Patent Publication Number: US-2006015583-A1

Title: Time management server, information terminal, time management system and time management method

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
      This application is based upon and claims the benefit of priority from prior Japanese Patent Application No. 2004-177558, filed on Jun. 15, 2004; the entire contents of which are incorporated herein by reference.  
     BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates to a time management server, an information terminal, a time management system and a time management method. The present invention particularly relates to a time management server, an information terminal, a time management system and a time management method, which are suitable for making times of information terminals coincide with each other.  
      2. Description of the Related Art  
      Heretofore, for example, data backup, which is storing data stored by a mobile phone in a personal computer other than the mobile phone, and transferring data to another mobile phone have been carried out. Moreover, an information terminal synchronizing with a standard time server for managing a standard time has been proposed (for example, refer to Japanese Patent Laid-Open Publication No. 2004-86494).  
      However, in the conventional backup or data transfer, it has been impossible to provide set-in-providing-source time information, which is set in a providing source information terminal for providing data, and providing source data in association with each other to a providing destination information terminal. Therefore, it has been difficult for the providing destination information terminal to store the data while maintaining a relationship between the providing source data and the set-in-providing-source time information. When maintaining the relationship is desired, storing the set-in-providing-source time information in the providing destination information terminal separately from the providing source data is required, and this has been cumbersome. Such a problem has been significant when there are many providing destination information terminals. Moreover, in such a method of synchronizing the information terminal with the standard time server, it has been impossible to make the times of the providing source information terminal and providing destination information terminal coincide with each other.  
     SUMMARY OF THE INVENTION  
      An object of the present invention is to easily maintain, in a providing destination terminal, a relationship between providing source data and set-in-providing-source time information in a providing source information terminal.  
      A time management server according to an embodiment of the present invention includes an acquisition unit configured to acquire providing source data and set-in-providing-source time information from a providing source information terminal, a calculation unit configured to calculate providing time information to be provided to a providing destination information terminal by using the set-in-providing-source time information and an inter-terminal reference time, and a providing unit configured to provide the providing source data and the providing time information to the providing destination information terminal.  
      The “providing source information terminal” is an information terminal of a providing source, which provides data. The “providing source data” is the data provided by the providing source information terminal. The “providing destination information terminal” is an information terminal of a providing destination to which the providing source information terminal provides the providing source data. The “set-in-providing-source time information” is information concerning a time set in the providing source information terminal. The “inter-terminal reference time” is a time common to the providing source information terminal and the providing destination information terminal, and is a time serving as a reference when the times of the providing source information terminal and the providing destination information terminal are made to coincide with each other. The “providing time information” is calculated by the time management server by using the set-in-providing-source time information and the inter-terminal reference time, and is information concerning the time to be provided to the providing destination information terminal.  
      According to the time management server as described above, the providing time information associated with the providing source data, which is calculated by using the set-in-providing-source time information and the inter-terminal reference time can be provided to the providing destination information terminal. Therefore, the providing destination information terminal can easily maintain the relationship between the providing source data and the set-in-providing-source time information in the providing source information terminal based on the acquired providing source data and providing time information.  
      An information terminal according to an embodiment of the present invention includes a storage unit configured to store calculated set time information associated with providing source data of a providing source information terminal, an acquisition unit configured to acquire the providing source data and providing time information from a time management server configured to provide the providing time information associated with the providing source data, which is calculated by using set-in-providing-source time information of the providing source information terminal and an inter-terminal reference time, and a registering unit configured to register the calculated set time information associated with the providing source data in the storage unit based on the providing time information. The “calculated set time information” is set-in-providing-source time information calculated based on the inter-terminal reference time and a difference on the basis of the set-in-providing-source time information and the inter-terminal reference time.  
      According to the information terminal as described above, the providing source data and the providing time information calculated by using the set-in-providing-source time information and the inter-terminal reference time can be acquired from the time management server. Then, the information terminal can register the calculated set time information associated with the providing source data in the storage unit based on the providing time information. Therefore, in the case of serving as the providing destination information terminal, the information terminal can easily maintain the relationship between the providing source data and the set-in-providing-source time information in the providing source information terminal.  
      An information terminal according to another embodiment includes a calculation unit configured to calculate a difference based on set-in-providing-source time information and an inter-terminal reference time, and a providing unit configured to provide providing source data and the difference to a providing destination information terminal.  
      The information terminal as described above serves as the providing source information terminal, and can provide the difference based on the set-in-providing-source time information and the inter-terminal reference time to the providing destination information terminal. Therefore, the providing destination information terminal can easily maintain the relationship between the providing source data and the set-in-providing-source time information in the providing source information terminal based on the acquired providing source data and providing time information.  
      An information terminal according to another embodiment includes a storage unit configured to store calculated set time information associated with providing source data of a providing source information terminal, an acquisition unit configured to acquire the providing source data and a difference based on set-in-providing-source time information of the providing source information terminal and an inter-terminal reference time from the providing source information terminal, and a registering unit configured to calculate the calculated set time information based on the difference and the inter-terminal reference time, and register the calculated set time information associated with the providing source data in the storage unit.  
      The information terminal as described above serves as the providing destination information terminal, and can acquire the providing source data and the difference based on the set-in-providing-source time information and the inter-terminal reference time from the providing source information terminal. Then, the information terminal can calculate the calculated set time information based on the difference and the inter-terminal reference time, and can store the calculated set time information associated with the providing source data in the storage unit. Therefore, the providing destination information terminal can easily maintain the relationship between the providing source data and the set-in-providing-source time information in the providing source information terminal.  
      A time management system according to an embodiment of the present invention includes a time management server configured to acquire providing source data and set-in-providing-source time information from a providing source information terminal, calculate providing time information to be provided to a providing destination information terminal by using the set-in-providing-source time information and an inter-terminal reference time, and provide the providing source data and the providing time information to the providing destination information terminal, and a providing destination information terminal configured to acquire the providing source data and the providing time information from the time management server, and register calculated set time information associated with the providing source data in a storage unit based on the providing time information.  
      According to the time management system as described above, the time management server can provide the providing time information associated with the providing source data, which is calculated by using the set-in-providing-source time information and the inter-terminal reference time to the providing destination information terminal. Then, the providing destination information terminal can register the calculated set time information associated with the providing source data in the storage unit based on the providing source data and the providing time information which are acquired from the time management server. Therefore, the providing destination information terminal can easily maintain the relationship between the providing source data and the set-in-providing-source time information in the providing source information terminal.  
      A time management system according to another embodiment includes a providing source information terminal configured to calculate a difference based on set-in-providing-source time information and an inter-terminal reference time, and provide providing source data and the difference to a providing source information terminal, and the providing destination information terminal configured to acquire the providing source data and the difference from the providing source information terminal, calculate calculated set time information based on the difference and the inter-terminal reference time, and register the calculated set time information associated with the providing source data in a storage unit.  
      According to the time management system as described above, the providing source information terminal can provide the providing source data and the difference based on the set-in-providing-source time information and the inter-terminal reference time to the providing destination information terminal. Then, the providing destination information terminal can calculate the calculated set time information based on the difference and the inter-terminal reference time, and can register the calculated set time information associated with the providing source data in the storage unit. Therefore, the providing destination information terminal can easily maintain the relationship between the providing source data and the set-in-providing-source time information in the providing source information terminal.  
      A time management method according to an embodiment of the present invention includes acquiring providing source data and set-in-providing-source time information form a providing source information terminal by a time management server, calculating providing time information to be provided to a providing destination information terminal by using the set-in-providing-source time information and an inter-terminal reference time by the time management server, providing the providing source data and the providing time information to the providing destination information terminal by the time management server, acquiring the providing source data and the providing time information from the time management server by the providing destination information terminal, and storing the calculated set time information associated with the providing source data in a storage unit based on the providing time information by the providing destination information terminal.  
      A time management method according to another embodiment includes calculating a difference based on set-in-providing-source time information and an inter-terminal reference time by a providing source information terminal, providing providing source data and the difference to a providing destination information terminal by the providing source information terminal, acquiring the providing source data and the difference from the providing source information terminal by the providing destination information terminal, calculating calculated set time information based on the difference and the inter-terminal reference time by the providing destination information terminal, and registering the calculated set time information associated with the providing source data in a storage unit by the providing destination information terminal. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a diagram showing a time management system according to a first embodiment of the present invention.  
       FIG. 2  is a block diagram showing an information terminal according to the first embodiment of the present invention.  
       FIG. 3  is a diagram showing a storage unit of the information terminal according to the first embodiment of the present invention.  
       FIG. 4  is a block diagram showing a time management server according to the first embodiment of the present invention.  
       FIG. 5  is a flowchart showing a procedure of a case where the information terminal according to the first embodiment of the present invention calculates a terminal reference time as calculated set time information.  
       FIG. 6  is a flowchart showing a procedure of a case where the time management server according to the first embodiment of the present invention calculates the terminal reference time as the calculated set time information.  
       FIG. 7  is a flowchart showing a procedure of a case where the information terminal according to the first embodiment of the present invention calculates data time information as the calculated set time information.  
       FIG. 8  is a flowchart showing a procedure of a case where the time management server according to the first embodiment of the present invention calculates the data time information as the calculated set time information.  
       FIG. 9  is a diagram showing a time management system according to a second embodiment of the present invention.  
       FIG. 10  is a flowchart showing a procedure of a case where an information terminal according to the second embodiment of the present invention calculates the terminal reference time as the calculated set time information.  
       FIG. 11  is a flowchart showing a case where the information terminal according to the second embodiment of the present invention calculates the data time information as the calculated set time information. 
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS  
      [First Embodiment] 
      (Time Management System)  
      As shown in  FIG. 1 , a time management system  100  includes plural information terminals  10   a ,  10   b  and  10   c , a reference time management device  20 , a network  30 , and plural time management servers  40   a  and  40   b.    
      Time and information concerning the time, such as set-in-providing-source time information, an inter-terminal reference time, providing time information, a difference based on the set-in-providing-source time information and the inter-terminal reference time, calculated set time information, a terminal reference time, and data time information, are hereinafter generically referred to as “time information”. The “terminal reference time” is a time serving as a reference in the information terminal itself. Therefore, the terminal reference time is used as a processing time of data and display time for the information terminal itself. The “data time information” is information concerning a time relating to the data.  
      The reference time management device  20  stores the inter-terminal reference time. The reference time management device  20  provides the inter-terminal reference time to the time management servers  40   a  and  40   b  and the information terminals  10   a  to  10   c  through the network  30 .  
      The time management servers  40   a  and  40   b  acquire providing source data and the set-in-providing-source time information from a providing source information terminal. The time management servers  40   a  and  40   b  calculate the providing time information to be provided to a providing destination information terminal by using the set-in-providing-source time information and the inter-terminal reference time. Then, the time management servers  40   a  and  40   b  provide the providing source data and the providing time information to the providing destination information terminal.  
      The time management servers  40   a  and  40   b  may connect to the providing source information terminal and the providing destination information terminal in parallel, or may connect to the providing source information terminal to acquire the providing source data therefrom, disconnect such a connection, and then connect to the providing destination information terminal to provide the acquired providing source data thereto. Moreover, it is not necessary for the time management servers  40   a  and  40   b  to provide the providing source data and the providing time information at the same time. If the providing time information can be associated with the providing source data, the providing source data and the providing time information may be provided separately. The number of time management servers  40   a  and  40   b  is not limited, either, and the number may be one or more than two.  
      Each of the information terminals  10   a  to  10   c  serves as either the providing source information terminal or the providing destination information terminal. In the case of serving as the providing source information terminal, each of the information terminals  10   a  to  10   c  provides the providing source data and the set-in-providing-source time information to the time management servers  40   a  and  40   b . In the case of serving as the providing destination information terminal, each of the information terminals  10   a  to  10   c  acquires the providing source data and the providing time information from the time management servers  40   a  and  40   b , and registers the calculated set time information associated with the providing source data based on the providing time information in a storage unit.  
      The information terminals  10   a  to  10   c  can serve as the providing source information terminal, for example, when the information terminals  10   a  to  10   c  ensure backup of the stored data by storing the data also in another information terminal, transfer the stored data to another information terminal, provide the data to the providing destination information terminal by processing, and so on. Meanwhile, the information terminals  10   a  to  10   c  can serve as the providing destination information terminal, for example, when the information terminals  10   a  to  10   c  receive the backup of the data from another information terminal, receive the transfer of the data therefrom, receive the provision of the data from the providing source information terminal by processing, and so on. The information terminals  10   a  to  10  include, for example, mobile phones, portable information terminals (PDA: personal digital assistants), personal computers, servers, and the like.  
      The time management servers and the information terminals may be connected to each other through the network  30  like the time management servers  40   a  and  40   b  and the information terminal  10   c , or may be connected not through the network  30  like the time management servers  40   a  and  40   b  and the information terminals  10   a  and  10   b . The network  30  includes, for example, a mobile communication network, a wireless LAN, the Internet, and the like.  
      Next, the information terminals  10   a  to  10   c  will be described in detail by using  FIG. 2 . The information terminal  10   a  includes an interface (hereinafter, described as “I/F”)  11   a , a communication unit  11   b , a time management unit  12 , a controller  13 , a display  14 , and a storage unit  15 . The information terminals  10   b  and  10   c  also have similar configurations to that of the information terminal  10   a.    
      The I/F  11   a  connects to the time management servers  40   a  and  40   b  and the other information terminals  10   b  and  10   c  not through the network  30 , and transmits/receives the providing source data and the time information thereto/therefrom. The I/F  11   a  may be one that connects to the time management servers  40   a  and  40   b  and the other information terminals  10   b  and  10   c  by cables, or may be one that connects to the time management servers  40   a  and  40   b  and the other information terminals  10   b  and  10   c  by an infrared ray and a radio wave. For example, the I/F  11   a  can use the IrDA that transmits/receives by the infrared ray, the Bluetooth (registered trademark) transmits/receives by the radio wave, and the like.  
      The communication unit  11   b  transmits/receives the providing source data and the time information to/from the time management servers  40   a  and  40   b  and the other information terminals  10   b  and  10   c  through the network  30 . The I/F  11   a  and the communication unit  11   b  input the received providing source data and time information to the time management unit  12 . The I/F  11   a  and the communication unit  11   b  acquire, from the time management unit  12 , the providing source data and the time information which are to be transmitted by the information terminal  10   a.    
      The storage unit  15  stores the calculated set time information associated with the providing source data of the providing source information terminal. The storage unit  15  can also store time information other than the calculated set time information and the other information. The storage unit  15  stores the data and time information of the other information terminals  10   b  and  10   c , and the data and time information of the information terminal  10   a  itself. Specifically, the storage unit  15  stores the providing source data and the time information which are to be provided from the other information terminals  10   b  and  10   c  that serves as the providing source information terminals when the information terminal  10   a  serves as the providing destination information terminal. In addition, the storage unit  15  stores the providing source data and the time information which are the data and the time information of the information terminal  10   a  itself and to be provided to the other information terminals  10   b  and  10   c , when the information terminal  10   a  serves as the providing source information terminal. Furthermore, the storage unit  15  stores the providing source data and time information of the plural information terminals  10   b  and  10   c.    
      Therefore, the storage unit  15  stores the providing source data and the time information for each of the information terminals  10   a  to  10   c . For example, the storage unit  15  stores the providing source data and the time information in association with terminal identification data for identifying the information terminals  10   a  to  10   c . The terminal identification data includes a user ID, terminal number, phone number, address and the like of the information terminal. Specifically, as shown in  FIG. 3 , the storage unit  15  can include storage areas  15   a  to  15   c  for storing the information concerning the respective information terminals  10   a  to  10   c . The respective storage areas  15   a  to  15   c  for storing information of the information terminals  10   a  to  10   c  can be distinguished by the terminal identification data.  
      The storage area  15   a  stores the information of the information terminal  10   a , and the terminal identification data “A” of the information terminal  10   a  is assigned thereto. The storage area  15   b  stores the information of the information terminal  10   b , and the terminal identification data “B” of the information terminal  10   b  is assigned thereto. The storage area  15   c  stores the information of the information terminal  10   c , and the terminal identification data “C” of the information terminal  10   c  is assigned thereto.  
      As shown in  FIG. 3 , the providing source data stored in the storage unit  15  includes user data, control data, and inside management information. The user data is data used by a user of the information terminal. The control data is data for controlling the information terminal. The user data and the control data are provided as the providing source data to the providing destination information terminal. The inside management information is data to be managed in the information terminal without being provided to the providing destination information terminal.  
      The set time information set in the information terminals  10   a  to  10   c  includes the terminal reference time, the data time information relating to the data, and the like. The storage unit  15  stores set time information (hereinafter, referred to as “self-set time information”) set in the information terminal  10   a  itself, and the set-in-providing-source time information set in the other information terminals  10   b  and  10   c  serving as the providing source information terminals. The self-set time information is stored in the storage area  15   a , and the set-in-providing-source time information of the information terminals  10   b  and  10   c  are stored in the storage areas  15   b  and  15   c , respectively.  
      The data time information relating to the user data and the control data is associated with the respective user data and control data. The data time information includes, for example, a difference between the terminal reference time of the information terminal  10   a  itself and acquired time information when the information terminal  10   a  acquires the providing source data and time information of other information terminals, a reception time and update time of the data, and the like. It is not necessary to associate the data time information with all of the user data and the control data. Moreover, common data time information may be associated with plural user data and control data. For example, the common data time information can be associated with plural user data acquired from the other information terminals at the same time. The number of user data and control data stored in the storage unit  15  is not limited.  
      The time management unit  12  is an acquisition unit configured to acquire the providing source data and the providing time information from the time management servers  40   a  and  40   b  configured to provide the providing time information associated with the providing source data. The providing time information is calculated by using the set-in-providing-source time information of the providing source information terminal and the inter-terminal reference time. Moreover, the time management unit  12  also functions as a registering unit configured to register the calculated set time information associated with the providing source data in the storage unit  15  based on the providing time information.  
      When the information terminal  10   a  serves as the providing destination information terminal, the time management unit  12  acquires the providing source data and providing time information of the providing source information terminal from the time management servers  40   a  and  40   b  through the I/F  11   a  or the communication unit  11   b . The terminal identification data of the providing source information terminal is associated with the providing source data and the providing time information.  
      The providing time information includes at least one of a set of the difference based on the set-in-providing-source time information and the inter-terminal reference time and the inter-terminal reference time, and the calculated set time information calculated based on the difference and the inter-terminal reference time. Moreover, the providing time information may also include the set-in-providing-source time information as it is. When acquiring, as the providing time information, the difference based on the set-in-providing-source time information and the inter-terminal reference time and the inter-terminal reference time, the time management unit  12  first calculates the calculated set time information based on the difference and the inter-terminal reference time.  
      For example, when acquiring the difference between the terminal reference time of the providing source information terminal and the inter-terminal reference time and the inter-terminal reference time, the time management unit  12  can calculate the terminal reference time in the providing source information terminal as the calculated set time information by adding the difference to the inter-terminal reference time. Moreover, when acquiring a difference based on the data time information of the providing source information terminal and the inter-terminal reference time and the inter-terminal reference time, the time management unit  12  can calculate the data time information in the providing source information terminal as the calculated set time information by correcting the data time information by using the inter-terminal reference time and the difference.  
      The time management unit  12  registers the calculated set time information associated with the providing source data in the storage area for the corresponding providing source information terminal in the storage unit  15 . For example, when the providing source information terminal is the information terminal  10   b , and the terminal identification data “B” is associated with the acquired providing source data and providing time information, the time management unit  12  registers the user data and control data as the providing source data, the data time information as the calculated set time information, and the terminal reference time in the storage area  15   b . The time management unit  12  registers the data time information associated with the user data and the control data. When acquiring the calculated set time information as it is as the providing time information, the time management unit  12  registers the acquired calculated set time information associated with the providing source data in the storage area for the corresponding providing source information terminal in the storage unit  15 . When also acquiring the set-in-providing-source time information as the providing time information, the time management unit  12  registers the set-in-providing-source time information in the storage area for the corresponding providing source information terminal in the storage unit  15  together with the above.  
      The time management unit  12  may acquire the providing source data and the providing time information at the same time, or may acquire either one thereof first. Moreover, the time management unit  12  may acquire the set-in-providing-source time information and the set of the difference and the inter-terminal reference time or the calculated set time information at the same time, or may acquire either one thereof first. When the time management unit  12  does not acquire the providing source data and the providing time information at the same time, or separately acquire the plural kinds of providing time information, the time management unit  12  can associate the providing time information with the providing source data or various kinds of providing time information with each other by using the terminal identification data, then register them in the storage unit  15 .  
      It is preferable that the set-in-providing-source time information and the calculated set time information are at least one of the terminal reference time in the providing source information terminal and the data time information of the providing source data in the providing source information terminal. According to this, a relationship between the providing source data and the terminal reference time or a relationship between the providing source data and the data time information in the providing source information terminal can be maintained also in the providing destination information terminal.  
      It is preferable that the time management unit  12  change and register the acquired data time information based on the calculated set time information (terminal reference time) in the case of registering the terminal reference time as the calculated set time information and registering the acquired data time information as the set-in-providing-source time information. According to this, the information terminals  10   a  to  10   c  can dynamically correct the data time information in response to the change of the terminal reference time. Then, the terminal reference times and data time information of the providing destination information terminal and the providing source information terminal can be made to coincide with each other. In addition, a relationship between the terminal reference time and the data time information in the providing source information terminal can be maintained also in the providing destination information terminal.  
      When the information terminal  10   a  serves as the providing source information terminal, the time management unit  12  acquires the user data and the control data as the providing source data, and the self-set time information such as the data time information and the terminal reference time as the set-in-providing-source time information, from the storage area  15   a  of the storage unit  15 . The time management unit  12  provides the acquired providing source data and set-in-providing-source time information in association with the terminal identification data “A” of the information terminal  10   a  and the terminal identification data of the providing destination information terminal to the time management servers  40   a  and  40   b  through the I/F  11   a  or the communication unit  11   b . The time management unit  12  may also provide the set-in-providing-source time information and the like to the time management servers  40   a  and  40   b  by itself. Alternatively, the time management unit  12  may receive a request for the set-in-providing-source time information from the time management servers  40   a  and  40   b  when the information terminal  10   a  connects to the time management servers  40   a  and  40   b , and may provide the set-in-providing-source time information and the like to the time management servers  40   a  and  40   b  in response to the request.  
      Moreover, the time management unit  12  may provide the providing source data and the set-in-providing-source time information at the same time, or may provide either one thereof first. For example, the time management unit  12  may provide the providing source data before the calculation of the providing time information in the time management servers  40   a  and  40   b , or may provide the providing source data after the calculation of the providing time information. Furthermore, the time management unit  12  may provide the data time information and the terminal reference time as the set-in-providing-source time information, or may provide either one thereof first. For example, the time management unit  12  first provides the terminal reference time and the providing source data. In this case, the time management unit  12  notifies whether or not data time information is associated with the providing source data of the time management servers  40   a  and  40   b . Then, the time management unit  12  may provide the data time information only in the case of receiving the request for the data time information from the time management servers  40   a  and  40   b.    
      The controller  13  acquires the user data, the control data, the terminal reference time and the data time information from the storage unit  13 , and outputs these to the display  14 . The display  14  displays the data and the time received from the controller  13 . In the case of outputting the data of the information terminal  10   a , the controller  13  acquires the data of the information terminal  10   a , and the data time information and the terminal reference time, which are associated with the data from the storage area  15   a , and outputs these. In the case of outputting the data of the information terminal  10   b , the controller  13  acquires the data of the information terminal  10   b , and the data time information and the terminal reference time, which are associated with the data from the storage area  15   b , and outputs these. The case of the information terminal  10   c  is the same.  
      Each of the information terminals  10   a  to  10   c  as described above can be achieved by allowing a computer to carry out a program for allowing the computer to function as: a storage unit configured to store the calculated set time information associated with the providing source data of the providing source information terminal, an acquisition unit configured to acquire the providing source data and the providing time information from the time management server configured to provide the providing time information associated with the providing source data, which is calculated by using the set-in-providing-source time information of the providing source information terminal and the inter-terminal reference time, and a registering unit configured to register the calculated set time information associated with the providing source data in the storage unit based on the providing time information.  
      Next, the time management servers  40   a  and  40   b  will be described more in detail by using  FIG. 4 . The time management server  40   a  includes an I/F  41   a , a communication unit  41   b , a time management unit  42 , and a storage unit  43 . The time management server  40   b  also has a similar configuration to that of the time management server  40   a.    
      The I/F  41   a  connects to the information terminals  10   a  to  10   c  not through the network  30 , and transmits/receives the providing source data and the time information thereto/therefrom. The I/F  41   a  may be one that connects to the information terminals  10   a  to  10   c  by cables, or may be one that connects to the information terminals  10   a  to  10   c  by an infrared ray or a radio wave. For example, the I/F  41   a  can use the IrDA and the Bluetooth (registered trademark).  
      The communication unit  41   b  transmits/receives the providing source data and the time information to/from the information terminals  10   a  to  10   c  through the network  30 . The I/F  41   a  and the communication unit  41   b  input the received providing source data and time information to the time management unit  42 . The I/F  41   a  and the communication unit  41   b  acquires, from the time management unit  42 , the providing source data and the providing time information which are transmitted by the time management server  40   a.    
      The storage unit  43  temporarily stores the providing source data and the set-in-providing-source time information, which are acquired from the providing source information terminal, the terminal identification data of the providing source information terminal and the providing destination information terminal, and the providing time information to be provided to the providing destination information terminal.  
      The time management unit  42  is an acquisition unit configured to acquire the providing source data and the set-in-providing-source time information from the providing source information terminal. The time management unit  42  also functions as a calculation unit configured to calculate the providing time information to be provided to the providing destination information terminal by using the set-in-providing-source time information and the inter-terminal reference time. Moreover, the time management unit  42  also functions as a providing unit configured to provide the providing source data and the providing time information to the providing destination information terminal.  
      The time management unit  42  acquires the providing source data associated with the terminal identification data of the providing source information terminal, the providing time information, and the terminal identification data of the providing destination information terminal, from the providing source information terminal through the I/F  41   a  or the communication unit  41   b . The time management unit  42  may acquire the set-in-providing-source time information and the like provided by the information terminals  10   a  to  10   c  themselves. Alternatively, the time management unit  42  may request the set-in-providing-source time information to the information terminals  10   a  to  10   c  connecting to the time management server  40   a , and may acquire the set-in-providing-source time information and the like provided in response to the request.  
      Moreover, the time management unit  42  may acquire the data time information and the terminal reference time at the same time, or may acquire either one thereof first. For example, the time management unit  42  first acquires the terminal reference time and the providing source data. In this case, the time management unit  42  receives the notice as to whether or not the data time information is associated with the providing source data. Then, when the data time information is associated with the providing source data, the time management unit  42  may request the data time information to the information terminals  10   a  to  10   c , and then acquire the data time information.  
      The time management unit  42  acquires the inter-terminal reference time from the reference time management device  20  through the I/F  41   a  or the communication unit  41   b . As described above, it is preferable that the time management unit  42  acquire the inter-terminal reference time after starting the processing for making the times of the providing source information terminal and providing destination information terminal coincide with each other, and acquire the inter-terminal reference time for each processing.  
      The time management unit  42  first calculates a difference based on the acquired set-in-providing-source time information and the inter-terminal reference time. For example, when acquiring the terminal reference time as the set-in-providing-source time information, the time management unit  42  can calculate a difference based on the terminal reference time and the inter-terminal reference time. When acquiring the data time information as the set-in-providing-source time information, the time management unit  42  can calculate a difference between the terminal reference time and the data time information. When providing the providing time information including the difference based on the set-in-providing-source time information and the inter-terminal reference time and the inter-terminal reference time, the time management unit  42  registers the acquired providing source data, the terminal identification data of the providing destination information terminal, and the calculated difference and the inter-terminal reference time which are the providing time information in association with the terminal identification data of the providing source information terminal in the storage unit  43 .  
      When providing the providing time information including the calculated set time information, the time management unit  42  further calculates the calculated set time information based on the difference and the inter-terminal reference time. For example, when calculating the difference between the terminal reference time of the providing source information terminal and the inter-terminal reference time, the time management unit  42  can calculate the terminal reference time as the calculated set time information by adding the difference to the inter-terminal reference time. Moreover, when calculating the difference based on the data time information of the providing source information terminal and the inter-terminal reference time, the time management unit  42  can calculate the data time information as the calculated set time information by correcting the data time information with the inter-terminal reference time and the difference. In this case, the time management unit  42  registers the acquired providing source data, the terminal identification data of the providing destination information terminal and the calculated set time information serving as the providing time information in association with the terminal identification data of the providing source information terminal in the storage unit  42 .  
      When providing the providing time information including the difference based on the set-in-providing-source time information and the inter-terminal reference time and the inter-terminal reference time or the providing time information including the calculated set time information, in the case of providing the acquired set-in-providing-source time information as the providing time information, the time management unit  42  registers the set-in-providing-source time information in the storage unit  43 . In the case of not providing the set-in-providing-source time information, the time management unit  42  may register the set-in-providing-source time information, or may discard the same without storing.  
      The time management unit  42  acquires the providing source data, the terminal identification data of the providing source information terminal and the providing destination information terminal, and the providing time information from the storage unit  43 . The time management unit  42  provides the providing source data and the providing time information associated with the terminal identification data of the providing source information terminal to the providing destination information terminal through the I/F  41   a  or the communication unit  41   b . The time management unit  42  may provide the providing source data and the providing time information at the same time, or may provide either one thereof first. Moreover, the time management unit  42  may provide the set-in-providing-source time information, and the difference and the inter-terminal reference time or the calculated set time information, which are the providing time information at the same time, or may provide either one thereof first.  
      Each of the time management servers  40   a  and  40   b  as described above can be achieved by allowing a computer to carry out a program for allowing the computer to function as: an acquisition unit configured to acquire the providing source data and the set-in-providing-source time information from the providing source information terminal; a calculation unit configured to calculate the providing time information to be provided to the providing destination information terminal by using the set-in-providing-source time information arid the inter-terminal reference time, and a providing unit configured to provide the providing source data and the providing time information to the providing destination information terminal.  
      (Time Management Method)  
      Next, a procedure of a time management method using the time management system  100  will be described. Description will be made below of the case where the information terminals  10   a  and  10   b  connect as the providing source information terminal and the providing destination information terminal to the time management server  40   a , respectively.  FIG. 5  shows a procedure of the case where the information terminal  10   b  calculates the terminal reference time as the calculated set time information.  
      The time management server  40   a  requests the terminal reference time to the information terminal  10   a  connecting thereto as the providing source information terminal (S 101 ). In response to the request, the information terminal  10   a  provides the providing source data and the terminal reference time of the self-set time information, as the set-in-providing-source time information (S 102 ). In this case, the information terminal  10   a  notifies that the data time information is associated with the providing source data.  
      The time management server  40   a  determines whether or not there exists the data time information associated with the acquired providing source data (S 103 ). When the data time information exists, the time management server  40   a  requests the data time information to the information terminal  10   a  (S 104 ). Then, the information terminal  10   a  provides the data time information to the time management server  40   a  (S 105 ). Next, the time management server  40   a  acquires the inter-terminal reference time from the reference time management device  20  (S 106 ). The time management server  40   a  goes to Step S 106  also in the case of determining in Step S 103  that the data time information associated with the providing source data does not exist. Note that the time management server  40   a  may acquire the terminal reference time and the data time information at the same time, or may first acquire the data time information and then acquire the terminal reference time.  
      The time management server  40   a  calculates the difference between the inter-terminal reference time and the terminal reference time acquired from the information terminal  10   a , and registers the difference with the providing source data and the like in the storage unit  43  (S 107 ). To the information terminal  10   b , the time management server  40   a  provides the providing source data, and as the providing time information, the difference between the inter-terminal reference time and the terminal reference time acquired from the information terminal  10   a , which is calculated in Step S 107 , and the inter-terminal reference time acquired in Step S 106  (S 108 ). The information terminal  10   b  calculates, as the calculated set time information, the terminal reference time in the information terminal  10   a  based on the acquired difference and inter-terminal reference time. The information terminal  10   b  registers the acquired providing source data and the calculated terminal reference time (calculated set time information) in the storage area of the storage unit  15  for storing the information of the information terminal  10   a  (S 109 ).  
      The time management server  40   a  determines whether there exists the data time information as the set-in-providing-source time information of the information terminal  10   a  (S 110 ). When the data time information exists, the time management server  40   a  provides the data time information to the information terminal  10   b  (S 111 ). The information terminal  10   b  changes the acquired data time information based on the terminal reference time (calculated set time information) of the information terminal  10   a , which is registered in the storage unit  15 , and registers the changed data time information in the storage area of the storage unit  15  for storing the information of the information terminal  10   a  (S 112 ). When it is determined in Step S 110  that the data time information does not exist, the time management server  40   a  ends the processing.  
       FIG. 6  shows a procedure of the case where the time management server  40   a  calculates the terminal reference time as the calculated set time information. First, Steps S 201  to S 207  similar to Steps S 101  to S 107  shown in  FIG. 5  are performed. Subsequently to Step S 207 , the time management server  40   a  calculates, as the calculated set time information, the terminal reference time in the information terminal  10   a  based on the difference between the inter-terminal reference time and the terminal reference time acquired from the information terminal  10   a , which is calculated in Step S 207 , and the inter-terminal reference time (S 208 ).  
      The time management server  40   a  provides the providing source data, and the calculated set time information as the providing time information, that is, the calculated terminal reference time in the information terminal  10   a , to the information terminal  10   b  (S 209 ). The information terminal  10   b  registers the acquired terminal reference time (calculated set time information) in the information terminal  10   a  in the storage area of the storage unit  15  for storing the information of the information terminal  10   a  (S 210 ). Then, Steps S 211  to S 213  similar to Steps S 110  to S 112  shown in  FIG. 5  are performed.  
       FIG. 7  shows a procedure where the information terminal  10   b  calculates the data time information as the calculated set time information. First, Steps S 301  to S 306  similar to Steps S 101  to S 106  shown in  FIG. 5  are performed. The time management server  40   a  calculates the difference based on the inter-terminal reference time and the data time information acquired from the information terminal  10   a , and registers the difference with the providing source data and the like in the storage unit  43  (S 307 ). The time management server  40   a  first provides the providing source data and the terminal reference time of the information terminal  10   a , which is the set-in-providing-source time information, as the providing time information, to the information terminal  10   b  (S 308 ). The information terminal  10   b  registers the acquired providing source data and terminal reference time of the information terminal  10   a  in the storage area of the storage unit  15  for storing the information of the information terminal  10   a  (S 309 ).  
      The time management server  40   a  determines whether there exists the data time information as the set-in-providing-source time information of the information terminal  10   a  (S 310 ). When the data time information exists, the time management server  40   a  provides, as the providing time information, the difference based on the inter-terminal reference time and the data time information acquired from the information terminal  10   a , which is calculated in Step S 307 , and the inter-terminal reference time acquired in Step S 306 , to the information terminal  10   b  (S 311 ). The information terminal  10   b  calculates, as the calculated set time information, the data time information in the information terminal  10   a  based on the acquired difference and inter-terminal reference time. The information terminal  10   b  registers the calculated data time information (calculated set time information) in the storage area of the storage unit  15  for storing the information of the information terminal  10   a  (S 312 ). When it is determined in Step S 310  that the data time information does not exist, the time management server  40   a  ends the processing.  
       FIG. 8  shows a procedure of the case where the time management server  40   a  calculates the data time information as the calculated set time information. First, Steps S 401  to S 410  similar to Steps S 301  to S 310  shown in  FIG. 7  are performed. When it is determined in Step S 410  that the data time information exists, the time management server  40   a  calculates, as the calculated set time information, the data time information in the information terminal  10   a  based on the difference on the basis of the inter-terminal reference time and the data time information acquired from the information terminal  10   a , which is calculated in Step S 407 , and the inter-terminal reference time (S 411 ).  
      The time management server  40   a  provides, to the information terminal  10   b , the calculated set time information as the providing time information, that is, the data time information in the information terminal  10   a , which is calculated in Step S 411  (S 412 ). The information terminal  10   b  registers the acquired data time information (calculated set time information) in the information terminal  10   a  in the storage area of the storage unit  15  for storing the information of the information terminal  10   a  (S 413 ). When it is determined in Step S 410  that the data time information does not exist, the time management server  40   a  ends the processing.  
      According to the time management system  100 , the time management servers  40   a  and  40   b , the information terminals  10   a  to  10   c , and the time management method, which are as described above, the time management servers  40   a  and  40   b  can provide the providing time information associated with the providing source data, which is calculated by using the set-in-providing-source time information and the inter-terminal reference time to the providing destination information terminal. Therefore, the providing destination information terminal can easily maintain the relationship between the providing source data and the set-in-providing-source time information in the providing source information terminal based on the acquired providing source data and providing time information. In particular, even in the case where the providing source information terminal provides the providing source data to plural providing destination information terminals, the relationship between the providing source data and the set-in-providing-source time information in the providing source information terminal can be easily maintained in the plural providing destination information terminals. Specifically, the relationship between the providing source data in the providing source information terminal and the terminal reference time or the data time information can be maintained in the providing destination information terminal.  
      Moreover, when each of the time management servers  40   a  and  40   b  calculates, as the providing time information, the difference based on the set-in-providing-source time information and the inter-terminal reference time, and provides the difference and the inter-terminal reference time, the providing destination information terminal can calculate the calculated set time information by using the difference and the inter-terminal reference time. Therefore, for example, control loads of the time management servers  40   a  and  40   b  can be reduced. Furthermore, when the time management servers  40   a  and  40   b  calculate and provide the calculated set time information as the providing time information, the providing destination information terminal can use the calculated set time information as it is. Therefore, for example, a control load of the providing destination information terminal can be reduced.  
      Moreover, the information terminals  10   a  to  10   c  can acquire the providing source data and the providing time information calculated by using the set-in-providing-source time information and the inter-terminal reference time from the time management servers  40   a  and  40   b . Then, based on the providing time information, the information terminals  10   a  to  10   c  can register the calculated set time information associated with the providing source data in the storage unit  15 . Therefore, in the case of serving as the information destination terminals, the information terminals  10   a  to  10   c  can easily maintain the relationship between the providing source data and the set-in-providing-source time information in the providing source information terminal.  
      Furthermore, the time management unit  12  can also acquire, as the providing time information, the difference based on the set-in-providing-source time information and the inter-terminal reference time and the inter-terminal reference time, calculate the calculated set time information based on the difference and the inter-terminal reference time, and register the calculated set time information in the storage unit  15 . According to this, each of the information terminals  10   a  to  10   c  can acquire, as the providing time information, the difference based on the set-in-providing-source time information and the inter-terminal reference time and the inter-terminal reference time from the time management servers  40   a  and  40   b , and calculate the calculated set time information by using the difference and the inter-terminal reference time.  
      [Second Embodiment] 
      As shown in  FIG. 9 , a time management system  200  includes the plural information terminals  10   a  and  10   b , the reference time management device  20 , and the network  30 . As described above, the time management system  200  can be configured without using the time management servers  40   a  and  40   b . In  FIG. 9 , the same reference numerals are assigned to substantially similar configurations to those in  FIG. 1 , and description thereof will be omitted. As shown in  FIG. 9 , the information terminals  10   a  and  10   b  may be connected to each other not through the network  30 , or may be connected to each other through the network  30 .  
      When serving as the providing source information terminal, each of the information terminals  10   a  and  10   b  calculates the difference based on the set-in-providing-source time information and the inter-terminal reference time, and provides the providing source data and the difference to the providing destination information terminals. When serving as the providing destination information terminal, each of the information terminals  10   a  and  10   b  acquires the providing source data and the difference from the providing source information terminal, calculates the calculated set time information based on the difference and the inter-terminal reference time, and registers the calculated set time information associated with the providing source data in the storage unit.  
      In the case of not using the time management servers  40   a  and  40   b , the time management unit  12  shown in  FIG. 2  functions as a calculation unit configured to calculate the difference based on the set-in-providing-source time information and the inter-terminal reference time. Moreover, the time management unit  12  also functions as a providing unit configured to provide the providing source data and the difference to the providing destination information terminal. Furthermore, the time management unit  12  functions as an acquisition unit configured to acquire the providing source data and the difference based on the set-in-providing-source time information of the providing source information terminal and the inter-terminal reference time from the providing source information terminal. Further, the time management unit  12  also functions as a registering unit configured to calculate the calculated set time information based on the difference and the inter-terminal reference time, and register the calculated set time information associated with the providing source data in the storage unit  15 .  
      When the information terminal  10   a  serves as the providing source information terminal, the time management unit  12  acquires the user data and the control data as the providing source data, and the self-set time information such as the data time information and the terminal reference time as the set-in-providing-source time information from the storage area  15   a  of the storage unit  15 . The time management unit  12  acquires the inter-terminal reference time from the reference time management device  20  through the communication unit  11   b.    
      For example, when acquiring the terminal reference time of the information terminal  10   a , which is the self-set time information, as the set-in-providing-source time information from the storage unit  15 , the time management unit  12  can calculate the difference based on the terminal reference time of the information terminal  10   a  and the inter-terminal reference time. When acquiring the data time information of the information terminal  10   a , which is the self-set time information, as the set-in-providing-source time information from the storage unit  15 , the time management unit  12  can calculate the difference based on the data time information of the information terminal  10   a  and the inter-terminal reference time. The time management unit  12  may calculate both the difference based on the terminal reference time and the inter-terminal reference time and the difference based on the data time information and the inter-terminal reference time, or may calculate either one thereof.  
      The time management unit  12  provides the acquired providing source data, the calculated difference, and the terminal identification data “A” of the information terminal  10   a  in association with each other to the providing destination information terminal through the I/F  11   a  or the communication unit  11   b . In addition to the difference, the time management unit  12  may provide the set-in-providing-source time information. For example, when providing the difference based on the terminal reference time of the information terminal  10   a  and the inter-terminal reference time, the time management unit  12  can provide the data time information of the information terminal  10   a  as the set-in-providing-source time information. Moreover, when providing the difference based on the data time information of the information terminal  10   a  and the inter-terminal reference time, the time management unit  12  can provide the terminal reference time of the information terminal  10   a  as the set-in-providing-source time information.  
      The time management unit  12  may provide the providing source data and the calculated difference at the same time, or may provide either one thereof first. For example, the time management unit  12  may provide the providing source data before calculating the difference, or may provide the providing source data thereafter. Moreover, also in the case of providing the set-in-providing-source time information in addition to the difference, the time management unit  12  may provide the difference and the set-in-providing-source time information at the same time, and may provide either one thereof first.  
      When the information terminal  10   a  serves as the providing destination information terminal, the time management unit  12  acquires the providing source data and the difference based on the set-in-providing-source time information of the providing source information terminal and the inter-terminal reference time through the I/F  11   a  or the communication unit  11   b . The time management unit  12  acquires the inter-terminal reference time from the reference time management device  20  through the communication unit  11   b.    
      The time management unit  12  calculates the calculated set time information based on the acquired difference and inter-terminal reference time. When acquiring the difference based on the terminal reference time of the providing source information terminal and the inter-terminal reference time, the time management unit  12  can calculate, as the calculated set time information, the terminal reference time in the providing source information terminal by adding the difference to the inter-terminal reference time. Moreover, when acquiring the difference based on the data time information of the providing source information terminal and the inter-terminal reference time, the time management unit  12  can calculate, as the calculated set time information, the data time information in the providing source information terminal by adding the difference to the inter-terminal reference time.  
      In a similar way to the case of the time management system  100  shown in  FIG. 1 , the time management unit  12  registers the calculated set time information associated with the providing source data in the storage area for the corresponding providing information terminal in the storage unit  15 . Note that the information terminals  10   a  and  10   b  operate in a similar way to the time management system  100  shown in  FIG. 1 , except these points.  
      Such functions of the information terminals  10   a  and  10   b  as the providing source information terminals can be achieved by allowing a computer to carry out a program for allowing the computer to function as: a calculation unit configured to calculate the difference based on the set-in-providing-source time information and the inter-terminal reference time, and a providing unit configured to provide the difference associated with the providing source data to the providing destination information terminal.  
      Moreover, such functions of the information terminals  10   a  and  10   b  as the providing destination information terminals can be achieved by allowing a computer to carry out a program for allowing the computer to function as: a storage unit configured to store the calculated set time information associated with the providing source data of the providing source information terminal, an acquisition unit configured to acquire the providing source data and the difference based on the set-in-providing-source time information of the providing source information terminal and the inter-terminal reference time from the providing source information terminal, and a registering unit configured to calculate the calculated set time information based on the difference and the inter-terminal reference time, and register the calculated set time information associated with the providing source data in the storage unit.  
      (Time Management Method)  
      Next, a procedure of a time management method using the time management system  200  will be described. Description will be made below of the case where the information terminal  10   a  serves as the providing source information terminal and the information terminal  10   b  serves as the providing destination information terminal.  FIG. 10  shows a procedure of the case where the information terminal  10   b  calculates the terminal reference time as the calculated set time information.  
      The information terminal  10   a  acquires the inter-terminal reference time from the reference time management device  20  (S 501 ). The information terminal  10   a  determines whether or not the data time information is associated with the user data and the control data, which are stored in the storage area  15   a  of the storage unit  15  (S 502 ). When the data time information is associated with those data, the information terminal  10   a  provides the data time information of the information terminal  10   a  as the set-in-providing-source time information to the information terminal  10   b  (S 503 ).  
      Next, the information terminal  10   a  calculates the difference based on the terminal reference time of the information terminal  10   a , which is the set-in-providing-source time information, and the inter-terminal reference time (S 504 ). Note that, even when it is determined in Step S 502  that the data time information is not associated, the information terminal  10   a  goes to Step S 504 , where it calculates the difference. The information terminal  10   a  provides the difference calculated in Step S 504  and the providing source data to the information terminal  10   b  (S 505 ).  
      The information terminal  10   b  acquires the inter-terminal reference time from the reference time management device  20  (S 506 ). The information terminal  10   b  calculates, as the calculated set time information, the terminal reference time in the information terminal  10   a  based on the acquired difference and the inter-terminal reference time. The information terminal  10   b  registers the acquired providing source data and the calculated terminal reference time (calculated set time information) in the storage area of the storing unit  15  for storing the information terminal  10   a  (S 507 ).  
      The information terminal  10   b  determines whether or not the information terminal  10   b  have acquired the data time information as the set-in-providing-source time information of the information terminal  10   a  (S 508 ). When having acquired the data time information, the information terminal  10   b  changes the acquired data time information based on the terminal reference time (calculated set time information) of the information terminal  10   a , which is registered in the storage unit  15 , and registers the changed data time information in the storage area of the storage unit  15  for storing the information of the information terminal  10   a  (S 509 ). In the case of determining in Step S 508  that the information terminal  10   b  has not acquired the data time information, the information terminal  10   b  ends the processing.  
       FIG. 11  shows a procedure of the case where the information terminal  10   b  calculates the data time information as the calculated set time information. The information terminal  10   a  acquires the inter-terminal reference time from the reference time management device  20  (S 601 ). The information terminal  10   a  determines whether or not the data time information is associated with the user data and the control data, which are stored in the storage area  15   a  of the storage unit  15  (S 602 ). When the data time information is associated with those data, the information terminal  10   a  calculates the difference based on the data time information of the information terminal  10   a , which is the set-in-providing-source time information, and the inter-terminal reference time (S 603 ).  
      The information terminal  10   a  provides the difference calculated in Step S 603  and the data time information of the information terminal  10   a  as the set-in-providing-source time information to the information terminal  10   b  (S 604 ). Next, the information terminal  10   a  provides the providing source data and the terminal reference time of the information terminal  10   a  as the set-in-providing-source time information to the information terminal  10   b  (S 605 ). Note that, even when it is determined in Step S 602  that the data time information is not associated, the information terminal  10   a  goes to Step S 605 , where it provides the terminal reference time of the information terminal  10   a  to the information terminal  10   b.    
      The information terminal  10   b  registers the acquired providing source data and the terminal reference time of the information terminal  10   a  in the storage area of the storage unit  15  for storing the information of the information terminal  10   a  (S 606 ). The information terminal  10   b  determines whether or not the information terminal  10   b  have acquired the data time information as the set-in-providing-source time information of the information terminal  10   a  (S 607 ). In the case of having acquired the data time information, the information terminal  10   b  acquires the inter-terminal reference time from the reference time management device  20  (S 608 ).  
      Then, the information terminal  10   b  calculates, as the calculated set time information, the data time information in the information terminal  10   a  based on the difference acquired in Step S 604  and the inter-terminal reference time. The information terminal  10   b  registers the calculated data time information (calculated set time information) in the storage area of the storage unit  15  for storing the information of the information terminal  10   a  (S 609 ). In the case of determining in Step S 607  that the information terminal  10   b  has not acquired the data time information, the information terminal  10   b  ends the processing.  
      According to the time management system  200 , the information terminal  10   a  and  10   b  and the time management method, each of the information terminals  10   a  and  10   b  serves as the providing source information terminal, and can provide the providing source data and the difference based on the set-in-providing-source time information and the inter-terminal reference time to the providing destination information terminal. Therefore, based on the acquired providing source data and providing time information, the information destination terminal can easily maintain the relationship between the providing source data and the set-in-providing-source time information in the providing source information terminal.  
      Moreover, each of the information terminals  10   a  and  10   b  serves as the providing destination information terminal, and can acquire the providing source data and the difference based on the set-in-providing-source time information and the inter-terminal reference time from the providing source information terminal. Then, each of the information terminals  10   a  and  10   b  can calculate the calculated set time information based on the difference and the inter-terminal reference time, and can register the calculated set time information associated with the providing source data in the storage unit. Therefore, the providing destination information terminal can easily maintain the relationship between the providing source data and the set-in-providing-source time information in the providing source information terminal.  
      In particular, even when the providing source information terminal provides the providing source data to plural providing destination information terminals, the relationship between the providing source data and the set-in-providing-source time information in the providing source information terminal can be easily maintained in the plural providing destination information terminals. Specifically, the relationship between the providing source data and the terminal reference time or the data time information in the providing source information terminal can be maintained in the providing destination information terminal.  
      Although the inventions have been described above by reference to certain embodiments of the inventions, the inventions are not limited to the embodiments described above. Modifications and variations of the embodiments described above will occur to those skilled in the art, in light of the above teachings. For example, either one of the time management servers  40   a  and  40   b  may store and provide the inter-terminal reference time, and function as the reference time management device  20 .