Patent Publication Number: US-2009228487-A1

Title: Image forming apparatus and access control method

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention is related to an image forming apparatus and an access control method, and more particularly to the image forming apparatus and the access control method for conducting an access control with respect to management information. 
     2. Description of the Related Art 
     In general, a memory capacity mounted in an image forming apparatus is less than a general computer. However, in some image forming apparatuses, information (for example, documents (image) information) is divided into a plurality tables to be managed, so as to suppress an information amount to load at once. In detail, in a case of managing information by a document unit, instead of managing all information regarding each document in one table, the information of the document is divided and managed in a plurality of tables: a table for managing a list of documents regarded as a management unit, a table for managing various information (for example, a page, a thumbnail, and a like) pertaining to the document, and a like. According to this management formation, when a thumbnail image is necessary, a record registered in the table of the thumbnail is simply loaded. Thus, it is not required to load information of the page and the like which is excessive information, to a memory. 
     Conventionally, as disclosed in Japanese Patent Application No. 2005-038371, in a case of dividing the management information into the plurality of tables and managing the plurality of tables, access control information such as an ACL (Access Control List) and a like is associated with each record for each table. 
     However, in many cases, it is appropriate to apply the same access control to both parent information corresponding to a document regarded as a management unit and child information accompanying the document. A user allowed to access the parent information is also allowed to access the child information. In order to realize the access control, in a conventional configuration, it is required to make consistency of the access control information respectively associating with the parent information and the child information. Thus, there is a problem in that a significantly complicated process is required. Also, there is another problem in that a consumption amount of the memory is increased by the access control information, since the access control information is redundantly managed. 
     SUMMARY OF THE INVENTION 
     The present invention solves or reduces one or more of the above problems. 
     In an aspect of this disclosure, there is provided an image forming apparatus, including: a first data management part configured to manage a list of first data concerning information regarded as a management unit; a second data management part configured to manage a list of second data concerning accompanying information which accompanies with the information regarded as the management unit; and a determination part configured to determine allowing or denying an operation request based on access control information recorded in a first recording medium associating with the first data with which the second data accompanies, in response to the operation request with respect to the second data. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the following, embodiments of the present invention will be described with reference to the accompanying drawings. 
         FIG. 1  is a diagram illustrating an example of a hardware configuration of an image forming apparatus according to an embodiment of the present invention; 
         FIG. 2  is a diagram illustrating an example of a software configuration of the image forming apparatus according to the embodiment of the present invention; 
         FIG. 3  is a conceptual diagram illustrating a configuration example of a database according to the embodiment of the present invention; 
         FIG. 4  is a diagram illustrating a configuration example of the database in a first implementation variation; 
         FIG. 5  is a diagram illustrating an example of a data structure of the database in the first implementation variation; 
         FIG. 6  is a diagram illustrating an example of recording a document table to a recording medium which is accessible at high speed in the first implementation variation; 
         FIG. 7  is a diagram for explaining a document cache table in the first implementation variation; 
         FIG. 8  is a diagram illustrating an example of recording only access right data of a few of operation types to the document cache table in the first implementation variation; 
         FIG. 9  is a diagram illustrating an example of a data structure of recording only the access right data of a few of operation types to the document cache table in the first implementation variation; 
         FIG. 10  is a sequence diagram for explaining process steps when a data operation is requested in the first implementation variation; 
         FIG. 11  is a diagram illustrating a configuration example of the database in a second implementation variation; 
         FIG. 12  is a diagram illustrating example of a data structure in the database of the second implementation variation; 
         FIG. 13  is a diagram illustrating an example of recording an access right table to a recording medium which is accessible at high speed in the second implementation variation; 
         FIG. 14  is a diagram for explaining an access right cache table in the second implementation variation; 
         FIG. 15  is a diagram illustrating an example of recording only the access right data of a few of operation types to the access cache table in the second implementation variation; 
         FIG. 16  is a diagram illustrating an example of a data structure of recording only the access right data of a few of operation types to the access right cache table in the second implementation variation; 
         FIG. 17  is a sequence diagram for explaining process steps when a data operation is requested in the second implementation variation; 
         FIG. 18  is a diagram illustrating a configuration example of the access right cache table in a third implementation variation; and 
         FIG. 19  is a sequence diagram for explaining an entry deletion process for deleting from the access right cache table in the third implementation variation. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     In the following, an embodiment of the present invention to will be described with reference to the accompanying drawings.  FIG. 1  is a diagram illustrating an example of a hardware configuration of an image forming apparatus according to an embodiment of the present invention. As an example of the image forming apparatus  10 ,  FIG. 1  illustrates a hardware configuration of a multi-functional apparatus realizing a plurality functions such as a printer, a copier, a scanner, a facsimile, and a like in a single chassis. 
     In  FIG. 1 , the image forming apparatus  10  includes a CPU (Central Processing Unit)  101 , a ROM (Read-Only Memory)  102 , a RAM (Random Access Memory)  103 , NVRAM (Non-Volatile RAM)  104 , an HDD (Hard Disk Drive)  105 , a LAN (Local Area Network) controller  106 , a facsimile device  107 , an image reading device  108 , a printing device  109 , an operation panel  110 , and a like, which are mutually connected to each other via a bus B. 
     The ROM  102 , the NVRAM  104 , the HDD  105 , or the like stores various programs, data used by the various programs, and a like. The RAM  103  is used as a storage area used to load a program, a working area of the program being loaded, and a like. The CPU  101  realizes functions described later, by processing the program loaded in the RAM  103 . 
     The LAN controller  106  realizes a communication through a network. The facsimile device  107  realizes facsimile sending and receiving functions. The image reading device  108  reads image data from a paper document. The printing device  109  prints the image data read by the image reading device  108 , image data received through the network, and a like, on a printing paper. The operation panel  110  is hardware including buttons, a liquid crystal panel, and a like for accepting an input from a user, notifying information to the user, and a like. 
       FIG. 2  is a diagram illustrating an example of a software configuration of the image forming apparatus  10  according to the embodiment of the present invention. In  FIG. 2 , the image forming apparatus  10  includes software functioning as a database  11 , a semantics DB (DataBase)  12 , a client  13 , a login management part  14 , and a like. 
     The database  11  is a so-called database engine, and systematically manages data subject to be managed in a predetermined format (for example, a spread sheet format such as a RDB (Relational Database). The semantics DB  12  interprets a meaning of data which are managed by the database  11 . That is, the database  11  is just a “box” which manages data in accordance with a schema being defined beforehand. The semantics DB  12  recognizes a meaning of the data stored the “box” and a concept of the data. The semantics DB  12  makes the database  11  conduct data management corresponding to the concept and also provides an operation means (an operation interface) corresponding to the concept. In  FIG. 2 , as the semantic DB  12 , a document management DB  121  and an account management DB  122  are illustrated. The document management DB  121  controls the database  11  to manage data concerning document information, and provides the operation means corresponding to the data to the client  13 . The account management DB  122  controls the database  11  to manage data concerning account information of a user, and provides the operation means corresponding to the data. 
     The client  13  expresses the entire program which uses (operates) the semantics DB  12 . The login management part  14  conducts an authentication for a user using the image forming apparatus  10  to log in, a management of a login state, and a like. 
       FIG. 3  is a conceptual diagram illustrating a configuration example of the database  11  according to the embodiment of the present invention. In  FIG. 3 , a management formation on the database  11  is conceptually depicted regarding the document information managed by the document management DB  121 . In the embodiment, the document information is managed by two tables: a document table  111  and a page table  112 . The document table  111  is a table for managing a list of data (sets of document data) expressing a document which is a maximum management unit of the document management DB  121 . That is, the document management DB  121  stores data (a record) for each document. In  FIG. 3 , document data A, B, and C are illustrated within the document table  111 . 
     The page table  112  is a table for managing a list of data (page data) concerning information for each page, as data accompanying or depending on a document. Accordingly, a plurality of sets of page data are associated with each set of document data A, B, and C of documents each including information of a plurality of pages. 
     In the management formation in which one set of the document information is divided into the plurality of tables, in the embodiment, access right data  113  is associated and shared with data (document data A, B, and C or page data) belonging to the same document information. The access right data  113  are data defining the access control information with respect to data as represented by the ACL (Access Control List). 
     That is, in this embodiment, instead of associating with the access control information for each set of data (each record) for each table (for example, for each set of document data A, B, and C and each set of page data), the access right data  113 , which are defined with respect to parent data (document data) of the maximum management unit in information subject to be managed, are applied to child data (page data) accompanying (belonging to) the data. By applying this management formation regarding the access control information, it is possible to easily realize consistency of the access control between the parent data and the child data, and it also reduces a consumption of resources for storing the access control information. 
     In the following, implementations of the management formation of the access right data  113  conceptually illustrated in  FIG. 3  will be described with separate examples in detail. 
       FIG. 4  is a diagram illustrating a configuration example of the database in a first implementation variation. In the first implementation variation as illustrated in  FIG. 4 , each set of the access right data  113  is included in each set of the document data A, B, and C. In  FIG. 4 , access right data  113   a  is included in the document data A, and access right data  113   b  is included in the document data B. The access right data  113  included in each set of the document data A, B, and C is applied to the page data belonging to the document data. In detail, the access right data  113   a  of the document data A are applied to data of page  1  (of the document data A) and data of page  2  (of the document data A). 
     In the first implementation variation, advantageously, it is possible to re-use the document table  111  which has existed, and it is also possible to simplify a design of a schema. 
       FIG. 5  is a diagram illustrating an example of a data structure of the database in the first implementation variation. In  FIG. 5 , each row of the document table  111  indicates one set of the document data, and each row of the page table  112  indicates one set of the page data. 
     The document table  111  manages data concerning items of identification, contents (bibliography information of a document name, creation date, and a like), and the access right data  113 . As illustrated, the access right data  113  forms a column of the document table  111 . In this configuration, the access right data  113  is included in the document data described with reference to  FIG. 4 . 
     In  FIG. 5 , a user name of a user possessing an operation right is registered for each type of operations (refer (R), write (W), and execute (X)). It should be noted that a configuration of the access right data  113  is not limited to the configuration illustrated in  FIG. 5 . For example, instead of for each user, the access control may be indicated with a role of the user. Alternatively, any one of various well-known configurations may be applied. The identification is used to identify each set of the document data A, B, and C. 
     On the other hand, the page table  112  manages identification, document identification, and contents (color, size, and a like of the bibliography information) for each set of the page data. The identification is used to identify each set of the page data. The document identification is used to identify the document data A, B, and C to which the page data belong. That is, by the document identification, it is possible to realize associating each set of page data with respective document data A, B, and C. 
     However, the access right data  113  are frequently used in searching for the document information or the like. Accordingly, if a recording location of the document table  111  including the access right data  113  is a recording medium which is accessible at higher speed than the page table  112 , it is possible to easily realize a high-speed search. 
       FIG. 6  is a diagram illustrating an example of recording the document table to the recording medium which is accessible at high speed in the first implementation variation. In the example in  FIG. 6 , the page table  112  is stored in the HDD  105 , and the document table  111  is stored in the NVRAM  104  which is accessible at higher speed than the HDD  105 . In general, an access speed affects a price of the recording medium. As shown in  FIG. 6 , instead of all tables forming the document information, only the document table  111  including the access right data  113  is stored in the recording medium which is accessible at the high speed. Accordingly, it is possible to reduce a storage space used in an expensive recording medium. 
     Moreover, in order to further save the area to use in the expensive recording medium, the following configuration may be applied.  FIG. 7  is a diagram for explaining the document cache table in the first implementation variation. 
     In  FIG. 7 , the document table  111  and the page table  112  are stored in HDD  105 . On the other hand, the document cache table  114  is formed in the NVRAM  104 . The document cache table  114  is used to cache the document data to use (operate). In  FIG. 7 , the document data A is copied to the document cache table  114 . 
     According to the configuration in  FIG. 7 , it is not required to store the entire document table  111  in the NVRAM  104 , and higher access speed can be realized to the access right data  113  of the document data, which are frequently accessed. Accordingly, compared with the configuration in  FIG. 6 , it is possible to further save the area to use in the expensive recording medium. It should be noted that the document cache table  114  is not always formed in a non-volatile recording medium. For example, the document cache table  114  may be formed in the non-volatile RAM  103 . 
     Moreover, in order to further save the area to use in the expensive recording medium, the following configuration may be applied.  FIG. 8  is a diagram illustrating an example of recording only the access right data of a few of operation types to the document cache table in the first implementation variation. 
     In  FIG. 8 , similar to  FIG. 7 , the document table  111  and the page table  112  are stored in the HDD  105 . The document cache table  114  is stores in the NVRAM  104 . However, the document cache table  114  has a different configuration. That is, in  FIG. 7 , the access right data  113  concerning one set of the document data are divided into the types of operations, the document data are recorded in the document cache table  114  by its division unit. The document table  111  in  FIG. 8  stores access right data R  113   ar  to refer, access right data W  113   aw  to write, and the access right data X  113   ax , which are divided from the access right data  113   a  of the document data A. Also, as an example, the access right data R  113   ar  alone are recorded in the document cache table  114 . 
     In general, in the access control information, information to refer to the document data A tends to be the most frequently accessed. Accordingly, by applying the configuration illustrated in  FIG. 8 , it is possible to realize higher access speed with respect to the most frequently accessed information, and it is possible to further save the area to use in the expensive recording medium. 
       FIG. 9  is a diagram illustrating an example of a data structure of recording only the access right data of a few of operation types to the document cache table in the first implementation variation. That is,  FIG. 9  illustrates a configuration example corresponding to the configuration in  FIG. 8  for each table. 
     As illustrated in  FIG. 9 , the access right data  113  concerning all operation types are not recorded in the document cache table  114 , and instead, only access right data  113   r  with respect to the refer (R) are recorded. The document table  111  and the page table  112  have the same configuration as illustrated in  FIG. 5 . 
     In the following, process steps of the image forming apparatus  10  in the first implementation variation will be described.  FIG. 10  is a sequence diagram for explaining process steps when a data operation is requested in the first implementation variation. 
     When the client  13  requests an operation (refers to a document name) with respect to document data (identification=0), which is conducted by a login user (Tanaka) (S 101 ), the document management DB  121  checks an access right with respect to this operation request (S 102 ) In detail, the document management DB  121  conducts a search of the document data indicated as an operation subject with respect to the document cache table  114  (S 103 ). When the document data are found, this process advances to step S 106 . When the document data are not found (not found in a cache), the document management DB  121  conducts the search similar to the step S 103 , with respect to the document table  111  (S 104 ) Subsequently, the document management DB  121  creates a record of the document data being searched, to the document cache table  114  (S 105 ). Then, the document data being searched are cached. 
     The process advances to step S 106 . In the step S 106 , the document management DB  121  acquires the access right data  113  corresponding to a requested operation type from the document data (hereinafter, called “current document data”) searched in the step S 103  or the step S 104 , and determines presence or absence of a right of the operation for the login user. If the login user has the right for the operation, the document management DB  121  conducts the operation (refers to the document name) with respect to the current document data (S 107 ), and returns an operation result to the client  13  (S 108 ). 
     Subsequently, when the client  13  requests an operation (refers to the size) to page data (identification=0) which belongs to the current document data, which is conducted by the login user (Tanaka) (S 109 ), the document management DB  121  checks the access right for this operation request (S 110 ). In detail, the document management DB  121  determines identification of parent document data to which page data belongs, by searching for document identification of the page data being the operation subject (S 111 ). 
     Subsequently, the parent document data are searched for with respect to the document cache table  114  (S 112 ). As illustrated in  FIG. 10 , in a case in that the parent document data has already been searched for, the parent document data can be searched for from the document cache table  114  at high possibility. However, if the search in the step S 112  fails, the parent document data may be searched from the document table  111 . 
     Subsequently, the document management DB  121  acquires the access right data  113  corresponding to the requested operation type from a searched parent document data, and determines presence or absence of a right of the operation which is conducted by the login user (S 113 ). The document management DB  121  determines presence or absence of the right with respect to page data to which belongs to the parent document data, based on the presence or absence of the right to the parent document data. Accordingly, the access right data  113  for the parent document data are applied to the page data. 
     If the right of the operation is given to the parent document data, the document management DB  121  searches for page data indicated as an operation subject with respect to the page table  112  (S 114 ). Subsequently, the document management DB  121  conducts the operation (refers to the size) to searched page data (S 115 ), and returns an operation result to the client  13  (S 116 ). 
     Next, a second implementation variation of the databases will be described.  FIG. 11  is a diagram illustrating a configuration example of the database in the second implementation variation. As illustrated in  FIG. 11 , in the second implementation variation, the access right data  113  is managed by associating with corresponding document data in the access right table  115  which is different from the document table  111 . 
     In the second implementation variation, advantageously, it is not required to define a schema for storing the access right data  113  for each of the semantics DB  12 . In detail, it is possible for the document management DB  121  and the account management DB  122  to use the same access right table  115 . Moreover, even if it is not possible to use the access right table  115  having the same contents, it is possible to use the access right table  115  having the same configuration. 
       FIG. 12  is a diagram illustrating example of a data structure in the database of the second implementation variation. 
     In  FIG. 12 , the document table  111  does not include a column of the access right data  113 . The page table  112  is the same as that in the first implementation variation. The access right table  115  manages identification, document identification, and a like for each set of the access right data  113 . The identification is used to identify each set of the access right data  113 . The document identification is used to identify the document data corresponding to the access right data  113 . That is, it can be realized to associate each set of access right data  113  with the document data by using the document identification. 
     In  FIG. 12 , an example is illustrated in that relations from the access right data  113  to the document data. Accordingly, the page data are indirectly associated with the access right data  113  through the document data. It may be possible to maintain identification of the page data in the access right table  115 . Also, in the document table  111  and the page table  112 , identification for the access right data  113  may be maintained. Thereby, it is possible to realize bidirectional association. 
     Moreover, if a recording location of the access right table  115  including the access right data  113  is a recording medium which is accessible at higher speed than the document table  111  and the page table  112 , it is possible to easily realize a high-speed search. 
       FIG. 13  is a diagram illustrating an example of recording the access right table to the recording medium which is accessible at high speed in the second implementation variation. In the example in  FIG. 13 , the document table  111  and the page table  112  are stored in the HDD  105 , and the access right table  115  is stored in the NVRAM  104  which is accessible at higher speed than the HDD  105 . By this configuration, it is possible to obtain the same effect as the configuration in  FIG. 7 . Moreover, in the second implementation variation, since the access right data  113  is separated from the document data, it is possible to reduce the storage space used in the recording medium more than the configuration in  FIG. 7 . 
     Moreover, in order to further reduce the storage space used in the expensive recording medium, the following configuration may be applied.  FIG. 14  is a diagram for explaining the access right cache table in the second implementation variation. 
     In  FIG. 14 , the document table  111 , the page table  112 , and the access right table  115  are stored in the HDD  105 . On the other hand, an access right cache table  116  is formed in the NVRAM  104 . The access right cache table  116  is used to cache the access right data  113  which is used (operated). In the example in  FIG. 14 , the access right data  113   a  is copied to the access right cache table  116 . 
     According to the configuration, it is not required to store the entire contents of the access right table  115  in the NVRAM  104 , and higher access speed can be realized to the access right data  113  of the document data, which are frequently accessed. Accordingly, compared with the configuration in  FIG. 6 , it is possible to further reduce the storage space used in the expensive recording medium. It should be noted that the access right cache table  116  is not always formed in a non-volatile recording medium. For example, the access right cache table  116  may be formed in the non-volatile RAM  103 . 
     Moreover, in order to further reduce the storage space used in the expensive recording medium, the following configuration may be applied.  FIG. 15  is a diagram illustrating an example of recording only the access right data of a few of operation types to the access cache table in the second implementation variation. 
     In  FIG. 15 , similar to  FIG. 14 , the document table  111 , the page table  112 , and the access right table  115  are stored in the HDD  105 . The access right cache table  116  is stored in the NVRAM  104 . However, the access right cache table  116  has a different configuration. That is, in  FIG. 14 , similar to  FIG. 8 , the access right data  113  are divided into the types of operations, the access right data  113  are recorded in the access right cache table  116  by its division unit. The access right cache table  116  in  FIG. 15  stores access right data R  113   ar  to refer, access right data W  113   aw  to write, and the access right data X  113   ax.    
     Accordingly, by applying the configuration illustrated in  FIG. 15 , it is possible to realize higher access speed with respect to the most frequently accessed information, and it is possible to further reduce the storage space used in the expensive recording medium. 
       FIG. 16  is a diagram illustrating an example of a data structure of recording only the access right data of a few of operation types to the access right cache table in the second implementation variation. That is,  FIG. 16  illustrates a configuration example corresponding to the configuration in  FIG. 15  for each table. 
     As illustrated in  FIG. 16 , the access right data  113  concerning all operation types are not recorded in the access cache table  116 , and instead, only access right data  113   r  with respect to the refer (R) are recorded. The document table  111 , the page table  112 , and the access right table  115  have the same configuration as illustrated in  FIG. 12 . 
     In the following, process steps of the image forming apparatus  10  in the second implementation variation will be described.  FIG. 17  is a sequence diagram for explaining process steps when a data operation is requested in the second implementation variation. 
     When the client  13  requests an operation (refers to a document name) with respect to document data (identification=0), which is conducted by a login user (Tanaka) (S 201 ), the document management DB  121  checks an access right with respect to this operation request (S 202 ) In detail, the document management DB  121  conducts a search of the document data indicated as an operation subject with respect to the access right cache table  116  (S 203 ). When the access right data  113  are found, this process advances to step S 206 . When the access right data  113  are not found (not found in a cache), the document management DB  121  conducts the search similar to the step S 203 , with respect to the access right table  115  (S 204 ). Subsequently, the document management DB  121  creates a record of the access right data  113  being searched, to the access right cache table  116  (S 205 ). Then, the access right data  113  being searched are cached. 
     The process advances to step S 206 . In the step S 206 , the document management DB  121  acquires the access right data corresponding to a requested operation type from the access right data  113  (hereinafter, called “current access right data”) searched in the step S 203  or the step S 204 , and determines presence or absence of a right of the operation for the login user. If the login user has the right of the operation, the document management DB  121  searches for the document data indicated as an operation subject, from the document table  111  (S 207 ). Subsequently, the document management DB  121  conducts the operation (refers to the document name) with respect to the searched document data (S 208 ), and returns an operation result to the client  13  (S 209 ). 
     Operations to the page data in steps S 210 , S 211 , S 212 , S 213 , S 214 , S 215 , S 216 , and S 217  are the same as operations in the steps S 109 , S 110 , S 111 , S 112 , S 113 , S 114 , S 115 , and S 116  in  FIG. 10 , and the explanations thereof are omitted. However, by conducting the steps S 210  through S 217 , instead of the document data stored in the document cache table  114 , presence or absence of the access right for the page data is determined based on the access right data  113  stored in the access right cache table  116 . 
     In the first implementation variation and the second implementation variation, it is configured to cache the access right data  113 . However, a memory area for the cache is limited. In order to appropriately hit the cache at high possibility, it is required to properly determine selecting the access right data  113  to delete from a cache area. In the following, a method for deleting the access right data  113  which has cached will be described in a third implementation variation of the databases. In the third implementation variation, different portions from the second implementation variation will be explained. 
       FIG. 18  is a diagram illustrating a configuration example of the access right cache table in the third implementation variation. Different from the above-described implementation variations, in the third implementation variation, the access right cache table  116   a  further manages a subject who operated, for each access right cache data  114   r.    
     For example, in the step S 204  in  FIG. 17 , when the access right data  113  is registered to the access right cache table  116   a , a user name of a user concerning an operation request is registered as the subject who operated. That is, the subject who operated is a subject (user) concerning an operation by which the access right data  113  is stored in the cache. For example, the access right data R  113   r  of identification “ 10 ” is registered to the access right cache table  116   a  in response to the operation by a user of a user name “TANAKA”. 
     The subject who operated in the access right cache table  116   a  is used, when deleting the access right data R  113   r , which becomes unnecessary at high possibility, from the access right cache table  116   a.    
       FIG. 19  is a sequence diagram for explaining an entry deletion process for deleting from the access right cache table in the third implementation variation. 
     When the login management part  13  detects a logout (end of an operation) of a user, the user name of the user who logged out is informed to the document management DB  121  (S 301 ). The document management DB  121  conducts a process for deleting the access right data  113   r , which becomes unnecessary at high possibility, from the access right cache table  116   a  in response to the logout (S 302 ). 
     In detail, the document management DB  121  searches for the access right data  113   r  in which the subject who operated is the same as the user name concerning the logout, from the access right cache table  116   a  (S 303 ). Subsequently, the document management DB  121  deletes the searched access right data  113   r  from the access right cache table  116   a  (S 304 ). 
     That is, a method for clearing the cache in the third implementation variation is based on experiences in that the document data subject to use is different corresponding to a user at highly possibility. In detail, in many cases, a user of document data is a creator of the document data. In addition, in many cases, the user of the document data is a person working in the same group as the creator. In the third implementation variation, when a certain user logs out (a utilization state of the user is released), the access right data  113   r  in which the user is the subject who operated are deleted from access right cache table  116   b . According to this configuration, it is possible to properly select the access right data  113   r  as a deletion subject from the access right cache table  116   b.    
     Alternatively, the method for clearing the cache may be combined with a well-known algorithm (FIFO (First-In First-Out)), an LRU (Least Recently Used), or a like. In the third implementation variation, the access right cache table  116  is illustrated. Alternatively, in the same manner, a subject who operated may be recorded for the document cache table  114 , and the document data may be deleted simultaneously when a user logs out. 
     Moreover, the cache may be formed with multi-levels. In detail, a cache table is formed with multi-levels depending on an access speed of a recording medium, and the access right data  113 , which are pushed out in accordance with an algorithm such as the FIFO, the LRU, or the like, are moved to a recording medium of slower access speed level by level. When the logout occurs, the access right data  113  in which the subject who operated is the same as the user name concerning the logout are deleted. 
     According to the present invention, it is possible to provide an image forming apparatus and an access control method, which effectively manage and use the access control information. 
     The present invention is not limited to the specifically disclosed embodiments, and variations and modifications may be made without departing from the scope of the invention. 
     The present application is based on the Japanese Priority Patent Application No. 2008-054818 filed Mar. 5, 2008, the entire contents of which are hereby incorporated by reference.