSD*(HSD/HSO)),

where:

        
        
        GSTD=the generalized term count for Term T in Segment Si of Document D,
        
            =WSD*NSTD, 


  
    
      H
      SD
    
    =
    
      
        ∑
        
          T
          =
          1
        
        
          L
          SD
        
      
      ⁢
      
        N
        STD
      
    
  




  
    
      
        H
        SO
      
      =
      
        
          ∑
          
            N
            =
            1
          
          
            N
            0
          
        
        ⁢
        
          
            (
            
              
                W
                SD
              
              *
              
                H
                SD
              
            
            )
          
          /
          
            
              ∑
              
                N
                =
                1
              
              
                N
                0
              
            
            ⁢
            
              W
              SD
            
          
        
      
    
    ,
    
      

    
    ⁢
    
      
        IDF
        ST
      
      =
      
        log
        ⁢
        
           
        
        ⁢
        
          (
          
            
              (
              
                
                  N
                  0
                
                +
                
                  K
                  3
                
              
              )
            
            ⁢
            
              /
            
            ⁢
            
              N
              ST
            
          
          )
        
        ⁢
        
          /
        
        ⁢
        log
        ⁢
        
           
        
        ⁢
        
          (
          
            
              N
              0
            
            +
            
              K
              4
            
          
          )
        
      
    
  



        
        
    
    


In this embodiment, if the document has only a single segment, then WSD may be considered to be equal to 1.0 for that segment, and the formula further reduces to: 



  
    S
    D
  
  =
  
    
      ∑
      
        T
        =
        1
      
      
        T
        0
      
    
    ⁢
    
      
        TF
        TD
      
      *
      
        IDF
        T
      
    
  




where:

    
    
        TFSTD=Robertson's generalized term frequency score for Term T in Segment Si of Document D
        
            =GTD/(GTD+K1+K2*(HD/HO)),

where:

        
        
        GTD=the generalized term count for Term T in Segment Si of Document D, =NTD, 



  
    
      
        
          H
          D
        
        =
        
          
            ∑
            
              T
              =
              1
            
            
              L
              D
            
          
          ⁢
          
            N
            TD
          
        
      
    
  
  
    
      
        
          
            H
            O
          
          =
          
            
              ∑
              
                N
                =
                1
              
              
                N
                0
              
            
            ⁢
            
              
                (
                
                  H
                  D
                
                )
              
              ⁢
              
                /
              
              ⁢
              
                N
                0
              
            
          
        
        ,
      
    
  




        IDFST=log ((N0+K3)/NT)/ log (N0+K4)
    
    


This is the conventional Robertson's term frequency score for an unsegmented text document.
In another embodiment of the system, in which a segment Si of a document D contains index terms automatically associated with the document D according to the system, the weight WSTD assigned to an index term Tn in segment Si of a document D is 



  
    
      W
      STD
    
    =
    
      
        
          f
          D
        
        ⁡
        
          (
          
            T
            n
          
          )
        
      
      /
      
        
          ∑
          
            T
            =
            1
          
          
            L
            SD
          
        
        ⁢
        
          
            f
            D
          
          ⁡
          
            (
            
              T
              t
            
            )
          
        
      
    
  
  ,




where fD (Tn) has the value set forth above, and LSD is the number of index terms in segment Si of document D.

In this embodiment of the system, other segments of a document D may contain the text of the document D itself, or portions of the text, or other index terms associated with the document by other methods.
In the embodiment of the system in which only the index terms automatically associated with the document by the system are utilized to carry out a search query, the formula for the score assigned to a document according to the system reduces to the following: 



  
    S
    D
  
  =
  
    
      ∑
      
        T
        =
        1
      
      
        T
        0
      
    
    ⁢
    
      
        TF
        TD
      
      *
      
        IDF
        T
      
    
  




where: SD is the total score for the document D,

    
    
        T0 is the number of terms which occur in the query Q,
        TFTD=Robertson's generalized term frequency score for Term T of Document D
        
            =GTD/(GTD+K1+K2),

where:

        
        
        GTD=the generalized term count for Term T of Document D,
        
            =fD(Tn)
        
        
    
    


In this embodiment, because the weights assigned to the index terms in a document are normalized, the “length” of every document is 1.0, and the denominator of Robertson's term frequency score considerably simplifies.
In a further embodiment of the system described herein, it is desired to present further information to a user who has visited a Web site, when the Web site has permitted the user to enter terms describing an item of interest to the user. In this embodiment, an item of interest may be considered to be a product or service, or a number of (related or unrelated) products or services. In response to the user providing terms related to the product(s) or service(s) which he is seeking (such as, for example, “automobiles, used”), the Web site may display for the user a list of categories. Each category (such as, for example, “Auto Dealers, Used Cars”) may contain information about merchants, stores or other sources (such as, for example, “Lannan Chevrolet, Oldsmobile”) for a particular variety of products or services which may relate to the product(s) or service(s) which the user is seeking. In this embodiment, merchants or stores who carry products or services may be assigned to more than one category (variety of product or service). The user then may select a particular category from the list of categories displayed to him, and the items of interest (merchants or stores) in that category will be displayed for him.
In this embodiment of the system described herein, it is desired to present additional material to a user who is searching for particular products or services, in addition to the list of categories which contain merchants or stores who may carry the desired product or service. For example, it may be desired to present the user with banner advertisements, such as for automobile financing, which relate to the product or service, such as automobiles, for which he is searching.
In one embodiment of the system described herein, there may be a very large number of individual merchants or stores to be organized into categories of products or services for presentation.
In this embodiment of the system, there are fewer categories of products or services than individual merchants or stores. While the number may vary without departing from the spirit and scope of the invention, in one embodiment of the system there may be about 20,000 categories. Each category has associated with it a set of terms (such as, for example, “Auto Dealers, Used Cars”) which describe the product(s) or service(s) which the merchants, stores or other sources associated with the category may provide. Each category further has associated with it a category identifier term which is unique to it, and serves to identify the category.
In this embodiment of the system, it is desired to choose a banner advertisement to present to a user. The banner advertisements in turn may be divided into categories. While the number may vary without departing from the spirit and scope of the invention, there may be about 50 categories into which the banner advertisements may be divided. (To avoid confusion with the categories into which the items of interest are divided, these banner advertisement categories will be referred to hereafter as “supercategories.”)
As illustrated by FIG. 10, it is desirable in this embodiment of the system to assign each category 2210 of merchants or stores to one and only one supercategory 2220 of banner advertisements. In this embodiment of the system, each supercategory has associated with it the sets of terms (such as, for example, “Auto Dealers, Used Cars”) which describe the product(s) or service(s) which the merchants, stores or other sources associated with the categories assigned to it may provide. Each supercategory further has associated with it the category identifier terms which are unique to the categories assigned to it.
According to FIG. 11, this method 2230 proceeds first at a step 2240 to select every category Ci of merchants or stores 2210 which has associated with it a term or terms (such as, for example, “Auto Dealers, Used Cars”) describing the product(s) or service(s) which the merchants, stores or other sources associated with the category may provide, that matches any term or terms in the user query Qi (such as “automobiles, used”).
After every such category Ci of merchants or stores 2210 is selected at the step 2240, control passes to a step 2340. At the step 2340, a new Query Q′i is prepared, consisting of the original user Query Qi with the addition of all terms which describe the product(s) or service(s) which the merchants, stores or other sources associated with the said categories Ci may provide, and with the further addition of the unique category identifier terms Ti which identify the categories Ci.
After the new Query Q′i is prepared at the step 2340, control passes to a step 2350, at which the new Query Q′i is run, on the collection C′o of supercategories 2220. There are a number of methods of running the query Q′i on the collection C′o of supercategories 2220, which will be known to one of ordinary skill in the art.
In one embodiment the query is run by utilizing Robertson's term frequency score, where the score for a supercategory SC is determined by: 



  
    
      S
      C
    
    =
    
      
        ∑
        
          T
          =
          1
        
        
          T
          0
        
      
      ⁢
      
        
          TF
          TD
        
        *
        
          IDF
          T
        
      
    
  
  ,




where:

    
    
        T0 is the number of terms which occur in the query Q′i,
        TFTD is Robertson's term frequency for term T in supercategory SC,
        
            =NTC/(NTC+K1+K2*(LC/L0)),

where:

        
        
        NTC is the number of times the term T occurs in supercategory SC,
        LC is the length of supercategory SC,
        L0 is the average length of a supercategory, and
        K1 and K2 are constants

and IDFT=log ((N+K3)/NT)/ log (N+K4)

where:

        N is the number of supercategories in the collection
        NT is the number of supercategories containing the term T, and
        K3 and K4 are constants.
    
    


In another embodiment of the system, the categories have been assigned to supercategories by a combination of methods. In this embodiment, a certain number of the categories may have been assigned to supercategories manually, while the remainder may have been assigned to supercategories utilizing a variety of automatic or semi-automatic index term augmentation techniques. While the number of categories assigned manually may vary without departing from the spirit and scope of the invention, and the number and type of automatic and semi-automatic index term augmentation techniques utilized may vary without departing from the spirit and scope of the invention, in one embodiment about 2,000 out of about 20,000 categories are assigned manually and the remainder by the semi-automatic technique of this system, which utilizes the co-occurrence of terms between the categories assigned manually and an unassigned category to help assign the unassigned categories.
In one embodiment of the system, it is further desired in evaluating queries Q′i and selecting a supercategory to assign differing weights to the terms and term identifiers associated with categories, depending on whether the category has been manually assigned to a supercategory, or assigned automatically or semi-automatically. While the weights thus assigned may vary without departing from the spirit and scope of the invention, in one embodiment the terms and term identifiers associated with categories manually assigned to supercategories are assigned a weight of 1.0, while the terms and term identifiers associated with categories assigned to supercategories by the semi-automatic method of the system described herein which utilizes the co-occurrence of terms between the manually-assigned categories and an unassigned category to help assign the unassigned categories are assigned a weight of 0.4.
In this embodiment, in order to evaluate the query Q′i the supercategories are considered to comprise multiple segments. In one segment are the terms and term identifiers associated with the categories assigned to the supercategory manually, while each of the other segments comprises the terms and term identifiers associated with the categories assigned to the supercategory by a particular automatic or semi-automatic method. In this embodiment the generalized term frequency score for a supercategory SC with respect to the query Q′i may be calculated as follows: 



  
    S
    C
  
  =
  
    
      ∑
      
        T
        =
        1
      
      
        T
        0
      
    
    ⁢
    
      
        ∑
        
          
            S
            i
          
          =
          1
        
        
          S
          0
        
      
      ⁢
      
        
          TF
          STC
        
        *
        
          IDF
          ST
        
      
    
  




where:

    
    
        SC is the total score for the supercategory SC,
        T0 is the number of terms which occur in the query Q′i,
        S0 is the number of segments in the supercategory SC,
        TFSTC=Robertson's generalized term frequency score for Term T in Segment Si of supercategory SC 
        
            =GSTC/(GSTC+K1+K2*WSC*(HSC/HSO)),

where:

        
        
        GSTC=the generalized term count for Term T in Segment Si of supercategory SC,
        
            =WSC*WSTC*NSTC,

where:

        
        
        WSC is the weight assigned to segment Si of the supercategories,
        WSTC is the weight assigned to term T in segment Si of supercategory SC, and
        NSTC is the number of times the term T occurs in segment Si of supercategory SC,
        HSC=the generalized length of segment Si of supercategory SC, 



  
    H
    SC
  
  =
  
    
      ∑
      
        T
        =
        1
      
      
        L
        SC
      
    
    ⁢
    
      
        W
        STC
      
      *
      
        N
        STC
      
    
  




where:

        LSC is the number of different terms in segment Si of supercategory SC,
        HSO=the generalized average length of segment Si of the supercategories, 



  
    
      H
      SO
    
    =
    
      
        ∑
        
          C
          =
          1
        
        
          C
          0
        
      
      ⁢
      
        
          (
          
            
              W
              SC
            
            *
            
              H
              SC
            
          
          )
        
        /
        
          
            ∑
            
              C
              =
              1
            
            
              C
              0
            
          
          ⁢
          
            W
            SC
          
        
      
    
  
  ,




where:

        C0 is the number of supercategories and
        K1 and K2 are constants (In one embodiment, K1 may be assigned a value of 0.5, and K2 1.5, but these values may be varied without departing from the spirit and scope of the invention.)
    
    


In this system, IDFST=the generalized inverted document frequency for term T,

    
    
        IDFST=log ((C0+K3)/CST)/ log (C0+K4)

where:

        C0 is the number of supercategories
        CST is the number of supercategories containing the term T in the segment Si,
        K3 and K4 are constants. (In one embodiment, K3 may be assigned a value of 0.5, and K4 1.0, but these values may be varied without departing from the spirit and scope of the invention.)
    
    


In the embodiment of the system in which the terms and term identifiers associated with categories manually assigned to a supercategory are assigned a weight of 1.0, and are assigned to one segment of the supercategory, while the terms and term identifiers associated with categories assigned to the supercategory by the semi-automatic method of the system described herein, which utilizes the co-occurrence of terms between the manually-assigned categories and an unassigned category to help assign the unassigned categories, are assigned to the other segment of the supercategory, and are assigned a weight of 0.4, the generalized term frequency score for a supercategory SC with respect to the query Q′i may be calculated as follows, where all terms in a segment are assigned equal weight WSTC: 



  
    S
    C
  
  =
  
    
      ∑
      
        T
        =
        1
      
      
        T
        0
      
    
    ⁢
    
      
        ∑
        
          
            S
            i
          
          =
          1
        
        2
      
      ⁢
      
        
          TF
          STC
        
        *
        
          IDF
          ST
        
      
    
  




where:

    
    
        SC is the total score for the supercategory SC,
        T0 is the number of terms which occur in the query Q′i,
        TFSTC=Robertson's generalized term frequency score for Term T in Segment Si of supercategory SC 
        
            =GSTC/(GSTC+K1+K2*WSC*(HSC/HSO)),

where:

        
        
        GSTC=the generalized term count for Term T in Segment Si of supercategory SC,
        
            =WSC*NSTC,

where:

        
        
        WSC, the weight assigned to segment Si of the supercategories,
        WSC=1.0 for the segment which comprises the terms and term identifiers associated with the categories manually assigned to the supercategory Si,
        WSC=0.4 for the segment which comprises the terms and term identifiers associated with the categories assigned to the supercategory Si by the semi-automatic method of the system described herein, which utilizes the co-occurrence of terms between the manually-assigned categories and an unassigned category to help assign the unassigned categories, and
        NSTC is the number of times the term T occurs in segment Si of supercategory SC,
        HSC=the generalized length of segment Si of supercategory SC, 



  
    H
    SC
  
  =
  
    
      ∑
      
        T
        =
        1
      
      
        L
        SC
      
    
    ⁢
    
      N
      STC
    
  




where:

        LSC is the number of different terms in segment Si of supercategory SC,
        HSO=the generalized average length of segment Si of the supercategories, 



  
    
      H
      SO
    
    =
    
      
        ∑
        
          C
          =
          1
        
        
          C
          0
        
      
      ⁢
      
        
          (
          
            
              W
              SC
            
            *
            
              H
              SC
            
          
          )
        
        /
        
          
            ∑
            
              C
              =
              1
            
            
              C
              0
            
          
          ⁢
          
            W
            SC
          
        
      
    
  
  ,




where:

        C0 is the number of supercategories and
        K1 and K2 are constants (In one embodiment, K1 may be assigned a value of 0.5, and K2 1.5, but these values may be varied without departing from the spirit and scope of the invention.)
    
    


In this system, IDFST=the generalized inverted document frequency for term T,

    
    
        IDFST=log ((C0+K3)/CST)/ log (C0+K4)

where:

        C0 is the number of supercategories
        CST is the number of supercategories containing the term T in the segment Si,
        K3 and K4 are constants. (In one embodiment, K3 may be assigned a value of 0.5, and K4 1.0, but these values may be varied without departing from the spirit and scope of the invention.)
    
    


After the new Query Q′i is run on the collection C′o of supercategories 2220 at the step 2350, control passes to a step 2360, at which the supercategory 2220 which achieves the highest score SC on the Query Q′i is selected. The process then continues, and a banner advertisement associated with the supercategory chosen at the step 2360 is displayed to the user who has presented the Query Qi. In addition, the user is presented with the set of categories Ci of merchants or stores 2210 which have associated with them a term or terms describing the product(s) or service(s) which the merchants, stores or other sources associated with the category may provide, that matches any term or terms in the user query. The user then has the opportunity to select any of the categories presented, and to have displayed to him the list of merchants, stores or other sources associated with the category.
In this system, when a user, who has been presented with the list of categories Ci, selects a particular category CS for presentation of its list of merchants, stores or other sources, control returns to the step 2340, with the collection of categories Ci replaced by the single category CS.
At the step 2340, a new Query Q′i is prepared, now consisting of the terms which describe the product(s) or service(s) which the merchants, stores or other sources associated with the single category CS may provide, and with the further addition of the unique category identifier term TS which identifies the category CS.
After the new Query Q′i is prepared at the step 2340, control passes to a step 2350, at which the new Query Q′i is run, on the collection C′o of supercategories 2220.
After the new Query Q′i is run on the collection C′o of supercategories 2220 at the step 2350, control passes to a step 2360, at which the supercategory 2220 which achieves the highest score on the Query Q′i is selected. The process then concludes, and a banner advertisement associated with the supercategory chosen at the step 2360 is displayed to the user. In addition, the list of merchants, stores or other sources of the product(s) or service(s) associated with the category CS is presented to the user.
While the invention has been disclosed in connection with the preferred embodiments shown and described in detail, various modifications and improvements thereon will become readily apparent to those skilled in the art. Accordingly, the spirit and scope of the present invention is to be limited only by the following claims.

## Claims

1. A method for automatically choosing index terms to be associated with a document D, for purposes of facilitating document retrieval processes, comprising:
creating a search query Q comprised of terms in document D; 
applying the search query Q to a collection of documents C0; 
selecting the N0 documents from the collection of documents C0 which achieve the highest scores upon application of the search query Q; and 
selecting IT terms for use as index terms for document D from among terms in the N0 documents based upon the co-occurrence of terms in the N0 documents with terms in the document D.

2. The method of claim 1, further comprising selecting the IT terms for use as index terms for document D by
(a) calculating, for terms Tk which occur in the N0 documents selected, the co-occurrence Cn (Tj, Tk) of the term Tk with terms Tj in document D: 
Cn (Tj, Tk)=log10(coki(Tj,Tk)+1)*idf(Tk)/log10(N0), 



  
    where
    ⁢
    
      :
    
    ⁢
    
       
    
    ⁢
    
      
        co
        ki
      
      ⁡
      
        (
        
          
            T
            j
          
          ,
          
            T
            k
          
        
        )
      
    
  
  =
  
    
      ∑
      
        n
        =
        1
      
      
        N
        0
      
    
    ⁢
    
       
    
    ⁢
    
      tf
      ⁢
      
         
      
      ⁢
      
        (
        
          
            T
            k
          
          ,
          n
        
        )
      
      *
      tf
      ⁢
      
         
      
      ⁢
      
        (
        
          
            T
            j
          
          ,
          n
        
        )
      
    
  




tf (Tk, n)=number of occurrences of term Tk in document n in the N0 documents, 
tf (Tj, n)=number of occurrences of term Tj in document n in the N0 documents, 
idf (Tk)=the inverted document frequency for the term Tk, 
=min (1.0, log10 (N/NT)/5.0) 
N=the number of documents in the collection C0 over which the query Q was run, 
NT=the number of documents in the collection C0 over which the query Q was run, which contained the term Tk 

(b) calculating, for terms Tk which occur in the N0 documents selected, the co-occurrencefD (Tk) of that term Tk with document D: 



  
    
      f
      D
    
    ⁡
    
      (
      
        T
        k
      
      )
    
  
  =
  
    
      ∏
      
        j
        =
        1
      
      
        T
        0
      
    
    ⁢
    
       
    
    ⁢
    
      
        (
        
          δ
          +
          
            
              C
              ni
            
            ⁡
            
              (
              
                
                  T
                  k
                
                ,
                
                  T
                  j
                
              
              )
            
          
        
        )
      
      
        idf
        ⁡
        
          (
          
            T
            j
          
          )
        
      
    
  




where 
Tj=a term in document D, 
T0=the number of terms in document D, 
idf (Tj)=the inverted document frequency for the term Tj, 
=min (1.0, log10 (N/N1)/5.0), 
N=the number of documents in the collection C0 over which the query Q was run, 
Nj=the number of documents in the collection C0 over which the query Q was run, which contained the term Tj and 
δ=a constant; and 

(c) selecting IT terms for use as index terms for document D from among terms in the N0 documents based upon the scores fD (Tk) achieved by the terms.

3. The method of claim 2, wherein the documents are Web pages.

4. The method of claim 2, wherein the documents are Web sites.

5. The method of claim 2, wherein the search query Q which is applied comprises all of the terms in document D.

6. The method of claim 2, wherein the search query Q which is applied comprises all of the terms in document D with preselected stop terms eliminated.

7. The method of claim 2, wherein the search query Q is applied to select documents from among the documents in the collection C0 by calculating for each document D in the collection C0 a score SD based upon the occurrence in the document D of terms in the search query Q.

8. The method of claim 7, wherein in applying the search query Q to the collection of documents C0 the total score SD for a document D in the collection C0 is 



  
    S
    D
  
  =
  
    
      ∑
      
        T
        =
        1
      
      
        T
        0
      
    
    ⁢
    
      
        TF
        TD
      
      *
      
        IDF
        T
      
    
  




where:
T0 is the number of terms in the search query Q, and 
TFTD is Robertson's term frequency for the term T in the document D, 
=NTD/(NTD+K1+K2*(LD/LO)), 


where:
NTD is the number of times the term T occurs in document D, 
LD is the length of document D, 
LO is the average length of documents in the collection C0 to be searched, and 
K1 and K2 are constants 

and IDFT=log((N+K3)/NT)/ log (N+K4)
where:
N is the number of documents in the collection C0 to be searched 
NT is the number of documents containing the term T in the collection C0 to be searched, 
K3 and K4 are constants.

9. The method of claim 8, wherein K1 equals 0.5, K2 equals 1.5, K3 equals 0.5, and K4 equals 1.0.

10. The method of claim 2, wherein all terms whose scores fD (Tk) exceed a given cutoff score are selected for use as index terms.

11. The method of claim 9, wherein the number N0 of documents chosen by application of the search query Q is 50, δ=0.01, and the number IT is 30.

12. The method of claim 2, wherein the number N0 of documents chosen by application of the search query Q is predetermined.

13. The method of claim 12, wherein the number N0 is 50.

14. The method of claim 2, wherein all documents whose scores upon application of the search query Q exceed a given cutoff score are selected.

15. The method of claim 2, wherein co-occurrences fD (Tk) are calculated for all terms contained in the N0 documents selected.

16. The method of claim 2, wherein co-occurrences fD (Tk) are calculated for all terms contained in the N0 documents selected, except that preselected stop terms are eliminated.

17. The method of claim 2, wherein δ=0.01.

18. The method of claim 2, wherein the number IT of terms chosen as index terms is predetermined.

19. The method of claim 17, wherein the number IT is 30.

20. A device for automatically choosing index terms to be associated with a document D, for purposes of facilitating document retrieval processes, comprising:
(a) means for creating a search query Q comprised of terms in document D; 
(b) means for applying the search query Q to a collection of documents C0; 
(c) means for selecting the N0 documents from the collection of documents C0 which achieve the highest scores upon application of the search query Q; and 
(d) means for selecting IT terms for use as index terms for document D from among terms in the N0 documents based upon the co-occurrence of terms in the N0 documents with terms in the document D.

21. The device of claim 20, further comprising means for selecting the IT terms for use as index terms for document D, which means are comprised of
(a) means for calculating, for terms Tk which occur in the N0 documents selected, the co-occurrence Cn (Tj,Tk) of that term Tk with terms Tj in document D: 


Cn (Tj, Tk)=log10(coki(Tj,Tk)+1)*idf(Tk)/ log10(N0), 



  
    where
    ⁢
    
      :
    
    ⁢
    
       
    
    ⁢
    
      
        co
        ki
      
      ⁡
      
        (
        
          
            T
            j
          
          ,
          
            T
            k
          
        
        )
      
    
  
  =
  
    
      ∑
      
        n
        =
        1
      
      
        N
        0
      
    
    ⁢
    
       
    
    ⁢
    
      tf
      ⁢
      
         
      
      ⁢
      
        (
        
          
            T
            k
          
          ,
          n
        
        )
      
      *
      tf
      ⁢
      
         
      
      ⁢
      
        
          (
          
            
              T
              j
            
            ,
            n
          
          )
        
        .
      
    
  





tf (Tk, n)=number of occurrences of term Tk in document n in the N0 documents, 
tf (Tj, n)=number of occurrences of term Tj in document n in the N0 documents, 
idf(Tk)=the inverted document frequency for the term Tk, 
=min (1.0, log10 (N/NT)/5.0) 

 N=the number of documents in the collection C0 over which the query Q was run, 
 NT=the number of documents in the collection C0 over which the query Q was run, which contained the term Tk 
(b) means for calculating, for terms Tk which occur in the N0 documents selected, the co-occurrence fD (Tk) of that term Tk with document D: 



  
    
      f
      D
    
    ⁡
    
      (
      
        T
        k
      
      )
    
  
  =
  
    
      ∏
      
        j
        =
        1
      
      
        T
        0
      
    
    ⁢
    
       
    
    ⁢
    
      
        (
        
          δ
          +
          
            
              C
              ni
            
            ⁡
            
              (
              
                
                  T
                  k
                
                ,
                
                  T
                  j
                
              
              )
            
          
        
        )
      
      
        idf
        ⁡
        
          (
          
            T
            j
          
          )
        
      
    
  




where 
Tj=a term in document D, 
T0=the number of terms in document D, 

idf(Tj)=the inverted document frequency for the term Tj, 
=min (1.0, log10(N/N1)/5.0), 

 N=the number of documents in the collection C0 over which the query Q was run, 
 NJ=the number of documents in the collection C0 over which the query Q was run, which contained the term Tj and 
δ=a constant; and 

(c) means for selecting IT terms for use as index terms for document D from among terms in the N0 documents based upon the scores fD (Tk) achieved by the terms.

22. The device of claim 21, wherein the documents are Web pages.

23. The device of claim 21, wherein the documents are Web sites.

24. The device of claim 21, wherein the search query Q which is applied comprises all of the terms in document D.

25. The device of claim 21, wherein the search query Q which is applied comprises all of the terms in document D with preselected stop terms eliminated.

26. The device of claim 21, wherein the search query Q is applied to select documents from among the documents in the collection C0 by calculating for each document D in the collection C0 a score SD based upon the occurrence in the document D of terms in the search query Q.

27. The device of claim 26, wherein in applying the search query Q to the collection of documents C0 the total score SD for a document D in the collection C0 is 



  
    S
    D
  
  =
  
    
      ∑
      
        T
        =
        1
      
      
        T
        0
      
    
    ⁢
    
      
        TF
        TD
      
      *
      
        IDF
        T
      
    
  




where:
T0 is the number of terms in the search query Q, and 
TFTD is Robertson's term frequency for the Term T in the Document D, 
=NTD/(NTD+K1+K2*(LD/LO)), 


where:
NTD is the number of times the term T occurs in document D, 
LD is the length of document D, 
LO is the average length of documents in the collection C0 to be searched, and 
K1 and K2 are constants 

and IDFT=log ((N+K3)/NT)/ log (N+K4)
where:
N is the number of documents in the collection C0 to be searched 
NT is the number of documents containing the term T in the collection C0 to be searched, 
K3 and K4 are constants.

28. The device of claim 27, wherein K1 equals 0.5, K2 equals 1.5, K3 equals 0.5, and K4 equals 1.0.

29. The device of claim 28, wherein the number N0 of documents chosen by application of the search query Q is 50, δ=0.01, and the number IT is 30.

30. The device of claim 21, wherein the number N0 of documents chosen by application of the search query Q is predetermined.

31. The device of claim 30, wherein the number N0 is 50.

32. The device of claim 21, wherein all documents whose scores upon application of the search query Q exceed a given cutoff score are selected.

33. The device of claim 21, wherein co-occurrences fD (Tk) are calculated for all terms contained in the N0 documents selected.

34. The device of claim 21, wherein co-occurrences fD (Tk) are calculated for all terms contained in the N0 documents selected, except that preselected stop terms are eliminated.

35. The device of claim 21, wherein δ=0.01.

36. The device of claim 21, wherein the number IT of terms chosen as index terms is predetermined.

37. The device of claim 36, wherein the number IT is 30.

38. The device of claim 21, wherein all terms whose scores fD (Tk) exceed a given cutoff score are selected for use as index terms.

39. A method for automatically assigning-an-index term to a document D, the method comprising:
selecting one or more index terms from a plurality of index terms; 
identifying one or more documents of a plurality of documents to which each of the one or more index terms has been assigned; 
comparing, for each of the one or more index terms, each of the identified documents to the document D; 
determining a score for each of the one or more index terms based on the comparing; and 
assigning the index term associated with the highest score to the document D.

40. The method of claim 39 wherein the comparing includes:
determining a log likelihood ratio between each of the identified documents and the document D.

41. The method of claim 39 wherein the score is a total score based on scores for each of the identified documents.

42. The method of claim 39 wherein the assigning includes:
assigning a predetermined number of the index terms associated with the highest scores to the document D.

43. A device for automatically assigning an index term to a document D, the device comprising:
means for selecting one or more index terms from a plurality of index terms; 
means for identifying one or more documents of a plurality of documents to which each of the one or more index terms has been assigned; 
means for comparing, for each of the one or more index terms, each of the identified documents to the document D; 
means for determining a score for each of the one or more index terms based on the comparing; and 
means for assigning the index term associated with the highest score to the document D.

44. The device of claim 43 wherein the means for comparing includes:
means for determining a log likelihood ratio between each of the identified documents and the document D.

45. The device of claim 43 wherein the score is a total score based on scores for each of the identified documents.

46. The device of claim 43 wherein the means for assigning includes:
means for assigning a predetermined number of the index terms associated with the highest scores to the document D.