Abstract:
A transmitting apparatus for transmitting data is disclosed, that comprises a means for allowing update notification information notifying a receiving side that data that is transmitted has been updated to contain information that identifies an updated data portion.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to a transmitting apparatus, a receiving apparatus, a transmitting-receiving system, a transmitting method, and a receiving method for transmitting and receiving data, in particular, those for delivering data to an unspecific number of clients such as many distributed databases.  
           [0003]    2. Description of the Related Art  
           [0004]    The applicant of the present invention has proposed a method for structuring a system that provides a service to a unspecific number of clients using a synchronous managing method based on a broadcast protocol for directory servers (referred to as Japanese Patent Application Nos. 10-277352 and 10-2773532). In those related art references, when a part or all of attributes of an entry are updated, the update information is filtered for a predetermined number of container entries at a time.  
           [0005]    Depending on the type of an application for a provided service, detailed conditions corresponding to a combination of a class and an attribute of an entry that is updated should be designated so as to filter update information. When the contents of a directory are structured for inquiring genre information or fee information, update information representing that fee information of the contents of a particular genre has changed should be extracted. A directory on the reception side should be selectively updated corresponding to the extracted update information.  
           [0006]    Next, such a situation will be practically described. In an environment of which a directory server that has a limited performance and a limited storage capacity as with a home set box is disposed on the receiving side, it may be impossible to obtain all directory update information that is broadcast. In such a situation, it is necessary to selectively obtain update information so as to reduce unnecessary storage cost and message process cost.  
           [0007]    As the directory tree that is transmitted becomes large, a process for selecting update information becomes important. However, conventional transmitting systems have not considered such a process.  
         OBJECTS AND SUMMARY OF THE INVENTION  
         [0008]    Therefore, an object of the present invention is to provide a transmitting apparatus, a receiving apparatus, a transmitting-receiving system, a transmitting method, and a receiving method that allow information representing that a particular attribute value of an entry that belongs to a particular class has been updated to be effectively transmitted corresponding to for example a request issued on the receiving side.  
           [0009]    A first aspect of the present invention is a transmitting apparatus for transmitting data, comprising a means for allowing update notification information notifying a receiving side that data that is transmitted has been updated to contain information that identifies an updated data portion.  
           [0010]    A second aspect of the present invention is a receiving apparatus for receiving data, comprising a means for receiving the data and update notification information notifying the receiving apparatus that the data has been updated and identifying a particular portion of an updated data portion corresponding to the received update notification information.  
           [0011]    A third aspect of the present invention is a transmitting-receiving system, comprising a transmitting unit for transmitting data, and a receiving unit for receiving transmitted data, wherein the transmitting unit transmits the data and update notification information notifying a receiving side that the data has been updated, the update notification information containing information identifying an updated data portion, and wherein the receiving unit receives the data and the update notification information and identifies a particular portion of an updated data portion corresponding to the received update notification information.  
           [0012]    A fourth aspect of the present invention is a transmitting method for transmitting data, comprising the step of allowing update notification information notifying a receiving side that data that is transmitted has been updated to contain information that identifies an updated data portion.  
           [0013]    A fifth aspect of the present invention is a receiving method for receiving data, comprising the step of receiving the data and update notification information notifying the receiving apparatus that the data has been updated and identifying a particular portion of an updated data portion corresponding to the received update notification information.  
           [0014]    According to the above-described aspects of the present invention, under a designated condition corresponding to a class and/or attribute of an entry that is updated, update information that is required on the receiving side can be extracted. 
       
    
    
       [0015]    These and other objects, features and advantages of the present invention will become more apparent in light of the following detailed description of a best mode embodiment thereof, as illustrated in the accompanying drawings.  
       BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]    [0016]FIG. 1 is a block diagram showing an example of the structure of a transmitting-receiving system according to the present invention;  
         [0017]    [0017]FIG. 2 is a block diagram showing the structure of a part of the system shown in FIG. 1;  
         [0018]    [0018]FIG. 3 is a schematic diagram for explaining a directory tree;  
         [0019]    [0019]FIG. 4 is a schematic diagram for explaining an entry;  
         [0020]    [0020]FIGS. 5A and 5B are schematic diagrams for explaining an attribute set defined for each class;  
         [0021]    [0021]FIG. 6 is a flow chart showing an example of a synchronous managing process for a container hierarchical structure;  
         [0022]    [0022]FIG. 7 is a detailed flow chart showing a part of the process shown in FIG. 6;  
         [0023]    [0023]FIG. 8 is a detailed flow chart showing another part of the process shown in FIG. 6;  
         [0024]    [0024]FIG. 9 is a flow chart showing an example of a leaf entry synchronous managing process;  
         [0025]    [0025]FIG. 10 is a detailed flow chart showing a part of the process shown in FIG. 9;  
         [0026]    [0026]FIG. 11 is a detailed flow chart showing another part of the process shown in FIG. 9;  
         [0027]    [0027]FIG. 12 is a flow chart showing a part of a filter designating process performed on the receiving side;  
         [0028]    [0028]FIG. 13 is a flow chart showing another part of the process shown in FIG. 12;  
         [0029]    [0029]FIG. 14 is a schematic diagram showing a real example of an entry class mask schema;  
         [0030]    [0030]FIG. 15 is a flow chart showing a part of a process for designating an entry class as an object of a filtering process performed on the receiving side;  
         [0031]    [0031]FIG. 16 is a flow chart showing another part of the process shown in FIG. 15; and  
         [0032]    [0032]FIG. 17 is a schematic diagram for explaining an effect of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0033]    Next, an embodiment of the present invention will be described. FIG. 1 shows an example of the structure of a data transmitting-receiving system according to an embodiment of the present invention. A transmitting side  1  manages many contents on a network (not shown) such as the Internet or a broadcast network in a tree-shaped hierarchical structure. The transmitting side  1  transmits directory information that represents the directory structure to a broadcast network  2 .  
         [0034]    As shown in FIG. 2, on the receiving side  3 , many receivers are connected to the broadcast network  2 . Each of receivers on the receiving side  3  can receive a broadcast through the broadcast network  2 . The receiving side  3  receives directory information that is broadcast through the broadcast network  2 , selects desired information from many contents on the broadcast network  2  and other networks, and obtain the selected information.  
         [0035]    As shown in FIG. 1, the transmitting side  1  is composed of a transmission side directory service client  10  (hereinafter, referred to as transmitting side client  10 ), a transmitting side directory server  11  (hereinafter, referred to as transmitting side server  11 ), and a transmitting side directory server replicater  12  (hereinafter, referred to as transmitting side replicater  12 ). The transmitting side client  10 , the transmitting side server  11 , and the transmitting side replicater  12  are mutually connected thorough for example the Internet or a broadcast network and they are mutually communicated.  
         [0036]    The transmitting side client  10  is a contents provider that provides contents through for example a network (not shown). The transmitting side client  10  changes and updates the directory structure. The transmitting side client  10  can be disposed at any location of the network. For example, the transmitting side server  11  inquiries the transmitting side client  10  for its contents, changes them, and manages the directory structure. A plurality of transmitting side servers  11  can be distributed on the network. The transmitting side replicater  12  detects a change or the like made in the contents managed by the transmitting side server  11  and structures difference update information (that will be described later) corresponding to the detected result.  
         [0037]    The receiving side  3  creates a local directory structure corresponding to the received difference update information. The receiving side  3  is composed of a receiving side directory server replicater  17  (hereinafter, referred to as receiving side replicater  17 ), a receiving side directory server  16  (hereinafter, referred to as receiving side server  16 ), and a receiving side directory service client  15  (hereinafter, referred to as receiving side client  15 ). The receiving side  3  can be for example a personal computer, an STB (Set Top Box), or an IRD (Integrated Receiver Decoder).  
         [0038]    The receiving side client  15  is application software, for example, WWW (World Wide Web) browser that can access the directory structure, obtain a plurality of formats of data, and display them. The receiving side server  16  is composed of a local database that stores directory information.  
         [0039]    The difference update information transmitted on the broadcast network  2  is received by the receiving side replicater  17 . The receiving side replicater  17  updates a database stored in the receiving side server  16  corresponding to the received difference update information and recreates the directory structure. The receiving side client  15  requests the receiving side replicater  17  for required information corresponding to data that is input by the user. Thus, the receiving side replicater  17  searches the database of the receiving side server  16  for the required information and returns an address of the required information to the receiving side client  15 . The receiving side client  15  can access information on a network (not shown) corresponding to the information returned from the receiving side replicater  17 .  
         [0040]    Next, with reference to FIG. 3, the directory structure will be described. The directory is hierarchically structured in a tree shape. Each node of the tree is referred to as entry. Each entry contains information. There are three types of entries that are defined as a root entry, a container entry, and a leaf entry. A container entry is an entry that contains a lower hierarchical entry. Hereinafter, a hierarchy composed of container entries is referred to as container hierarchy.  
         [0041]    Entries other than a root entry and a container entry are referred to as leaf entries. A leaf entry is an end node that does not contain a lower hierarchical entry.  
         [0042]    The highest hierarchical entry of the directory tree is referred to as root entry. The root entry is an entry that represents the whole world of the directory structure. In the following description, it is assumed that a container entry contains at least one leaf entry or one container entry.  
         [0043]    Each entry has a plurality of attributes. Among them, a name that uniquely identifies an entry in the directory tree is referred to as entry name. With an entry name, the location of each entry can be designated in the directory structure. In the example, shown in FIG. 3, the root entry is assigned the entry name A. A leaf entry as an immediately lower hierarchical entry of the root entry is assigned the entry name A.B. A container entry as an immediately lower hierarchical entry of the root entry is assigned the entry name A.C. Likewise, each entry in the hierarchical structure is assigned a unique entry name that represents the path to the root entry and that is delimited by periods.  
         [0044]    Next, with reference to FIG. 4, the structure of an entry will be described. As was described above, each entry has a plurality of attributes. Among them, an attribute that represents the name of an entry uniquely identified in the directory tree is referred to as entry name. Each attribute is composed of a set of an attribute name and an attribute value. Each entry belongs to a particular class. As shown in FIGS. 5A and 5B, each class defines a set of particular attributes. Examples of classes are classes for video information and audio information.  
         [0045]    In this example, a class is an abstractive representation of a collection of objects that have the same characteristic. An object is a “substance” that exists in the real world. An example of an object is a book object “King Lear” written by Shakespeare. Another example of an object is a book object “I am a cat” written by Soseki Natsume. When the two book objects are abstractively represented, a class “book” can be defined. In the “book” class, an attribute name “title” and an attribute name “writer” can be defined.  
         [0046]    Next, a synchronous managing method for synchronizing directory information stored in the transmitting side server  11  on the transmitting side  1  with directory information stored in the receiving side server  16  on the receiving side  3  will be described. First of all, with reference to FIG. 6, the synchronous managing process of the hierarchical structure of container entries will be described. At step S 1 , the transmitting side client  10  changes the container hierarchical structure managed by the transmitting side server  11 . For example, the transmitting side client  10  performs a changing process for adding a new container entry or a leaf entry as an immediately lower hierarchical entry of a particular container entry. Alternatively, the transmitting side client  10  performs another changing process for deleting a container entry or a leaf entry as an immediately lower hierarchical entry of a particular container entry.  
         [0047]    At step S 2 , the transmitting side replicater  12  detects a change of the contents managed by the transmitting side server  11  and generates container structure update information (hereinafter, referred to as Msg.  1 ) corresponding to the detected result. The generated Msg.  1  is broadcast to the broadcast network  2 . The Msg.  1  is cyclically broadcast a predetermined number of times.  
         [0048]    At step S 3 , the Msg.  1  that has been broadcast at step S 2  is received by the receiving side replicater  17 . At step S 3 , the container hierarchical structure managed corresponding to the directory information stored in the receiving side server  16  is changed corresponding to the received Msg.  1 . As a result, the container hierarchical structure of the directory information is synchronized between the transmitting side  1  and the receiving side  3 .  
         [0049]    The format of the Msg.  1  is for example as follows:  
                                                                       Container Structure Update Message {                message ID           difference update information           Mask Schema                }                      
 
         [0050]    The “message ID” is identification information of the Msg.  1 . For example, the “message ID” is an integer that is incremented whenever the Msg.  1  is generated. The “difference update information” is information that represents the content of a change of the container hierarchical structure. The “mask schema” is mask information necessary for the receiving side  3  to selectively receive the Msg.  1  that is broadcast.  
         [0051]    The “mask schema” is defined for example as follows:  
                                                                       Mask Schema {                Mask Schema Version           Total Mask Length           Set of Container Entry Mask Schema                }                      
 
         [0052]    The “mask schema version” is similar to the “message ID”. The “total mask length” represents the total length of the mask values of the entire container entry hierarchy in the unit of bits or bytes. The mask value is a value of for example three bits assigned to each mask as will be described later. The “set of container entry mask schema” is a container entry mask schema that represents a mask corresponding to each container entry.  
         [0053]    The “container entry mask schema” is defined for example as follows.  
                                                                       Container Entry Mask Schema {                Container Entry Name           Offset Length           Mask Length           Assigned Mark Value                }                      
 
         [0054]    The “container entry name” is a character string as a container entry name. The “offset length” is an offset of a mask value that represents a mask corresponding to the relevant container entry against the first bit position or the first byte position of all the mask values. The “mask length” represents the length of a mask in the unit of bits or bytes. The “assigned mask value” is a bit (byte) string assigned as a mask value.  
         [0055]    Next, with reference to FIG. 7, the process performed at step S 2  will be described in detail. Each step of the process shown in FIG. 7 is performed by the transmitting side replicater  12 . At step S 10 , the transmitting side replicater  12  reads information of the container entry hierarchy managed by the transmitting side server  11  and stores the read information as a copy  1 . The copy  1  is stored to a record medium or a storage medium such as a memory or a hard disk of the transmitting side replicater  12 . At step S 11 , predetermined time is set to a timer and then the timer is started.  
         [0056]    At step S 12 , it is determined whether or not the predetermined time has elapsed. When the determined result at step S 12  is Yes (namely, the predetermined time has elapsed), the flow advances to step S 13 . Otherwise, the flow returns to step S 12 . At step S 13 , the information of the container entry hierarchy stored in the transmitting side server  11  is read and stored as a copy  2 . The copy  2  is stored to a record medium or a storage medium such as a memory or a hard disk of the transmitting side replicater  12 .  
         [0057]    At step S 14 , the content of the copy  1  is compared with the content of the copy  2 . At step S 15 , a process corresponding to the compared result is performed. In other words, when the determined result at step S 15  is Yes (namely, there is a difference between the content of the copy  1  and the content of the copy  2 ), the flow advances to step S 16 . Otherwise, the flow returns to step S 11 . At step S 16 , a Msg.  1  that is difference update information between the copy  1  and the copy  2  is generated. The generated Msg.  1  is broadcast to the receiving side replicater  17  through the broadcast network  2 . At step S 17 , the content of the copy  1  is substituted with the content of the copy  2 . Thereafter, the flow returns to step S 11 .  
         [0058]    In such a process, it is determined whether or not the hierarchical relation of container entries is changed at intervals of a predetermined time period. When a change of the hierarchical relation of container entries is detected, the Msg.  1  is generated corresponding to the detected result and then the generated Msg.  1  is broadcast.  
         [0059]    Next, with reference to FIG. 8, the process performed at step S 3  shown in FIG. 6 will be described in detail. Each step shown in FIG. 8 is performed by the receiving side replicater  17 . At step S 20 , the transmitting side replicater  12  receives the Msg.  1  that has been broadcast from the transmitting side replicater  12  through the broadcast network  2 . At step S 21 , it is determined whether or not the Msg.  1  has been received first time. When the determined result at step S 21  is Yes (namely, the Msg.  1  has been received first time), the flow advances to step S 23 . Otherwise, the flow advances to step S 22 .  
         [0060]    At step S 23 , the message ID of the Msg.  1  received at step S 20  is stored as a copy  3  to a record medium or a storage medium such as a memory or a hard disk of the receiving side replicater  17 . At step S 24 , corresponding to the difference update information contained in the Msg.  1  received at step S 20 , the directory information managed by the receiving side server  16  is updated. As a result, the structure of the container hierarchy represented by the directory information is updated. Thereafter, the flow returns to step S 20 .  
         [0061]    On the other hand, at step S 22 , it is determined whether or not the message ID of the Msg.  1  received at step S 20  is the same as the copy  3 . When the determined result at step S 20  is Yes (namely, the message ID of the Msg.  1  is the same as the copy  3 ), the flow returns to step S 20 . Otherwise, the flow advances to step S 23 .  
         [0062]    Next, with reference to FIG. 9, a synchronous managing method for leaf entries will be described. At step S 30 , the transmitting side client  10  updates leaf entries as immediately lower hierarchical entries of a particular container entry in the directory structure managed by the transmitting side server  11 . For example, the transmitting side client  10  adds a new leaf entry as an immediately lower hierarchical entry of a particular container entry. Alternatively, the transmitting side client  10  deletes or modifies a leaf entry as an immediately lower hierarchical entry of a particular container entry.  
         [0063]    At step S 31 , the transmitting side replicater  12  detects a change of a leaf entry as an immediately lower hierarchical entry of a particular container entry. Corresponding to the detected result, the transmitting side replicater  12  generates leaf entry update information (hereinafter, referred to as Msg. x 1 ) representing that a leaf entry as an immediately lower hierarchical entry of a particular container entry has been updated. The Msg. x 1  will be described later. The transmitting side replicater  12  cyclically broadcasts the generated Msg. x 1  to a plurality of receiving side replicaters  17  through the broadcast network  2 .  
         [0064]    At step S 32 , the receiving side replicater  17  receives the Msg. x 1  that has been broadcast. The receiving side replicater  17  changes a relevant leaf entry managed as directory information stored in the receiving side server  16  corresponding to the received Msg. x 1 . Thus, leaf entries as directory information are synchronized between the transmitting side  1  and the receiving side  3 .  
         [0065]    The format of the Msg. x 1  is for example as follows.  
                                                                       Leaf Entry Update Message {                Message ID           Filtering Mask           Difference Update Information                }                      
 
         [0066]    The “message ID” is identification information of the Msg. x 1 . The “message ID” is for example an integer that is incremented by 1 whenever the Msg. x 1  is newly generated. The “filtering mask” is information necessary for the receiving side  3  to selectively receive the Msg. x 1  that is broadcast. The “difference update information” is information representing that a leaf entry has been updated.  
         [0067]    The structure of the filtering mask is defined for example as follows:  
                                                                       Filtering Mask {                Mask Schema Version           Mask Value                }                      
 
         [0068]    The “mask schema version” is similar to the message ID. The “mask value” is a bit string or a byte string of a mask. The structure of the “mask value” is defined by a mask schema corresponding to the “mask schema version”. The “filtering mask” is used for a filtering process so that the receiving side  3  effectively selects information from many massages Msg. x 1  that are broadcast.  
         [0069]    Next, with reference to FIG. 10, the process performed at step S 31  will be described in detail. Each step of the process shown in FIG. 10 is performed by the transmitting side replicater  12 . At step S 40 , the names of all leaf entries as lower hierarchical entries of a particular container entry are read. The names of the leaf entries that have been read are stored as a copy  4  to a record medium or a storage medium such as a memory or a hard disk of the transmitting side replicater  12 .  
         [0070]    At step S 41 , predetermined time is set to a timer. At step S 42 , it is determined whether or not the predetermine time has elapsed in the timer. When the determined result at step S 42  is Yes (the predetermined time has elapsed), the flow advances to step S 43 . Otherwise, the flow returns to step S 42 . At step S 43 , the names of all leaf entries as lower hierarchical entries of a particular container entry of the transmitting side server  11  are read. The read hierarchical relation is stored as a copy  5 . The copy  5  is stored to a record medium or a storage medium such as a memory or a hard disk of the transmitting side replicater  12 .  
         [0071]    At step S 44 , the content of the copy  4  is compared with the content of the copy  5 . At step S 45 , it is determined whether or not there is a difference between the content of the copy  4  and the content of the copy  5 . When the determined result at step S 45  is Yes (namely, there is a difference between the content of the copy  4  and the content of the copy  5 ), the flow advances to step S 46 . Otherwise, the flow returns to step S 41 . At step S 46 , an Msg. x 1  as difference update information representing the difference between the copy  4  and the copy  5  is generated. The generated Msg. x 1  is broadcast to the receiving side replicater  17  through the broadcast network  2 . Thereafter, the flow advances to step S 47 . At step S 47 , the content of the copy  4  is substituted with the content of the copy  5 . Thereafter, the flow returns to step S 40 .  
         [0072]    The process shown in FIG. 10 is performed by the transmitting side replicater  12  for all container entries of the directory structure managed by the transmitting side server  11 .  
         [0073]    Next, with reference to FIG. 11, the process performed at step S 32  shown in FIG. 9 will be described in detail. Each step of the process shown in FIG. 11 is performed by the receiving side replicater  17 . At step S 50 , an Msg. x 1  that has been broadcast by the transmitting side replicater  12  through the broadcast network  2  is received. At step S 51 , it is determined whether or not the Msg. x 1  has been received first time. When the determined result at step S 51  is Yes (namely, the Msg. x 1  has been received first time), the flow advances to step S 53 . Otherwise, the flow advances to step S 52 .  
         [0074]    At step S 53 , the message ID of the Msg. x 1  received at step S 50  is stored as a copy  6 . The copy  6  is stored to a record medium or a storage medium such as a memory or a hard disk of the receiving side replicater  17 . At step S 54 , directory information managed by the receiving side server  16  is updated corresponding to the difference update information contained in the Msg. x 1  received at step S 50 . Leaf entries represented by the directory information are updated. Thereafter, the flow returns to step S 50 .  
         [0075]    At step S 52 , it is determined whether or not the message ID of the Msg. x 1  received at step S 50  is the same as the copy  6 . When the determined result at step S 52  is Yes (namely, the message ID of the Msg. x 1  is the same as the copy  6 ), the flow returns to step S 50 . Otherwise, the flow advances to step S 53 .  
         [0076]    Next, a filter designating process performed on the receiving side will be described. Before performing a filtering process, the receiving side replicater  17  should designate a portion of the container entry hierarchy. To do that, the receiving side replicater  17  performs a process for generating a target mask list (namely, data as a list of filtering masks corresponding to a portion of the container entry hierarchy required by the receiving side client  15 ). In addition, the receiving side replicater  17  performs a process for selectively receiving container structure update information Msg.  1 ′ containing filtering masks in the target mask list (the container structure update information Msg.  1 ′ will be described later).  
         [0077]    Next, with reference to FIG. 12, the process for generating a target mask list will be described. Each step of the process shown in FIG. 12 is performed by the receiving side replicater  17 . At step S 70 , container structure update information Msg.  1  is received. At step S 71 , it is determined whether or not the Msg.  1  has been received first time. When the determined result at step S 71  is Yes (namely, the Msg.  1  has been received first time), the flow advances to step S 73 . Otherwise, the flow advances to step S 72 .  
         [0078]    At step S 73 , the message ID of the Msg.  1  received at step S 70  is stored to a record medium or a storage medium such as a memory or a hard disk of the receiving side replicater  17 . At step S 74 , corresponding to the content of the container structure update information Msg.  1  received at step S 70 , a container entry hierarchy is generated. The generated container entry hierarchy is presented to the receiving side client  15  so as to prompt the user or the like for selecting a desired portion thereof. For example, the receiving side client  15  displays information of the supplied container entry hierarchy on a predetermined displaying portion. The user or the like selects a desired portion of the container entry hierarchy. Information representing the selected container entry hierarchy is supplied from the receiving side client  15  to the receiving side replicater  17 .  
         [0079]    At step S 75 , filtering masks corresponding to the container entry hierarchy selected at step S 74  are designated. A list of designated filtering masks is stored as a target mask list to a record medium or a storage medium such as a memory or a hard disk of the receiving side replicater  17 . Thereafter, the flow returns to step S 70 .  
         [0080]    At step S 72 , it is determined whether or not the message ID of the Msg.  1  received at step S 70  is the same as the copy  10 . When the determined result at step S 72  is Yes (namely, the message ID of the Msg.  1  is the same as the copy  10 ), the flow returns to step S 70 . Otherwise, the flow advances to step S 73 .  
         [0081]    Next, with reference to FIG. 13, the process for selectively receiving leaf update information Msg. x 1 ′ through the broadcast network  2  will be described. Each step of the process shown in FIG. 13 is performed by the receiving side replicater  17 . At step S 80 , the leaf update information Msg. x 1  is received. At step S 81 , it is determined whether or not a filtering mask of the Msg. x 1  received at step S 80  is contained in the target mask list. When the determined result at step S 81  is Yes (namely, a filtering mask of the Msg. x 1  is contained in the target mask list), the flow returns to step S 80 . Otherwise, the flow advances to step S 82 .  
         [0082]    At step S 82 , it is determined whether or not the Msg. x 1  has been received first time. When the determined result at step S 82  is Yes (namely, the Msg. x 1  has been received first time), the flow advances to step S 84 . Otherwise, the flow advances to step S 83 . At step S 84 , the message ID of the Msg. x 1  received at step S 80  is stored as a copy  11 . At step S 85 , the Msg. x 1  received at step S 80  is selected as an object that is processed. In other words, the Msg. x 1  is selected as an Msg. x 1 ′. Thereafter, the flow returns to step S 80 .  
         [0083]    At step S 83 , it is determined whether or not the message ID of the Msg. x 1  received at step S 80  is the same as the copy  11 . When the determined result at step S 83  is Yes (namely, the message ID of the Msg. x 1  is the same as the copy  11 ), the flow advances to step S 80 . Otherwise, the flow advances to step S 84 .  
         [0084]    According to the embodiment of the present invention, an entry class mask schema is used so as to filter update information of an entry corresponding to a class to which the entry belongs and attributes defined in the class. The entry class master schema is defined for example as follows:  
                                                                       Entry Class Mask Schema {                Entry Class Mask Schema Version           Total Entry Class Mask Length           Set of an Entry Class Mask Schema                }                      
 
         [0085]    The “entry class mask schema version” is an integer that is incremented by for example 1 whenever an entry class mask schema is generated (namely, an entry class is generated). The “total entry class mask length” represents the length of all mask values in the unit of bits or bytes. The “set of an entry class mask schema” is an array of entry class mask schemas that are entry class mask schema information corresponding to individual classes.  
         [0086]    The “an entry class mask schema” is defined for example as follows.  
                                                                       an Entry Class Mask Schema {                Entry Class Name           Off Set Length           Mask Length           Set of Attribute Mask                }                      
 
         [0087]    The “entry class name” is a character string representing the name of an entry class. The “off set length” represents an offset from the first bit (byte) position of the total class mask length corresponding to the entry class in the unit of bits or bytes. The “mask length” represents the length of a mask in the unit of bits or bytes. The “set of attribute mask” is an array of attribute masks.  
         [0088]    An attribute mask is defined for example as follows:  
                                                                       Attribute Mask {                Attribute Name           Assigned Mask Value                }                      
 
         [0089]    The “attribute name” is a character string representing an attribute name. The “assigned mask value” is a bit (byte) string assigned to the attribute.  
         [0090]    Next, a real example of an entry class mask schema will be described. An example of a class is a video contents class. Examples of attribute names of the video contents class are a “title”, a “rental fee”, and a “shop ID list”. These attribute names “title”, “rental fee”, and “shop ID list” are assigned for example “001”, “010”, and “100”, respectively. Thus, the mask length is three bits.  
         [0091]    Next, an example of an entry class mask schema will be described. In the following, a comment is described in parentheses “( )”. In a real entry class mask schema, a comment can be omitted.  
                                                                                                                                                                                     an Entry Class Mask Schema {                “Video” (Entry Class Name)           0 (Off Set Length)           3 (Mask Length)           Set of Attribute Mask {                Attribute Mask {                “title” (Attribute Name), 001                (Assigned Mask Value)                }           Attribute Mask {                “rental fee” (Attribute Name), 010                (Assigned Mask Value)                }           Attribute Mask {                “shop ID list” (Attribute Name),                100 (Assigned Mask Value)                }                }                }                      
 
         [0092]    Another example of a class is a book contents class. Examples of attribute names of the book contents class are a “title” and a “retail price”. These attribute names are assigned respective bit strings as assigned mask values. For example, “01” and “10” are assigned to “title” and “retail price”, respectively. Thus, the mask length is 2 bits.  
         [0093]    An example of an entry class mask schema is as follows. A comment is described in parentheses “( )”. In a real entry class mask schema, a comment can be omitted.  
                                                                                                                                                       an Entry Class Mask Schema {                “Book” (Entry Class Name)           3 (Off Set Length)           2 (Mask Length)           Set of Attribute Mask {                Attribute Mask {                “title” (Attribute Name), 01                (Assigned Mask Value)                }           Attribute Mask {                “rental price” (Attribute Name), 10                (Assigned Mask Value)                }                }                }                      
 
         [0094]    Next, an example of an entry class mask schema containing masks for the above-described video entry class and book entry class is as follows. A comment is described in parentheses “( )”. In a real entry class mask schema, a comment can be omitted.  
                                                                                                                                                                                                                                                                                         Entry Class Mask Schema {                1 (Entry Class Mask Schema Version)           5 (Total Entry Class Mask Length)           Set of an Entry Class Mask Schema {           an Entry Class Mask Schema {                “Video” (Entry Class Name)           0 (Off Set Length)           3 (Mask Length)           Set of Attribute Mask {                Attribute Mask {                “title” (Attribute Name), 001            (Assigned Mask Value)                }           Attribute Mask {                “rental fee” (Attribute name),            010 (Assigned Mask Value)                }           Attribute Mask {                “shop ID list” (Attribute            Name), 100 (Assigned Mask Value)                }                }                }           an Entry Class Mask Schema {                “Book” (Entry Class Name)           3 (Off Set Length)           2 (Mask Length)           Set of Attribute Mask {                Attribute Mask {                “title” (Attribute Name), 01            (Assigned Mask Value)                }           Attribute Mask {                “rental price” (Attribute            Name), 10 (Assigned Mask Value)                }                }                }                }                      
 
         [0095]    In the above-described entry class mask schema, the total entry class mask length is 5. The off set lengths of the entry class mask schemas for “video” and “book” are 0 (bit) and 3 (bits), respectively. Thus, as shown in FIG. 14, a mask bit string of 3 bits for “video” and a mask bit string of 2 bits for “book” are described (namely, a total of 5 bits).  
         [0096]    Next, a notifying process for notifying the receiving side of a generated entry class mask schema will be described. When a new entry class is defined in the transmitting side server  11  and the receiving side server  16 , the transmitting side replicater  12  notifies a plurality of receiving side replicaters  17  of an entry class mask schema update message (hereinafter, referred to as Msg. y 1 ) through the broadcast network  2 . The Msg. y 1  contains an entry class mask schema. At that point, the entry class is defined by the transmitting side server  11  and the receiving side server  16  at the same time.  
         [0097]    The Msg. y 1  is defined for example as follows.  
                                                                       Entry Class Mask Schema Update Message {                Message ID           Entry Class Mask Schema                }                      
 
         [0098]    The “message ID” is an integer that is incremented by for example 1 whenever the Msg. y 1  is generated. The “entry class mask schema” contains the above-described entry class mask schema.  
         [0099]    Next, selections of an entry class and attributes thereof used in the filtering process performed on the receiving side will be described. When the receiving side replicater  17  receives the Msg. y 1 , the receiving side replicater  17  performs a filtering process for entry difference update information corresponding to the received Msg. y 1 . Before performing the filtering process, the receiving side client  15  should designate an entry class for the filtering process.  
         [0100]    Such an entry class can be designated when a filtering region of a container hierarchy is designated. In other words, a product of a condition for an entry class and a condition for a filtering region of the container hierarchy may be used as a filtering condition. Alternatively, a condition for an entry class and a condition for a filtering region of the container hierarchy may be separately designated.  
         [0101]    The receiving side replicater  17  performs a process for generating a target entry class mask list. In addition, the receiving side replicater  17  performs a process for selectively receiving an entry class filtering mask contained in the generated target entry class mask list through the broadcast network  2 .  
         [0102]    An entry class filtering mask is a filtering mask corresponding to a container entry class required by the receiving side client  15 . A container entry class required by the receiving side client  15  can be considered as a container entry class that is accessed many times. A target entry class mask list is data of a list of entry class filtering masks.  
         [0103]    Leaf update information Msg. x 1 ′ is defined for example as follows. As was described above, the Msg. x 1 ′ contains an entry class filtering mask as a filtering mask.  
                                                                       Leaf Entry Update Message {                Message ID           Entry Class Filtering Mask           Difference Update Information                }                      
 
         [0104]    An entry class filtering mask is defined for example as follows.  
                                                                       Entry Class Filtering Mask {                Entry Class Mask Schema Version           Entry Class Mask Value                }                      
 
         [0105]    The “entry class mask value” is a bit string or a byte string of an entry class mask. The structure of the “entry class mask value” is defined by an entry class mask schema corresponding to the “entry class mask schema version”.  
         [0106]    An example of a target entry class mask list is as follows. It is based on a real example of the above-described entry class mask schema (see FIG. 14).  
         [0107]    Entry Class Mask Schema Version: 1  
         [0108]    mask: 00100  
         [0109]    mask: 00010  
         [0110]    As is clear from FIG. 14, a mask “00100” is used when the receiving side is interested in only an update of a video title. Likewise, a mask “00010” is used when the receiving side is interested in only an update of a retail price.  
         [0111]    Next, with reference to FIG. 15, a process for storing a target entry class mask list will be described. At step S 301 , an Msg. y 1  is received. At step S 302 , it is determined whether or not the Msg. y 1  has been received first time. When the determined result at step S 302  is Yes (namely, the Msg. y 1  has been received first time), the flow advances to step S 304 . Otherwise, the flow advances to step S 303 .  
         [0112]    At step S 304 , the message ID of the Msg. y 1  received at step S 301  is stored as a copy  12 . The copy  12  is stored to a record medium or a storage medium such as a memory or a hard disk of the receiving side replicater  17 . At step S 305 , a list of entry classes and attributes thereof is generated corresponding to the Msg. y 1  received at step S 301 . The list is presented to the receiving side client  15  so as to prompt the user to select desired entry classes and attributes.  
         [0113]    At step S 306 , a list of entry filtering masks selected at step S 305  is stored as a target entry class mask list. The target entry class mask list is data of a list of entry class filtering masks of container entries required by the receiving side client  15 . The target entry class mask list is stored to a record medium or a storage medium such as a memory or a hard disk of the receiving side replicater  17 .  
         [0114]    At step S 303 , it is determined whether or not the message ID of the Msg. y 1  received at step S 301  is the same as the copy  12 . When the determined result at step S 303  is Yes (namely, the message ID of the Msg. y 1  is the same as the copy  12 ), the flow returns to step S 301 . Otherwise, the flow advances to step S 304 .  
         [0115]    Next, with reference to FIG. 16, a process for selectively receiving leaf update information Msg. x 1  containing entry class filtering masks of the target entry class mask list through the broadcast network  2  will be described. At step S 401 , leaf update information Msg. x 1  is received. At step S 402 , it is determined whether or not an entry class filtering mask of the Msg. x 1  received at step S 401  is contained in the target entry class mask list.  
         [0116]    When the determined result at step S 402  is Yes (namely, an entry class filtering mask of the Msg. x 1  is contained in the target entry class mask list), the flow advances to step S 403 . Otherwise, the flow advances to step S 401 . At step S 403 , it is determined whether or not the Msg. x 1  has been received first time. When the determined result at step S 403  is Yes (namely, the Msg. x 1  has been received first time), the flow advances to step S 405 . Otherwise, the flow advances to step S 404 .  
         [0117]    At step S 405 , the message ID of the Msg. x 1  received at step S 401  is stored as a copy  13 . The copy  13  is stored to a record medium or a storage medium such as a memory or a hard disk of the receiving side replicater  17 . Thereafter, the flow advances to step S 406 . At step S 406 , the Msg. x 1  received at step S 401  is selected as an object that is processed. hereafter, the flow returns to step S 401 .  
         [0118]    On the other hand, at step S 404 , it is determined whether or not the message ID of the Msg. x 1  received at step S 401  is the same as the copy  13 . When the determined result at step S 404  is Yes (namely, the message ID of the Msg. x 1  is the same as the copy  13 ), the flow returns to step S 401 . Otherwise, the flow advances to step S 405 .  
         [0119]    According to the present invention, under the condition of a combination of a class and an attribute of an entry that is updated, update information can be filtered. When contents of a directory are structured for inquiring genre information or fee information, only update information representing that fee information of the contents of a particular genre has changed can be extracted. Thus, a directory on the reception side can be updated corresponding to the extracted update information.  
         [0120]    In addition, according to the present invention, the contents of a directory tree managed by the receiving side directory can be affected by preference of the receiving side client. In other words, only a portion that is frequently accessed by the receiving side client can be stored and/or updated in the directory tree. Thus, the storage cost of the directory information on the receiving side can be reduced. In addition, an information storage medium can be effectively used. Moreover, the process efficiency against a search request of a directory client to the contents of the transmitting side directory can be remarkably improved.  
         [0121]    According to the present invention, difference update information of a leaf entry that belongs to a scope designated as a set of a particular container entry in the directory hierarchy and entries as lower hierarchical entries thereof can be filtered. In addition, even if leaf entries that belong to a particular class are disposed in a plurality of scopes, update information of attributes of the class can be effectively filtered.  
         [0122]    Thus, in a combination of a filtering process for a scope and a filtering process for a class, even if the hierarchy of the directory becomes large, difference update information can be effectively obtained. For example, in a tree structure of which leaf entries that belong to three types of classes a, b, and c co-exist as shown in FIG. 17, processes corresponding to various filtering conditions and combinations thereof can be performed. For example, (1) attribute update information of a leaf entry that belongs to the class b is obtained from leaf entries designated with information that represents a scope. As another example, (2) only attribute update information of a leaf entry that belongs to the class b is obtained regardless of a designated scope.  
         [0123]    Although the present invention has been shown and described with respect to a best mode embodiment thereof, it should be understood by those skilled in the art that the foregoing and various other changes, omissions, and additions in the form and detail thereof may be made therein without departing from the spirit and scope of the present invention.