Patent Publication Number: US-2021173844-A1

Title: Information processing apparatus and non-transitory computer readable medium storing program

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based on and claims priority under 35 USC 119 from Japanese Patent Application No. 2019-220555 filed Dec. 5, 2019. 
     BACKGROUND 
     (i) Technical Field 
     The present invention relates to an information processing apparatus and a non-transitory computer readable medium storing a program. 
     (ii) Related Art 
     JP2010-108268A discloses an apparatus that obtains a relation between documents. In the apparatus, a relation-source location extraction unit in a document relation extraction unit selects a document relation extraction rule matching with a document type of a relation source document stored in a relation-source document storage unit, from a document relation extraction rule storage unit. The relation-source location extraction unit extracts a location satisfying a relation-source location extraction condition in the rule, as a relation source location, from the text of the relation source document. A related document search condition generation unit generates a related document search condition from words included in the relation source location, in accordance with the rule. A related document searching unit searches for a related document of which the type matches with a related document type defined in the rule and which satisfies a related document search condition in the rule, among related documents stored in the relation-source document storage unit. The related document searching unit stores a relation between the relation-source document and the related document, in a document relation storage unit of a storage device. 
     SUMMARY 
     Aspects of non-limiting embodiments of the present disclosure relate to an information processing apparatus and a non-transitory computer readable program recording medium that obtain a relation between documents. 
     Aspects of certain non-limiting embodiments of the present disclosure overcome the above disadvantages and/or other disadvantages not described above. However, aspects of the non-limiting embodiments are not required to overcome the disadvantages described above, and aspects of the non-limiting embodiments of the present disclosure may not overcome any of the disadvantages described above. 
     According to an aspect of the present disclosure, there is provided an information processing apparatus including an acquisition unit that acquires input information including (i) feature information indicating a feature of similarity of a content between a first document element and a second document element, (ii) an attribute of the first document element, and (iii) an attribute of the second document element, and a generation unit that generates relation information corresponding to the input information acquired by the acquisition unit, by an AI which has learned to generate the relation information indicating a relation between the first document element and the second document element from the input information in advance by machine learning, in which each of the contents of the first document element and the second document element is formed of one or more parts, and the feature information is obtained based on similarity information indicating similarity of a pair of the parts between the first document element and the second document element. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Exemplary embodiment(s) of the present invention will be described in detail based on the following figures, wherein: 
         FIG. 1  is a diagram illustrating a configuration of an entire system including a document service system; 
         FIG. 2  is a diagram illustrating an example of a document creation operation in the system in  FIG. 1 ; 
         FIG. 3  is a diagram illustrating a hardware configuration of a computer on which the document service system is mounted; 
         FIG. 4  is a diagram illustrating an example of a database construction and maintenance processing procedure performed by the document service system; 
         FIG. 5  is a diagram illustrating a structure of a document; 
         FIG. 6  is a diagram illustrating a data structure of a document property in a database; 
         FIG. 7  is a diagram illustrating a data structure of an element property in the database; 
         FIG. 8  is a diagram illustrating relation information in the database; 
         FIG. 9  is a diagram illustrating an example of an information providing screen provided by the document service system; 
         FIG. 10  is a diagram illustrating a processing procedure for generating the information providing screen, which is performed by the document service system; 
         FIG. 11  is a diagram illustrating another example of the information providing screen provided by the document service system; 
         FIG. 12  is a diagram illustrating another example of the processing procedure for generating the information providing screen, which is performed by the document service system; 
         FIG. 13  is a diagram illustrating still another example of the information providing screen provided by the document service system; 
         FIG. 14  is a diagram illustrating still another example of the processing procedure for generating the information providing screen, which is performed by the document service system; 
         FIG. 15  is a diagram illustrating an example of a graph display provided by the document service system; 
         FIG. 16  is a diagram illustrating a part of a procedure of notification processing performed by the document service system; 
         FIG. 17  is a diagram illustrating a procedure of causing an AI that determines the type of relation between document elements, to perform learning; 
         FIG. 18  is a diagram illustrating processing of calculating similarity between paragraphs of the document elements in total; 
         FIG. 19  is a diagram illustrating information on the similarity between paragraphs in a database; 
         FIG. 20  is a diagram illustrating an example of a procedure of determining the type of relation between document elements, by using the AI; and 
         FIG. 21  is a diagram illustrating another example of the procedure of determining the type of the relation between the document elements, by using the AI. 
     
    
    
     DETAILED DESCRIPTION 
     Example of Entire System 
       FIG. 1  illustrates an entire system for using a document, which includes a document service system  100  being an exemplary embodiment of an information processing apparatus according to an exemplary embodiment of the present invention. 
     In the example, a document service system  100  is connected to an internal network  40  in a certain company. One or more document management systems for managing various internal documents, such as a design document management system  10  or a company rule management system  20 , are connected to the internal network  40 . A client  30  such as a personal computer operated by a user is connected to the internal network  40 . 
     Various document management systems such as a law management system  60  and an XX standard management system  70  that manages standard documents of an “XX” technology are provided on the Internet  50 . Apparatuses such as the document service system  100  and a client  30  on the internal network  40  are capable of accessing documents of the document management system on the Internet  50 . 
     In a case where one document related to another document in an internal document management system such as the design document management system.  10  is changed, the document service system  100  provides a service (for example, notifying a concerned person of the change) corresponding to the change of the one document for the another document. 
     As illustrated in  FIG. 2 , a case where a user in a company creates a design document A of a product, registers the created document in the design document management system  10 , and maintains the registered document is considered. Since the product is required to be designed to satisfy various laws and various company rules, the design document A is also created with reference to other documents such as the laws and the company rules. For example, the design document A is created with reference to the Road Transport Vehicle Law registered in a law DB  62  of the law management system  60  and a completion inspection implementation rule registered in a company rule DB  22  of the company rule management system  20 . The law in the law DB  62  and the rule in the company rule DB  22  are updated at any time in accordance with the revision. 
     In a case where the Road Transport Vehicle Law and the completion inspection implementation rule are revised, the content of the design document A may be required to be updated, but the update is not always necessary. For example, in a case where the revised part of the law or the like is different from the part on which the content of the design document A depends, the content of the design document A is not required to be updated. 
     In addition, even though the design document A is created based on a certain part of the law, various methods of depending on the part are provided. For example, there is a case where a section of the law is cited in the design document A by copying the section itself, and there is a case where coincidence of terms between the relevant part of the law and a part of the design document A can be found just by describing the part of the design document A while checking the relevant part of the law. In the former case, necessity to correct the cited part in the design document A by the section of the law being revised is high. On the contrary, in the latter case, the degree of necessity for a response of the design document A to the revision of the relevant part of the law is lower than the degree of necessity in the former case. 
     Thus, in the exemplary embodiment, the document service system  100  provides a participant of a document, such as a person in charge of managing the design document A, with, for example, a service of supporting an operation of determining whether or not the document is required to be changed in response to a change of another document related to the above document. 
     Here, the “document” refers to data in any data format, and the data format is not particularly limited. For example, the document may refer to data in a text data format or in various document file formats such as a PDF format. The document may refer to image data in various image data formats or a moving image data. The document may refer to data in a structured document format such as a Hypertext Markup Language (HTML) format or an Extensible Markup Language (XML) format. 
     In this specification, “a participant” for a document refers to an individual or a user group involved in maintaining the content of the document. The participant may be, for example, a person in charge of maintenance of the content of the document, or may have a role of urging the person in charge to perform the maintenance. For example, a user who has created the document or a user who has updated the document is a representative example of the participant. A document may be configured with a plurality of document elements, and a participant may be set for each document element. 
     Example of Hardware Configuration 
     The document service system  100  is implemented by causing a computer to execute a program representing a function of the system. 
     Here, for example, as illustrated in  FIG. 3 , a computer serving as a base of the document service system  100  has a circuit configuration as follows, as hardware. In the circuit configuration, a processor  102 , a memory (main storage device)  104  such as a random access memory (RAM), a controller for controlling an auxiliary storage device  106  such as a flash memory, a solid state drive (SSD), and a hard disk drive (HDD), an interface with various input and output devices  108 , and a network interface  110  for controlling a connection with a network such as a local area network are connected to each other via a data transmission path such as a bus  112 , for example. A program in which the processing content of each function of the document service system  100  is described is installed on the computer via the network or the like, and is stored in the auxiliary storage device  106 . Functions of the document service system  100  are realized by the processor  102  executing the program stored in the auxiliary storage device  106  using the memory  104 . 
     In the embodiments above, the term “processor”  102  refers to hardware in a broad sense. Examples of the processor include general processors (e.g., CPU: Central Processing Unit) and dedicated processors (e.g., GPU: Graphics Processing Unit, ASIC: Application Specific Integrated Circuit, FPGA: Field Programmable Gate Array, and programmable logic device). 
     In the embodiments above, the term “processor”  102  is broad enough to encompass one processor  102  or plural processors  102  in collaboration which are located physically apart from each other but may work cooperatively. The order of operations of the processor  102  is not limited to one described in the embodiments above, and may be changed. 
     Other apparatuses such as the design document management system  10 , the company rule management system  20 , and the client  30  are also configured using a computer as a base, similar to the document service system  100 . 
     Database Construction 
     An example of database construction processing used for the document service system  100  providing a service will be described with reference to  FIGS. 4 to 8 . The database is constructed in the auxiliary storage device  106  in the document service system  100 . 
     For example, the document service system  100  periodically visits predetermined document management systems inside and outside a company, such as the design document management system  10 , the company rule management system  20 , and the law management system  60 , so as to acquire and analyze a document group registered in the document management systems. In this case, the document service system  100  analyzes information of which a notification is made. A procedure illustrated in  FIG. 4  shows a process performed when the document service system  100  acquires one document from any document management system (S 10 ). 
     In this case, the processor  102  in the document service system  100  analyzes the structure of the acquired document to divide the document into document element units (S 12 ). The structure analysis is performed, for example, by processing of converting a document into an HTML format. Various tools for HTML conversion are provided. In S 12 , a tool appropriate for the file format of the document may be used. Alternatively, the structure analysis may be performed using a known technology of recognizing the structure of a heading, a chapter, a section, a paragraph, or the like from the document content. In a case where the acquired document is already a structured document in the XML format or the like, the process of S 12  may be omitted. 
     Then, the processor  102  determines whether or not data of a document identical to the document acquired in S 10  is registered in a database (S 14 ). Here, “identical” does not mean that the entire contents of the documents are identical to each other, but that the documents have the identical identification information. The identification information of a document is referred to as a document ID. In S 14 , whether or not information on a document having a document ID identical to a document ID of the acquired document is in the database is determined. 
     As the document ID, for example, a combination of identification information of the document management system (for example, company rule management system  20  or law management system  60 ) as an acquisition source of the document and identification information of the document in the document management system may be used. For example, a uniform resource locator (URL) of the document in the document management system may be used as the document ID of the document. 
     In a case where the determination result in S 14  is No, the document acquired in S 10  is a document that the processor  102  firstly encounters. In this case, the processor  102  registers information on the document acquired in S 10  and information on each document element obtained by the structure analysis in S 12 , in the database (S 16 ). 
     The processor  102  calculates the similarity of the content of each document element with contents of other document elements registered in the database, and registers the obtained similarity in the database for each document element (S 17 ). The similarity of the content between the document elements may be obtained, for example, in a manner that a text string included in the document element is vectorized, and similarity between the obtained vectors of the document elements is calculated by a known method (for example, cosine similarity). As a method of vectorizing the text string of the document element, a known method such as term frequency-inverse document frequency (TF-IDF) or doc2vec may be used. 
     Here, “the other document element” being a partner for obtaining the similarity with the document element obtained in S 12  is typically a document element of another document registered in the database. However, the present invention is not limited to the above method, and the similarity between the document elements obtained in S 12  may be further calculated. 
     The processor  102  calculates the similarity between the document acquired in S 10  and another document registered in the database, and registers the similarity of the calculation result in the database (S 18 ). For example, text strings obtained in a manner that text strings of headings of a chapter and a section in the document obtained by the structure analysis in S 12  are arranged and merged in order of appearing are set as text strings indicating characteristics of the document, and the text strings are vectorized. The similarity between the vectors of the text strings indicating the characteristics of the documents obtained in this manner is obtained as the similarity between the documents. A method of calculating the similarity between documents is not limited to this. In addition, for example, a tree structure configured with document elements (for example, chapters, sections, and paragraphs) in a document may be set as characteristics of the document, and the similarity between the characteristics may be set as the similarity between documents. 
     In a case where the determination result in S 14  is Yes, data of the document acquired in S 10  is registered in the database of the document service system  100 . In this case, the processor  102  examines whether or not the document acquired in S 10  and each document element obtained in S 12  have been changed from the document and document element registered in the database (S 20 ). In this step, for example, for each document element obtained in S 12 , the processor compares the content of the document element (that is, text string) with the content of the identical document element (that is, document element having the identical identification information) in the database. In a case where both the contents coincide with each other, the processor determines that the document elements are not changed. In a case where both the contents do not coincide with each other, the processor determines that the document elements are changed. A case where the document element identical to the document element obtained in S 12  is not in the database or a case where a document element identical to a document element in the database is not provided in the structure analysis result in S 12  corresponds to an example of a case where the document element is changed. A case where any one or more document elements are determined to be changed refers to a case where the entire document is changed. A case where there is no document element determined to be changed refers to a case where the entire document is not changed. 
     The processor  102  determines whether or not the change in the document or the document element has been detected in S 20  (S 22 ). In a case where the change has been detected, the processor  102  applies information on the detected change in the database (S 24 ). For example, in a case where the content of a certain document element has been changed, the content of the document element in the database is updated to the content after the change. For a document element of which no change has been detected, the information registered in the database is not required to be changed. In a case where the change of the document element in the document is detected, information such as the update date and time of the document in the database is changed. 
     The processor  102  calculates the similarity of the content between the document element of which the change of the content has been detected in S 20 , and another document element in the database. The processor updates the value of the similarity between the document elements, which has been registered in the database, to a value obtained by the calculation (S 26 ). In a case where the document element of which the change of the content has been detected in S 20  is a new document element which is not in the database, the processor calculates the similarity between the new document element and another document element in the database, and registers the similarity in the database. In a case where deletion of the document element which has been in the database is detected in S 20 , information on the similarity between the deleted document element and another document element may be deleted from the database. The process of S 26  is not performed on the document element of which the change has not been detected. 
     The processor  102  calculates the similarity between the document acquired in S 10  and another document in the database in a manner similar to that in S 18 . Then, the processor updates the similarity between this document and another document in the database, in accordance with the calculation result (S 28 ). 
     An example of information registered in the database in the document service system  100  will be described with reference to  FIGS. 5 to 8 . 
       FIG. 5  illustrates information on a structure analysis result of two documents  200  and  210  registered in the database by HTML. The document  200  has an H 1  element (for example, title of the document) as a child document element (referred to as a child element below), and the H 1  element has two H 2  elements as child elements. The H 2  elements have two H 3  elements and one H 3  element, as a child element, respectively. As described above, structure information on the document  200  is represented by a tree structure illustrated in  FIG. 5 . Unique identification information is assigned to the document and each document element. Data representing the tree structure illustrated in  FIG. 5  is registered, as the structure information on the document, in the database in association with the identification information of the document. 
     Property data (referred to as “document property”) for each of the documents  200  and  210  and property data (referred to as “element property”) for each document element are registered in the database. 
     The similarity between the document  200  and the document  210  is calculated and registered in the database. The similarity of the content between the document elements is calculated and registered in the database. 
       FIG. 6  illustrates an example of a data structure of the document property registered in the database. The document property of the document illustrated in  FIG. 6  includes items such as a document ID, a document name, a document characteristic, a creator, the creation date and time, the last updater, the update date and time, the acquisition date and time, and a storage location of the document. The document name is, for example, a filename of the document. The document characteristic refers to data indicating the characteristics of the document. For example, as described above, a text string obtained by arranging and merging text strings of headings of a chapter and a section in the document in order of appearing is provided as an example of the document characteristic. The resultant obtained by vectorizing the text string may be used as the document characteristic. The creator indicates the user ID of a user who has firstly created the document, and the creation date and time indicate the date and time of creation. The last updater indicates the user ID of a user who has updated the document last, and the update date and time indicate the date and time of the update. The types of information on the creator, the creation date and time, the last updater, and the update date and time may be acquired from attribute data of the file of the document, for example. The acquisition date and time indicate the date and time on which the processor  102  has acquired the document last from the document management system such as the company rule management system  20  or the law management system  60 . The storage location refers to information of specifying the document management system in which the document has been originally stored (for example, URL of the document management system). 
     In S 18  and S 26  in the procedure of  FIG. 4  described above, such information on the document property and information on the tree structure of the document obtained in S 12  are registered in the database. 
       FIG. 7  illustrates an example of a data structure of the element property registered in the database. The element property of the document element illustrated in  FIG. 7  include items such as an element ID, an element name, an element content, a content characteristic, a creator, the creation date and time, the last updater, the update date and time, the acquisition date and time, and a storage location of the document element. The element ID refers to identification information of the document element. For example, a set of a document ID of a document including the document element and a number uniquely assigned to the document element in the document may be used as the element ID. The element name refers to the name of the document element. For example, in a case where the document element includes a heading, the heading may be used as the element name. In a case where the document element does not include the heading, a text string having a predetermined number of characters at the head of the document element may be used as the element name. The element content refers to data of the content of the document element. For example, in a case where the document element is a text, the element content is a text string of the text. The element characteristic refers to data indicating the characteristic of the document element, and is obtained by vectorizing the text string of the document element described above, for example. The creator indicates the user ID of a user who has firstly created the document, and the creation date and time indicate the date and time of creation. In a case where the original document file (or the document management system that manages the original document file) has information on the creator or the creation date and time for each document element, the information is registered in the item of the creator or the creation date and time in the element property. In a normal case where the file of the original document has only the creator and the creation date and time in a document unit, the creator and the creation date and time of the document are registered in the creator and the creation date and time of the document element included in the document in the element property. 
     The last updater indicates the user ID of a user who has updated the document element last, and the update date and time indicate the date and time of the update. In a case where the original document file (or the document management system that manages the original document file) has information on the last updater or the update date and time for each document element, the information is registered in the item of the last updater or the update date and time in the element property. In a normal case where the file of the original document has only the last updater and the update date and time in a document unit, values of the last updater and the update date and time of the document when the change of the content of the document element is detected are registered in the items of the last updater and the update date and time of the document element included in the document in the element property. Whether or not the content of the document element has been changed is determined by comparing the element content or the content characteristic of the document element obtained in S 12  with the element content or the content characteristic of the document element in the database having the identical element ID. 
     The acquisition date and time refers to the date and time on which the processor  102  has acquired the document element last. The acquisition date and time is identical to the acquisition date and time of the document including the document element. The storage location refers to information of specifying the document management system in which the document element has been originally stored, and is identical to the storage location of the document including the document element. 
     In S 16  of the procedure of  FIG. 4  described above, information on each item of such element property is registered in the database. In S 24 , the processor updates the value of each item of the element property of the document element of which the change has been detected, to a value corresponding to the content of the change. 
     In a case where the document is acquired from an external document management system (for example, document management system outside the internal network  40 ), acquiring information on all items of the document property and the element property illustrated in  FIGS. 6 and 7  for the above document may not be possible. Such an item is set to a null value, or a value obtained by the document service system  100  based on another type of information is set. For example, for a document acquired from the law management system  60 , difficulty in obtaining information on the creator, the creation date and time, the last updater, and the update date and time from the document or the law management system  60  is considered. In this case, the items of the creator, the creation date and time, and the last updater may be set to null values. In a case where the change of the document element in the acquired document has been detected in S 20  of the procedure in  FIG. 4 , the document service system  100  may set the date and time of the acquisition to the update date and time of the document element and the document. 
     The item group of the document property and the element property illustrated in  FIGS. 6 and 7  are only examples. The document property and the element property are not required to include all of the illustrated items, and may include items that are not illustrated. 
       FIG. 8  illustrates relation information between document elements registered in the database. The relation information illustrated in  FIG. 8  is associated with a pair of element IDs of two document elements. The relation information includes a value of the similarity of the content between the two document elements and the type of relation between the document elements, which is determined from the value. In the example, the types of relation between document elements are classified into several types in accordance with the magnitude of the similarity of the content between the document elements. For example, in a case where the similarity of the content between the document elements is equal to or greater than 0.95 (that is, 95%), the type of relation between the document elements is named “citation”. The type of relation in a case where the similarity of the content between the document elements is equal to or greater than 0.80 and smaller than 0.95 is named “similar”. In a case where the similarity is equal to or greater than 0.60 and smaller than 0.80, the type of relation is named “reference”. Ina case where the similarity is smaller than 0.60, the two document elements are determined to be unrelated. 
     Although not illustrated in  FIG. 8 , the date and time on which the similarity or the type of relation is determined may be further registered in the relation information. 
     In S 17  and S 26  in the procedure of  FIG. 4 , the similarity between the document elements and the type of the relation corresponding to the similarity are determined, and the values are registered in the relation information illustrated in  FIG. 8 . 
     The relation information illustrated in  FIG. 8  is merely an example. As the relation information, information that includes similarity but does not include the type of relation may be used, and conversely, information that does not include similarity but includes the type of relation may be used. 
     Services Provided by Document Service System 
     An example of a service provided by the document service system  100  using the constructed database will be described. 
       FIG. 9  illustrates an information providing screen  300  provided by the document service system  100  to the user. The information providing screen  300  provides information on document elements  332  and  342  related to changed document elements  322  and  324  among documents  320  designated by a user. The information is provided in a form of a graph  310  of a relation between the document  320  and the document elements  322 ,  324 ,  332 , and  342 . 
     All document elements related to the changed document elements  322  and  324  are not displayed on the information providing screen  300 , but only a document element of which the user is a participant (for example, person who has created or updated the document element) is displayed. For the document element of which the user is a participant, the user is expected to perform a change operation in response to the change of the document elements  322  and  324 . Thus, the user is provided with the information on the document element. On the contrary, for the document element of which the user is not the participant, a possibility that the user does not perform a corresponding operation such as correction even though the information is provided to the user is high. Thus, providing the information is not performed. 
     Here, an example in which a creator or an updater included in the element property of the document element is provided as the participant of the document element is described. In addition, a user or a user group having an edit authority for the document element or a document including the document element may be set as the participant of the document element. 
     In the example illustrated in  FIG. 9 , a document designated by the user is a document having a document name of “service quality assurance guide”. In the document, a document element  322  having an element name of “Regulation  7 ” and a document element  324  having an element name of “Regulation  11 ” are detected as the changed document elements. Whether or not the document element has been changed may be determined based on, for example, whether or not the document element is updated within a period that goes back by a predetermined length (for example, one month) from the current time. That is, in a case where the last update date and time of the document element is within the period, “the document element has been changed” is determined. In a case where the last update date and time is before the period, “the document element has not been changed” is determined. The length of the period may be designated by the user. The user may be able to designate both the start and end of the period. A designation field of “period” at the lower right portion of the information providing screen  300  is used for designation of the user. 
     In the example illustrated in  FIG. 9 , a document element  332  having a relation of “reference” to the changed document element  322  is provided. The document element  332  is a document element belonging to a document  330  having a document name of “family operating environment .docx” and has an element name of “3. operation specification”. A document element  342  having a relation of “reference” to the changed document element  324  is provided. The document element  342  is a document element belonging to a document  340  having a document name of “quality check result report .xlsx” and has an element name of “2. implementation target”. 
     In the example illustrated in  FIG. 9 , document elements  326  and  328  having a relation of “similar” to each other are shown in a document element group of the document  320 . 
     The graph  310  shows a node group indicating the documents  320 ,  330 , and  340 , a node group indicating document elements  322  to  328 ,  332 , and  342 , and an edge group indicating a relation between the nodes. A text string indicating the type of relation indicated by an edge is displayed near each edge. For example, a text string of “reference” is shown at an edge indicating the relation between the document elements  322  and  332 . A text string of “similar” is shown at an edge indicating the relation between the document elements  326  and  328 . For example, a text string of “parent” is shown at an arrow-like edge extending from the document element  322  to the document  320 . This indicates that the document  320  is a parent in the tree structure as viewed from the document element  322 . 
     In the graph  310 , the nodes of the changed document  320  and the changed document elements  322  and  324  are highlighted in a special display form indicating that the change has been performed. 
     The document elements  332  and  342  related to the changed document elements  322  and  324  and the nodes of the documents  330  and  340  that are the parents of the document elements  332  and  342  are also highlighted in another display form. In the example illustrated in  FIG. 9 , the relation between the document elements  322  and  332  and the relation between the document elements  324  and  342  are both “reference”. Thus, the highlighted display forms of the document element  332  and the document element  342  are identical to each other. On the contrary, in a case where the two types of relation are different from each other, the highlighted display forms of the document element  332  and the document element  342  are different from each other. For example, as illustrated in  FIG. 13  described later, a node of the document element  352  having a relation of “citation” to the changed document element  324  is displayed in a display form which is more prominent than that for the “reference” relation. Since the similarity of the content between the two document elements is much higher in “citation” than in “reference”, the necessity to correct the content in response to the changed document element is considered to be much higher in “citation”. 
       FIG. 10  illustrates an example of a processing procedure of creating the information providing screen  300  illustrated in  FIG. 9 . 
     In the procedure of  FIG. 10 , the processor  102  of the document service system  100  provides an input screen for inputting search conditions and the like to the client  30  in a form of a web page, for example. The processor receives the input of the search conditions and the like from the user (S 30 ). The processor  102  searches the database for a document that satisfies the input search condition (S 32 ). The processor provides the client  30  with a screen showing a list of documents as the search result, and receives the selection of the interested document from the user (S 34 ).  FIG. 9  illustrates an example of a case where the user selects the document  320  “service quality assurance guide” as an interested document. 
     The processor  102  examines the element property of each document element belonging to the interested document selected by the user, to specify the document element which has been changed within a predetermined period and determine whether there is a changed document element (S 36 ). In a case where there is no changed document element in the interested document, the processor  102  generates a screen indicating that there is no changed document element in the interested document, and causes the client  30  to display the screen (S 38 ). 
     In a case where the determination result in S 36  is Yes, the processor  102  obtains a document element related to the specified changed document element from the relation information in the database (see  FIG. 8 ). The processor extracts a document element of which the user is a participant among the obtained document elements (S 40 ). The extraction may be performed with reference to the element property of the obtained document element. The processor  102  generates a graph  310  indicating the relation between a set of the changed document element obtained in S 36  and the document to which the obtained document element belongs, and a set of the document element extracted in S 40  and the document to which the extracted document element belongs. Then, an information providing screen  300  including the graph  310  is provided to the client  30  (S 42 ). The processor  102  determines the display mode of the node for each document element to be displayed on the graph  310 , in accordance with whether or not the document element is changed, or the type of relation between this document element and the changed document element. 
       FIG. 11  illustrates another example of the information providing screen  300  provided by the document service system  100  to the user. 
     In the graph  310  illustrated in  FIG. 11 , among the document elements  332  and  342  of which users are participants and which are related to the changed document elements  322  and  324  in the interested document  320 , the document element  332  of which the content is not changed after the change of the document elements  322  and  324  is highlighted. On the contrary, the content of the document element  342  related to the changed document element  324  has been changed after the change of the document element  324 , and thus the document element  342  is not highlighted. 
     In a case where the document element  322  is changed, whether the document element related to the document element  322  is required to be changed is checked. In a case where the document element is required to be changed, the change is performed on the document element. Thus, the user is urged to check a document element by highlighting the unchanged document element among document elements related to the changed document element. 
       FIG. 12  illustrates an example of a processing procedure of creating the information providing screen  300  illustrated in  FIG. 11 . In the procedure of  FIG. 12 , steps of performing the similar processing to the procedure of  FIG. 10  are denoted by the identical reference signs, and description thereof will be omitted. 
     In the procedure of  FIG. 12 , the processor  102  determines whether or not the document element extracted in S 40  is changed after the corresponding changed document element has been changed (S 50 ). For example, in a case where the last update date and time of the document element as a determination target is later than the last update date and time of the corresponding changed document element, the change is determined, in S 50 , to be completed, and otherwise the document element is determined, in S 50 , not to be changed. In the example of  FIG. 10 , since the last update date and time of the document element  332  is earlier than the last update date and time of the corresponding changed document element  322 , the document element  332  is determined not to be changed. 
     The processor  102  generates the graph  310  and highlights the node of the document element determined, in S 50 , not to be changed in the graph  310  in a special display form for a notification indicating that the document element is not changed. Then, the information providing screen  300  including the graph  310  is provided to the client  30  (S 42 A). 
     The user selects the changed document element  322  and the node of the document element  332  which has been highlighted and not changed, on the information providing screen  300  displayed in the client  30 . In response, the processor  102  of the document service system  100  provides the client  30  with a screen of displaying the latest content of the selected document element. The user checks the content of each document element on the screen, and determines whether the content of the document element  332  is required to be changed. In a case where the change of the document element  332  is determined to be required, the user performs a required change of the content of the document element  332 . In response to the change, the processor  102  changes the element content or the content characteristic of the element property (see  FIG. 7 ) of the document element  332  in the database. The processor  102  accesses the document management system that manages the document to which the document element  332  belongs, using the information on the storage location in the element property. The processor applies the change to a part corresponding to the document element  332  in the original document. 
     After a document element has been changed, the user may check whether a document element related to the changed document element is changed in response to the change. As a result, the user may determine that the change is not required. In this case, although the content of the latter document element has not been changed, the required check has already been completed. Thus, in a case where the highlight is displayed on the graph  310 , the user is required to perform the useless check. Therefore, the processor  102  of the document service system  100  not only receives the edit of the content on the screen of displaying the content of the selected document element on the information providing screen  300 , but also receives the designation of whether or not the content is checked. In a case where the designation that the check from the user is performed is made, the last update date and time of the document element is changed to the designated time. Thus, a situation in which the document element is highlighted to display being not changed on the subsequent information providing screen  300  does not occur. 
       FIG. 13  illustrates still another example of the information providing screen  300  provided by the document service system  100  to the user. 
     In the graph  310  illustrated in  FIG. 13 , in addition to the node group illustrated in  FIG. 9 , nodes of another document element  352  of which the user is a participant and which is related to the changed document element  322  and a document  350  (document name “functional specification.xlsx”) being the parent of the document element  352  are displayed. The document element  352  has a relation of “citation” to the changed document element  324 . That is, the content of the document element  352  is identical or very close to the content of the document element  324 . Although the other document elements  342  also has a relation with the identical document element  324 , the relation is “reference” in which the similarity of the content between the document elements is much lower than “citation”. For this reason, the node of the document element  352  is highlighted in a display form indicating the relation of “citation”, and the display form is more conspicuous than the display form indicating the relation of “reference”. 
     In this example, in a case where the document service system  100  detects the document element  352  having a relation of “citation” to the changed document element  322 , the document service system  100  updates the content of the document element  352  to match with the content of the changed document element  322 . That is, for example, the content of the changed document element  322  is overwritten on the document element  352 . 
     The update is performed on the element content (see  FIG. 7 ) of the document element  352  in the database of the document service system  100 . The similar update is performed on original data of the document  350  in the document management system (not illustrated) that manages the document  350  including the document element  352 . 
     The update may be automatically performed by the document service system  100  without waiting for the check of the user. As another example, the user is required to check whether or not the update is performed. In a case where an instruction to perform update is obtained from the user, the document service system  100  may perform the update. 
       FIG. 14  illustrates an example of a processing procedure of the document service system  100  in the example of  FIG. 13 . In the procedure of  FIG. 12 , steps of performing the similar processing to the procedure of  FIG. 10  are denoted by the identical reference signs, and description thereof will be omitted. 
     In the procedure of  FIG. 14 , the processor  102  examines whether or not a document element (referred to as a target element) having a relation of “citation” to the changed document element (referred to as a changed element) is provided among document elements extracted in S 40 . In a case where the target element is provided, the processor updates the element content of the target element in the database in the document service system  100  and the document in the document management system that manages the document including the target element, so as to match with the changed content of the changed element (S 55 ). With this update, the content characteristic, the last updater, the update date and time, and the like of the element property of the target element in the database and the document characteristic, the last updater, the update date and time, and the like of the document property (see  FIG. 6 ) of the document including the target element are also updated. 
     The processor  102  provides the client  30  with a screen for inquiring whether or not to update the target element. In a case where an instruction to perform the update is made on the screen by the user, S 55  may be performed. In a case where an instruction indicating that the update is not performed is input from the user on the screen, the processor  102  does not perform S 55 . 
     The processor  102  generates the graph  310 , and highlights the node of the document element having a relation of “citation” to the changed document element in the graph  310 , in a special display form indicating “citation”. Then, the processor provides the client  30  with the information providing screen  300  including the graph  310  (S 42 B). 
     In the above description, the three examples of the information providing screen  300 , which are illustrated in  FIGS. 9, 11, and 13  are separately described. However, the display control in the three examples may be combined. For example, a document element having a relation to a changed document element is displayed in a display form corresponding to the type of relation, and, in a case where the latter document element is not changed after the former has been changed, the highlight indicating that the document element is not changed is added to the latter. 
       FIG. 15  illustrates another example of the graph  310  in the information providing screen  300  provided by the document service system  100  to the user. 
     The graph  310  illustrated in  FIG. 15  is obtained by adding a document element  334  and nodes of document elements A, B, C, D, X, and Y to the graph  310  illustrated in  FIG. 9  and changing the relation between the document elements  322  and  334  from “reference” to “similar”. As described above, “similar” has a higher similarity of the content between the document elements than the similarity for “reference”. 
     The document element  334  (element name “4. operating environment”) is a document element in the document  330 , and has a relation of “citation” to the changed document element  322  in the document  320 . The document elements A, B, and C have a relation of “citation”, “similar”, and “reference” to the document element  334 , respectively. The document element D has a relation of “citation” to the document element A. 
     The document elements X and Y have a relation of “citation” and “similar” to the document element  332 , respectively. 
     As described above, the document elements A, B, C, D, X, and Y which do not have a direct relation to the changed document element  322  are also displayed on the graph  310  of  FIG. 15 . The display control of the document element which does not have a direct relation to the changed document element will be described below. 
     Here, in the following description, a changed document element in a document designated by the user is referred to as a changed element, and a document element having a direct relation to the changed element is referred to as a primary element. An element having a relation to the primary element is referred to as a secondary element, and a document element having a relation to the secondary element is referred to as a tertiary element. In the example of  FIG. 15 , the document elements  322  and  324  are changed elements, and the document elements  332 ,  334  and  342  are primary elements. The document elements A, B, C, X, and Y are secondary elements, and the document element D is a tertiary element. The secondary and tertiary elements do not have a direct relation to the changed element. In the following description, a relation between the changed element and the primary element is referred to as a primary relation. A relation between the primary element and the secondary element is referred to as a secondary relation. A relation between the secondary element and the tertiary element is referred to as a tertiary relation. In general, the relation between the (n−1)-th ordered element and the n-th ordered element is an n-ordered relation (n is an integer of 1 or more). However, in this case, the changed element is a zero-order element. 
     First, the processor  102  of the document service system  100  restricts the types of secondary relations to be included in the graph  310 , that is, to be displayed, in accordance with the type of the corresponding primary relation. That is, as the type of the primary relation becomes “stronger”, the number of the types of the corresponding secondary relations included in the graph  310  are increased. The “weaker” relation is harder to be included in the graph  310 . The primary relation is included in the graph  310  regardless of the type, but, regarding the secondary relation, only the type restricted in accordance with the type of the corresponding primary relation is included in the graph  310 . In the three types of relations exemplified above, “citation”, “similar”, and “reference”, “citation” is the strongest, the next is “similar”, and the weakest is “reference”. The strength relation reflects the magnitude relation of the content similarity between the document elements forming the respective types of relations. 
     In the example of  FIG. 15 , in a case where the primary relation is “citation”, all three types of secondary relations are displayed. In a case where the primary relation is “similar”, only two types of secondary relations of “citation” and “similar” are displayed. In a case where the primary relation is “reference”, only one type of secondary relation “citation” is displayed. 
     For example, regarding the primary element  334  having a primary relation of “citation” to the changed element  322 , all types of secondary relations “citation” (that is, relation to the secondary element A), “similarity” (that is, relation to the secondary element B), and “reference” (that is, relation to the secondary element C) are displayed. 
     On the other hand, regarding the primary element  332  having a primary relation of “similar” to the changed element  322 , only two types of secondary relations “citation” (that is, relation to the secondary element X) and “similar” (that is, relation to the secondary element Y) are displayed. Even though there is a secondary element having a secondary relation of the type “reference” to the primary element  332 , the secondary relation and the secondary element are not displayed on the graph  310 . 
     Regarding the primary element  342  having a primary relation of “reference” to the changed element  324 , the secondary relation and the secondary element are not displayed on the graph  310 . For the primary element having the primary relation of “reference” to the changed element, the secondary relation of the type “citation” being the strongest may be displayed. However, in the example of  FIG. 15 , the secondary element having a secondary relation of “citation” to the primary element  342  is not provided. Thus, such a secondary element is not displayed. Even though the secondary element having a relation of “similar” or “reference” to the primary element  342  is provided, this secondary element is not displayed on the graph  310 . 
     The processor  102  may determine the upper limit value of n of the n-th ordered relation included in the graph  310 , in accordance with the type of the primary relation. 
     In the example of  FIG. 15 , regarding a relation extending from the primary relation of “citation” between the document elements  322  and  334 , the relation up to the third order in maximum is included in the graph  310 . On the contrary, regarding a relation extending from the primary relation of “similar” weaker than “citation”, the relation is included in the graph  310  only up to the second order. Since the primary relation between the document elements  322  and  332  is “similar”, even in a case where a tertiary element having a strong tertiary relation such as “citation” to the secondary element X related to the primary element  332  is provided, the tertiary relation and the tertiary element are not displayed on the graph  310 . 
     In the example of  FIG. 15 , even though a document element is related to the changed document element in the document searched in S 32 , the document element included in the identical document (that is, searched document) to a document of the changed document element is not displayed on the graph  310  provided for the user. This is because the user does not normally have an edit authority for the searched document or the document element in the searched document. However, for each document element related to the changed document element, whether or not the user has an edit authority is checked. In a case where the user has the edit authority, even the document element in the identical document to the document for the changed document element may be displayed on the graph  310 . 
     Another Example of Service 
     In the example described above, the document service system  100  simply records the change of the document element in the database at a time point at which the document service system detects the change of the document element. Information on the change is provided to the user at a time point at which the user designates a document including the document element, and the information providing screen  300  for the document is provided to the user in response to the designation. 
     As another example of this, processing of notifying a participant of another document element having a relation to a document element in a case where the document service system  100  detects that the content of the document element has been changed will be described below. 
       FIG. 16  illustrates an example of the procedure of this processing. The procedure of  FIG. 16  illustrates a group of steps following S 28  in the procedure illustrated in  FIG. 4 . 
     In the procedure of  FIG. 16 , in a case where the processor  102  detects the changed document element in S 22  (see  FIG. 4 ), the processor  102  extracts a document element group having a relation to the changed document element from relation information (see  FIG. 8 ) in the database (S 60 ). The processor  102  obtains information on a participant of the document element from the database for each extracted document element and notifies the participant of the change in a notification method corresponding to the type of relation (S 62 ). A plurality of methods, for example, as follows are provided as a method of notifying the participant: a method of displaying the notification in a notification field on a portal page displayed in a case where the participant logs into the document service system  100 ; a method of display a message for causing the change to be known, on a screen such as the information providing screen  300  provided to the participant by the document service system  100  in a form of a pop-up screen; and a method of transmitting an e-mail to an e-mail address of the participant, which has been registered in the document service system  100  by the participant. The notification field is not displayed so long as the participant does not log into the document service system  100 . However, the notification by e-mail reaches the participant even in a period in which the participant does not log into the document service system  100 . Thus, the e-mail is more noticeable to the participant. In S 62 , the notification is performed by a method which is more noticeable to the participant as the type of the relation is stronger. For example, in a case where the type of the relation is “reference” and “similar”, only display in the notification field on the portal page of the participant is performed. However, in a case where the type of the relation is “citation” being stronger than others, the participant is notified by e-mail in addition to the display into the notification field. 
     The exemplary embodiment described above are merely exemplary, and various modifications may be made within the scope of the present disclosure. 
     For example, in the exemplary embodiment, the type of the relation between the document elements is determined in accordance with the similarity of the content between the document elements, but this is just an example. 
     For example, a user who has created or updated a document element may register another document element having a relation with the document element and the type of the relation in the document service system  100 . 
     A device that provides a user with a function of editing a document (for example, a document editing application provided by the client  30 ) may determine a relation between document elements in accordance with an operation performed by the user while the user is editing a document element, and the device may register the determined relation in the document service system  100 . For example, in a case where the user copies a document element a in a document A opened on a screen of the device to a document element b in another document B opened on the screen by a copy and paste operation, the device determines that the document element b has the type of relation of “citation” to the document element a. Then, the device registers the relation of “citation” in the document service system  100 . For example, in a case where another document element d is opened on the screen (copy and paste of the document elements d to c is not performed) while the user is editing a document element c opened on the screen, the device determines that the document element c has a relation of “reference” to the document element d. 
     Exemplary Embodiment of Association Between Document Elements 
     In the above-described example, descriptions are made focusing on a method of determining the type of relation based on the similarity between contents of the document elements, as a method of associating the document elements (that is, determining the type of relation between the two document elements) with each other. The similarity used here indicates the degree of the similarity between the entire contents of two document elements. 
     Another method of associating document elements with each other will be described below. In this method, a document element is divided into a plurality of parts, and similarity between the parts in the document elements is obtained. Then, the type of relation between the document elements is determined based on the similarity between the parts. In this method, the attribute of the document element is applied to determination of the type of relation between the document elements. 
     Here, the “part” configuring the document element refers to a document element located at a level lower than the document element in a tree-like structure of the document, which is obtained by analyzing the structure of the document. For example, regarding a document element at a chapter level, a document element at a level of a section or a paragraph corresponding to a descendant of the document element on a tree-like structure is an example of the “part”. 
     In one example, the attribute of a document including the document element is directly used as the attribute of the document element used as a material for determining the type of relation between the document elements. The attributes of a document, which are used as the attributes of the document element include a storage location, a creator, the creation date and time, the last updater, the update date and time, the acquisition date and time, a search tag assigned to the document by a person, and the like. 
     An attribute unique to a document element may be used as the material for determining a relation between document elements. For example, in a case of a system that manages the history of creation or update for each document element, attributes such as a creator, the creation date and time, the update date and time, and the last updater of the document element may be recorded. 
     The type of relation between document elements may be determined based on one specific attribute of the document elements, or may be determined based on a set of a plurality of specific attributes (for example, a set of a storage location and a creator). 
     The types of relation between document elements include, for example, citation, being similar, and reference. The type of relation may be freely defined by the user of the system. A case where there is no relation between document elements may be defined as one of the types of relation (for example, type named “unrelated”) between document elements. 
     In the exemplary embodiment, the type of relation between document elements is determined using an AI (artificial intelligence). The AI receives an input including feature information indicating a feature of similarity between contents of two document elements and attributes of the two document elements, and performs learning in response to the input, so as to output the type of relation between the two document elements. Here, the feature information indicating the feature of the similarity between the contents of the two document elements is obtained based on similarity information indicating the similarity between parts of the two document elements. The similarity information indicating the similarity between the parts refers to, for example, similarity between the contents of the parts. The AI (not illustrated) is built in the document service system  100  (see  FIG. 1 ) or in a device that can communicate with the document service system  100 . A method of mounting the AI is not particularly limited. Any known machine learning method such as a regression method (for example, a neural network and a support vector machine), or a method using a tree such as a decision tree may be used. The AI may be configured as software, configured as a hardware circuit, or configured as a combination of a hardware circuit and software. 
       FIG. 17  illustrates an example of a processing procedure of causing the AI to determine the type of relation between document elements by machine learning. Description will be made below on the assumption that the processor  102  in the document service system  100  performs the processing procedure. However, this is just an example, and a learning system for causing the AI to perform learning may perform the processing procedure. In this case, the document service system  100  uses the learned AI. 
     In the processing procedure, the processor  102  acquires learning sample data (S 70 ). The sample data includes a large number of pairs of document elements, and further includes additional information for each pair. The additional information includes the attribute of each document element included in the pair and information on the type of relation between the document elements. The information on this type of relation is used as teacher data in a case where the AI is caused to perform learning. For example, such information is set for the pair by a person in advance. 
     Then, the processor  102  divides each document element of the pair into paragraph units (S 72 ). The paragraph is an example of a part configuring the document element. The paragraph is configured with one or more sentences. 
     The processor  102  calculates similarity between paragraphs in the document elements of the pair (S 74 ). In this step, the processor calculates the similarity for all combinations which may be obtained by the paragraph of one document element and the paragraph of the other document element in the pair. 
     For example, in the example of  FIG. 18 , a document element A- 1  in a document A includes three paragraphs A- 1 - 1 , A- 1 - 2 , and A- 1 - 3 . A document element B- 1  in a document B includes three paragraphs B- 1 - 1 , B- 1 - 2 , and B- 1 - 3 . In the example, nine combinations of 3×3 paragraphs are obtained with the document elements A- 1  and B- 1 . In S 74 , the similarity is calculated for each of the nine combinations. Here, the similarity between paragraphs may be obtained, for example, in a manner that a text string included in each paragraph is vectorized, and the degree of similarity between the obtained vectors is calculated with a known method such as cosine similarity. As a method of vectorizing a text string of a document element, various methods such as TF-IDF and doc2vec are provided. FIG. illustrates information on the similarity between paragraphs in document elements, which has been obtained in this manner. In  FIG. 19 , IDs of two paragraphs are registered in fields of “Paragraph  1 ” and “Paragraph  2 ”. The similarity between the two paragraphs is registered in a field of the similarity. The example of  FIG. 19  shows values as the calculation results of the similarity for three of the nine combinations. 
     The processor  102  generates feature information indicating the similarity between the document elements, from the information on the similarity between the paragraphs in the document elements, which has been calculated in S 74  (S 76 ). 
     In one example, the processor obtains the feature information indicating the similarity between document elements, from one or more representative values selected in accordance with a predetermined criterion among similarities between paragraphs in the document elements. For example, the maximum value of the similarity between paragraphs in the document elements may be selected as a representative value, and the maximum value may be used as the feature information. 
     As another example, among similarities between paragraphs in the document elements, similarities which correspond to a higher level and of which the number is a predetermined value, or similarities which are equal to or greater than a threshold value may be selected as the representative values. The statistical feature amount (for example, average value, median value, or most frequent value) of distribution of the selected representative values may be used as the feature information. In addition, a set of a plurality of statistical feature amounts of distribution of the selected representative values (for example, set of the maximum value and the average value, and set of the maximum value and the half-value width) may be used as the feature information. From another viewpoint, in the example, several representative pairs are selected based on the similarity among pairs of paragraphs between document elements, and the feature information indicating the feature of the similarity between the document elements is calculated based on the similarity of the representative pair. 
     As another example, the statistical feature amount of the entire distribution of similarity between paragraphs in document elements, or a set of the feature amounts may be used as the feature information indicating the similarity between the document elements. 
     Then, the processor  102  causes the AI to perform learning, by applying input data and teacher data to the AI (S 78 ). The feature information on the pair of the document elements, which has been generated in S 76 , and one or more predetermined attributes of each document element are set as the input data. The information indicating the type of relation of the pair is set as the teacher data. 
     The steps of S 72  to S 78  are repeated for each pair of sentence elements included in the prepared sample data, and thereby the AI can obtain the type of relation between the document elements from the input feature information on the pair of the document elements and the input attribute of each document element. 
     Next, an example of a processing procedure of obtaining the type of relation between document elements using the learned AI will be described with reference to  FIG. 20 . The processing procedure is performed by the processor  102  in the document service system  100 . The processing procedure is an example of the detailed processing of S 17  in a procedure of constructing and maintaining the database, which is illustrated in  FIG. 4 . In S 17 , the processor calculates the content similarity between the document elements, and obtains the type of relation from the content similarity. However, in the procedure of  FIG. 20 , the learned AI is used for determining the type of relation. 
     In the procedure of  FIG. 20 , the processor  102  performs the processing of S 80  to S 92  for each document element in an interested document (that is, document acquired in S 10  of  FIG. 4 ). The document element as a target of the processing of S 80  to S 92  is referred to as an interested element below. 
     The processor  102  acquires information on each paragraph included in the interested element from the database (S 80 ). The paragraph is the lowest-level document element in a tree structure formed by a group of document elements in the document. The tree structure is obtained in S 12  of the procedure of  FIG. 4 . In S 80 , the processor  102  acquires information on, for example, a sentence of each paragraph corresponding to the descendant of the interested element in the tree structure. 
     Then, the processor  102  performs the processing of S 82  to S 92  for each document element (referred to as a partner element below) in the database. In the processing, the type of relation between the interested element and the partner element is registered in the database. 
     More specifically, the processor  102  firstly acquires the information on the paragraph included in the partner element from the database (S 82 ). Then, the processor  102  calculates the similarity between paragraphs in the interested element and the partner element (S 84 ), and generates feature information indicating the similarity between the interested element and the partner element from the calculated similarity group (S 86 ). The processing of S 84  and S 86  is similar to the processing of S 74  and S 76  in  FIG. 17 . 
     The processor  102  inputs the feature information generated in S 86 , one or more predetermined attributes of the interested element, and one or more predetermined attributes of the partner element to the learned AI (S 88 ). In response to the input, the AI outputs information on the type of relation between the interested element and the partner element. 
     Then, the processor  102  determines whether or not the type of relation output from the AI is other than “unrelated” (S 90 ). In a case where the determination result is Yes, the processor  102  registers the value output by the AI, as the type of relation between the interested element and the partner element, in relation information in the database (S 92 ). The relation information here is different from the relation information illustrated in  FIG. 8  in that the field of the similarity is not included. In a case where the determination result in S 90  is No, the processor  102  skips S 92  or registers a value indicating unrelation, as the type of relation between the interested element and the partner element, in the relation information. 
     Descriptions are made above on the assumption that the procedure of  FIG. 20  is the detailed procedure of S 17  in the procedure of  FIG. 4 . However, the procedure of  FIG. 20  may be performed on two input document elements regardless of the procedure of  FIG. 4 . 
     Next, another example of the procedure of determining the type of relation between document elements will be described with reference to  FIG. 21 . 
     In the procedure of  FIG. 20 , for all paragraphs in the interested element, the similarity to each paragraph of the document element in the database is calculated. However, in the procedure of  FIG. 21 , only for the paragraph which has been previously changed, the similarity to a paragraph in another document element is re-calculated. The processing procedure of  FIG. 21  is an example of the detailed processing of S 26  in the procedure illustrated in  FIG. 4 . 
     In the procedure of  FIG. 21 , the processor  102  performs processing of S 100  to S 112  for each document element (referred to as an interested element below) determined to be changed in S 20  in  FIG. 4  among document elements in the interested document (that is, document acquired in S 10  in  FIG. 4 ). 
     The processor  102  acquires information on each paragraph included in the interested element from the database (S 100 ). Then, the processor  102  specifies a paragraph which has been changed after the previous acquisition, among paragraphs in the interested element (S 101 ). In S 101 , for example, for each paragraph in the acquired interested element, the processor determines whether or not the paragraph is changed, by comparing the content of the paragraph to the content of the paragraph stored in the database. 
     Then, the processor  102  performs the processing of S 102  to S 112  for each document element (referred to as a partner element below) in the database. 
     More specifically, the processor  102  firstly acquires the information on the paragraph included in the partner element from the database (S 102 ). Then, the processor  102  calculates the similarity of the changed paragraph specified in S 101  among the paragraphs in the interested element, to each paragraph in the partner element (S 104   a ). For a paragraph determined not to be changed in S 101  among the paragraphs in the interested element, the processor  102  acquires the similarity between this paragraph and each paragraph in the partner element, from the database (S 104   b ). The latest similarity between paragraphs, which has been previously calculated is stored in the database (for example, see  FIG. 19 ). In S 104   b , the processor acquires the similarity between the paragraphs from the stored information. The information on the similarity recalculated in S 104   a  among pieces of information on the similarity between paragraphs in the database is applied into the database at an appropriate timing (for example, after the processing in  FIG. 21  is ended). 
     In a case where the similarity between paragraphs, which has been calculated in S 104   a  is compared with the similarity between paragraphs, which has been acquired in S 104   b , the similarity is obtained for all combinations of the paragraphs in the interested element and the paragraphs in the partner element. The processor  102  generates feature information indicating the similarity between the interested element and the partner element, from the group of the similarity between paragraphs, which has been calculated in S 104   a  and the group of the similarity between paragraphs, which has been acquired in S 104   b  (S 106 ). The processing of S 106  may be similar to the processing of S 86  in the procedure of  FIG. 20 . 
     The processor  102  inputs the feature information generated in S 106 , one or more predetermined attributes of the interested element, and one or more predetermined attributes of the partner element to the learned AI (S 108 ), and thus obtains information on the type of relation output by the AI in response to the input. The processor  102  determines whether or not the type of relation output from the AI is other than “unrelated” (S 110 ). In a case where the determination result is Yes, the processor  102  registers the value output by the AI, as the type of relation between the interested element and the partner element, in relation information in the database (S 112 ). In a case where the determination result in S 110  is No, the processor  102  skips S 112  or registers a value indicating unrelation, as the type of relation between the interested element and the partner element, in the relation information. 
     Descriptions are made above on the assumption that the procedure of  FIG. 21  is the detailed procedure of S 26  in the procedure of  FIG. 4 . However, the procedure of  FIG. 21  may be performed on two input document elements regardless of the procedure of  FIG. 4 . 
     In S 74  and S 76 , S 84  and S 86 , S 104   a , S 104   b , and S 106  in the procedures illustrated in  FIGS. 17, 20, and 21 , the similarity between the contents of the paragraphs is used. Instead of the similarity itself, another evaluation value may be used based on the similarity. For example, the processor may obtain an evaluation value indicating the similarity between paragraphs, based on a combination of the similarity between the contents of two paragraphs and the attributes of the two paragraphs. Then, the processor may use the evaluation value instead of the similarity in the above steps. For this, for example, the processor may use a function for calculating the evaluation value from the similarity between two paragraphs and a specific attribute of each paragraph. In a more specific example, as a function for calculating an evaluation value from the similarity and the attribute “last updater”, a function of causing the evaluation value to be higher in a case where the last updaters of two paragraphs are identical to each other than in a case where the last updaters are different from each other even though the similarity is equal is used. As the attribute of the paragraph, the attribute of the document element including the paragraph or the attribute of the document including the document element may be used. An attribute unique to a paragraph may be provided for each paragraph. 
     A case using a paragraph as apart configuring a document element is described above as an example, but this is just an example. A part configuring a document element A may be a document element being a descendant of the document element Ain a tree structure of a document element group configuring the document. 
     In the example described with reference to  FIGS. 17 to 21 , the AI obtains the type of relation between document elements. However, regardless of the type of relation, the AI may obtain any type of information indicating the relation between document elements, for example, the presence or absence of the relation and strength of the relation. 
     In the method of associating document elements described above, the feature information indicating the similarity between document elements is obtained from the similarity between parts (for example, paragraphs) configuring the document elements. For this reason, for example, in a case where there are pairs of parts, which are very similar to each other even though parts are little similar to each other in all document elements, the similarity between the contents of the document elements may be determined to be high. Also, in this method, considering not only the similarity between the contents of the document elements but also the attributes of the document elements, the type of relation between the document elements is determined. Thus, the more accurate determination result is expected to be obtained than a case of not considering the attributes. 
     In the exemplary embodiment described above, the document element is an element that forms a document. Here, there may be a document in a larger unit having individual documents managed by the document management system as constituent elements. In this case, the former individual document is a document element for the latter large unit document. For example, in a case where a hypertext configured with a plurality of documents linked by hyperlinks is regarded as a document of a large unit, the plurality of documents correspond to document elements in a case of being viewed from the hypertext. 
     The foregoing description of the exemplary embodiments of the present invention has been provided for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Obviously, many modifications and variations will be apparent to practitioners skilled in the art. The embodiments were chosen and described in order to best explain the principles of the invention and its practical applications, thereby enabling others skilled in the art to understand the invention for various embodiments and with the various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the following claims and their equivalents.