Abstract:
A wireless tag system which does not require any anti-collision process or, if an anti-collision process is required, can reduce the number of tags that need to participate in the anti-collision process to make the anti-collision process proceeds fast. The wireless tag system comprises a plurality of wireless slave tags which have respective unique IDs, a plurality of wireless master tags arranged for the slave tags and storing the unique IDs of the slave tags and a wireless tag access control device which accesses the master tags to acquire the unique IDs of the slave tags from the master tags and subsequently accessing the slave tags by using the acquired unique IDs of the slave tags.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   This invention relates to a wireless tag system adapted to communications between a plurality of wireless tags (to be also referred to as IC tags hereinafter) and a read/write device and also to a wireless tag access control device, a wireless tag access control method, a wireless tag access control program and a tag that can be used for such a wireless tag system. 
   2. Description of Related Art 
   As a result of the rapid development of IC technologies in recent years, wireless tag systems using ICs have become very popular and are currently spreading very fast (see, inter alia, Patent Document 1: Jpn. Pat. Appln. Laid-Open Publication No. 2003-196360). 
   With such a wireless tag system, a plurality of wireless tags are attached to respective objects that have to be held under control so that any of the tags can be accessed by way of a read/write device in order to read information from and/or write information to it, thereby systematizing and facilitating the operation of controlling the objects of control. 
   When accessing a wireless tag (to be referred to simply as tag hereinafter), the read/write device firstly operates for an anti-collision process and acquires the unique IDs (to be referred to as UIDs hereinafter) of the tags of the system. Subsequently, it accesses the tag by using the acquired UID of the tag. 
     FIG. 21  of the accompanying drawings is a flow chart of the operation of the read/write device for an anti-collision process. 
   Referring to  FIG. 21 , the read/write device firstly transmits a group select command to the tags and waits for acknowledgements from the tags (Step S 1 ). Then, it determines if it has properly received acknowledgements from the tags and acquired the UIDs of the tags (Step S 2 ). If it is determined that the read/write device has properly acquired the UIDs (Step S 2 , Yes), the device transmits a read command (READ) to the tags and receives an acknowledgement from the tags (Step S 3 ). Thereafter, the tags do not respond to any Fail command nor to any Success command from the read/write device. 
   Then, the read/write device determines if it has received acknowledgements consecutively for not less than a predetermined number of times (Step S 4 ). If it is determined that it has not received acknowledgements for a predetermined number of times (Step S 4 , Yes), the read/write device terminates the process. If, on the other hand, it is determined that it has received acknowledgements for the predetermined number of times (Step S 4 , No), the read/write device transmits a Success command and receives an acknowledgement from the tags (Step S 5 ). 
   On the other hand, if it is determined that the read/write device has not properly acquired the UIDs (Step S 2 , No), the read/write device determines if it has not received acknowledgements because there were collisions of acknowledgements from the tags (Step S 6 ). If, on the other hand, it is determined that the read/write device has received acknowledgements (Step S 6 , Yes), it transmits a Fail command to the tags and receives an acknowledgement from the tags (Step S 7 ). 
   If it is determined that the read/write device has not received acknowledgements because there were collisions of acknowledgements from the tags (Step S 6 , No), it determines if it has not received an acknowledgement from any of the tags or not (Step S 8 ). If it is determined that the read/write device has not received an acknowledgement from any of the tags (Step S 8 , No), it terminates the process. However, if the read/write device has received at least an acknowledgement (Step S 8 , Yes), it proceeds to the above described processing operation of Step S 4  and that of Step S 5 . 
     FIG. 22  of the accompanying drawings is a flow chart of the operation of a tag for an anti-collision process from the start of power supply. 
   Firstly, as power is supplied, the tag turns its mode of operation to a ready mode (Step S 21 ). Then, it determines if it has received a command from the read/write device (Step S 22 ). If it is determined that the tag has not received any command (Step S 22 , No), it repeats the processing operation of Step S 22 . If, on the other hand, it is determined that the tag has received a command (Step S 22 , Yes), the tag determines if it has received a group select command or not (Step S 23 ). 
   If it is determined that the tag has received a group select command (Step S 23 , Yes), it turns its mode of operation to an ID mode (Step S 24 ) and then returns to the ready mode. If, on the other hand, it is determined that the tag has not received a group select command (Step S 23 , No), the tag determines if its mode of operation is an ID mode or not (Step S 25 ). If it is determined that the mode of operation is an ID mode (Step S 25 , Yes), the tag further determines if it has received a fail command or not (Step S 26 ). 
   If it is determined that the tag has not received a fail command (Step S 26 , No), it determines if it has received a success command or not (Step S 27 ). If it is determined that the tag has received a success command (Step S 27 , Yes), it updates the reading of the counter in the tag by decrementing the reading by −1 (Step S 28 ) and determines if the reading of the counter in the tag is 0 or not (Step S 29 ). If it is determined that the reading of the counter in the tag is 0 (Step S 29 , Yes), the tag transmits its own UID (unique ID) to the read/write device (Step S 30 ). 
   If, on the other hand, it is determined that the tag has received a fail command (Step S 26 , Yes) as a result of the operation of determining if it has received a fail command or not (Step S 26 ), it determines if the reading of the counter in the tag is 0 or not (Step S 31 ) and, if it is determined that the reading of the counter in the tag is 0 (Step S 31 , Yes), the tag updates the reading of the counter by incrementing it by +1 (Step S 32 ). If, on the other hand, it is determined in Step S 31  that the reading of the counter in the tag is not 0 (Step S 31 , No), the tag generates a random number of 1 or 0 (Step S 33 ) and determines if the generated random number is −0 or not (Step S 34 ). If it is determined that the generated random number is −0 (Step S 34 , Y), the tag transmits its own UID to the read/write device (Step S 35 ). 
   Thus, with an anti-collision process as described above, it is possible for the read/write device to acquire the UID of each tag, while preventing mutual interferences of a plurality of tags. 
   In order to prevent collisions, an anti-collision process as described above is conducted while restricting the transmission of tag UIDs for part of the tags and the process is repeated until the read/write device receives the UIDs of all the tags. Therefore, the processing operation proceeds fast when the number of tags is small because the probability of collisions is low. However, as the number tags increases, the number of times of repeating the process has to be raised in order to prevent collisions and hence the process is accompanied by a problem that a considerably long time is required before acquiring the UIDs of all the tag. 
   SUMMARY OF THE INVENTION 
   In view of the above identified problem hitherto known, it is therefore an object of the present invention to provide a wireless tag system that does not require any anti-collision process or, if an anti-collision process is required, can reduce the number of tags that need to participate in the anti-collision process to make the anti-collision process proceeds fast along with a wireless tag access control device, a wireless tag access control method, a wireless tag access control program and a tag that can be used for such a wireless tag system. 
   In an aspect of the present invention, the above object is achieved by providing a wireless tag system comprising: a plurality of wireless slave tags which have respective unique IDs; a plurality of wireless master tags arranged for the slave tags and storing the unique IDs of the slave tags; and a wireless tag access control device which accesses the master tags to acquire the unique IDs of the slave tags from the master tags and subsequently accessing the slave tags by using the acquired unique IDs of the slave tags. 
   Preferably, in a wireless tag system according to the present invention, dedicated commands are defined respectively for the master tags and the slave tags and the wireless tag access control device selectively accesses either the master tags or the slave tags by using the corresponding one of the dedicated commands. 
   Preferably, in a wireless tag system according to the present invention, group addresses are defined respectively for the master tags and the slave tags and the wireless tag access control device selectively accesses either the master tags or the slave tags by specifying the corresponding one of the group addresses. 
   Preferably, in a wireless tag system according to the present invention, a plurality of combinations of a master tag and slave tags are provided and at least a super master tag storing the unique IDs of the plurality of master tags is provided for the plurality of master tags, the wireless tag access control device being adapted to access the super master tag in order to acquire the unique IDs of the plurality of master tags and access the master tags by using the acquired unique IDs of the master tags. 
   Preferably, in a wireless tag system according to the present invention, at least one of the master tags and at least one of the slave tags are combined to operate as a single tag and the unique IDs of the slave tags stored in the master tags include its own unique Ids. 
   Preferably, in a wireless tag system according to the present invention, the master tag is facsimiled in numbers and the facsimiled master tags are identifiable. 
   Preferably, in a wireless tag system according to the present invention, the master tags store positional information of the slave tags in correspondence to the unique IDs of the slave tags stored in the master tags. 
   In another aspect of the present invention, there is provided a wireless tag access control device which accesses wireless tags comprising: a unique ID acquiring section which accesses at least a master tag provided for a plurality of slave tags and acquiring the unique IDs of the slave tags stored in the master tag; and a slave tag accessing section which accesses the slave tags by using the unique IDs of the slave tags acquired by the unique ID acquiring section. 
   Preferably, in a wireless tag access control device according to the present invention, dedicated commands are defined respectively for the master tags and the slave tags so that accesses either the master tags or the slave tags are selectively accessed by using the corresponding one of the dedicated commands. 
   Preferably, in a wireless tag access control device according to the present invention, group addresses are defined respectively for the master tags and the slave tags so that either the master tags or the slave tags are selectively accessed by specifying the corresponding one of the group addresses. 
   Preferably, a wireless tag access control device according to the present invention further comprises a positional information acquiring section for acquires positional information of the slave tags corresponding to the acquired unique IDs of the slave tags, the device being adapted to access the slave tags according to the unique IDs and the positional information. 
   In still another aspect of the present invention, there is provided a wireless tag access control method which accesses a plurality of wireless tags, the method being adapted to provide at least a master tag storing the unique IDs of a plurality of slave tags which have respective unique IDs, the method comprising: a slave tag UID acquiring step which accesses the master tag and acquiring the unique IDs of the plurality of slave tags stored in the master tag; and a slave tag accessing step which accesses the slave tags by using the acquired unique IDs of the slave tags. 
   Preferably, in a wireless tag access control method according to the present invention, dedicated commands are defined respectively for the master tags and the slave tags so that either the master tags or the slave tags are selectively accessed by using the corresponding one of the dedicated commands. 
   Preferably, in a wireless tag access control method according to the present invention, group addresses are defined respectively for the master tags and the slave tags so that either the master tags or the slave tags are selectively accessed by specifying the corresponding one of the group addresses. 
   Preferably, in a wireless tag access control method according to the present invention, a plurality of combinations of a master tag and slave tags are provided and at least a super master tag storing the unique IDs of the plurality of master tags is provided for the plurality of master tags, the wireless tag access control method being adapted to access the super master tag in order to acquire the unique IDs of the plurality of master tags and access the master tags by using the acquired unique IDs of the master tags. 
   Preferably, in a wireless tag access control method according to the present invention, at least a master tag is facsimiled in numbers from the master tags and slave tags and the facsimiled master tags are identifiable so that each tag is identified and selectively accessed. 
   Preferably, in a wireless tag access control method according to the present invention, an identifying section is provided for each tag to indicate the tag to be in use or not in use so that, when an unusable state is detected for at least one of the facsimiled master tags, the information stored in the master tag detected as unusable and the other facsimiled master tags is written in the facsimiled master tags not in use and the tags in which the information is written are indicated to be in use by the identifying section so as to make the other master tags and the master tag facsimiled master tags. 
   In still another aspect of the present invention, there is provided a wireless tag access control program which causes a computer to execute a wireless tag access control method which accesses a plurality of wireless tags, the program being adapted to provide at least a master tag storing the unique IDs of a plurality of slave tags which have respective unique IDs, the program comprising: a slave tag UID acquiring step which accesses the master tag and acquiring the unique IDs of the plurality of slave tags stored in the master tag; and a slave tag accessing step which accesses the slave tags by using the acquired unique IDs of the slave tags. 
   Preferably, in a wireless tag access control computer program according to the present invention, dedicated commands are defined respectively for the master tags and the slave tags so as to cause a computer to selectively access either the master tags or the slave tags by using the corresponding one of the dedicated commands. 
   In still another aspect of the present invention, there is provided a wireless tag comprising a wireless antenna and a memory section and adapted to be accessed by a read/write device by means of a wireless signal; the wireless tag storing unique IDs of wireless tags other than itself in the memory section so that they may be accessed by the read/write device by means of the unique IDs. 
   Thus, the invention provides an advantage that no anti-collision process is required or, if an anti-collision process is required, the number of tags that need to participate in the anti-collision process can be remarkably reduced to make the anti-collision process proceeds fast. This advantage becomes even more remarkable particularly in a situation where a large number of slave tags, or thousands to tens of thousands of slave tags, have to be processed because it is not necessary for a read/write device to collectively store the UIDs of such large number of slave tags. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic block diagram of a first embodiment of wireless tag system according to the invention, illustrating the overall configuration thereof; 
       FIG. 2  is a schematic block diagram of a master tag and a slave tag, showing the configuration thereof; 
       FIG. 3  is a flow chart of the operation of the first embodiment; 
       FIG. 4  is a conceptual illustration of a second embodiment; 
       FIG. 5  is a flow chart of the operation of the second embodiment; 
       FIG. 6  is a conceptual illustration of a third embodiment; 
       FIG. 7  is flow charts of the operation of the third embodiment; 
       FIG. 8  is a conceptual illustration of a fourth embodiment; 
       FIG. 9  is a flow chart of the operation of the fourth embodiment; 
       FIG. 10  is an illustration of the command format of a fifth embodiment; 
       FIG. 11  is a conceptual illustration of a sixth embodiment; 
       FIG. 12  is a flow chart of the operation of the sixth embodiment; 
       FIG. 13  is a conceptual illustration of a seventh embodiment; 
       FIG. 14  is a conceptual illustration of an eighth embodiment; 
       FIG. 15  is a conceptual illustration of a ninth embodiment; 
       FIG. 16  is a flow chart of the operation of the ninth embodiment; 
       FIG. 17  is a conceptual illustration of a tenth embodiment; 
       FIG. 18  is a flow chart of the operation of the tenth embodiment; 
       FIG. 19  is a conceptual illustration of the processing operation for updating the data on the slave tags registered in a master tag; 
       FIG. 20  is a conceptual illustration of the processing operation for initializing slave tags and master tags; 
       FIG. 21  is a flow chart of the operation of a read/write device in a conventional anti-collision process; and 
       FIG. 22  is a flow chart of the operation of a tag in a conventional anti-collision process. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Now, the present invention will be described in greater detail by referring to the accompanying drawings that illustrate preferred embodiments of the invention. 
   [First Embodiment] 
     FIG. 1  is a schematic block diagram of the first embodiment of wireless tag system according to the invention, illustrating the overall configuration thereof. Referring to  FIG. 1 , the wireless tag system comprises a plurality of slave tags  1 , at least a master tag  2  arranged for the plurality of slave tags  1 , a read/write device (R/W)  3  adapted to access the master tag  2  and the slave tags  1  and communicate with any of them, a PC  4  that controls the read/write device  3  and a server  5  connected to the PC  4  and adapted to provide the PC  4  with necessary information. 
   The plurality of slave tags  1  respectively have their own UIDs (UID 1 A through UID 6 A). The master tag  2  stores the UIDs (UID 1 A through UID 6 A) of the slave tags  1  and is adapted to transmit the UIDs of all the slave tags  1  in response to a request from the read/write device  3 . The read/write device  3  can receive the transmitted UIDs and transfer them to the PC  4 . The master tag  2  can delete or replace any of the stored UIDs and add one or more than one new UID in response to a request from the read/write device  3 . 
   Each of the slave tags  1  stores predetermined management information on the objects of management (e.g., wears, books, building components, packages) (not shown) so as to be readable/writable to the read/write device  3  in addition to its own UID. Preferably, the slave tags  1  are arranged within the communicable area of the read/write device  3  with the master tag  2  and attached respectively to objects of management, for example. 
   The PC  4 , the read/write device  3  or the PC  4  and the read/write device  3  in combination operate as a wireless tag access control device according to the invention that can access the wireless tags (slave tags  1 , master tag  2 ). While a plurality of slave tags  1  are provided in this embodiment, the present invention is applicable to a a system that comprises a single slave tag  1 . 
     FIG. 2  is a schematic block diagram of a master tag and a slave tag, showing the configuration thereof. 
   Each of the tags  1 ,  2  comprises a tag chip (IC chip)  6  and a loop antenna  7 . The tag chip  6  in turn comprises an analog/digital converter  8  for converting an analog signal such as a radio signal, into a digital signal for internal processing, a command analyzing/processing section  9  for analyzing a command and carrying out a predetermined processing operation and a memory section  10 . In the master tag  2 , the memory section  10  stores the UID of the tag, the above described UIDs (UID 1 A through UID 6 A) of the slave tags  1  and other necessary pieces of information. The slave tag  1  stores predetermined management information in addition to its own UID. The memory section  10  also stores address information on the each of the tags. 
   Now, the operation of the first embodiment will be described by referring to the flow chart of  FIG. 3  in terms of the processing operation that is carried out by the tag access control device (the read/write device and the PC) to access the slave tags  1 . 
   Firstly, the tag access control device transmits a data read command to the master tag  2 , using the UID of the master tag  2  (Step S 101 ). After receiving data from the master tag  2  (Step S 102 , Yes), it acquires the UIDs of all the slave tags  1  stored in the memory section  10  of the master tag  2  (Step S 103 ). Then, it transmits a data read/write command to the slave tags  1 , using the acquired UIDs of the slave tags  1 , (Step S 104 ). When the read/write operation relating to all the slave tags  1  is completed (Step S 105 , No), it ends the processing operation. 
   Thus, with the above-described first embodiment, it is possible to acquire the UIDs of the slave tags without carrying out an anti-collision processing operation relative to the slave tags by acquiring the UIDs of the slave tags from the master tag  2  and accesses the slave tags  1  to remarkably improve the efficiency of the management. Note that, in a wireless tag access control device according to the invention, a UID acquiring section is responsible for Step S 101  through Step S 103 , whereas a slave tag accessing section is responsible for Step S 104 . 
   When a single master tag  2  is provided, it is accessed by using its own UID. If there are a plurality of master tags  2 , either an anti-collision processing operation is carried out or a group address is used as will be described hereinafter. However, according to the invention, it is possible to dramatically reduce the number of necessary tags if compared with an arrangement where an anti-collision processing operation needs to be carried out for all the slave tags. Therefore, it may be clear that the present invention can carry out the anti-collision processing operation remarkably quickly. 
   [Second Embodiment] 
   In the second embodiment, dedicated commands are provided in order to discriminate the access to the master tag and the access to the slave tags. 
     FIG. 4  is a conceptual illustration of the second embodiment. In  FIG. 4 , (a) shows a situation where a single master tag  2  and a plurality of slave tags  1  exist. It is necessary to firstly access the master tag  2  in order to acquire the UIDs of the slave tags stored in the master tag  2 . The master tag  2  can be accessed efficiently by separately preparing an access command which accesses the master tag  2  and an access command which accesses the slave tags. This arrangement provides an additional managemental advantage that, when the slave tags need to be accessed, they can be accessed without involving the master tag. 
   In  FIG. 4 , (b) shows an example of command format. With this format, the master tag  2  is selected when the command code is “0x00” so that all the subsequent commands are regarded as those solely for the master tag  2 . On the other hand, the slave tags  1  are selected when the command code is “0x01” so that all the subsequent commands are regarded as those solely for the slave tags  1 . 
   Referring to  FIG. 5  illustrating a flow chart of the operation of the second embodiment, as a processing operation for selecting a command is started, it is determined if the coming communication is to be held with the master tag or not (Step S 111 ). If the coming communication is to be held with the master tag (Step S 111 , Yes), the command for the master tag is selected (Step S 112 ) and the selected command is transmitted (Step S 113 ). If, on the other hand, the coming communication is to be held not with the master tag but with the slave tags (Step S 111 , No), the command for the slave tags is selected (Step S 114 ) and the selected command is transmitted (Step S 113 ). 
   [Third Embodiment] 
   In the third embodiment, group addresses are provided so as to be able to identify the master tag and the slave tags which are accessed. 
     FIG. 6  is a conceptual illustration of the third embodiment.  FIG. 6(   a ) shows an example of command format. If the command code is “0x00” and the group address is “10” while the data is “0x80”, it is clearly seen from (b) of  FIG. 6  that the data “0x80 ” stored at address “10” is carried by tag B. Thus, it is possible to tell if a given command is for the master tag or for the slave tags by using group addresses as described above to a great advantage of improving the efficiency of management. 
     FIGS. 7(   a ) and  7 ( b ) show flow charts of the operation of the third embodiment.  FIG. 7(   a ) shows a flow chart for the access control device, whereas  FIG. 7(   b ) shows a flow chart for the tags. 
   As shown in  FIG. 7(   a ,) when a processing operation is started, the wireless tag access control device determines if the coming communication is for the master tag or not (Step S 121 ). If it is determined that the coming communication is for the master tag (Step S 121 , Yes), the wireless tag access control device selects the group address for identifying the master tag (Step S 122 ) and then selects and transmits the command (Step S 123 ). If, on the other hand, it is determined that the coming communication is not for the master tag (Step S 121 , No), the wireless tag access control device selects the group address for identifying the slave tags (Step S 124 ) and proceeds to Step S 123 . 
   Now, referring to  FIG. 7(   b ) showing a flow chart for the tags, firstly it is determined if the group address is for its own group or not (Step S 131 ). If it is determined that the group address is for its own group (Step S 131 , Yes), the tag or each of the tags analyzes the command and carries out a corresponding processing operation (Step S 132 ). If, on the other hand, it is determined that the group address is not for its own group (Step S 131 , No), it simply terminates the operation. 
   [Fourth Embodiment] 
   The fourth embodiment is adapted to an arrangement where there are more than one group of a master tag and slave tags. In the fourth embodiment, a dedicated command is provided so that only the master tag of each group may participate in the anti-collision processing operation. 
     FIGS. 8(   a ) and  8 ( b ) show a conceptual illustration of a fourth embodiment.  FIG. 8(   a ) shows that there are more than one group (two in the illustrated instance), or groups G 1 , G 2 , of a master tag and slave tags. In this case, it is necessary to firstly carry out an anti-collision processing operation for the master tags  2  in order to acquire the UIDs of the master tags for the purpose of acquiring the UIDs of the slave tags. When carrying out the anti-collision processing operation, the UIDs of the master tags can be acquired with ease if it is possible to discriminate the tags (master tags) that need to participate in the anti-collision processing operation from the slave tags. Therefore, it is desirable to provide a command which causes only the master tags to participate in the anti-collision processing operation. 
     FIG. 8(   b ) shows an example of a command format. Only the master tags are put into a mode for participating in the anti-collision processing operation when the command is “0x00”. On the other hand, only the slave tags are put into a mode for participating in the anti-collision processing operation when the command is “0x01”. 
     FIG. 9  is a flow chart of the operation of the fourth embodiment. Firstly, because the anti-collision processing operation is started only for the master tags, the command for specifying the master tags for the anti-collision processing operation is selected (Step S 141 ) and the selected command is transmitted (Step S 142 ) to end the processing operation. 
   [Fifth Embodiment] 
   The fifth embodiment corresponds to the third embodiment in the sense that, where there are a plurality of groups of a master tag and slave tags, a group address is used to specify the master tag of a groups as shown in (a) of  FIG. 8 . 
     FIG. 10  is an illustration of the command format of the fifth embodiment. Referring to  FIG. 10 , if the command code, the group address and the data for the group are respectively “0x00”, “10” and “0x80”, only the tag whose group address and data are respectively “10” and “0x80” can be selected as master tag. In the wireless tag access control device, as the processing operation of the step of specifying the master tag is carried, that of the step of selecting the group address of the master tag and that of the step of transmitting the command which have the group address are carried out sequentially. 
   [Sixth Embodiment] 
   The sixth embodiment is adapted to accommodate a situation where there are a plurality of master tags as in the case of a plurality of groups of a master tag and slave tags by providing a super master tag that stores the UIDs of the master tags. 
   Assume that there are groups G 1 , G 2  of a master tag and slave tags as shown in  FIG. 11 . Then, a super master tag  11  is provided to store the UIDs of the master tags  2 . Then, referring to  FIG. 12 , the wireless tag access control device firstly accesses the super master tag  11  and acquires the UIDs (UID( 0 ), UID( 1 )) of the plurality of master tags  2  (Step S 151 ) and subsequently accesses the master tags by using the acquired UIDs of the master tags to acquire the UIDs of the slave tags stored in each master tag (Step S 152 ). 
   Thus, with the sixth embodiment, it is not necessary to carry out an anti-collision processing operation if there are a plurality of master tags so that the processing operation proceeds fast to a great advantage of management. 
   [Seventh Embodiment] 
   In the seventh embodiment, one of the slave tags is used as master tag. In other words, one of the slave tags operates both as master tag and slave tag. 
     FIG. 13  is a conceptual illustration of the seventh embodiment. Referring to  FIG. 13 , the master tag stores the UIDs of a plurality of slave tags and one of the UIDs is the UID of the master tag. With this arrangement, the master tag registers its own UID both as that of a slave tag and as that of the master tag so that it can operate as slave tag. 
   [Eighth Embodiment] 
   In the eighth embodiment, the master tag is facsimiled in numbers (e.g., duplicated) to raise the reliability of the system. 
     FIG. 14  is a conceptual illustration of the eighth embodiment. Referring to  FIG. 14 , two master tags  2 A,  2 B that store the UIDs of the same slave tags are provided to control the UIDs of the slave tags. If the wireless tag access control device cannot read the UIDs of the slave tags from the master tag  2 A, it reads the UIDs of the slave tags from the master tag  2 B. With this arrangement, the system shows an enhanced degree of reliability because, if one of the master tags fails or shows some other trouble, the other master tag can provide the UIDs of the slave tags. It is also possible to facsimile the slave tags to further enhance the reliability of information management. 
   [Ninth Embodiment] 
   In the ninth embodiment, the master tag is facsimiled in numbers (e.g., duplicated) to raise the reliability of the system in terms of UID management of the slave tags as in the case of the eighth embodiment and, at the same time, the facsimiled master tags are made identifiable so that the system can be restored if it fails. 
     FIG. 15  is a conceptual illustration of the ninth embodiment.  FIG. 16  is a flow chart of the operation of the ninth embodiment. 
   Referring to the drawings, each tag is provided with a restoration flag area (identifying section for identifying if the tag is in use or not in use)  13  and restoration flag “0” is written to each tag that is in use. Restoration flag “1” is written to each unused tag that is to be used for restoration. If one of the facsimiled master tags (tag  2 A) fails (Step S 161 , Yes), an unused tag (tag  2 C) is searched for by searching for the tag with restoration flag “1” out of the master tags in the communication area and, if an unused tag is found (Step S 162 , Yes), the data (the UIDs of the slave tags) of the master tag  2 B that is the duplicate of the failed master tag are transferred (copied) to the tag  2 C (Step S 163 ) and the flag of the master tag is set to “1” (Step S 164 ). Thereafter, the master tag  2 B and the master tag  2 C are used as facsimiled (duplicated) master tags. 
   [Tenth Embodiment] 
   In the tenth embodiment, positional information of the slave tags are stored in the master tag along with the UIDs of the slave tags. 
     FIG. 17  is a conceptual illustration of the tenth embodiment. Referring to  FIG. 17 , positional information of the slave tags  1 A,  1 B is stored in the master tag  2 D so that, when the slave tags are applied to large product such as a building component (not shown), it is possible to access either of the tags and modify the information stored in the tag depending on the positions of the tags. 
   More specifically, as shown in  FIG. 17 , positional information  21   b  on the applied (bonded) position of each slave tag is added to the UID information  21   a  as slave tag information  21  that is stored in the master tag  2 D. In the case of a large product such as a building component, it may be desired to write different pieces of information respectively to different parts of the products. For example, a lower part of the product is to be painted in a step of the building operation, the data on the time and date of the painting operation may have to be written to the tag applied to the lower part of the product. Then, it is possible to read the slave tag information  21  in the master tag  2 D and write the necessary data (management information) only to the tag for the lower part of the product. 
     FIG. 18  is a flow chart of the operation of the tenth embodiment when writing information in a slave tag. 
   Referring to  FIG. 18 , firstly, the wireless tag access control device accesses the master tag  2 D and acquires the UID 21   a  and the positional information  21   b  of each of the slave tags  1 A,  1 B from the slave information  21  (Step S 171 ). Then, it selects and acquires the UID of the slave tag that has the right positional information (Step S 172 ). As it acquires the UID of the slave tag which have the right positional information, it accesses the slave tag, using the UID and operates for writing the necessary data (Step S 173 ). Note that the positional information acquiring section is responsible for the operation of Step S 171 . 
   The present invention is described above by way of preferred embodiments. Now, the processing operation for updating the data (UIDs) of the slave tags registered in the master tag(s) will be described below. While the data updating processing operation will be described in terms of the first embodiment below, it is similarly applicable to the other embodiments including the second embodiment through tenth embodiment. 
   Referring to  FIG. 19 , the data updating processing operation may be repeated at regular time intervals (or at a predetermined clock time or predetermined clock times). The PC of the wireless tag access control device acquires the UIDs of the slave tags from the master tag by way of the read/write device (P 1 ) and sequentially reads the data of the slave tags, using the UIDs (P 2  through P 4 ). If a slave tag (UID 3  in the illustrated instance) goes out of control, no acknowledgement can be received from the slave tag with the UID (P 4 ). Therefore, the PC decides that the slave tag has gone out of control of the PC (the commodity carrying the slave tag may have been moved to the outside) and issues an order to the master tag for erasing the UID. Upon receiving the order, the master tag deletes the UID of the slave tag (P 5 ). Then, the processing operation described above for the preferred embodiments is carried out for the remaining slave tags (P 6 ). Note that the relationship between the super master tag and the master tags in the sixth embodiment is similar to the above-described relationship between the master tag and the slave tags. So is the relationship between the master tag and the slave tags in the seventh embodiment where one of the slave tags is used as master tag. In the seventh embodiment, if it is judged that the slave tag that is operating as master tag has gone out of control, some other slave tag may be registered as master tag. 
   Now, the processing operation of initializing the slave tags and the master tag(s) will be described below by referring to  FIG. 20 . The PC carries out an anti-collision processing operation by way of the read/write device and acquires the UIDs of all the tags including the slave tags and the master tag(s) (P 11 ). As the PC identifies the UID of the master tag (assuming that the master tag is provided with a UID that can be discriminated from the UIDs of the other tags), it handles all the tags with the UIDs other than the UID of the master tag as slave tags and writes and stores the UIDs in the master tag (P 12 ). In the case where some slave tags operate also as so many master tags as in the eighth embodiment, the PC may assign a master tag to any UID group and store the UIDs of the slave tags of the group in the master tag. 
   After the initialization, the information in the master tag can be updated in a similar manner when a slave tag is added. More specifically, an anti-collision processing operation is carried out for the slave tags and, if it is determined that there is a UID of a slave tag that is not registered in the master tag, it is written to the master tag appropriately. 
   The present invention is described above in detail by way of preferred embodiments. Thus, the present invention provides a wireless tag access control program which causes the computer of a wireless tag access control device according to the invention to execute the processing operation of any of the flow charts described above and illustrated in the accompanying drawings. More specifically, such a program can be executed by the computer of a wireless tag access control device according to the invention when it is stored in a computer-readable recording medium. Computer-readable recording mediums that can be used for the purpose of the present invention include transportable recording mediums such as CD-ROMs, flexible disks, DVD disks, magnetic optical disks and IC cards along with data bases that retain computer programs, other computers, their data bases and transmission mediums on communication lines.