Abstract:
The invention has an object to guarantee, when rewritable paper is used, authenticity of information shown on the rewritable paper. Provided is an information management method for managing information concerning a medium executed in an information management system including: the medium capable of representing on a surface thereof object information that is contents concerning an object; a management apparatus for managing a history of operation on the medium; and a printing apparatus for representing the object information on the medium and erasing the represented object information from the medium, the information management method comprising: holding, by the management apparatus, a correspondence among an identifier of the medium, the object information represented on the medium, and a valid period of the object; and recording, by the management apparatus, a start of the valid period of the object when the printing apparatus represents the object information on the medium.

Description:
CLAIM OF PRIORITY 
       [0001]    The present application claims priority from Japanese patent application JP 2006-130392 filed on May 9, 2006, the content of which is hereby incorporated by reference into this application. 
       BACKGROUND OF THE INVENTION 
       [0002]    This invention relates to an information management system for managing a medium like a document, and more particularly, to a technology for managing a medium whose information is rewritable. 
         [0003]    In recent years, more and more media (rewritable paper), whose information is rewritable, have been used. For instance, when the rewritable paper is applied to baggage tags in physical distribution, it becomes possible to use one sheet of paper multiple times, which contributes to conservation of the environment. Technologies for managing information mentioned on such baggage tags are proposed. 
         [0004]    For instance, in JP 2004-302614 A, a contents sharing system is disclosed which includes a print device, an RFID read device, a client terminal, and a data storage management apparatus. In this contents sharing system, correspondences, in which ID codes of RFID tags of information indication media with RFID tag, on which contents information saved in the data storage management apparatus on a network has been printed, and the contents information have been associated with each other on a one-to-one basis, are registered in the data storage management apparatus. In response to a request to rewrite contents information on an information indication medium, an ID code is read from an RFID tag of the information indication medium, contents information corresponding to the ID code is searched from the data storage management apparatus, and the found contents information is printed on another information indication medium with RFID tag. 
         [0005]    Also, in JP 2004-213372 A, a commodity management method is disclosed with which distribution information composed of various information generated by a distribution hub terminal at each distribution hub in a commodity distribution process is stored in a distribution DB. With this commodity management method, based on a search condition received from the distribution hub terminal, the distribution information corresponding to the search condition is searched from the distribution DB. This search condition includes at least a commodity code for identifying a commodity. 
         [0006]    When such rewritable paper is used, however, it is possible to rewrite indication contents thereof, so there has been a problem that it is not guaranteed that the information indicated on the rewritable paper is correct information written by a user having proper authority. In particular, as compared with a case where ordinary paper is used, in the case of the rewritable paper, it is difficult to notice a situation where mentioned information has been tampered, so it is required to guarantee that the mentioned information is authentic. 
         [0007]    This invention has an object to guarantee, when rewritable paper whose print contents are rewritable is used, authenticity of information shown on the rewritable paper. 
       SUMMARY OF THE INVENTION 
       [0008]    A representative aspect of this invention is as follows. That is, there is provided an information management method for managing information concerning a medium executed in an information management system including: the medium capable of representing on a surface thereof object information that is contents concerning an object; a management apparatus for managing a history of operation on the medium; and a printing apparatus for representing the object information on the medium and erasing the represented object information from the medium, the information management method comprising: holding, by the management apparatus, a correspondence among an identifier of the medium, the object information represented on the medium, and a valid period of the object; and recording, by the management apparatus, a start of the valid period of the object when the printing apparatus represents the object information on the medium. 
         [0009]    According to a mode of this invention, it becomes possible to confirm whether object information shown on a medium is authentic. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    The present invention can be appreciated by the description which follows in conjunction with the following figures, wherein: 
           [0011]      FIG. 1  is a conceptual diagram showing processing by an information management system according to an embodiment of this invention; 
           [0012]      FIG. 2  is an explanatory diagram showing a medium on which the information has been printed according to the embodiment of this invention; 
           [0013]      FIG. 3  is a block diagram showing a configuration of an information management system according to a first embodiment of this invention; 
           [0014]      FIG. 4  is an explanatory diagram showing a tag ID/object ID correspondence table according to the first embodiment of this invention; 
           [0015]      FIG. 5  is an explanatory diagram showing an object information according to the first embodiment of this invention; 
           [0016]      FIG. 6  is an explanatory diagram showing a print information according to the first embodiment of this invention; 
           [0017]      FIG. 7  is a construction diagram showing an additional contents information according to the first embodiment of this invention; 
           [0018]      FIG. 8A  is an explanatory diagram showing a user information concerning a user according to the first embodiment of this invention; 
           [0019]      FIG. 8B  is an explanatory diagram showing a user information concerning another user according to the first embodiment; 
           [0020]      FIG. 8C  is an explanatory diagram showing a user information concerning another user according to the first embodiment; 
           [0021]      FIG. 9  is an explanatory diagram showing a history information according to the first embodiment of this invention; 
           [0022]      FIG. 10  is an explanatory diagram showing obtainment of relative coordinates on paper by the digital pen according to the first embodiment of this invention; 
           [0023]      FIG. 11A  is an explanatory diagram showing an example of a stroke set according to a first embodiment of this invention; 
           [0024]      FIG. 11B  is an explanatory diagram of the stroke information according to the first embodiment of this invention; 
           [0025]      FIG. 12  is a flowchart showing tag print processing according to the first embodiment of this invention; 
           [0026]      FIG. 13  is a flowchart showing a tag read processing according to the first embodiment of this invention; 
           [0027]      FIG. 14  is a flowchart showing a tag write processing according to the first embodiment of this invention; 
           [0028]      FIG. 15  is a flowchart showing a tag erasing processing according to the first embodiment of this invention; 
           [0029]      FIG. 16  is a block diagram showing an information management system according to a second embodiment of this invention; 
           [0030]      FIG. 17  is a flowchart showing offline a data conversion processing according to the second embodiment of this invention; 
           [0031]      FIG. 18  is a detailed flowchart showing a offline data conversion processing according to the second embodiment of this invention. 
           [0032]      FIG. 19  is a flowchart showing a preparation processing for common key encryption communication according to the embodiments of this invention; 
           [0033]      FIG. 20  is a flowchart showing a preparation processing for public key/secret key encryption communication; and 
           [0034]      FIG. 21  is a flowchart showing a processing for searching for a series of procedures concerning an object. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0035]    First, an outline of this invention will be described. 
         [0036]      FIG. 1  is a conceptual diagram of processing by an information management system, to which this invention has been applied, and shows a life cycle of a rewritable medium in this invention. 
         [0037]    This invention manages a medium, electronic information relating to information shown on the medium, a time of writing onto the medium, and a time of changing of a state of the medium by associating them with one another using means for identifying the medium and means for obtaining the information written on the medium. In addition to the information shown on the medium itself, electronic information managed in this invention includes additional content relating to the information shown on the medium. 
         [0038]    First, a medium  1 , to which a uniquely identifiable identifier (medium ID) has been given, is created. It is possible to print characters and the like on a surface of this medium  1  and erase the characters and the like from the medium surface (1). It is possible to uniquely identify this medium. For instance, as this medium, it is possible to use paper to which a dot pattern that is recognizable by a digital pen has been given. Also, it is possible to use a wireless tag whose identifier is readable by a read device. Further, it is possible to use a two-dimensional barcode printed on paper. 
         [0039]    In addition, as a method of printing and erasing information printed on the medium, it is possible to use a technique with which switching between a color development state and a color erased state is achieved based on a cooling speed after heating using a leuco dye. Also, it is possible to use an erasable ink (e-blue, for instance) with which switching from a color development state to a color erased state is performed by cutting a binding between a color former and a coloring matter through heating and binding a color erasing agent and the coloring matter with each other. 
         [0040]    In this embodiment, as means for obtaining the medium ID, a digital pen is used. When the digital pen is used, it becomes possible to use an identifier (dot pattern ID) of a dot pattern on the medium obtained with the digital pen as the medium ID. 
         [0041]    After that, some information is printed on the created medium. In this case, the medium  1  (medium ID) and electronic information (print source file and additional contents, for instance) relating to the contents printed on the medium are linked to each other (2). For instance, as shown in  FIG. 2 , the medium  1 , on which the information has been printed, is affixed to a commodity  2  as a label and is used for identification of the commodity. 
         [0042]    Following this, in course of distribution, the medium ID is obtained by touching the medium using a digital pen  14 , an inquiry is issued to a server based on the obtained medium ID, and the linked electronic information is obtained (3). In this case, the electronic information may be provided after it has been confirmed that an operator has a right to obtain the electronic information. It is possible for the operator to confirm that the information printed on the medium is authentic by checking the obtained electronic information and the information printed on the medium against each other. 
         [0043]    Then, after information has been written on the medium using the digital pen  14 , the electronic information is updated to reflect the written information (4). Also when the information is written, after it has been confirmed that the operator has a right to obtain the electronic information, the electronic information is updated to reflect the written information. 
         [0044]    Next, when the information printed on the medium and the written information are erased, the medium becomes reusable. In this case, the link between the medium ID and the electronic information is cut (5). It is possible to use the medium, whose information has been erased and link with the electronic information has been cut, by printing information in (2) again. 
         [0045]    After that, when the medium undergoes writing and erasing many times, it becomes impossible to cleanly erase information on the medium, so the medium is disposed. In this case, it is stored that the medium has been disposed (6). 
         [0046]    In other words, in this invention, during a period from a time (2), at which the information has been printed on the medium, to a time (5) at which the information has been erased from the medium, the medium ID and the electronic information concerning the information shown on the medium are linked with each other. 
         [0047]    In other words, in an embodiment of this invention, the medium and the electronic information concerning the information shown on the medium are associated with each other and are managed using means for identifying the medium such as a combination of a digital pen and a dot pattern. In addition, the medium and the information written on the medium are associated with each other and are managed using hand-written information obtainment means. Then, when the information is printed on the medium, the medium and the electronic information are linked with each other. Also, when the information is erased from the medium, the link between the medium and the electronic information is removed. 
         [0048]    Next, embodiments of this invention will be described with reference to the accompanying drawings. 
       First Embodiment 
       [0049]      FIG. 3  is a block diagram showing a construction of an information management system according to a first embodiment. 
         [0050]    The information management system in the first embodiment includes a server  11 , client terminals  12 , digital pens  14 , a network  18 , and a location information server  19 . 
         [0051]    The server  11 , the client terminals  12 , and the location information server  19  are connected to one another through the network  18 . The client terminals  12  and the digital pens  14  are connected in a wireless manner based on Bluetooth, a wireless LAN, a mobile telephone system, infrared rays, or the like. Alternatively, the client terminals  12  and the digital pens  14  may be connected in a wired manner using a universal serial bus (USB) protocol or the like. 
         [0052]    The server  11  manages information concerning media and provides the client terminals  12  with the information concerning the media. The server  11  includes a calculation unit  111 , a data communication unit  112 , and a data management unit  113 . The calculation unit  111  includes a CPU and a memory. The CPU invokes and executes various programs, thereby performing computation concerning processing carried out at the server  11 . 
         [0053]    The data management unit  113  is constructed by a nonvolatile storage medium (magnetic disk drive, for instance) and stores the various programs executed at the calculation unit  111 . Also, the storage unit  113  stores a tag ID/object ID correspondence table  21  as shown in  FIG. 4 , object information  22  as shown in  FIG. 5 , print information  23  as shown in  FIG. 6 , additional contents information  24  as shown in  FIG. 7 , user information  25 A and the like as shown in  FIG. 8A ,  FIG. 8B , and  FIG. 8C , history information  26  as shown in  FIG. 9 , and stroke information  27  as shown in  FIG. 11B . 
         [0054]    The data communication unit  112  includes a network interface. The network interface is a LAN card that is capable of performing communication using a TCP/IP protocol, for instance. The server  11  is capable of communicating with a device connected to the network  18 , such as the client terminal  12 , through the network interface. 
         [0055]    Each client terminal  12  is a computer device used by a user and transfers information received from each digital pen  14  to the server  11 . To the client terminal  12 , printers  13  are connected. 
         [0056]    The client terminal  12  includes a calculation unit  121 , a data communication unit  122 , a pen input unit (not shown), an operation input unit (not shown), and a data display unit (not shown). The calculation unit  121  includes a CPU and a memory. The CPU invokes and executes various programs, thereby performing computation concerning processing carried out at the client terminal  12 . 
         [0057]    The data communication unit  122  is a network interface and is, for instance, a LAN card that is capable of performing communication using a TCP/IP protocol. With this construction, the client terminal  12  is capable of performing communication with the server  11  through the network  18 . 
         [0058]    The pen input unit is connected with the digital pen  14  in a wireless manner (in accordance with Bluetooth or a wireless LAN, for instance) or a wired manner (using a USB protocol, for instance) and collects information about coordinates and the like obtained by the digital pen  14 . It should be noted that the pen input unit and the data communication unit  122  may be the same interface. 
         [0059]    The operation input unit is a keyboard, for instance, and is used by a user to input information. The data display unit is constructed using a liquid crystal display, for instance, and displays information concerning a medium obtained from the server  11 . 
         [0060]    Each printer  13  prints information including a predetermined dot pattern on a medium according to an instruction from the client terminal  12 . As shown in  FIG. 2 , this medium, on which the information has been printed, is used as a label affixed to a commodity. 
         [0061]    Like in the case of an ordinary pen, with the digital pen  14 , it is possible to annotate characters, figures, and the like to a paper medium. Also, the digital pen  14  includes a micro-camera at its tip end and obtains image information of a dot pattern printed on the paper. Further, the digital pen  14  holds a pen ID set in advance. Still further, the digital pen  14  includes a communication interface for connection with the client terminal  12  in a wireless or wired manner. 
         [0062]    For instance, as shown in  FIG. 10 , the digital pen  14  obtains dot pattern information printed on a document. It is possible to calculate coordinates in a dot pattern space from this dot pattern information. Also, it is possible to identify coordinates on a paper plane from the dot pattern information obtained by the digital pen  14  by referring to the location information server  19 . 
         [0063]    It should be noted that it is also possible for the digital pen  14  to transmit, through a mobile telephone system or a wireless LAN system, the identified absolute coordinates, a time at which the dot pattern has been obtained, and the pen ID directly to the server  11  not through the client terminal  12 . 
         [0064]    The location information server  19  is a computer device including a CPU, a memory, a storage device and the like. The location information server  19  holds a database on which the absolute coordinates in the dot pattern space calculated by the digital pen  14  and the coordinates on the paper plane are associated with each other, and provides the coordinates on the paper plane based on the dot pattern on the paper plane. 
         [0065]      FIG. 4  is a construction diagram of the tag ID/object ID correspondence table  21  according to the first embodiment. 
         [0066]    The tag ID/object ID correspondence table  21  is information storing relations between media and information shown on the media and states of the media, and is stored in the data management unit  112  of the server  11 . The tag ID/object ID correspondence table  21  contains, for each medium, a tag ID  211  and a used object ID  212 . 
         [0067]    The tag ID  211  is a unique identifier of the medium. The used object ID  212  is a unique identifier of information shown on the medium. Attributes of the information identified by the object ID are recorded in the object information  22 . With the object ID, it is possible to identify the information printed on a surface of the medium as well as additional contents as shown in  FIG. 7  relating to the information printed on the surface of the medium. 
         [0068]    As the used object ID  212 , a state (“disposed” or “unused”) of the medium is stored as well. 
         [0069]    In other words, when the used object ID  212  is set at “disposed”, this means that the medium having the tag ID has been physically disposed. Therefore, by newly creating a medium having the same tag ID, it becomes possible to use this tag ID again. In this embodiment, even when the medium has been disposed, the tag ID is not deleted but data of the tag ID may be deleted. 
         [0070]    Also, when the used object ID  212  is set at “unused”, this means that the tag exists but is not used. More specifically, it is meant that the medium has been created but has never been used or the medium was used in the past but information has been erased, and therefore the used object ID has been erased. 
         [0071]    With the tag ID  211  and the used object ID  212  listed on the tag ID/object ID correspondence table  21 , it is possible to find a relation between the medium and the information shown on the medium. Also, the tag ID  211  and the used object ID  212  have a one-to-one relation at all times. In other words, the number of media possessing the tag ID is only one and the number of tags associated with the object ID is only one at all times. 
         [0072]    Then, through printing of the information on the surface of the medium, the tag ID  211  and the object ID  212  are linked with each other. Also, when the printed information is erased from the medium, or the medium, on which the information has been printed, is disposed, the link between the tag ID  211  and the object ID  212  is removed. 
         [0073]    Therefore, in read processing shown in  FIG. 13 , write processing shown in  FIG. 14 , and erase processing shown in  FIG. 15  to be described later, the object ID  212  is identified from the tag ID  211  and other information (object information  22  shown in  FIG. 5 , print information  23  shown in  FIG. 6 , additional contents information  24  shown in  FIG. 7 , user information  25  shown in  FIG. 8A  to  FIG. 8C , history information  26  shown in  FIG. 9 , and stroke information  27  shown in  FIG. 11B ) are searched for, so when the tag ID  211  and the used object ID  212  are not linked with each other on the tag ID/object ID correspondence table  21 , it is impossible to search for these information. The tag ID/object ID correspondence table  21  holds a link relation between the tag ID  211  and the used object ID  212  at a current time. Therefore, when the link between the tag ID and the used object ID is already removed, it is required to search for these information by referring to the object information  22  described below. 
         [0074]      FIG. 5  is a construction diagram of the object information  22  according to the first embodiment. 
         [0075]    The object information  22  is information storing an attribute of each object and is stored in the data management unit  112  of the server  11 . The object information  22  contains an object ID  220 , a tag ID  221 , a start date and time  222 , an end date and time  223 , a creation user ID  224 A, at least one read user ID  224 B, at least one write user ID  224 C, a print ID  225 , an additional contents ID  226 , a stroke ID  227 , and a history ID  228 . 
         [0076]    The object ID  220  is a unique identifier of information shown on a medium. The tag ID  221  is a unique identifier of the medium on which the information identified with the object ID has been shown. As the object ID  220  and the tag ID  221 , a pair that is the same as the pair of the used object ID  212  and the tag ID  211  recorded on the tag ID/object ID correspondence table  21  is recorded. 
         [0077]    The start date and time  222  is a date and time of printing of the information identified with the object ID on the medium. The end date and time  223  is a date and time of erasing of the information identified with the object ID from the medium. In other words, a period from the start date and time  222  to the end date and time  223  is a valid period of indication of the information identified with the object ID on the medium. 
         [0078]    The creation user ID  224 A is a unique identifier of a user who printed the information identified with the object ID on the medium. Each read user ID  224 B is a unique identifier of a user who is permitted to read information (additional contents or the like) relating to the information identified with the object ID. Each write user ID  224 C is a unique identifier of a use who is permitted to change the information identified with the object ID. It should be noted that in this example, multiple read user IDs  224 B and multiple write user IDs  224 C are registered, each user having a right with respect to each processing. 
         [0079]    The print ID  225  is a unique identifier of the information printed on the surface of the medium and is a link to the print information  23  as shown in  FIG. 6 . The print ID  225  is additionally recorded when information is overprinted on the medium (information is further printed without erasing already printed information). 
         [0080]    The additional contents ID  226  is a unique identifier of additional contents accompanying the information printed on the surface of the medium and is a link to the additional contents information  24  as shown in  FIG. 7 . 
         [0081]    The stroke ID  227  is a unique identifier of information (stroke set) hand-written on the surface of the medium and is a link to the stroke information  27  as shown in  FIG. 11B . When information is written on the medium, the stroke ID  227  is additionally recorded. 
         [0082]    Each stroke set is a collection of mutually related lines (strokes) and is obtained using layout analysis in character recognition, for instance. In the layout analysis, the mutually related lines are identified based on times, at which the lines have been annotated, and/or positional relations among the lines, thereby obtaining the stroke set. In other words, strokes annotated at near times and near locations constitute one stroke set. 
         [0083]    The history ID  228  is a link to the history information  28  as shown in  FIG. 9  showing a history of operation of the information identified with the object ID. 
         [0084]      FIG. 6  is a construction diagram of the print information  23  according to the first embodiment. 
         [0085]    The print information  23  is information concerning contents printed on a medium and is stored in the data management unit  112  of the server  11 . The print information  23  contains a print ID  230 , a print date and time  231 , a print user ID  232 , and print contents  233 . 
         [0086]    The print ID  230  is a unique identifier determined for each print processing onto the medium. The print date and time  231  is a date and time of printing of information onto the medium. The print user ID  232  is a unique identifier of a person who printed the information on the medium. The print contents  233  are a unique identifier of the contents printed on the medium and are a file name of electronic data printed. 
         [0087]      FIG. 7  is a construction diagram of the additional contents information  24  according to the first embodiment. 
         [0088]    The additional contents information  24  is information concerning additional contents accompanying information shown on a medium and is stored in the data management unit  112  of the server  11 . The additional contents information  24  contains an additional contents ID  240 , an addition date and time  241 , an addition user ID  242 , and additional data  243 . 
         [0089]    The contents ID  240  is a unique identifier of the additional contents. The addition date and time  241  is a date and time of addition of the contents. The addition user ID  242  is a unique identifier of a person who added the contents. 
         [0090]    The additional data  243  is the contents added to the information shown on the medium. It does not matter whether the additional data  243  is contents that are not printed on the medium or contents that overlap the contents printed on the medium. 
         [0091]      FIG. 8A  to  FIG. 8C  are each a construction diagram of the user information according to the first embodiment. 
         [0092]    The user information  25 A shown in  FIG. 8A  is information concerning a user, who uses the information management system according to this embodiment, and is stored in the data management unit  112  of the server  11 . The user information  25 A contains a user ID  250 A, a user name  251 A, at least one printer IDs  252 A, and at least one pen IDs  253 A. 
         [0093]    The user ID  250 A is a unique identifier of the user. The user name  251 A is a name (or company name) of the user. Each printer ID  252 A is a unique identifier of a printer  13  used by the user. Each pen ID  253 A is a unique identifier of a digital pen  14  possessed by the user. In this embodiment, multiple printer IDs  252 A and multiple pen IDs  253 A are registered. 
         [0094]    The user information  25 A has been described above. Other user information  25 B shown in  FIG. 8B  and user information  25 C shown in  FIG. 8C  also contain the same items and are stored in the data management unit  112  of the server  11 . 
         [0095]    In this specification, three types of users are described as the user information  25 A,  25 B, and  25 C. For instance, a user identified with “U0000123” is a producer of a commodity for which information has been printed (label has been created) on a medium. Also, a user identified with “U0000456” is a distributor of the commodity. Further, a user identified with “U0000789” is a consumer of the commodity. 
         [0096]    Here, when the object information  22  is referred to, it is shown that the user “U0000123” is a creation user, so it can be understood that the user is a person who printed the information (created the label) on the medium. Also, the user “U0000123” is a read user and a write user, so he/she has a right to read additional contents and a right to write information. 
         [0097]    On the other hand, the user “U0000456” is a read user but is not a write user, so he/she has a right to read the additional contents but does not have a right to write information on the medium and update the additional contents. Also, the user “U0000789” is a read user and is also a write user, so he/she has a right to read the additional contents and a right to write information. 
         [0098]    By changing read and write right limitations from user to user in this manner, it becomes possible to prevent tampering of information in the course of distribution. In other words, even when information shown on a medium is tampered, it becomes possible for a user to confirm whether the information shown on the medium is authentic by obtaining electronic information relating to the information shown on the medium and checking the obtained electronic information and the information indicated on the medium against each other. 
         [0099]      FIG. 9  is a construction diagram of the history information  26  according to the first embodiment. 
         [0100]    The history information  26  is information concerning operation performed on a medium of this embodiment and is generated when any operation is performed on the medium. The history information  26  is stored in the data management unit  112  of the server  11  and contains a history ID  260 , a operating date and time  261 , a operating user ID  262 , a operation tag ID  263 , a operation object ID  264 , a operation kind  265 , at least one operation ID  266 , and a operation result  267 . 
         [0101]    The history ID  260  is a unique identifier of operation. The operating date and time  261  is a date and time at which the operation has been performed. The operating user ID  262  is a unique identifier of a user who performed the operation. 
         [0102]    The operation tag ID  263  is a unique identifier of the medium that is a target of the operation. The operation object ID  264  is a unique identifier of information shown on the medium that is a target of the operation. 
         [0103]    The operation kind  265  indicates a kind of the operation. There are various operation kinds  265  such as “print”, “read”, “write”, “erase”, and “disposal”. When print processing shown in  FIG. 12  is carried out, “print” is recorded. When read processing shown in  FIG. 13  is carried out, “read” is recorded. When write processing shown in  FIG. 14  is carried out, “write” is recorded. When erase processing shown in  FIG. 15  is carried out, “erase” is recorded. 
         [0104]    Each operation ID  266  is information used in the operation. In an example shown in  FIG. 9 , it is recorded that printing identified with a print ID “I0054213” has been performed and additional contents identified with “H0099875” have been generated as a result of the printing. It should be noted that when the operation kind  265  is “write”, stroke information  27  is recorded as a operation ID  266 . 
         [0105]    The operation result  267  shows a result of the operation and “success” or “failure” is recorded. 
         [0106]      FIG. 10  is an explanatory diagram of obtainment of relative coordinates on paper by the digital pen  14  according to the embodiment of this invention. 
         [0107]    The digital pen  14  comprises a CPU, a memory, a communication interface, a camera  141 , a battery, and a writing pressure sensor. Further, the digital pen  14  comprises a pen tip with which it is possible to write characters, symbols, and the like on paper with ink or graphite. 
         [0108]    The digital pen  14  is used together with a medium (sheet)  20  on which dots  203  for location detection have been printed. Here, the dots  203  will be described by magnifying a part  201  of the sheet  20 . On the sheet  20 , multiple small dots  203  have been printed. Those dots  203  have been printed at locations displaced from intersections (reference points)  202  of virtual lattice lines upwardly, downwardly, rightwardly, or leftwardly. 
         [0109]    When a character or a figure is annotated to the paper with the digital pen  14 , the annotated character or the like remains on the paper in such a manner that visual recognition is possible. When detecting that the pen tip has contacted the paper using the writing pressure sensor, the digital pen  14  photographs the dots  203  printed on the paper with the camera  141 . For instance, the digital pen  14  photographs an area containing six by six dots  203 . 
         [0110]    The digital pen  14  computes absolute coordinates, at which the dot pattern exists, from a combination of displacement manners of respective photographed dots. Those absolute coordinates are coordinates at which the dot pattern exists in a vast plane area. The vast plane area is an entire area in which arrangement of dot patterns without overlapping is possible. 
         [0111]    The digital pen  14  transmits the computed absolute coordinates to the client terminal  12  through the digital pen interface  13 . The client terminal  12  transmits the absolute coordinates transmitted from the digital pen  14  to the location information server  19 . The location information server  19  identifies the location (dot pattern ID) of the paper in the vast plane area and coordinates (relative coordinates) on the paper sheet based on the absolute coordinates transmitted from the digital pen  14  and transmits the identified dot pattern ID and relative coordinates to the server  11 . 
         [0112]    In the manner described above, the server  11  obtains the dot pattern ID and the relative coordinates from the dot pattern photographed by the digital pen  14 . 
         [0113]    Through periodic obtainment (in units of a fixed time, for instance) by the digital pen  14  of information about contact locations of the pen tip, it is possible to find movement of the pen tip. Then, the digital pen  14  transmits the absolute coordinates corresponding to the photographed dot pattern, a photographed time of the dot pattern and the pen ID to the client terminal  12 . 
         [0114]    The server  11  obtains the relative coordinates from the location information server  19  based on the absolute coordinates computed by the digital pen  14 . The server  11  generates a path (stroke information) of the pen tip from the obtained relative coordinates and the photographed time of the dot pattern. 
         [0115]    It should be noted here that the location information server  19  may be included in the server  11  instead of being provided separately. 
         [0116]    Also, it is not required for the digital pen  14  to use the location information server  19  in order to identify the dot pattern ID and the relative coordinates. For instance, the sheet identification may be achieved using an identification number printed on the paper, a barcode printed on the paper, or an IC tag embedded in the paper. In addition, it is possible to identify locations (relative coordinates) on the sheet using a tablet. It should be noted that one of the sheet identification using an IC tag or the like and the location identification on the sheet using the tablet may be combined with the absolute coordinate identification by the location information server  19 . In this case, it becomes possible to alleviate a load of processing in which the document management system identifies the dot pattern ID and the relative coordinates. 
         [0117]      FIG. 11A  shows an example of a stroke set according to a first embodiment of this invention. 
         [0118]    The stroke set shows a symbol “         ”  751  annotated with the digital pen  14 . In this embodiment, as shown in the drawing, a left upper corner is set as an origin, a horizontal direction is set as an X axis, and a vertical direction is set as a Y axis, thereby determining locations of the strokes. As described above, the stroke set is a collection of mutually related lines (strokes) and is identified based on written times of the lines and/or positional relations among the lines. 
         [0119]      FIG. 11B  is a construction diagram of the stroke information  27  stored in the server  11  according to the first embodiment of this invention. 
         [0120]    The stroke information  27  contains stroke set information  27 A and  27 B and stroke coordinate information  27 C. 
         [0121]    The stroke set information  27 A contains a stroke ID  270 , a write user ID  271 , a write pen ID  272 , an input start date and time  273 , the number of sampling points  274 , and a pointer  275 . 
         [0122]    The stroke ID  270  is a unique identifier of the stroke set. The pen ID  272  is a unique identifier of the digital pen  14  used to annotate the stroke. 
         [0123]    The input start date and time  273  is a date and time of start of annotation of the stroke set. The number of sampling points  274  is the number of points contained in the stroke. The digital pen  14  periodically obtains a location of its pen tip and the number of points obtained from the start to the end of the stroke is recorded. The pointer  275  is a pointer with respect to the stroke coordinate information  27 C. 
         [0124]    The stroke coordinate information  27 C contains X coordinates  276 , Y coordinates  277 , and difference times  278 . 
         [0125]    Each X coordinate  276  is a relative coordinate in a direction of the X axis shown in  FIG. 11A  and is expressed in units of millimeters, for instance. Each Y coordinate  277  is a relative coordinate in a direction of the Y axis shown in  FIG. 11A  and is expressed in units of millimeters, for instance. Each difference time  278  expresses an obtainment time of the relative coordinates by the digital pen  14 . It should be noted that as the difference time  278 , an elapsed time from the input start date and time  273  is recorded. 
         [0126]    Next, processing in the information management system according to the embodiment of this invention will be described. 
         [0127]      FIG. 12  is a flowchart of tag print processing according to the first embodiment. 
         [0128]    First, a user operates the client terminal  12  to input an instruction to print information on a medium. In this case, the user designates the medium, on which the information is to be printed, by reading a dot pattern printed on a surface of the medium with a touch of the medium using the digital pen  14 . The digital pen  14  sends the read dot pattern to the client terminal  12 . 
         [0129]    The client terminal  12  transmits a print instruction containing an ID of the user, who operated the client terminal  12 , and the dot pattern obtained by the digital pen  14  to the server  11 . 
         [0130]    On receiving the print instruction from the client terminal  12 , the server  11  obtains the user ID contained in the received print instruction and obtains a tag ID from the dot pattern ID contained in the received print instruction (S 101 ). In this case, when a medium is new on which nothing is printed, it is impossible to obtain a dot pattern from the medium with the digital pen  14 . When it is impossible for the digital pen  14  to obtain a dot pattern, the server  11  generates a new tag ID. 
         [0131]    The server  11  judges whether a print target medium is unused based on whether the digital pen  14  has obtained a dot pattern. In addition, the server  11  judges whether a state of the medium (print target medium) having the obtained tag ID is “unused” by referring to the tag ID/object ID correspondence table  21  (S 102 ). 
         [0132]    When it is found as a result of the judgment that the medium is unused, printing on the medium is possible, so the server  11  generates object information  22  to be printed on the medium, print information  23 , and additional contents information  24  (S 103 ). Then, the processing proceeds to step S 104 . 
         [0133]    In step S 104 , the server  11  identifies a file recording contents to be printed by referring to the print contents  233  of the print information  23  and transmits a print command to the printer  13 . Then, on receiving the print command, the printer  13  prints designated information on the medium (S 104 ). 
         [0134]    After that, the server  11  creates history information  26  in which “print” has been recorded as the operation kind  265 . As the operation ID  266 , the server  11  records the print ID  230  of the print information  23  generated in step. S 104  (S 105 ). 
         [0135]    On the other hand, when it is not found in step S 102  that the used object ID  212  is “unused”, the server  11  judges whether the user ID obtained in step S 101  is contained as the write user ID  224 C by referring to the object information  22  using an object ID  211  corresponding to the tag ID  211  (S 106 ). 
         [0136]    When it is found as a result of the judgment that the identifier of the user, who instructed the printing, is contained as the write user ID  224 C, this means that the user has a right to change information indicated on the medium, so the server  11  adds the print ID  225  and the contents ID  226  of the object information  22  (S 107 ). After that, the processing proceeds to step S 104 , in which the server  11  transmits a print command to the printer  13 . 
         [0137]    On the other hand, when it is not found in step S 106  that the identifier of the user, who instructed the printing, is contained as the write user ID  224 C, this means that the user does not have a right to change the information indicated on the medium, so the server  11  notifies the client terminal  12  that the user does not have a right to change the indicated information. On receiving the notification that the user does not have a right to read additional contents, the client terminal  12  displays, on the data display unit, that the user does not have a right to read the additional contents. It should be noted that the notification that the user does not have a read right may be issued to the user by vibrating the digital pen  14  and/or emitting a warning sound from the digital pen  14  (S 108 ). After that, the processing proceeds to step S 105 , in which the history information  26  is created. 
         [0138]    It should be noted that when it is found in step S 102  that the used object ID  212  is “disposed”, this means that a print target medium should not exist, so the processing is terminated due to an error. 
         [0139]      FIG. 13  is a flowchart of tag read processing according to the first embodiment. 
         [0140]    First, a user operates the client terminal  12  to input an instruction to read additional contents relating to information shown on a surface of a medium. In this case, the user designates the medium, from which the information is to be read, by reading a dot pattern printed on the surface of the medium with a touch of the medium using the digital pen  14 . The digital pen  14  sends the read dot pattern to the client terminal  12 . 
         [0141]    The client terminal  12  transmits an additional contents read instruction containing an ID of a user, who operated the client terminal  12 , and the dot pattern obtained by the digital pen  14  to the server  11 . 
         [0142]    On receiving the additional contents read instruction from the client terminal  12 , the server  11  obtains the user ID contained in the received read instruction and obtains a tag ID from the dot pattern ID contained in the received read instruction (S 111 ). 
         [0143]    The server  11  identifies an object ID  212  corresponding to the obtained tag ID  211  by referring to the tag ID/object ID correspondence table  21  using the obtained tag ID. Then, the server  11  judges whether the user ID obtained in step S 111  is contained as the read user ID  244 B by referring to the object information  22  using the identified object ID (S 112 ). 
         [0144]    When it is found as a result of the judgment that the identifier of the user, who instructed the reading, is contained as the read user ID  224 B, this means that the user has a right to read the additional contents, so the server  11  identifies the print information  23  from the print ID  225  and reads the print contents  233 . Also, the server  11  identifies the additional contents information  24  from the contents ID  226  and reads the additional data  243 . Further, the server  11  identifies the stroke information from the stroke ID  227  and reads the stroke information  27 . Still further, the server  11  searches for the history information  26  using the object ID and reads the history information  26  for the medium (S 113 ). 
         [0145]    Then, the server  11  transmits the read print contents, additional data, stroke information, and history information to the client terminal  12 . On receiving the print contents, additional data, stroke information, and history information, the client terminal  12  displays the received data on the data display unit (S 114 ). 
         [0146]    It should be noted that the client terminal  12  displays the print contents, additional data, stroke information, and history information in this embodiment but only a part of these information may be displayed. 
         [0147]    In this case, the print contents and the stroke information are displayed so that they are superimposed on an image of the medium. It is possible for the user to confirm whether the information shown on the medium is authentic by comparing the information shown on the surface of the medium and the information displayed by the client terminal  12  with each other. In addition, it is possible for the user to see detailed information (additional data) relating to the information shown on the medium. 
         [0148]    On the other hand, when it is not found in step S 112  that the identifier of the user, who instructed the reading, is contained as the read user ID  224 B, this means that the user does not have a right to read the additional contents, so the server  11  notifies the client terminal  12  that the user does not have such a right. On receiving the notification that the user does not have an additional contents read right, the client terminal  12  displays, on the data display unit, that the user does not have an additional contents read right. It should be noted that the notification that the user does not have a read right may be issued to the user by vibrating the digital pen  14  and/or emitting a warning sound from the digital pen  14  (S 115 ). 
         [0149]    After that, the server  11  creates the history information  26  in which “read” has been recorded as the operation kind  265  (S 116 ). It should be noted that when the user does not have a read right and has failed in reading the additional contents, the history information  26 , in which “failure” has been recorded as the operation result  267 , is generated. 
         [0150]    It should be noted that the read processing shown in  FIG. 13  is based on the assumption that a link between the tag ID and the used object ID is valid but when information has been erased from the medium and the link between the tag ID and the used object ID has been removed, in the read processing shown in  FIG. 13 , it is impossible to read the information indicated on the medium and the information relating to the information indicated on the medium. 
         [0151]    In this case, the user designates the tag ID and a search target time. The server  11  extracts an object ID  220 , which corresponds to a tag ID  221  that is the same as the designated tag ID and also corresponds to a start date and time  222  and an end date and time  223  between which the designated time is contained, by referring to the object information  22 . Then, like in step S 113  described above, the server  11  reads the print information  23 , additional contents information  24 , stroke information  27 , and history information  26 . 
         [0152]    In this case, when there is no object ID corresponding to the search target time designated by the user, the server  11  notifies the user that there is no corresponding result. 
         [0153]      FIG. 14  is a flowchart of tag write processing according to the first embodiment. 
         [0154]    First, a user writes information, such as characters, on a surface of a medium using the digital pen  14 . When touching the medium, the digital pen  14  reads a dot pattern printed on the surface of the medium and identifies the medium on which the characters are to be written. In addition, the digital pen  14  obtains strokes of the characters or the like written by the user on the medium. 
         [0155]    The client terminal  12  transmits an ID of the user who operated the client terminal  12 , the dot pattern obtained by the digital pen  14 , and a write notification of stroke information obtained by the digital pen  14  to the server  11 . 
         [0156]    On receiving the write notification from the client terminal  12 , the server  11  obtains the user ID contained in the write notification and obtains a tag ID from the dot pattern ID contained in the write notification (S 121 ). 
         [0157]    The server  11  identifies an object ID  212  corresponding to the tag ID  211  by referring to the tag ID/object ID correspondence table  21  using the obtained tag ID. Then, the server  11  judges whether the user ID obtained in step S 121  is contained as a write user ID  224 C by referring to the object information  22  using the identified object ID (S 122 ). 
         [0158]    When it is found as a result of the judgment that the identifier of the user who performed the writing is contained as the write user ID  224 C, this means that the user has a right to change information indicated on the medium, so the server  11  generates the stroke information  27  of the strokes obtained by the digital pen  14  and records an identifier of the generated stroke set information as the stroke ID  227  (S  123 ). In this case, if necessary, the server  11  may add the additional contents information  24  concerning the written information. 
         [0159]    In this case, billing information concerning transfer of a commodity, to which the medium is affixed, may be contained in the added additional information. In other words, through annotation (of a check mark or a signature) in a predetermined area on the medium by the user, billing approval with respect to the user is requested. Then, through annotation into a predetermined area, a bill payment obligation is imposed on the user. 
         [0160]    On the other hand, when it is not found in step S 122  that the identifier of the user, who performed writing, is contained as the write user ID  224 C, this means that the user does not have a right to change the information indicated on the medium, so the server  11  notifies the client terminal  12  that the user does not have such a right. On receiving the notification that the user does not have a write right, the client terminal  12  displays, on the data display unit, that the user does not have a right to write characters or the like. It should be noted that the notification that the user does not have a write right may be issued to the user by vibrating the digital pen  14  and/or emitting a warning sound from the digital pen  14  (S 124 ). 
         [0161]    After that, the server  11  creates the history information  26  in which “read” has been recorded as the operation kind  265  (S 125 ). It should be noted that when the user does not have a write right, the history information  26 , in which “failure” has been recorded as the operation result  267 , is generated. 
         [0162]      FIG. 15  is a flowchart of tag erasing processing according to the first embodiment. 
         [0163]    First, a user operates the client terminal  12  to input an instruction to erase information shown on a surface of a medium. In this case, the user designates a medium to be erased, by reading a dot pattern printed on the surface of the medium with a touch of the medium using the digital pen  14 . The digital pen  14  sends the read dot pattern to the client terminal  12 . 
         [0164]    The client terminal  12  transmits an erasing instruction containing an ID of the user, who operated the client terminal  12 , and the dot pattern obtained by the digital pen  14  to the server  11 . 
         [0165]    On receiving the erasing instruction from the client terminal  12 , the server  11  obtains the user ID contained in the received erasing instruction and obtains a tag ID from the dot pattern ID contained in the received erasing instruction (S 131 ). 
         [0166]    The server  11  identifies the object ID  212  corresponding to the obtained tag ID  211  by referring to the tag ID/object ID correspondence table  21  using the obtained tag ID. Then, the server  11  judges whether the user ID obtained in step S 131  is contained as the write user ID  224 C by referring to the object information  22  using the identified object ID (S 132 ). 
         [0167]    When it is found as a result of the judgment that the identifier of the user, who instructed the reading, is contained as the write user ID  224 C, this means that the user has a right to change the information indicated on the medium, so it is possible for him/her to erase the information shown on the surface of the medium. Therefore, the server  11  identifies the object information  22  from the tag ID and records the end date and time  223 . In addition, the server  11  changes the used object ID  212  on the tag ID/object ID correspondence table  21  to “unused” (S 133 ). Following this, the information shown on the surface of the medium is erased by the printer  13 . As already mentioned, it is possible to display characters on the surface of the medium used in this embodiment and erase them from the medium surface based on a cooling speed after heating. 
         [0168]    On the other hand, when it is not found in step S 132  that the identifier of the user, who instructed the erasing, is contained as the write user ID  224 C, this means that the user does not have a right to change the information indicated on the medium, so the server  11  notifies the client terminal  12  that the user does not have a right to erase the information shown on the surface of the medium. On receiving the notification that the user does not have an erase right, the client terminal  12  displays, on the data display unit, that the user does not have a right to erase the information shown on the surface of the medium. It should be noted that the notification that the user does not have an erase right may be issued to the user by vibrating the digital pen  14  and/or emitting a warning sound from the digital pen  14  (S 135 ). 
         [0169]    After that, the server  11  creates the history information  26  in which “erase” has been recorded as the operation kind  265  (S 116 ). It should be noted that when the user does not have an erase right and has failed in erasing information, the history information  26 , in which “failure” has been recorded as the operation result  267 , is generated. 
         [0170]    As described above, in the first embodiment of this invention, it becomes possible to manage a medium and electronic information concerning the medium by associating them with each other. In other words, when information is printed on the medium, a tag ID and a used object ID are linked with each other. Also, when the information is erased from the medium, the link between the tag ID and the used object ID is removed. As a result, it becomes possible to manage the medium and the electronic information concerning the medium by associating them with each other. 
         [0171]    Also, by comparing the information printed on the medium and the electronic information held at the server with each other, it becomes possible to confirm whether the information currently shown on the medium is authentic. 
         [0172]    Further, a user&#39;s right is confirmed at the time of writing of information onto the medium, so the electronic information will not be tampered by an unauthorized user. 
         [0173]    Here, a method of data communication between the server  11  and the client terminal  15  will be described. 
         [0174]    The server  11  and the client terminal  15  perform data communication through the network  18 . Fundamentally, from the viewpoint of security, it is preferable that the network  18  uses a private line. However, there is a case where a network opened to the public, such as the Internet, is used with consideration given to cost or the like. Therefore, it is preferable that even when a network opened to the public, such as the Internet, is used, it is possible to perform secure data communication. As data communication means therefor, two means will be described, one of which is encryption communication means using a common key and the other of which is public key/secret key encryption communication means using a public key and a secret key. 
         [0175]    The encryption communication means based on a common key is a method with which data is encrypted/decrypted at each of a data transmission source and a data reception destination using the same common key. Therefore, at the server  11  and the client terminal  15 , it is required to perform processing shown in  FIG. 19  in advance as a preparation for communication. 
         [0176]    First, a common key is created at the server  11  (S 161 ). After that, the server  11  distributes the created common key to each client terminal  15  (S 162  to S 164 ). As a method of distributing the common key, for instance, there is a method with which common key information is copied to a recording medium, such as a flexible disk (FD) or a compact disc (CD), on a server  11  side and the common key is copied to each client terminal  15  from the medium recording the common key information. 
         [0177]    In data transmission from the server  11  to the client terminal  15  and data transmission from the client terminal  15  to the server  11  using the common key, encryption is performed using the common key at the transmission source and decryption is performed using the common key at the reception destination. This makes it possible to perform secure data communication. As an algorithm for the encryption, it is possible to use a known encryption system such as the Data Encryption Standard (DES). 
         [0178]    In the case of the common key, however, there is a danger that once the common key has been leaked, every data communication between the server  11  and the client terminal  15  will be intercepted. Therefore, as another encryption communication means, a case will be described below in which the encryption communication means using a public key and a secret key is applied. 
         [0179]    The encryption communication means using a public key and a secret key in this embodiment is a method with which data is encrypted at a data transmission source using a public key of a data reception destination and the data is decrypted at the data reception destination using a secret key of the data reception destination. Therefore, at the server  11  and the client terminal  15 , it is required to perform processing shown in  FIG. 20  in advance as a preparation for communication. 
         [0180]    First, at each of the server  11  and the client terminal  15 , a secret key and a public key are created (S 171 , S 172 ). Next, the public key of the server  11  is distributed to the client terminal  15  (S 173  to S 175 ). As a method of distributing the public key, it is possible to use a method with which the key is copied to a medium like in the case of the common key encryption communication means described above. Also, it is possible to use a method with which information of the server public key is transmitted as it is through the network  18 . 
         [0181]    Next, the public key of the client terminal  15  is distributed to the server (S 176  to S 178 ). As a method of distributing the public key, it is possible to use any of the methods described above for the server public key. Also, it is possible to use a method with which data of the public key of the client terminal  15  is encrypted using the public key of the server  11  received in advance and the encrypted public key is transmitted to the server  11  through the network  18 . As an algorithm for the encryption, it is possible to use a general encryption system using a public key and a secret key such as RSA. 
         [0182]    As a result of the public key exchange between the server  11  and each client terminal  15 , data transferred from the server  11  to the client terminal  15  is encrypted using the public key of the client terminal and is decrypted using the secret key of the client terminal. On the other hand, data transferred from the client terminal  15  to the server  11  is encrypted using the public key of the server and is decrypted using the secret key of the server. This makes it possible to perform secure data communication. 
         [0183]    It should be noted that the distribution of the public key of the server  11  (S 173  to S 175 ) and the distribution of the public key of the client terminal  15  (S 176  to S 178 ) may be performed in a reverse order. 
         [0184]    With one of the two encryption means described above, it becomes possible to transmit data concerning this invention securely. 
         [0185]    Finally, processing for searching for a series of procedures concerning an object, such as attachment of a tag to the object, reading of data from the tag, and writing of data to the tag, will be described using  FIG. 21 . 
         [0186]    First, a user designates an object that is a search target and obtains an object ID (S 181 ). When a tag is affixed to the object, an object ID  212  is obtained from an ID of the affixed tag by referring to the tag ID/object ID correspondence table  21 . It should be noted that when a link between the object and the tag is already removed, the user directly designates an object ID or the user designates a tag ID and a search target time and an object ID  220  is obtained from the designated information by referring to the object information  22 . 
         [0187]    Next, the object information  22  corresponding to the object ID is searched for and contents of the found object information  22  are read (S 182 ). In addition, the history information  26  corresponding to the object ID is searched for by referring to the operation object ID  263  of the history information  26  and contents of the found history information  26  are read (S 183 ). 
         [0188]    Finally, the read object information  22  and history information  26  are presented to the user (S 184 ). Through this object procedure search processing, it is possible to obtain a history of a series of operation with respect to a target object. As a result, it becomes possible to realize the traceability of an object. 
       Second Embodiment 
       [0189]      FIG. 16  is a block diagram of an information management system according to a second embodiment. 
         [0190]    The information management system according to the second embodiment differs from the information management system according to the first embodiment described above in that in addition to an online client terminal  12  connected with a network  18 , a local client terminal  15  that is not connected with the network  18  is provided. It should be noted that each construction that is the same as a construction in the first embodiment is given the same reference numeral and the detailed description thereof will be omitted. 
         [0191]    The information management system according to the second embodiment includes a server  11 , client terminals  12  and  15 , digital pens  14 , a network  18 , and a location information server  19 . 
         [0192]    The server  11 , the client terminal  12 , and the location information server  19  are connected to one another through the network  18 . In ordinary cases, the local client terminal  15  is not connected to the network  18 . 
         [0193]    In other words, the online client terminal  12  is capable of communicating with the server  11  at all times. On the other hand, the local client terminal  15  is incapable of communicating with the server  11  in ordinary cases but is connected to the network  18  as necessary and becomes capable of communicating with the server  11 . 
         [0194]    The client terminal  15  and each digital pen  14  are connected in a wireless manner based on Bluetooth, a wireless LAN, a mobile telephone system, infrared rays, or the like. Alternatively, they may be connected in a wired manner using a universal serial bus (USB) protocol or the like. 
         [0195]    The client terminal  15  includes a calculation unit  151 , a data communication unit  152 , a data management unit  153 , a pen input unit (not shown), an operation input unit (not shown), and a data display unit (not shown). The calculation unit  151  includes a CPU and a memory. The CPU invokes and executes various programs, thereby performing computation concerning processing carried out at the client terminal  15 . 
         [0196]    The data communication unit  152  is a network interface and is, for instance, a LAN card that is capable of performing communication using a TCP/IP protocol. With this construction, when connected with the network  18 , the client terminal  15  becomes capable of communicating with the server  11 . 
         [0197]    The data management unit  153  is constructed by a nonvolatile storage medium (magnetic disk drive, for instance) and stores the various programs executed at the calculation unit  151 . Also, the storage unit  153  stores the tag ID/object ID correspondence table  21  shown in  FIG. 4 , object information  22  shown in  FIG. 5 , print information  23  shown in  FIG. 6 , additional contents information  24  shown in  FIG. 7 , user information  25 A and the like shown in  FIG. 8A  to  FIG. 8C , history information  26  shown in  FIG. 9 , and stroke information  27  shown in  FIG. 11B . These tag ID/object ID correspondence table  21 , object information  22 , print information  23 , additional contents information  24 , history information  26 , and stroke information  27  stored at the client terminal  15  do not match their corresponding information held at the server  11  under a state where the client terminal  15  is not connected with the server  11 . 
         [0198]    In other words, when any operation is performed at the local client terminal  15 , the client terminal  15  generates an object ID according to its own rule. Therefore, there is a case where different object IDs are associated with the same tag ID. 
         [0199]    The pen input unit is connected with each digital pen  14  in a wireless manner (based on Bluetooth or a wireless LAN, for instance) or a wired manner (using a USB protocol, for instance) and collects information about coordinates and the like obtained by the digital pen  14 . It should be noted that the pen input unit and the data communication unit  152  may be the same interface. 
         [0200]    The operation input unit is a keyboard, for instance, and is used by a user to input information. The data display unit is constructed using a liquid crystal display, for instance, and displays information concerning a medium obtained from the server  11 . 
         [0201]    In  FIG. 16 , one online client terminal  12  and one local client terminal  15  are illustrated but multiple online client terminals  12  and multiple local client terminals  15  may be provided. In other words, it may be made possible to make a switching as to whether a segment constructed by multiple local client terminals  15  is connected to the network  18 . 
         [0202]    In ordinary cases, the local client terminal  15  is not connected to the network  18  and therefore is incapable of communicating with the server  11 . Consequently, when operation on a medium is performed, a new object ID is generated without cooperating with the server  11 , so there is a case where an object ID that is different from that of the server  11  is linked to the same tag ID. In other words, the local client terminal  15  is incapable of obtaining a global object ID unless inquiring the server  11 . 
         [0203]    Therefore, when the client terminal  15  is connected to the network  18 , there occurs a problem that there are multiple tag ID-to-object ID links. Consequently, there is a necessity to perform object ID conversion when the client terminal  15  is connected to the network  18 . 
         [0204]      FIG. 17  is a flowchart of offline data conversion processing according to the second embodiment. 
         [0205]    The offline data conversion processing is carried out at the server  11  when the local client terminal  15  is connected to the network  18  and communicates with the server  11 . 
         [0206]    On detecting connection of the local client terminal  15 , the server  11  obtains information accumulated in the local client terminal  15  (S 141 ). Then, the server  11  judges whether any local object IDs exist in the information obtained from the client terminal  15  (S 142 ). Therefore, it is sufficient that the local client terminal  15  and the server  11  generates object IDs using different systems. 
         [0207]    When no local object ID exists in the information obtained from the client terminal  15 , this means that conversion of every local object ID in the information obtained from the client terminal  15  has been completed, so the server  11  ends this offline data conversion processing. 
         [0208]    On the other hand, when any local object IDs exist in the information obtained from the client terminal  15 , the server  11  obtains information concerning each unconverted object ID (S 143 ). Then, the server  11  searches for a global object ID and converts the local object ID into the global object ID (S 144 ). 
         [0209]    After that, various information held at the client terminal  15  is copied to the server  11  (S 145 ). 
         [0210]      FIG. 18  is a detailed flowchart of the offline data conversion processing according to the second embodiment and shows the details of the processing in steps from S 143  to S 145  in  FIG. 17 . 
         [0211]    The client terminal  15  identifies a tag ID  211  corresponding to a local object ID  212  by referring to the object information  22  held at itself (S 156 ). Also, the client terminal  15  obtains a operating date and time  261  corresponding to the local object ID  264  by referring to the history information  26  held at itself (S 157 ). 
         [0212]    On the other hand, the server  11  identifies an object ID  212  using the tag ID identified at the client terminal  15  by referring to the object information  22  held at itself. Then, the server  11  obtains the start date and time  222  and the end date and time  223  by referring to the object information  22  using the identified object ID (S 151 ). 
         [0213]    After that, the operating date and time  261  obtained from the local client terminal  15  and the start date and time  222  and the end date and time  223  held at the server  11  are compared with each other (S 152 ). Then, when the operating date and time  261  is between the start date and time  222  and the end date and time  223  corresponding to the same tag ID, it is judged that the local object ID and the global object ID held at the server  11  correspond to the same object (S 153 ). 
         [0214]    When a result of this object ID correspondence judgment is affirmative, the object information  22  held at the server  11  is copied to the object information  22  held at the client terminal  15  (S 154 ). As a result, the local object ID is converted into the global object ID. 
         [0215]    After that, the print information  23 , additional contents information  24 , history information  26 , and stroke information  27  held at the client terminal  15  are copied to their corresponding information held at the server  11  (S 155 ). 
         [0216]    As described above, according to the second embodiment of this invention, even in a system in which the client terminal  15  is not connected with the server  11  at all times, it becomes possible to appropriately manage a medium and electronic information concerning the medium. Also, when the client terminal  15  is connected to the server  11 , an identifier (object ID) of information printed on the medium is converted, so it becomes possible to integrate even electronic information generated through an operation by the client terminal  15  alone into electronic information of the server  11 . 
         [0217]    While the present invention has been described in detail and pictorially in the accompanying drawings, the present invention is not limited to such detail but covers various obvious modifications and equivalent arrangements, which fall within the purview of the appended claims.