Abstract:
A document association device includes: a document designating unit configured, to receive designation of a first document and a second document to be referred to from the first document; a dividing unit configured to divide the second document into a plurality of portions; a relevant portion identifying unit configured to compare contents of the respective portions of the divided second document with contents of a predetermined portion of the first document, and identify the portion having the highest degree of association with the predetermined  - portion among the plurality of portions as a relevant portion; and an associating unit configured to associate the relevant portion of the second document with the predetermined portion of the first document, to enable calling up of the relevant portion from the predetermined portion.

Description:
[0001]    The entire disclosure of Japanese Patent Application No. 2015-153775 filed on Aug. 4, 2015 including description, claims, drawings, and abstract are incorporated herein by reference in its entirety. 
       BACKGROUND OF THE INVENTION 
       [0002]    Field of the Invention 
         [0003]    The present invention relates to a document association device that associates documents with each other, a document association system, and a program. 
         [0004]    Description of the Related Art 
         [0005]    Mobile devices such as smartphones and tablet PCs have rapidly spread in recent years, and electronic documents are often viewed on these mobile devices. For example, information materials are often viewed on mobile devices during conferences. In some conferences, a main document main text) and auxiliary information materials are provided as conference materials, and the participants are sometimes requested to refer to the auxiliary information materials while reading the main text. 
         [0006]    For example, in a case where a request for reference to a document B as another document (such as “for more detail, see document. B”) is issued while a user is viewing a document A, as shown in  FIG. 19 , a user opens the document B after closing the document A that has been open ( FIG. 19B ), or opens the document A and the document B at the same time ( FIG. 19C ). The user detects the relevant portion from the document B, and refers to the portion. After referring to the document B, the user closes the document B, and returns to viewing of the document A. 
         [0007]    Since most mobile devices have small-sized displays, it is necessary for a user to often perform a scrolling operation or rescale characters when searching the document B for a portion to be referred to. As a result, the operation becomes complicated. Further, the portions to be referred to in the document B are not clearly specified in many cases. In such a case, searching the document B for a relevant portion is even more troublesome. 
         [0008]    JP 2013-020437 A discloses an example of a technique for facilitating reference to another document from one document. In a case where each document has chapter numbers, and documents associated with one another are to be created, at least one document should be created, so that the format for the other documents is created in accordance with the already created document, and association information serving as information about links among the documents can be automatically generated. 
         [0009]    Further, there is a technique for aiding an operation to manually create link information for associating a specific portion in a link destination document file with a specific portion in a link source document file (see JP 2000-035969 A), and there is a technique for generating links in accordance with operation information or the like received at the time of document viewing (see JP 2014-186644). Further, there is a technique for determining a document having a high degree of association with one document in accordance with document names and information about authors (see JP 2009-020639 A). 
         [0010]    In a case where a document includes a request for reference to another document, and the document to be referred to is simply designated, a viewer needs to take a lot of trouble to search the document for the relevant portion. Therefore, it is preferable to further designate the portion to be referred to in the document. To simplify the operation to open the document to be referred to, the link information for calling up the relevant portion of the document to be referred to is preferably buried in the reference source document. 
         [0011]    However, in a case where the author of a document has not buried such link information in the document, a viewer of the document needs to take a lot of trouble to search for the relevant portion and display the relevant portion, as described above. 
         [0012]    The technique disclosed in JP 2013-020437 A is effective in creating a document. However, any link cannot be put to a relevant portion after a document is created. By the technique disclosed in JP 2000-035969 A, creating the link information is easier, but the link information is manually created. Therefore, creating the link information is still troublesome. The technique disclosed in JP 2014-186644 A is incapable of coping with first-time viewing of a target document By the technique disclosed in WP 2009-020639 A, a relevant document can be detected, but it is not possible to determine which portion in the document has the highest degree of association. 
       SUMMARY OF THE INVENTION 
       [0013]    The present invention has been made to solve the above problems, and an object thereof is to provide a document association device that automatically detects a portion relevant to a predetermined portion of one document from another document, and associates the relevant portion with the predetermined portion so that the relevant portion can be called up from the predetermined portion of the one document and be displayed, a document association system, and a program. 
         [0014]    The summary of the present invention for achieving the above object lies in the following aspects of the invention. 
         [0015]    [1] To achieve the abovementioned object, according to an aspect, a document association device reflecting one aspect of the present invention comprises: 
         [0016]    a document designating unit configured to receive designation of a first document and a second document to be referred to from the first document; 
         [0017]    a dividing unit configured to divide the second document into a plurality of portions; 
         [0018]    a relevant portion identifying unit configured to compare contents of the respective portions of the divided second document with contents of a predetermined portion of the first document, and identify the portion having the highest degree of association with the predetermined portion among the plurality of portions as a relevant portion; and 
         [0019]    an associating unit configured to associate the relevant portion of the second document with the predetermined portion of the first document, to enable calling up of the relevant portion from the predetermined portion. 
         [0020]    In the above embodiment, the document association device detects a portion (the relevant portion) having a high degree of association with a predetermined portion of the first document from the second document, and associates the relevant portion of the second document with the predetermined portion of the first document so that the relevant portion of the second document can be called up from the predetermined portion of the first document. For example, information about a link to the relevant portion of the second document is buried in the predetermined portion of the first document. 
         [0021]    [2] According to the document association device of item. 1, the document association device preferably further comprises 
         [0022]    a reference source extracting unit configured to search the first document for a predetermined keyword indicating reference to the second document, and extract a portion including the predetermined keyword from the first document, the portion including the predetermined keyword being the predetermined portion. 
         [0023]    In the above embodiment, if the first document includes a keyword such as “see document B”, this portion is extracted as a reference source of another document. 
         [0024]    [3] According to the document association device of Item. 1 or 2, the document association device preferably further comprises 
         [0025]    a saving unit configured to save a document having association information buried in the first document, the association information being designed for enabling calling up of the relevant portion from the predetermined portion. 
         [0026]    In the above embodiment, the document having the association information buried therein is saved, so that the document can be reused in later viewing. 
         [0027]    [4] According to the document association device of item. 3, the document association device preferably further comprises 
         [0028]    a save confirming unit configured to present a user with the relevant portion to be associated with the predetermined portion of the first document, and receive a selective response indicating whether to save the document having the association information buried in the first document, 
         [0029]    wherein, when the save confirming unit receives a selective response indicating that the document is to be saved, the saving unit saves the document having the association information buried in the first document. 
         [0030]    In the above embodiment, the relevant portion is presented to the user before the document having the association information buried therein is saved. Thus, the user can determine whether to save the document having the association information buried therein, after confirming validity of the automatically detected relevant portion. 
         [0031]    [5] According to the document association device of Item. 3 or 4, the saving unit preferably buries link information in the predetermined portion of the first document, the link information being designed for calling up the relevant portion of the second document. 
         [0032]    In the above embodiment, link information is buried as the association information. 
         [0033]    [6] According to the document association device of Item. 3 or 4, the saving unit preferably extracts the relevant portion from the second document, and buries the extracted relevant portion in the first document, to enable calling up and display of the relevant portion from the predetermined portion of the first document, without affecting original contents of the first document. 
         [0034]    In the above embodiment, the contents of the relevant portion are buried in the first document, so as not to affect the original contents of the first document. That is, the contents of the relevant portion are buried in a portion other than the body text of the first document. For example, the contents of the relevant portion are buried in a comments field or a remarks column. 
         [0035]    [7] According to the document association device of any one of Items. 3 to 6, the saving unit preferably receives designation of a saving location of the document having the association information buried in the first document from a user, and saves the document including the buried association information in the designated saving location. 
         [0036]    In the above embodiment, the user can choose the location in which the document having the association information buried therein is to be saved. 
         [0037]    [8] According to the document association device of any one of Items. 1 to 7, the dividing unit preferably performs the division in accordance with tag information defining a document structure. 
         [0038]    In the above embodiment, a document in the XML (eXtensible Markup Language) format is divided after the structure of the document is checked in accordance with tag information indicating chapters and paragraphs, for example. 
         [0039]    To achieve the abovementioned object, according to an aspect, a document viewer system reflecting one aspect of the present invention comprises: 
         [0040]    the document association device of any one of Items. 1 to 8; and 
         [0041]    a viewer device configured to allow a user to view a document, the viewer device including a display unit, 
         [0042]    wherein, when receiving a predetermined operation on the predetermined portion while the first document associated by the associating unit is being viewed, the viewer device calls up and displays the relevant portion. 
         [0043]    [10] To achieve the abovementioned object, according to an aspect, a non-transitory recording medium storing a computer readable program implemented in an information processing terminal, reflecting one aspect of the present invention comprises: 
         [0044]    a document designating step of receiving designation of a first document and a second document to be referred to from the first document; 
         [0045]    a dividing step of dividing the second document into a plurality of portions; 
         [0046]    a relevant portion identifying step of comparing contents of the respective portions of the divided second document with contents of a predetermined portion of the first document, and identifying the portion having the highest degree of association with the predetermined portion among the plurality of portions as a relevant portion; 
         [0047]    an associating step of associating the relevant portion of the second document with the predetermined portion of the first document, to enable calling up of the relevant portion from the predetermined portion; 
         [0048]    a step of displaying the associated first document; and 
         [0049]    a step of calling up and displaying the relevant portion when a predetermined operation on the predetermined portion is received while the first document is displayed. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0050]    The above and other objects, advantages and features of the present invention will become more fully understood from the detailed description given hereinbelow and the appended drawings which are given by way of illustration only, and thus are not intended as a definition of the limits of the present invention, and wherein: 
           [0051]      FIG. 1  is a diagram showing an example structure of a document viewer system  5  according to first and second embodiments of the present invention; 
           [0052]      FIG. 2  is a block diagram schematically showing the structure of a document association device; 
           [0053]      FIG. 3  is a diagram showing the functional structure related to the document association process to be performed by the document association device; 
           [0054]      FIG. 4  is a block diagram schematically showing the structure of a document viewer device; 
           [0055]      FIG. 5  is a flowchart showing an outline of an entire process of associating and viewing documents in the document viewer system; 
           [0056]      FIG. 6  is a flowchart showing the association process (step S 102  in  FIG. 5 ) in detail; 
           [0057]      FIG. 7  is a diagram showing a specific example of the association process; 
           [0058]      FIG. 8  is a flowchart showing the document viewing process step S 103  in  FIG. 5 ) in detail; 
           [0059]      FIG. 9  is a diagram showing a specific example of a series of procedures for associating, viewing, and saving documents; 
           [0060]      FIG. 10  is a diagram showing an example case where a relevant portion in a document B is buried in a comments field in a document A; 
           [0061]      FIG. 11  is a diagram showing associated documents A and B that are generated in a case where a document A and a document B are associated with each other; 
           [0062]      FIG. 12  is a diagram showing an example of associated documents that are generated in a case where the number of documents to be associated is three or greater; 
           [0063]      FIG. 13  is a diagram showing another example of an associated document that is generated in a case where the number of documents to be associated is three or greater; 
           [0064]      FIG. 14  is a diagram showing yet another example of an associated document that is generated in a case where the number of documents to be associated is three or greater; 
           [0065]      FIG. 15  is a flowchart showing an outline of an entire process of associating and viewing documents in a second embodiment; 
           [0066]      FIG. 16  is a diagram showing a specific example of a series of procedures for viewing, associating, and saving documents in the second embodiment; 
           [0067]      FIG. 17  is a diagram showing a process of generating and saving an associated document in a case where a document A is viewed in the second embodiment; 
           [0068]      FIG. 18  is a diagram showing a specific example of a series of procedures for associating, viewing, and saving documents in a document viewer device according to a third embodiment; and 
           [0069]      FIGS. 19A to 190  are diagrams showing an example of a conventional operation to refer to a document from a reference source document. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0070]    Hereinafter, various embodiments of the present invention will be described with reference to the drawings. However, the scope of the invention is not limited to the illustrated examples. 
         [0071]      FIG. 1  shows an example structure of a document viewer system  5  according to a first embodiment of the present invention. The document viewer system.  5  includes a document association device  10  and a document viewer device  30  that can be connected to the document association device  10  via a network  2 . The document viewer device  30  is a portable information processing terminal, such as a smartphone or a tablet. The document association device  10  is a server that provides a document association function. A personal computer (PC)  3  and the like are also connected to the network  2 . 
         [0072]    In the document viewer system  5 , an e-mail message that is a notice of a conference and has a document A and a document B attached thereto is transmitted from the PC  3  to the document viewer device  30 , for example. The document A and the document B are conference materials. The user of the document viewer device  30  designates the document A and the document B attached to the received e-mail message, and requests the document association device  10  to perform an association process on these documents. The document viewer device  30  that has received the request searches the document A for a keyword. (a reference request) indicating reference to another document, such as “see document B”, and extracts a portion including the reference request as a reference source portion from the document A. 
         [0073]    The document B is then searched for the portion having the highest degree of association with the reference source portion (the chapter having the highest degree of association with the reference source portion in the case of a chaptered document, for example), and the portion is determined to be a relevant portion. The relevant portion is associated with the portion of the reference request in the document A so that the relevant portion can be called up from the portion of the reference request. In this case, association information for calling up the relevant portion is buried in the portion of the reference request. The association information is information about the link to the relevant portion, or the relevant portion is buried as the association information in the document A so as not to affect the original contents of the document A. For example, the contents of the relevant portion are buried in a portion other than the body text, such as a comments field or a remarks column. 
         [0074]    When the already associated document A is being viewed, and the association information that is for calling up the relevant portion in the document B and is buried in the document A is selected, the document viewer device  30  calls up the relevant portion in the document B, and displays the relevant portion. 
         [0075]    As described above, in the document viewer system  5 , one document is searched for a reference request, a portion relevant to the portion of the reference request is automatically found out from a reference destination document, and the relevant portion is associated with the portion of the reference request in the one document so that the relevant portion can be called up from the portion of the reference request. Thus, even in a document that does not have information about any link to a reference destination, an appropriate reference destination can be readily called up from a reference source. 
         [0076]      FIG. 2  is a block diagram schematically showing the structure of the document association device  10 . In the document association device  10 , a read only memory (ROM)  12 , a random access memory (RAM)  13 , a hard disk device  14 , an operating unit  15 , a display unit  16 , a communication unit  17 , and the like are connected, via a bus, to a central processing unit (CPU)  11  that collectively controls operation of the document association device  10 . 
         [0077]    The CPU  11  operates on the basis of an operating system (OS) program, and executes programs, such as middleware and application programs. The ROM  12  is a read only memory in which the activation program and various fixed data are stored. 
         [0078]    The hard disk device  14  is a large-capacity nonvolatile storage device. The OS program, the program for a document association process, and the like are stored in the hard disk device  14 . As the CPU  11  executes the program for a document association process, the function of the document association device  10  is achieved. The hard disk device  14  further functions as a document storage unit  18  that stores documents to be associated and already associated documents. 
         [0079]    The RAM  13  is a memory that is used as a work area or the like in which various kinds of data are temporarily stored when the CPU  11  executes a program. 
         [0080]    The display unit  16  is formed with a liquid crystal display that displays various kinds of information. The operating unit  15  functions to receive various operations and inputs from the user. The operating unit  15  is formed with a keyboard, a mouse, a touch panel provided on the display screen of the display unit  16 , or the like. 
         [0081]    The communication unit  17  functions to communicate with the PC  3 , the document viewer device  30 , and other external devices through the network  2 . 
         [0082]      FIG. 3  shows the functional structure related to the document association process to be performed by the document association device  10 . The document association device  10  is formed with a CPU or the like that functions as a document designating unit  21 , a reference source extracting unit  22 , a dividing unit  23 , a relevant portion identifying unit  24 , an associating unit  25 , a viewing control wait  26 , a save confirming unit  27 , and a saving unit  28 . 
         [0083]    The document designating unit  21  receives designation of a first document and a second document to be referred to from the first document. The reference source extracting unit  22  searches the first document for a predetermined keyword indicating reference to the second document, and extracts a portion including the predetermined keyword as the reference source portion from the first document The dividing unit  23  divides the second document into portions. 
         [0084]    The relevant portion identifying unit  24  compares the contents of the reference source portion in the first document with the contents of each of the divided portions of the second document, and identifies the relevant portion that is the portion having the highest degree of association with the reference source portion among the divided portions. The associating unit  25  associates the relevant portion in the second document with the reference source portion in the first document so that the relevant portion can be called up from the reference source portion (or buries the association information in the first document). 
         [0085]    The viewing control unit  26  controls viewing of a document. The save confirming unit  27  presents the user with the relevant portion to be associated with the reference source portion in the first document, and receives a selective response indicating whether a document having the association information buried in the first document is to be saved. When the save confirming unit  27  receives a selective response indicating that the document having the association information buried in the first document is to be saved, the saving unit  28  saves the document having the association information buried in the first document (this document will be referred to as the associated document). 
         [0086]      FIG. 4  is a block diagram schematically showing the structure of the document viewer device  30 . In the document viewer device  30 , a ROM  32 , a RAM  33 , a nonvolatile memory  34 , an operating unit  35 , a display unit  36 , a communication unit  37 , and the like are connected to a CPU  31  via a bus. 
         [0087]    The CPU  31  operates on the basis of an OS program, and executes programs, such as middleware and application programs. The ROM  32  stores the activation program and various fixed data. The RAM  33  is used as a work area or the like in which various kinds of data are temporarily stored when the CPU  31  executes a program. 
         [0088]    The nonvolatile memory  34  is a memory in which stored contents are saved even when the power is switched off, and stores various settings and application programs. The application program for viewing a document associated with another document by the document association device  10  (this application program will be referred to as the viewing application) is stored in the nonvolatile memory  34 . 
         [0089]    The display unit  36  is formed with a liquid crystal display or the like. The operating unit  35  functions to receive various operations and inputs from the user. The operating unit  35  is formed with a touch panel  35 a provided on the display screen of the display unit  36 , a small number of hardware switches, or the like. 
         [0090]    The communication unit  37  functions to communicate with the PC  3 , the document association device  10 , and other external devices through the network  2 . 
         [0091]      FIG. 5  is a flowchart showing an outline of an entire process of associating and viewing documents in the document viewer system  5 . The document association device  10  accepts selection of documents to be associated (step S 101 ), and performs the association process on all the selected documents (step S 102 ). After that the user views an associated document with the document viewer device  30  (step S 103 ), and this process comes to an end when the user finishes the viewing (step  104 ). As described above, in the entire process shown in  FIG. 5 , the association process is performed on all the documents prior to viewing of a document. 
         [0092]      FIG. 6  shows the association process (step S 102  in  FIG. 5 ) in detail. In this example, a relevant portion in the document B is associated with a reference request in the document A.  FIG. 7  shows a specific example of an association process. The document A and the document B are structured documents, and are chaptered. 
         [0093]    The document association device  10  searches the document A for a keyword (a reference request) indicating reference to another document, such as “see document B” (step S 201 ). In this example, the document A is sequentially searched for a reference request, starting from the top. 
         [0094]    If a reference request is found (Yes in step S 202 , and step  1  in  FIG. 7 ), a portion including the reference request is extracted as the reference source portion from the document A (step S 203 , and step  2  in  FIG. 7 ). In this example, the chapter including the reference request in the chaptered document A (or a character string included, in the chapter) is extracted as the reference source portion. 
         [0095]    Morphological analysis is then carried out on the character string in the reference source portion, to separate the character string into words (or extract the words included in the character string), and create a word list (step S 204 , and step  3  in  FIG. 7 ). 
         [0096]    The document B designated as the reference destination by the reference request is divided into portions (step S 205 , and step  4  in  FIG. 7 ). In this example, the document B is divided into chapters. In a case where the document B is a document in the XML format, for example, the document structure can be determined, from tag information. In view of this, the document B is divided in accordance with the tag information. In this example, the document B is divided into chapters in accordance with tag information indicating chapters. When the reference source portion is extracted from the document A, the reference source portion may be extracted in accordance with tag information indicating chapters or the like. 
         [0097]    For each of the chapters after the division, the document association device  10  creates a word list by extracting words from the chapter (step S 206 , and step  5  in  FIG. 7 ). 
         [0098]    The words included in the reference source portion are compared, with the words included in each of the chapters after the division of the document B, and the chapter in the document B having the largest number of times the words match is identified as the relevant portion (step S 207 , and step  6  in  FIG. 7 ). 
         [0099]    The association information (link information in this example) about the relevant portion (the chapter having the highest degree of association) in the document B is inserted and attached to the portion of the reference request in the document A (step S 208 , and step  7  in  FIG. 7 ). If the document A is in the HTML (Hyper Text Markup Language) or XML format, the association information to be attached can be buried by using the tag information. 
         [0100]    The process then returns to step S 201 , and the next reference request is searched for. If there is no next reference request (No in step S 202 ), this process comes to an end. 
         [0101]      FIG. 8  shows the document viewing process (step S 103  in  FIG. 5 ) in detail. The document viewer device  30  displays the document A to be viewed (step S 301 ). If the association information attached to the portion of the reference request is selected while the document A is being viewed (Yes in step S 302 ), the relevant portion in the document B indicated by the association information is called up from the document A, and is displayed (step S 303 ). When the display of the relevant portion is closed (step S 304 ), the user is asked whether the association information is to be saved (step S 305 ). If a selective response indicating that the association information is to be saved is received (Yes in step S 305 ), a document having the association information buried therein (an associated document) is created, and is saved in a location designated by the user (step S 306 ). The process then returns to step S 302 . 
         [0102]    If a selective response indicating that the association information is not to be saved is received (No in step S 305 ), any document having the association information buried therein is not saved, and the process returns to step S 302 . When a viewing ending operation is received (No in step S 307 ), this process comes to an end. 
         [0103]    In the process shown in  FIG. 8 , an inquiry as to whether the association information is to be saved is made at the time when the display of the relevant portion is closed. However, an inquiry as to whether the association information is to be saved may be made at the time when an operation to end the viewing of the document A is received, and, if a response indicating that the association information is to be saved is received, the associated document A may be saved in a location designated by the user. 
         [0104]      FIG. 9  shows a specific example of a series of procedures for associating, viewing, and saving documents. In this example, a received e-mail message that is a notification of a conference is to be viewed on the document viewer device  30 . A document A and a document B are attached as the conference materials to this e-mail message. The user of the document viewer device  30  selects the document A and the document B as the documents to be associated (P 1 ). 
         [0105]    Upon receipt of the selection, the document viewer device  30  transmits and uploads the selected documents A and B to the document association device  10 . The document association device  10  registers the documents A and B received from the document viewer device  30  as the documents to be associated (P 2 ). 
         [0106]    The document association device  10  performs an association process on each of the documents A and B (P 3 ). Specifically, a process of associating relevant portions in the document B with respective reference requests in the document A is performed, and a process of associating relevant portions in the document A with respective reference requests in the document B is performed. 
         [0107]    The user of the document viewer device  30  selects a document to be viewed from, among the documents registered in the document association device  10  (P 4 ). In this example, the user of the document viewer device  30  accesses the document association device  10  from the document viewer device  30 , displays a list of the documents that can be viewed, and selects a desired document to be viewed from the displayed list. 
         [0108]    In this example, the document A is selected. If an operation to select a portion including a reference request (a portion to which association information (link information) is attached) is received from the user while the document A selected as the document to be viewed is displayed on the document viewer device  30  and is being viewed (P 5 ), the relevant portion is called up from the document B in accordance with the link information, and is displayed on the document viewer device  30  (P 6 ). For example, a pop-up window is displayed on the screen, and the relevant portion in the document B is displayed in the pop-up window. 
         [0109]    When the display of the relevant portion in the document B is closed, the user of the document viewer device  30  is asked whether the association information is to be saved (P 7 ). If an instruction to save the association information is received, the associated document A and the associated document B are saved in locations designated by the user (P 8 ). 
         [0110]    The buried association information is not limited to link information. Instead, the relevant information (particularly, a character string) in the document B may be buried so that the relevant portion can be called up from the reference request in the document A. For example, the relevant portion in the document B may be buried in a comments field or a remarks column that can be called up from the portion of the reference request. That is, the relevant portion in the document B is buried in a portion other than the body text of the document A so as not to affect the original contents of the document A.  FIG. 10  shows an example case where the relevant portion in the document B is buried in a comments field in the document A. 
         [0111]      FIG. 11  shows associated documents that are generated in a case where a document A and a document B are associated with each other. The document A includes a request for reference to the document B, and the document B includes a request for reference to the document A. In this case, an associated document A is generated by burying information about a link to the document B in the document A, and an associated document B is generated by burying information about a link to the document A in the document B. The associated document A and the associated document B are then saved. 
         [0112]      FIG. 12  shows an example case where three or more documents are to be associated with one another. A document A includes a request for reference to a document B and a request for reference to a document C, the document B includes a request for reference to the document A and a request for reference to the document C, and the document C includes a request for reference to the document A. In this case, an associated document A is generated by burying information about a link to the document B and information about a link to the document C in the document A, an associated document B is generated by burying information about a link to the document A and information about a link to the document C in the document B, and an associated document C is generated by burying information about a link to the document A in the document C. The associated documents A, B, and C are then saved. 
         [0113]      FIG. 13  shows another example case where three or more documents are to be associated with one another. A document A includes a request for reference to another document, but which document to be referred to is not specified. In this case, a link to the portion having the highest degree of association in the document B and a link to the portion having the highest degree of association in the document C are created for the single reference request in the document A. An associated document A is created by burying information about the link to the document B and information about the link to the document C in the document A. The associated document A is then saved. 
         [0114]      FIG. 14  shows vet another example case where three or more documents are to be associated with one another. A document A includes a request for reference to another document, but which document to be referred to is not specified. In this case, a link to the portion having the highest degree of association in the document B and the document C is created for the portion of the reference request in the document A. For example, in a case where the relevant portion having the highest degree of association exists in the document C, a link to the relevant portion in the document C is created for the reference request in the document A, and an associated document A is created by burying information about the link to the document C in the document A. The associated document A is then saved. 
         [0115]    The user can select one of the operations shown in  FIGS. 13 and 14 . 
         [0116]    Next, a second embodiment of the present invention is described. 
         [0117]    The respective structures of a document viewer system  5 , a document association device  10 , and a document viewer device  30  are the same as those of the first embodiment. 
         [0118]      FIG. 15  is a flowchart showing an outline of an entire process of associating and viewing documents in the second embodiment. First, selection of documents to be associated is received (step S 401 ). Selection of a document to be viewed among the documents selected as the documents to be associated is received (step S 402 ). After the selection of a document to be viewed is received, an association process is performed only on the document to be viewed (step S 403 ), and viewing of the document is started (step S 404 ). When the viewing is ended (step S 405 ), this process comes to an end. 
         [0119]    As described above, in the process shown in  FIG. 15 , a document to be viewed is designated, and an association process is performed only on the designated document. Step  5403  is the same as step S 102  in  FIG. 5 , and is specifically shown in  FIG. 6 . Step S 404  is the same as step S 103  in  FIG. 5 , and is specifically shown in  FIG. 8 . 
         [0120]      FIG. 16  shows a specific example of a series of procedures for associating, viewing, and saving a document. In this example, a received e-mail message that is a notification of a conference is to be viewed on the document viewer device  30 . A document A and a document B are attached as the conference materials to this e-mail message. The user of the document viewer device  30  selects the document A and the document B as the documents to be associated (P 11 ). 
         [0121]    The document viewer device  30  transmits and uploads the selected documents A and B to the document association device  10 . The document association device  10  registers the documents A and B received from the document viewer device  30  as the documents to be associated (P 12 ). 
         [0122]    The user of the document viewer device  30  then selects a document to be viewed from among the documents registered in the document association device  10  (P 13 ). In this example, the user of the document viewer device  30  accesses the document association device  10  from the document viewer device  30 , displays a list of the documents that can be viewed, and selects a desired document to be viewed from the displayed list. 
         [0123]    In this example, the document A is selected. The document association device  10  performs an association process on the document A selected as the document to be viewed (P 14 ). Specifically, a process of associating relevant portions in the document B with respective reference requests in the document A is performed. Any association process is not performed on the document B. 
         [0124]    If an operation to select a portion including a reference request (a portion to which link information is attached) is received from the user while the document A subjected to the association process is displayed on the document viewer device  30  and is being viewed (P 15 ), the relevant portion is called up from the document B in accordance with the link information, and is displayed on the document viewer device  30  (P 16 ). For example, a pop-up window is displayed on the screen, and the relevant portion in the document B is displayed in the pop-up window. 
         [0125]    When the display of the relevant portion in the document B is closed, an inquiry as to whether the association information is to be saved is made (P 17 ). If an instruction to save the association information is received, the associated document A is saved in a location designated by the user (P 18 ). At this point, the document B as the reference destination may also be saved. 
         [0126]    In the second embodiment, when a document to be viewed is designated, a process of associating the document to be viewed with the reference destination is performed. If an association process is performed to associate all the documents with one another as in the first embodiment, the association process might unnecessarily be performed even on a document that is not to be viewed by the user. In the second embodiment, however, such unnecessary processing is not performed. 
         [0127]    In the first embodiment, all the documents are associated with one another before a viewing instruction is received. Accordingly, the waiting time from the reception of a viewing instruction till the start of viewing can be made shorter than that in a case where an association process is performed after the start of viewing. In the second embodiment, an association process may be performed in the background of document viewing, to shorten the waiting time. 
         [0128]      FIG. 17  shows an associated document that is generated in a case where a document A is viewed in the second embodiment. The document A includes a request for reference to the document B, and the document B includes a request for reference to the document A. As the document A is selected as the document to be viewed, the document B is associated with the document A. When the link information buried in the reference request is selected at the time of the viewing, the relevant portion in the document B is called up and displayed. If an instruction to save the association information is received after the viewing of the document A is ended, an associated document A having the information about the link to the document B buried in the document A is saved. 
         [0129]    Next, a third embodiment of the present invention is described. 
         [0130]    In the first and second embodiments, the document viewer device  30  and the document association device  10  are provided independently of each other in the document viewer system  5 . In the third embodiment, however, the document viewer device  30  also has the functions of the document association device  10 . That is, the viewing application of the document viewer device  30  performs a document association process. The contents of the process are the same as those in the first and second embodiments, and therefore, explanation of them is not made herein. 
         [0131]      FIG. 18  shows a specific example of a series of procedures for associating, viewing, and saving documents in the document viewer device  30  of the third embodiment. In this example, a received e-mail message that is a notification of a conference is to be viewed on the document viewer device  30 . A document A and a document B are attached as the conference materials to this e-mail message. The user of the document viewer device  30  selects the document A and the document B as the documents to be associated (P 21 ). 
         [0132]    Upon receipt of the selection, the document viewer device  30  performs an association process on each of the documents A and B (P 22 ). Specifically, a process of associating relevant portions in the document B with respective reference requests in the document A is performed, and a process of associating relevant portions in the document A with respective reference requests in the document B is performed. 
         [0133]    The user selects a document to be viewed from among the documents registered in the document viewer device  30  (P 23 ). In this example, the document A is selected. If an operation to select a portion including a reference request (a portion to which link information is attached) is received from the user while the document A selected as the document to be viewed is displayed on the document viewer device  30  (P 24 ), the relevant portion is called up from the document B in accordance with the link information, and is displayed on the document viewer device  30  (P 25 ). For example, a pop-up window is displayed on the screen, and the relevant portion in the document B is displayed in the pop-up window. 
         [0134]    When the display of the relevant portion in the document B is closed, an inquiry as to whether the association information is to be saved is made (P 26 ). If an instruction to save the association information is received, the associated document A and the associated document B are saved in locations designated by the user (P 27 ). 
         [0135]    Although embodiments of the present invention have been described so far with reference to the accompanying drawings, specific structures are not limited to those embodiments, and modifications and additions within the scope of the invention are included in the present invention. 
         [0136]    An associated document may be overwritten on the original document, or may be saved as a different document in a different location. For example, in a case where an associated document A and an associated document B are to be saved in different locations from the original documents A and B, the link information to be buried in the associated document A is rewritten during the saving process, to indicate the new location in which the associated document B is to be saved. Likewise, the link information to be buried in the associated document B is rewritten during the saving process, to indicate the new location in which the associated document A is to be saved. 
         [0137]    In the above embodiments, the words included in the respective chapters after the document to be referred to is divided are compared with the words included in the reference source portion, and the chapter with the largest number of times the words match is identified as the relevant portion having the highest degree of association. However, the method of measuring a degree of association is not limited to that. For example, a degree of association may be measured by carrying out semantic analysis on paragraphs. 
         [0138]    A relevant portion (a character string) is not necessarily buried in a comments field or a remarks column in the reference source document A relevant portion may be buried in the header portion of the reference source document, if the relevant portion can be called up later without affecting the original contents of the reference source document. For example, the relevant portion is buried in the header portion, and information about a link to the relevant portion in the header portion is also attached to the reference source portion. With this arrangement, when the link information is selected while the body text is being viewed, the relevant portion in the header portion is called up and displayed. 
         [0139]    Although the reference source portion is extracted and the document to be referred to is divided on a chapter basis in the above embodiments, the unit of extraction and division is not limited to that. For example, the unit of extraction and division may be one or more paragraphs. 
         [0140]    As for the keyword(s) for determining a reference request, one or more keywords may be set in advance. 
         [0141]    In a case where the portion (chapter) to be referred to is designated by a reference request, such as “chapter 5 in document B”, chapter 5 in the document B should be identified as the relevant portion. 
         [0142]    Although the present invention has been described and illustrated in detail, at is clearly understood that the same is by way of illustrated and example only and is not to be taken by way of limitation, the scope of the present invention being interpreted by terms of the appended claims.