Abstract:
A file retrieval device, operable to retrieve a valid file name for reading a plurality of file main bodies from a recording medium in which the plurality of file main bodies and file related information that includes a file names respectively allocated to the plurality of file main bodies and respectively depending on different file systems are recorded and which is coordinated with one file system in advance, the file retrieval device, including: a first extracting unit, operable to extract the file name depending on the file system identical with the one file system from the file related information; a validity deciding unit, operable to decide validity of the file name depending on the file system other than the one file system; a second extracting unit, operable to extract the file name depending on the file system related to the file name decided to be valid by the validity deciding unit for the file main body the file name of which is not extracted by the first extracting unit; and an output unit, operable to output the file names extracted by the first and second extracting units.

Description:
BACKGROUND 
     1. Field of the Invention 
     The present invention relates to a retrieving technique of a file recorded on a recording medium. 
     2. Description of the Related Art 
     In recent years, recording media of a large capacity as well as a CD (Compact Disk), a DVD (Digital Versatile Disk), a memory card or the like have been increased and many and many kinds of digital content files (files of image data or music data) have been processed by using these media. Ordinarily, these recording media can be read by various kinds of devices such as a computer, a printer, a television or the like. Accordingly, a technique for improving what is called a compatibility between the devices of the media has been developed so that a movement and an exchange through the recording media can be safely carried out. 
     MVP (Music Photo Video: a registered trademark of Optical Storage Technology Association) is one of it and this is a systematic standard that makes it possible to read the recording media by various kinds of devices. Further, a technique has been also known that the files are efficiently managed by such a standard to improve a convenience (for instance, see JP-A-2005-327257). 
     In the above-described related art, an importance is attached to efficiency in view of what is called a management, for instance, to efficiently manage the files and improve a convenience and an importance is not attached to en efficiency in view of a speed such as a reading speed (a speed for retrieving a file) of the recording media. 
     In the case of the MPV standard, information showing the contents of a file main body recorded on the recording media is recorded in the recording media. This information is called a manifest. This information is used so that it can be instantaneously decided what kind of file main body is recorded on the recording media without recognizing the presence thereof one by one. However, in the manifest, a plurality of file names respectively corresponding to a plurality of file systems can be written in one file main body. Therefore, in order to read the file main body, one file name needs to be specified. When there is a file name corresponding to the file system used during recording it in the recording media, the file name can be used unconditionally to use it as a retrieved result. When such a file name does not exist, the plurality of file names described in the manifest are used to recognize whether or not the file main body can be accessed. In such a collating process of the file main body, much time is required. When the number of files is more increased, the influence thereof is the more increased. 
     SUMMARY 
     An advantage of some aspects of the invention is to provide a file retrieval device and a file retrieval method that retrieve a valid file name at high speed when recording media is read in which other file names of a plurality of file systems are attached to a file main body and a file name corresponding to the file system of the recording media does not exist. 
     According to an aspect of the invention, there is provided a file retrieval device, operable to retrieve a valid file name for reading a plurality of file main bodies from a recording medium in which the plurality of file main bodies and file related information that includes a file names respectively allocated to the plurality of file main bodies and respectively depending on different file systems are recorded and which is coordinated with one file system in advance, the file retrieval device, comprising: 
     a first extracting unit, operable to extract the file name depending on the file system identical with the one file system from the file related information; 
     a validity deciding unit, operable to decide validity of the file name depending on the file system other than the one file system; 
     a second extracting unit, operable to extract the file name depending on the file system related to the file name decided to be valid by the validity deciding unit for the file main body the file name of which is not extracted by the first extracting unit; and 
     an output unit, operable to output the file names extracted by the first and second extracting units. 
     According to a preferred embodiment, the validity deciding unit may specify the file system in accordance with a priority determined in advance and decide the validity of the file name depending on the specified file system. 
     According to a preferred embodiment, the priority may be determined in such a way the file system having a smaller number of the maximum number of characters of the file name has the higher priority. 
     According to a preferred embodiment, the validity deciding unit may access the file main body to which the file name is allocated in accordance with the file name depending on the file system other than the one file system, and when the validity deciding unit can normally access the file main body, the validity deciding unit may decide that the file name is valid. 
     The present disclosure relates to the subject matter contained in Japanese patent application No. 2006-227440 filed in Japan on Aug. 24, 2006 which is expressly incorporated herein by reference in its entirety. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be described with reference to the accompanying drawings, wherein like numbers reference like elements. 
         FIG. 1  is a schematic diagram of a structural example of a media reading device according to one embodiment of the present invention. 
         FIG. 2  is a diagram showing one example of the described contents of a manifest. 
         FIG. 3  is a diagram showing the features and the priority of file systems that can be described in the manifest. 
         FIG. 4  is a diagram showing a procedure of a file retrieving process according to one embodiment of the present invention. 
         FIG. 5  is a flowchart of a procedure of a media file system according to the one embodiment of the present invention. 
         FIG. 6  is a flowchart of a procedure of a non-media file system of the file retrieving process according to the one embodiment of the present invention. 
     
    
    
     DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     Now, a media reading device according to one embodiment of the present invention will be described below by referring to the drawings. 
       FIG. 1  is a schematic diagram of a structural example of a media reading device according to the embodiment of the present invention. 
     The media reading device  101  according to the embodiment reads a recording media  106  to retrieve a file main body recorded on the recording media  106  at high speed and read an actual file main body in accordance with a result. The media reading device  101  includes a function as a file retrieval device for retrieving a file name that can be read from the recording media  106 . 
     In the recording media  106 , a file main body as an object to be retrieved (for instance, an image file or a music file or the like) and information showing the contents of the file main body (refer it to as “file related information”, hereinafter) are recorded. Further, to the recording media  106 , one file system (refer it to as a “file system of media” hereinafter) is allocated. This file system means a file system used when data is recorded on the recording media  106 . The media reading device  101  uses the file related information to retrieve a file at high speed. 
     The file related information indicates information for showing a kind or a position of the file main body recorded on the recording media and includes at least a file name for specifying the file main body and a file system that can use the file name. Here, the file name means a file name that can specify the file main body and, for instance, a file name including path information when the file main body is recorded in a tree structure. Further, the file system includes, for instance, FAT16, FAT32, NTFS, HFS, etc. Accordingly, the media reading device  101  can consider a media recorded in accordance with, for instance, an MPV standard to be an object to be read. In this case, a manifest in the MPV standard corresponds to the file related information. 
     In the file related information, a plurality of file names depending on the file system can be described for one file main body. In the plurality of file names, valid file names that can access an actual file main body and invalid file names that cannot access the file main body are mixed owing to a relation of the media to the file system. A retrieval of the file carried out by the media reading device  101  is to find out a valid file name relative to the file main body recorded in the recording media  106 . Accordingly, the list of the valid file names obtained thereby is a retrieved result. However, as can be understood from a below-described explanation, whether or not all file main bodies can be actually accessed is not recognized. In a part of the file main bodies, a file name assumed to be accessed with high possibility is regarded as a retrieved result. Therefore, an access by all the file names included in the retrieved result is not assured. For convenience sake, the file names including the file name assumed to be accessed with high possibility are referred to as valid file names. 
     In order to retrieve such a recording media  106 , the media reading device  101  includes a control part  102 , a storing part  103 , a reading part  104  and a file retrieving part  105 . 
     The control part  102  controls the entire operation of the media reading device  101  to carry out a retrieving process of the file main body. Specifically, the control part  102  controls the reading part  104  to read information recorded on the recording media  106 , then controls the file retrieving part  105  to retrieve the valid file in accordance with the read information and controls the storing part  103  to store the result thereof to carry out the retrieving process. 
     The storing part  103  stores information necessary for retrieving the file or the retrieved result obtained by retrieving the file. The information necessary for retrieving the file that is stored in the storing part  103  includes a priority table for determining a sequence of file systems to be retrieved or information showing a validity or an invalidity of the file system (they will be described below). 
     The reading part  104  reads the information recorded on the recording media  106 . As the information to be read, for instance, the file related information or the file systems of the media or the like are exemplified. Since the file related information and the file systems of the media are the information necessary for retrieving the file, the file related information and the file systems of the media are read by the reading part  104  and then supplied to the file retrieving part  105 . Further, the reading part  104  decides whether the filename as an object is valid so that the file name can access the actual file main body or invalid so that the file name cannot access the actual file main body. That is, the reading part carries out a collating process for recognizing the presence of the file main body designated by the file name or recognizing whether or not the file main body is the same as shown by the information. This collating process is carried out by, for instance, recognizing whether or not the actual file main body can be opened by the file name. 
     The file retrieving part  105  retrieves the file main body recorded on the recording media  106  in accordance with the information read from the recording media  106  by the reading part  104 . Specifically, the file retrieving part  105  refers to the file related information and the file systems of the media and the priority table stored in the storing part  103  to retrieve the valid file names of all the file main bodies recorded on the recording media  106 . Then, the list of the file names obtained as the retrieved result is stored in the storing part  103 . 
     The file retrieving part  105  includes a media file system procedure executing part  105   a  and a non-media file system procedure executing part  105   b.  These parts are executing parts for carrying out the retrieving processes of the file names by respectively different procedures (described below). The file retrieving part  105  obtains the retrieved result by the combination of these retrieving processes. Namely, when a desired file name is not found by the retrieving process carried out by the media file system procedure executing part  105   a,  the file retrieving part  105  obtains the retrieved result by the retrieving process carried out by the non-media file system procedure executing part  105   b.    
     The media file system procedure executing part  105   a  retrieves the file name in accordance with a below-described media file system procedure. Namely, the media file system procedure executing part  105   a  retrieves whether or not there is a file name corresponding to the file system coinciding with the file system of the media among a plurality of file names for the one file main body described in the file related information. If such a file name is found out, this is regarded as the retrieved result of the file main body. Here, the collating process is not carried out for recognizing the presence of the file main body designated by the file name or whether or not the file main body is the same as indicated by the information. That is, the media file system procedure executing part  105   a  preferentially takes a reliability of the file system of the media and saves the collating process to carry out the retrieving process at high speed. If there is an error in the file system, the file name, or the recorded file main body, the error is permitted to obtain the retrieved result. In this case, the media reading device  101  may meet the error by carrying out an error process when the media reading device actually reads the file main body having the error. This is based on a fact that to obtain the retrieved result at high speed by relying on the file system as described above is more advantageous than to collate all file main bodies and take much time in order to eliminate such an error. 
     On the other hand, the non-media file system procedure executing part  105   b  retrieves the file name in accordance with a below-described non-media file system procedure. That is, this procedure is to retrieve a file name that can access the actual file main body or may possibly access the file main body in file names corresponding to other file systems (non-media file systems) than the file system of the media among a plurality of file names for the one file main body described in the file related information. This procedure is carried out on the basis of below-described two principles. 
     Namely, according to a first principle, even when the file system as an object is the non-media file system, if this file system is valid relative to the recording media  106 , the system is regarded as a valid file system and all file names corresponding to the file system are considered to be valid. This principle may be said to be a principle that preferentially takes the reliability of the file system. Specifically, after the collating process is carried out once to the file name corresponding to a certain file system to decide whether the file name is valid or invalid, the decided result is applied to all the file names corresponding to the same file system. For instance, when the collating process is carried out to FN 1  of three file names FN 1 , FN 2  and FN 3  whose file systems are completely the same, and accordingly, the actual file main body can be accessed, FN 2  and FN 3  are also regarded as the valid file names in addition to FN 1 . On the contrary, when the actual file main body cannot be accessed, all FN 1 , FN 2  and FN 3  are regarded as the invalid file names. 
     According to a second principle, when a retrieval is carried out on the basis of the first principle, the retrieval is performed in accordance with the priority of the file systems that the sequence of the file systems to be retrieved is previously determined. For instance, when three file names respectively corresponding to three file systems of FS 1 , FS 2  and FS 3  are attached to a certain file main body, if the priority of the file systems is previously determined in such a way that FS 2  is higher than FS 1  and FS 1  is higher than FS 3 , the collating process of the file name corresponding to FS 2  is initially carried out (Here, when the validity or the invalidity of FS 2  is already decided, the collating process does not need to be carried out in accordance with the first principle). As result, when the file name is decided to be invalid, the validity or the invalidity of the file name corresponding to FS 1  is decided. In such a way, when the retrieving process is advanced in accordance with the priority of the file systems to find the valid file name or complete the decision of all the file names, the retrieving process is finished. 
     The structure of the media reading device  101  is described above, and the media reading device  101  may be realized by, for instance, a general-purpose computer such as a personal computer. In this case, the retrieving process carried out by the file retrieving part  105  can be realized by, for instance, a computer program, an ASIC (Application Specific Integrated Circuit) or the combination of the program and the ASIC. 
     Now, a case that data is recorded on the recording media  106  on the basis of the MPV standard is assumed and more specifically described below. 
     As described above, in the MPV standard, a file called a manifest corresponds to the file related information. The manifest indicates information related to the contents of the file main body recorded on the recording media  106  that is described in an XML form.  FIG. 2  shows one example of the manifest  200 . 
     In the manifest  200 , in a range enclosed by an AssetList tag  201 , information showing what kind of file main body is recorded in the recording media  106  is recorded. 
     For instance, a Still tag  202  shows that one still image file (ID designates ID001401) is recorded on the recording media  106 . Further, an Audio tag  208  shows that one moving image file (ID designates ID001500) is recorded in the recording media  106 . In the ranges enclosed by the Still tag  202  and the Audio tag  208 , the detailed information of the respective file main bodies is described. 
     As the detailed information, the file name of the file main body can be described by a LastURL tag  203 . Further, a file system tag  204  is used together with the LastURL tag  203 , so that the file name and the file system that can use the file name can be described together. Thus, a plurality of file names depending on the file system can be described for one file body. In  FIG. 2 , in the still image file having the ID of ID001401, file names ISO001. JPG205, Ntfs001.jpg206 and FAT001.JPG207 in the cases of three file systems of ISO9660-1, NTFS and FAT16 are respectively described. 
     As can be understood from the above description, when the media reading device  101  retrieves the file main body on the basis of the manifest  200 , the media reading device  101  firstly grasps the information of the file main body (refer it to as “file main body information”, hereinafter)  209  described in the recording media  206  by using the Still tag  202  or the Audio tag  208  as a key. Then, the media reading device  101  grasps the file name from the respective file main body information  209  by using the LastURL tag  203  as the key. When a plurality of file names are described, the media reading device  101  finds out one valid file name among them. In the case of the manifest  200  in  FIG. 2 , for the still image file having the ID of ID001401, one file name is selected from the three file names of ISO001. JPG205, Ntfs001.jpg206 and FAT001.JPG207. However, when it is decided that any of the file names is invalid, the still image file is not included in the retrieved result. 
       FIG. 3  is shows the file systems (including a case that the file system tag  204  is not described) that can be described in the manifest  200 , the features and the priority thereof. In this case, the number of characters herein indicates the number of characters of the file names excluding path information. 
     The file systems are different in their describing forms of the file names (for instance, whether or not the number of characters is limited or whether or not a big letter is discriminated from a small letter) or managing methods of an access right depending on a classification. Accordingly, in order to access the recorded file main body, a file name corresponding to the file system identical with the file system of the media needs to be used as a general rule. On the other hand, even when the describing forms of the file names are the same or the describing forms are different between certain file systems, the file systems may have compatibility. In such a case, even when the file names are the same or not the same between these systems, the file main body may be accessed by using the file name due to the compatibility of the file systems. Therefore, the file name corresponding to the file system identical with the file system of the media does not necessarily need to be used. 
     In  FIG. 3 , the features of the describing forms of the file names are described respectively for the file systems. 
     Ordinarily, the file names whose number of character is limited to a smaller value, a possibility that the file names are the same is the higher. For instance, both FAT16 and IS09960-1 have the describing forms that the number of characters is limited to 11 with an 8.3 form and a big letter is not discriminated from a small letter. Thus, the possibility that the file names are the same is high. As compared therewith, though both FAT 32 and NTFS also have the same describing forms, the possibility that the file names are the same is low. Further, Windows (a registered trademark) includes NTFS, FAT32 and FAT16. Accordingly, when the file system of the media is the Windows (the registered trademark), the file name corresponding to the NTSF, the FAT 32 or the FAT 16 described in the manifest  200  may be possibly used so that the file can be accessed. 
     By considering the above-described features, the priority of the file systems can be determined so that a file system considered to have a higher possibility of the same file name as or a compatibility with the file system of the media is preferentially to become an object to be retrieved. The priority shown in  FIG. 3  is determined on the basis of the above-described consideration. A table in which the file systems are allowed to correspond to the priority in  FIG. 3  is a priority table. However, the priority shown in  FIG. 3  indicates only one example. For instance, a priority table by which the file systems can be retrieved at higher speed may be statistically studied and changed. 
     The sequence of the file systems to be retrieved is determined on the basis of this priority table, so that the valid file names can be retrieved at higher speed. 
       FIG. 4  shows a procedure of a file retrieving process according to this embodiment. Here, to explain the procedure of the file retrieving process, it is assumed that as the file system of the media, ISO9660-2 is used, as the manifest  200 , the manifest shown in  FIG. 2  is used and as the priority table, the priority shown in  FIG. 3  is used, respectively. 
     Initially, as the first file main body information  209  described in the manifest  200 , here, the information of the still image file ID001401 is set as an object to be retrieved. In the information of the still image file, three file names of ISO001.JPG, Ntfs001.jpg and FAT001.JPG are described and respectively correspond to ISO9660-1, NTFS and FAT16. 
     Firstly, the file retrieving part  105  retrieves the file name corresponding to the file system of the media in accordance with the media file system procedure. That is, the file retrieving part  105  compares the file system of the media with the above-described three file systems respectively to recognize whether or not the file system of the media corresponds to the file systems (( 1 ), ( 2 ), ( 3 )). In this case, since any of them does not correspond to the file system of the media, the media file system procedure is finished under a state the retrieved result is not obtained. The retrieving process shifts to the non-media file system procedure. 
     In the non-media file system procedure, the file names are retrieved in accordance with the above-described two principles. Namely, the sequence of the file systems to be retrieved is determined in accordance with the priority table. Referring to the priority table, since FAT16 has the highest priority, the file retrieving part  105  initially compares FAT16 with the above-described three file systems respectively to recognize whether or not FAT16 corresponds to the three file systems (( 4 ), ( 5 ), ( 6 )). Here, since FAT16 is included in the above-described three file systems, the corresponding file system is found ( 6 )). Thus, the file retrieving part  105  controls the media reading part  104  to carry out the collating process and decides whether or not the file name of FAT001.JPG corresponding to FAT16 is valid. Here, when the FAT001.JPG is valid, this is considered to be the retrieved result to finish the retrieval of the information of the still image file of ID001401. However, here, an explanation will be given by assuming that the file name is invalid. When the collating process is carried out in such a way to decide that the file name is valid or invalid, the file retrieving part  105  stores the result thereof in the storing part  103  as information showing the validity or the invalidity of the file system. Namely, here, the file retrieving part  105  stores the information that FAT16 is invalid in the storing part  103 . 
     After the retrieval of the FAT16 is completed, the file retrieving part  105  retrieves ISO9660-1 having a secondly highest priority as an object to be retrieved. Also in the case of ISO9660-1, since the corresponding file system is found (( 7 )), the file retrieving part  105  controls the media reading part  104  to carry out the collating process to decide whether or not the corresponding file name ISO001.JPG is valid. Here, when the IS0001.JPG is valid, the file retrieving part  105  stores information that the ISO9660-1 is valid in the storing part  103  to consider this file name to be the retrieved result and finishes the retrieving process of the information of the still image file of ID001401. 
     Then, second file main body information  209  described in the manifest  200 , here, the information of a still image file of ID001404 is set as an object to be retrieved. In the information of the still image file, three file names of ISO002.JPG, Ntfs002.jpg and FAT002.JPG are described and respectively correspond to ISO9660-1, NTFS and FAT16 as in the first file main body information  209 . 
     A procedure of a retrieving process is also the same as that of the first file main body information  209 . That is, the file retrieving part  105  initially retrieves a file name corresponding to the file system of the media ( 8 ,  9 ,  10 ) in accordance with the media file system procedure. Also in this case, since there is no file name corresponding to the file system of the media, the media file system procedure is completed under a state that the retrieved result is not obtained and the retrieving process shifts to the non-media file system procedure. 
     In the non-media file system procedure, FAT16 having the highest priority is firstly retrieved. However, since it is already stored that the FAT16 is invalid, the file retrieving part  105  does not retrieve the FAT16 as an object to be retrieved to shift the object to be retrieved to ISO9660-1 having a secondly highest priority. 
     The collating process of the ISO9660-1 is already carried out to store the information that the ISO9660-1 is valid. Therefore, the file retrieving part  105  unconditionally considers file name of ISO002.JPG corresponding to the file system of ISO9660-1 to be the retrieved result without carrying out the collating process and finishes a retrieving process of the information of the still image file of ID001401. 
     The file retrieving part  105  carries out the retrieving processes according to the above-described method to all the file main body information described in the manifest  200  to obtain the retrieved results. 
     As described above, the result of the collating process of the file name previously retrieved in the file main body information  209  is used so that the collating process of subsequent file names can be omitted and the files can be retrieved at high speed. 
       FIGS. 5 and 6  are flowcharts of a file retrieving process according to the embodiment of the present invention. 
     Especially,  FIG. 5  shows the flowchart of the media file system procedure and  FIG. 6  shows the flowchart of the non-media file system procedure, respectively. S 508  in  FIG. 5  corresponds to the non-media file system procedure shown in  FIG. 6 . 
     Now, referring to  FIG. 5 , a flow of the media file system procedure will be described below. 
     When the retrieving process is started (S 501 ), the media reading part  104  reads the file system of the media and the manifest  200  from the recording media  106  to supply them to the file retrieving part  105  (S 502 ). Then, the media file system procedure and the non-media file system procedure are carried out by the file retrieving part  105  that receives the file system of the media and the manifest  200 . 
     Initially, the file retrieving part  105  grasps the file main body information  209  from the manifest  200  by using the Still tag  202  or the Audio tag  208  as the key. Then, the file main body information  209  in which the retrieval is not yet completed is considered to be an object to be retrieved to advance the retrieving process (S 503 ). 
     Then, the file retrieving part  105  obtains the file names described in the manifest  200  together with the file systems thereof by using the LastURL tag  203  and the file system tag  204  as the keys from the file main body information  209  as the object to be retrieved (S 504 ). 
     Here, the file retrieving part  105  recognizes whether or not the file system obtained in the S 504  corresponds to the file system of the media (S 505 ). 
     When the file systems correspond to each other (S 505 :YES), the file retrieving part  105  stores the file name obtained in the S 504  in the storing part  103  as the retrieved result to complete the retrieving process of the file main body information  209  as the object to be retrieved (S 506 ). 
     On the other hand, when the file systems do not correspond to each other (S 505 :NO), if all the file names of the file main body information  209  of the object to be retrieved are completely recognized (S 507 :YES), the non-media file system procedure is carried out (S 508 ). Then, the file retrieving part  105  stores the retrieved result obtained by the non-media file system procedure in the storing part  103  to finish the retrieving process of the file main body information  209  as the object to be retrieved. 
     When all the file names of the file main body information  209  as the object to be retrieved are not completely recognized (S 507 :NO), a next file name and a file system are obtained to recognize whether or not the file system corresponds to the file system of the media. 
     After the retrieving process of the file main body information  209  as one object to be retrieved is completed, the file retrieving part  105  decides whether or not the retrieval of all the file main body information  209  described in the manifest  200  is completed (S 509 ). If there is the file main body information  209  whose retrieval is not finished (S 509 :NO), the processes from S 503  to S 508  are repeated until the file main body information whose retrieval is not finished does not exist. 
     When all the file main body information  209  described in the manifest  200  is completely retrieved (S 509 :YES), the file retrieving process is completely finished (S 510 ). 
     Now, referring to  FIG. 6 , a flow of the non-media file system procedure will be described below. 
     When the non-media file system procedure is started (S 601 ), the file retrieving part  105  obtains the priority table from the storing part  103 . Then, the file retrieving part  105  refers to the priority table to determine the file systems to be retrieved in order of higher priority (S 602 ). 
     Here, it is decided whether or not the file systems determined in the S 602  need to be retrieved (S 603  to S 606 ). Namely, when the collating process is already carried out to the file system and it is stored that the file system is invalid, the file system is not considered to be an object to be retrieved and the file system having a secondly highest priority is considered to be an object to be retrieved (S 603 :YES). Further, when this file system corresponds to the file system of the media, this file system is not considered to be the object to be retrieved (S 604 :YES), because the file system having the secondly highest priority is already considered to be the object to be retrieved in the media file system procedure. Further, when the file system of the media has a short file name and this file system has a long file name, this file system is not considered to be an object to be retrieved (S 605 :NO and S 606 :NO). In this case, a compatibility between the file system cannot be obtained and there is not possibility that the file main body can be accessed. 
     Then, the file retrieving part  105  obtains the file names described in the manifest  200  together with the file systems thereof by using the LastURL tag  203  and the file system tag  204  as the keys from the file main body information  209  as the object to be retrieved (S 607 ). 
     Here, the file retrieving part  105  recognizes whether or not the file system obtained in the S 607  corresponds to the file system as the object to be retrieved (S 608 ). 
     When the file system does not correspond to the file system as the object to be retrieved (S 608 :NO), a recognition as to whether or not all file names of the file main body information  209  as the object to be retrieved correspond to the file system as the object to be retrieved is repeated (S 607  to S 609 ). When all the file names of the file main body information  209  as the object to be retrieved do not correspond to the file system as the object to be retrieved (S 609 :YES), the file retrieving part  105  tries to change the file system as the object to be retrieved (S 617 ). 
     When the file system corresponds to the file system as the object to be retrieved (S 608 :YES), the file retrieving part  105  decides whether or not the file name obtained in the S 607  is valid in accordance with a below-described method. 
     Namely, when the file system is already decided to be a valid file system by the collating process (S 610 ; YES), the file name obtained in the S 607  is unconditionally stored in the storing part  103  as the retrieved result of the file as the object to be retrieved (S 611 ) to finish the retrieving process by the non-media file system procedure of the file as the object to be retrieved (S 618 ). 
     On the other hand, when the collating process is not yet carried out (S 610 :NO), a collating process is carried out for recognizing whether or not the file main body can be accessed by the file name. As a result, when it is decided that the file name is valid (S 613 :YES), the file retrieving part  105  stores in the storing part  103  that the file system as the object to be retrieved is a valid file system (S 614 ). Further, the file retrieving part  105  stores the file name in the storing part  103  as the retrieved result (S 615 ) to finish the retrieving process by the non-media file system procedure of the file main body information  209  as the object to be retrieved (S 618 ). 
     As a result of the collating process, when it is decided that the file name is invalid (S 613 :NO), the file retrieving part  105  stores in the storing part  103  that the file name is invalid (S 616 ). After that, the file retrieving part  105  decides whether or not the file systems that are not yet considered to be objects to be retrieved remain in the priority table (S 617 ). When the file systems that are not yet considered to be the objects to be retrieved do not remain (S 617 :YES), the retrieving process by the non-media file system procedure of the file main body information  209  as the object to be retrieved is finished (S 618 ). On the contrary, when the file systems that are not considered to be the objects to be retrieved remain (S 617 :NO), the file system having a subsequently highest priority is selected as an object to be retrieved to repeat the same processes (S 602  to S 617 ). 
     Since the above-described retrieving process is carried out, when the recording media is read in which the different file names are attached to a plurality of file systems for the file main body and there is no file name corresponding to the file system of the recording media, a valid file name can be retrieved at high speed. 
     Accordingly, the file main body recorded on the recording media can be retrieved at high speed. 
     The above-described embodiment is simply exemplified for explaining the present invention and it is to be understood that the scope of the present invention is not limited to the above-described embodiment. The present invention may be embodied in other various ways without departing from the gist thereof. 
     For instance, in the above-described embodiment, each file main body information is read and the collating process of the file names included therein is carried out to decide the validity of the file system. However, before the file main body information is read, all or a part of the file systems may be previously decided to be valid. 
     According to the present invention, when the recording media is read in which the different file names are attached to the plurality of file systems for the file main body and there is no file name corresponding to the file system of the recording media, the valid file name can be retrieved at high speed.