Abstract:
A cyclic referencing management method and apparatus, a parsing method and apparatus, and a computer readable recording medium storing a program to implement the methods are provided. The method for managing cyclic referencing that may occur by mutual references of assets in a file provided to control assets in a multimedia application environment, includes: detecting an asset generating cyclic referencing; and ignoring the asset generating cycling referencing. According to the methods and apparatuses, cyclic referencing that can occur in a file to control assets can be detected and processed such that the system can be prevented from entering an indefinite loop or causing an erroneous operation.

Description:
This application claims the priority of U.S. Provisional Application No. 60/558,549, filed on Apr. 2, 2004, in the United States Patent Trademark Office, and Korean Patent Application No. 2004-36951, filed on May 24, 2004, in the Korean Intellectual Property Office, the disclosures of which are incorporated herein in their entirety by reference. 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to controlling assets such as digital content in a multimedia application environment, and more particularly, to a cyclic referencing management method and apparatus, a parsing method and apparatus, and a computer readable recording medium storing a program to implement the methods. 
   2. Description of the Related Art 
   Recently, media such as digital still images, video, digital audio, and text have been processed and reproduced by using a personal computer (PC). Also, as apparatuses generating these media, for example, digital cameras, digital camcorders, digital audio players (MP3, WMA), are increasingly widely used, a variety of types of digital content are massively generated. 
   However, in order to manage the content, that is, multimedia data, which are massively generated, file based experiences are requested to users, and if thus managed data, to which attributes, such as a data reproduction order or method, are given, is reproduced in an apparatus other than a PC, the attribute data given in the PC is lost and only original data is transferred. That is, interoperability of data and data attributes among consumer electronic products, PCs, and digital content generating apparatuses is very weak at present. Examples of weakness of interoperability will now be explained. 
     FIG. 1  is a reference diagram explaining the concept of MusicPhotoVideo (MPV) according to a conventional technology. 
   Referring to  FIG. 1 , by using a digital camera  10 , a photo or video clip is generated, the generated photo or video clip is moved to a PC  11 , works such as edition are performed, and the worked content are burned on an optical recording medium such as a CD-R/Video-CD, and a DVD-R/+R. The thus burned optical recording medium can reproduce the content in a DVD player  12  or a TV  13 . 
   Also, the content worked in the PC can be transferred to a printer  14  to be printed, and to an online medium  15 . 
   Thus, by using a digital camera, a photo is captured, and attribute data, such as a slide show order or a time interval between photos determined when a slide show function is used to confirm the capture photos in the digital camera, or relations between the captured photos determined when a panorama function is used, is stored together with the original data. If this digital camera is connected to a TV through an audio/video (AV) cable and an image is transmitted to the TV, content with each attribute expressed can be viewed by a user. However, if the digital camera is connected to a PC through a universal serial bus (USB) cable, only the original data is transmitted to the computer and all the attached attributes are lost. 
   This is because the digital camera and the PC have information structures different to each other. As shown in the above example, the attribute data stored in the digital camera, that is, metadata, has no interoperability with the PC. In order to compensate these data between digital apparatuses for weak interoperability, a standard referred to as MusicPhotoVideo (MPV) has been being prepared. That is, the MPV is a standard to further ease expression, exchange, processing, and reproduction of metadata such as digital music, photo, and video in consumer electronics (CE) apparatuses and IT apparatuses. The MPV standard, which is currently being prepared by Optical Storage Technology Association (OSTA), defines manifest, metadata, and practice to process and reproduce sets of content, such as digital photos, video, and audio, stored in a storage medium such as an optical disk, a memory card, a computer hard disk, or exchanged according to Internet protocols. The manifest is an independent extensible markup language (XML) document file and is obtained by grouping all MPV elements. 
   The MPV is generally broken down into two parts: MPV core specification (MPV Core-Spec.) and Profile. The MPV Core includes three basic elements: collection, metadata, and identifier. The collection includes a manifest as a root member, an album, marked assets (MarkedAsset), and an asset list (AssetList). An asset is a basic unit of content processed by the MPV and there are two types of assets: a simple media asset such as digital photos, video, digital audio, and documents, etc., and a composite media asset such as digital photos+digital audio, digital still multi-shot sequences, digital still panorama sequences, etc. Based on the content recorded in an MPV file having this structure, MPV software controls such that an asset is read and reproduced. That is, the MPV file is placed between MPV software and data referred to as an asset, and plays a linking role. Accordingly, the MPV file can be regarded as a file system in a higher level operating similarly to the conventional file system. 
   The asset that is a basic unit of content processed in the MPV will now be explained in more detail with reference to  FIGS. 2 and 3 . 
     FIG. 2  is a diagram showing an example of MPV simple assets according to the conventional technology. Simple assets correspond to physical storage entities. As simple assets, there are a still  21 , a video  22 , an audio  23 , a text  24 , a print  25 , a document  26 , and a manifest link (ManifestLink)  27 . 
     FIG. 3  is a diagram showing an example of MPV composite assets according to the conventional technology. Composite assets are meaningful groups of media assets. These composite assets correspond to ordinary capture modes of a digital camera. 
   As composite assets, there are a still with audio (StillWithAudio)  31 , a still multi-shot sequence (StillMultishotSequence)  32 , a still panorama sequence (StillPanoramaSequence)  33 , a Par  34 , and a Seq  35 . 
   Among these, the Par  34  or Seq  35  permits arbitrary expression of media assets different to each other in types. That is, while other composite assets are fixed in that simple assets contained in respective composite assets are predefined, simple assets contained in the Par or Seq are not fixed such that simple assets can be arbitrarily combined. 
   The Par defines a composite asset when a set of assets are generated in synchronization with each other. Referring to  FIG. 3 , it can be seen that Par  34  is formed with a group of assets, which are arranged to be parallel. The Seq defines a composite asset when a set of assets are generated in a predetermined order. Referring to  FIG. 3 , it can be seen that Seq  35  is formed with a group of assets, which are arranged in a predetermined order. 
   The usage of the Seq will now be explained. 
     FIG. 4A  is an example of an MPV file explaining a usage example of &lt;mpv:Seq&gt; according to the conventional technology. 
   Referring to  FIG. 4A , it can be seen that a manifest  1  is at the top level that is the largest in an MPV file, and an asset list  40  is at a level immediately below the top level. 
   Then, the lower levels of the asset list  40  include &lt;mpv:Seq&gt;  41  whose identifier (mpv:id) is “seq001”, &lt;mpv:Still&gt;  42  whose identifier is “still001”, &lt;mpv:Still&gt;  43  whose identifier is “still002”, &lt;mpv:Still&gt;  44  whose identifier is “still003”, &lt;mpv:Still&gt;  45  whose identifier is “still004”, &lt;mpv:StillWithAudio&gt;  46  whose identifier is “sa001”, &lt;mpv:Audio&gt;  47  whose identifier is “audio001”, &lt;mpv:Audio&gt;  48  whose identifier is “audio002”, and &lt;mpv:Audio&gt;  49  whose identifier is “audio003”. 
   Thus, the assets  41  through  49  at the levels lower than the asset list  40  are child assets of the asset list  40 , and reversely, the asset list  40  is the parent asset of the child assets  41  through  49 . 
   Among these child assets, &lt;mpv:Seq&gt;  41  and &lt;mpv:StillWithAudio&gt;  46  are composite assets and the remaining assets, &lt;mpv:Still&gt; and &lt;mpv:Audio&gt;, are simple assets. 
   Simple assets each have a LastURL indicating the location of content for referencing the asset. For example, a still asset whose identifier (ID) is “still001” expresses “images/still01.jpg”, as the LastURL indicating the location of still001 content. 
   In the composite assets, &lt;mpv:Seq&gt;  41  internally has 6 child assets. 
   That is, it can be seen that the first child asset of &lt;mpv:Seq&gt; 41  refers to an audio whose ID is “audio001”. The second child asset refers to a still whose ID is “still001”, the third child asset refers to an audio whose ID is “audio002”, the fourth child asset refers to a StillWithAudio whose ID is “sa001”, the fifth child asset refers to a still whose ID is “still002”, and the sixth child asset refers to a still whose ID is “still003”. 
   In the composite assets, the StillWithAudio  46  internally has 2 child assets. 
   The first child asset refers to a still whose ID is “still004”, and the second child asset refers to an audio whose ID is “audio003”. 
   In the composite assets as described above, it can be seen that the StillWithAudio has only a still and an audio as assets, as shown in its name, while &lt;mpv:Seq&gt; can have any assets as its child assets. 
   Thus, &lt;mpv:Seq&gt; can have any type of reference assets with an ending of Ref, as in, for example, mpv:StillRef, and mpv:AudioRef. Accordingly, it is very complex to extract information from this asset. For example, in order to obtain actual information of &lt;mpv:Still&gt; embedded in &lt;mpv:StillWithAudioRef&gt; assigned by &lt;mpv:Seq&gt;, the following steps are required: 
   1. In order to obtain &lt;mpv:StillWithAudioRef&gt; whose mpv:idRef is “sa001”, parsing &lt;mpv:Seq&gt; whose mpv:id is “seq001” is performed, 
   2. in order to obtain &lt;mpv:StillRef&gt;, parsing &lt;mpv:StillWithAudio&gt; whose mpv:id is “sa001” is performed, and 
   3. mpv:idRef attribute of &lt;mpv:StillRef&gt; in &lt;mpv:StillWithAudio&gt; is obtained and &lt;mpv:Still&gt; whose mpv:id is “still004” is found. 
     FIG. 4B  is a diagram of a tree structure explaining the structure of the MPV file shown in  FIG. 4A . 
   Referring to  FIG. 4B , an AssetList  40  is below a manifest  1 , and 9 child assets  41  through  49  are below the AssetList  40 . 
   Each child asset of &lt;mpv:Seq&gt;  41  refers to a child asset of the AssetList  40 . 
   This structure is an ordinary form of using &lt;mpv:Seq&gt; that is a composite asset. 
     FIG. 5A  is an example of an MPV file explaining another usage example of &lt;mpv:Seq&gt; according to the conventional technology. 
   Referring to  FIG. 5A , an AssetList has 5 child assets. 
   The first child asset  51  is &lt;mpv:Seq&gt; whose ID is “seq001” and which has a child asset referring to an asset whose ID is “seq002”. 
   The second child asset  52  is &lt;mpv:Seq&gt; whose ID is “seq002” and which has a child asset referring to an asset whose ID is “still001”, and a child asset referring to an asset whose ID is “seq003”. 
   The third child asset  53  is &lt;mpv:Seq&gt; whose ID is “seq003” and which has a child asset referring to an asset whose ID is “still002”. 
   The fourth child asset  54  is a still asset whose ID is “still001”. 
   The fifth child asset  55  is a still asset whose ID is “still002”. 
     FIG. 5B  is a diagram of a tree structure explaining the structure of the MPV file shown in  FIG. 5A . 
   Referring to  FIG. 5B , &lt;mpv:Seq&gt;  51  that is the first child asset of the AssetList refers to &lt;mpv:Seq&gt;  52  that is the second child asset, and &lt;mpv:Seq&gt;  52  that is the second child asset refers to &lt;mpv:Seq&gt;  53  that is the third child asset. Also, &lt;mpv:Seq&gt;  53  that is the third child asset refers to “still002” that is a simple asset. 
   Though &lt;mpv:Seq&gt; continuously refers to another &lt;mpv:Seq&gt;, an asset that is finally referred to is “still002” that is a simple asset. Accordingly, a problem such as cyclic reference does not occur. 
   Thus, it can be seen that a composite asset like &lt;mpv:Seq&gt; or &lt;mpv:Par&gt; is made to have a plurality of primary assets as children. Though this composite structure of a composite asset has an advantage that a greater variety of reproduction scenarios can be implemented, there may occur a variety of problems due to many children. One of these problems is “cyclic referencing”, which will now be explained with reference to  FIGS. 6A and 6B . 
     FIG. 6A  is an example of an MPV file explaining a case where cyclic referencing occurs due to use of &lt;mpv:Seq&gt; according to the conventional technology. 
   Referring to  FIG. 6A , an AssetList has 3 child assets that are all &lt;mpv:Seq&gt;. 
   The first child asset  61  is &lt;mpv:Seq&gt; whose ID is “seq001”, and refers to an asset whose ID is “seq002”. 
   The second child asset  62  is &lt;mpv:Seq&gt; whose ID is “seq002” and refers to an asset whose ID is “seq003”. 
   The third child asset  63  is &lt;mpv:Seq&gt; whose ID is “seq003” and refers to an asset whose ID is “seq001”. 
   In this situation, a cyclic referencing problem occurs. That is, since the third child asset from the top again refers to the first child asset, these 3 child assets are entering an infinite loop. 
     FIG. 6B  is a diagram of a tree structure explaining the structure of the MPV file shown in  FIG. 6A . 
   Referring to  FIG. 6B , child asset seq001  61  refers to child asset seq002  62 , child asset seq002  62  refers to child asset seq003  63 , and child asset seq003  63  refers to child asset seq001  61 . Accordingly, it can be seen that a loop is generated among seq001, seq002, and seq003, which generates a cyclic referencing problem in which getting out of the loop is impossible. 
     FIG. 7  is another example of an MPV file explaining a case where cyclic referencing occurs due to use of &lt;mpv:Seq&gt; according to the conventional technology. 
   Referring to  FIG. 7 , an AssetList has a child asset, &lt;mpv:Seq&gt;  71 , whose ID is “seq0000”. The child asset  71  has a child asset, &lt;mpv:SeqRef&gt;, which refers to an asset whose ID is “seq0000”. Since the parent asset  71  and the child asset  72  refer to each other, an infinite loop occurs between the two and the system may operate as if it halts. Accordingly, a cyclic referencing problem occurs. 
   However, in the conventional technology, if a cyclic referencing problem occurs while an MPV parser parses an MPV file, the parser reports to the application that the MPV data is incorrect, or the system operates incorrectly as if it halts. Accordingly, data contained in the MPV file cannot be used any more. 
   SUMMARY OF THE INVENTION 
   The present invention provides a cyclic referencing management method and apparatus, and a parsing method and apparatus, by which even when cyclic referencing occurs in an MPV file, a system can be operated normally and data contained in the MPV file can be used, and a computer readable recording medium storing a program implementing the methods. 
   According to an aspect of the present invention, there is provided a cyclic referencing management method for managing cyclic referencing occurring by mutual references of assets in a file provided to control assets in a multimedia application environment, the method including: detecting an asset generating cyclic referencing; and ignoring the asset generating cycling referencing. 
   The asset generating the cyclic referencing may include &lt;mpv:Seq&gt; or &lt;mpv:Par&gt;. 
   According to another aspect of the present invention, there is provided a cyclic referencing management method for managing cyclic referencing occurring by mutual references of assets in a file provided to control assets in a multimedia application environment, the method including: detecting an asset capable of generating cyclic referencing; detecting a child asset referring to the detected asset, among child assets of the detected asset; and ignoring the detected child asset. 
   Detecting the child asset referring to the detected asset, among child assets of the detected asset includes: comparing mpv:id that is the identifier of the detected asset, with mpv:idRef that is a reference identifier of the child asset referring to another asset, among the child assets of the asset; and detecting a child asset having mpv:idRef identical to the mpv:id. 
   According to still another aspect of the present invention, there is provided a parsing method for parsing a file provided to control assets in a multimedia application environment, the method including: determining whether or not the file complies with an extensible markup language (XML) file rule and a MusicPhotoVideo (MPV) file rule; parsing the entire assets contained in the file if the file complies with the XML file rule and MPV file rule; detecting an asset generating cyclic referencing while parsing the asset; and ignoring the asset generating the cyclic referencing. 
   According to yet still another aspect of the present invention, there is provided a cyclic referencing management apparatus for managing cyclic referencing occurring by mutual references of assets in a file provided to control assets in a multimedia application environment, the apparatus including: a cyclic referencing management unit which detects an asset generating cyclic referencing and ignores the asset generating cycling referencing. 
   The asset generating the cyclic referencing may include &lt;mpv:Seq&gt; or &lt;mpv:Par&gt;. 
   According to a further aspect of the present invention, there is provided a cyclic referencing management apparatus for managing cyclic referencing occurring by mutual references of assets in a file provided to control assets in a multimedia application environment, the apparatus including: a detection unit which detects an asset capable of generating cyclic referencing; an identifier storage unit which stores the identifier of the detected asset; an identifier comparison unit which detects a child asset referring to the asset having the stored identifier, among child assets of the detected asset; and a cyclic referencing processing unit which ignores the detected child asset. 
   The identifier comparison unit may compare mpv:id that is the identifier of the stored asset, with mpv:idRef that is a reference identifier of the child asset referring to another asset, among the child assets of the asset, and detect a child asset having mpv:idRef identical to the mpv:id. 
   According to an additional aspect of the present invention, there is provided a parsing apparatus for parsing a file provided to control assets in a multimedia application environment, the apparatus including: a cyclic referencing management unit which detects an asset generating cyclic referencing while parsing an asset contained in an MPV file complying with an XML file rule and an MPV file rule, and ignores the asset generating the cyclic referencing. 
   The cyclic referencing management unit may generate reproduction control information to prohibit reproduction of the asset generating the cyclic referencing, and transmit the generated reproduction control information to an apparatus for controlling reproduction of the asset contained in the MPV file. 
   According to an additional aspect of the present invention, there is provided a computer readable recording medium having embodied thereon a computer program for a cyclic referencing management method for managing cyclic referencing occurring by mutual references of assets in a file provided to control assets in a multimedia application environment, wherein the method includes: detecting an asset generating cyclic referencing; and ignoring the asset generating cycling referencing. 
   According to an additional aspect of the present invention, there is provided a computer readable recording medium having embodied thereon a computer program for a cyclic referencing management method for managing cyclic referencing occurring by mutual references of assets in a file provided to control assets in a multimedia application environment, wherein the method includes: detecting an asset capable of generating cyclic referencing; storing the identifier of the detected asset; detecting a child asset referring to the asset having the stored identifier, among child assets of the detected asset; and ignoring the detected child asset. 
   According to an additional aspect of the present invention, there is provided a computer readable recording medium having embodied thereon a computer program for a parsing method for parsing a file provided to control assets in a multimedia application environment, wherein the method includes: determining whether or not the file complies with an extensible markup language (XML) file rule and a MusicPhotoVideo (MPV) file rule; parsing the entire assets contained in the file if the file complies with the XML file rule and MPV file rule; detecting an asset generating cyclic referencing while parsing the asset; and ignoring the asset generating the cyclic referencing. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and other features and advantages of the present invention will become more apparent by describing in detail exemplary embodiments thereof with reference to the attached drawings in which: 
       FIG. 1  is a reference diagram explaining the concept of MusicPhotoVideo (MPV) according to a conventional technology; 
       FIG. 2  is a diagram showing an example of MPV simple assets according to the conventional technology; 
       FIG. 3  is a diagram showing an example of MPV composite assets according to the conventional technology; 
       FIG. 4A  is an example of an MPV file explaining a usage example of &lt;mpv:Seq&gt; according to the conventional technology; 
       FIG. 4B  is a diagram of a tree structure explaining the structure of an MPV file shown in  FIG. 4A ; 
       FIG. 5A  is an example of an MPV file explaining another usage example of &lt;mpv:Seq&gt; according to the conventional technology; 
       FIG. 5B  is a diagram of a tree structure explaining the structure of an MPV file shown in  FIG. 5A ; 
       FIG. 6A  is an example of an MPV file explaining a case where cyclic referencing occurs due to use of &lt;mpv:Seq&gt; according to the conventional technology; 
       FIG. 6B  is a diagram of a tree structure explaining the structure of an MPV file shown in  FIG. 6A ; 
       FIG. 7  is another example of an MPV file explaining a case where cyclic referencing occurs due to use of &lt;mpv:Seq&gt; according to the conventional technology; 
       FIG. 8  is a diagram of the entire structure of an apparatus to solve the cyclic referencing according to the present invention; 
       FIG. 9  is a detailed diagram of a cyclic referencing management unit shown in  FIG. 8 ; 
       FIG. 10  is a flowchart of the steps performed by a method to solve cyclic referencing according to the present invention; 
       FIG. 11  is a detailed flowchart of the method to solve cyclic referencing shown in  FIG. 10 ; and 
       FIGS. 12A through 12C  are reference diagrams explaining an identification (ID) to be stored in an ID storage unit when an MPV file shown in  FIG. 6A  is parsed. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   The present invention will now be described more fully with reference to the accompanying drawings, in which exemplary embodiments of the invention are shown. 
   In order to solve the cyclic referencing problem, in the present invention, if the occurrence of cyclic referencing in an MPV is detected, the connection of an asset generating the cyclic referencing such that parsing is performed only for assets before the cyclic referencing occurs, and the asset generating the cyclic referencing is ignored such that the asset cannot be reproduced. Thus, by detecting and ignoring the asset generating the cyclic referencing, the system can be prevented from entering an infinite loop and other assets contained in the MPV file can be used. 
   First, an apparatus to solve cyclic referencing according to the present invention will now be explained with reference to  FIG. 8 . 
     FIG. 8  is a diagram of the entire structure of an apparatus to solve the cyclic referencing according to the present invention. This apparatus can be applied to content generation products such as a PC, a DVD player, a DVD recorder, an MP3 player, a digital video camera (DVC), and a digital still camera (DSC). 
   Referring to  FIG. 8 , the apparatus includes a storage medium  81 , an MPV parser  82 , a reproduction control unit  84 , a video output unit  85 , and an audio output unit  86 . 
   The storage medium  81  stores an MPV file to be parsed by the MPV parser  82 , and content referred to in the MPV file and reproduced by the reproduction control unit  84 . The storage medium  81  can be any one of, for example, a memory, a memory stick, an optical disk, and a hard disk. 
   The MPV parser  82  reads out an MPV file from the storage medium  81 , parses a variety of assets and metadata recorded in the MPV file, and provides reproduction control information that enables reproduction of content stored in the storage medium  81 , to the reproduction control unit  84 . In particular, MPV parser  82  according to the present embodiment includes a cyclic referencing management unit  83  for resolving a cyclic referencing problem. 
   The cyclic referencing management unit  83  detects whether or not cyclic referencing occurs while an MPV file is parsed, and if cyclic referencing occurs, performs processing to ignore an asset generating the cyclic referencing. More specifically, here, to ignore means generating reproduction control information such that the asset generating the cyclic referencing cannot be reproduced any more, and providing the generated reproduction control information to the reproduction control unit  84 . 
   If the result of parsing in the MPV parser  82 , that is, the reproduction control information, is received, the reproduction control unit  84  controls such that content stored in the storage medium  81  can be reproduced based on the received reproduction control information. At this time, according to the present embodiment, the reproduction control unit  84  controls according to the reproduction control information on the asset generating the cyclic referencing such that the asset generating the cyclic referencing cannot be reproduced. 
   The video output unit  85  displays content corresponding to an image such as a digital photo provided by the reproduction control unit  84 . 
   The audio output unit  86  outputs an audio signal output from the reproduction control unit  84 . 
     FIG. 9  is a detailed diagram of the cyclic referencing management unit  83  shown in  FIG. 8 . 
   Referring to  FIG. 9 , the cyclic referencing management unit  83  includes a cyclic referencing capable asset detection unit  91 , an ID insertion unit  92 , an ID comparison unit  93 , an ID deletion unit  94 , and an ID storage unit  95 . 
   The cyclic referencing capable asset detection unit  91  detects assets that can generate cyclic referencing in the MPV file, that is, &lt;mpv:Par&gt; or &lt;mpv:Seq&gt;. The cyclic referencing capable asset detection unit  91  can be disposed outside the cyclic referencing management unit  83  to transmit a signal indicating that a cyclic referencing capable asset is detected, to the cyclic referencing management unit  83 . 
   When &lt;mpv:Par&gt; or &lt;mpv:Seq&gt; is detected, for ID insertion, the ID insertion unit  92  stores the ID of &lt;mpv:Par&gt; or &lt;mpv:Seq&gt;, that is, mpv:id, into ID storage unit (RefIDSet)  95 . 
   The ID comparison unit  93  compares the ID of an asset referred to by the child asset of &lt;mpv:Par&gt; asset or &lt;mpv:Seq&gt; asset, with the ID stored in the ID storage unit  95 . When the comparison result indicates that the IDs are identical, the ID comparison unit transmits a signal indicating that cyclic referencing occurs, to the cyclic referencing processing unit  96 . When there are no more child assets to be parsed after all child assets contained in &lt;mpv:Par&gt; or &lt;mpv:Seq&gt; are parsed, the ID deletion unit  94  deletes all IDs stored in the ID storage unit  95  to prepare for the next cyclic referencing management. 
   When a signal indicating that cyclic referencing occurs is received from the ID comparison unit  93 , the cyclic referencing processing unit  96  performs processing to ignore an asset generating the cyclic referencing. The processing to ignore the asset is, for example, generating reproduction control information to prevent the asset generating the cyclic referencing from being reproduced. 
   The ID storage unit (RefIDSet)  95  stores mpv:id that is the ID of &lt;mpv:Par&gt; asset or &lt;mpv:Seq&gt; asset contained in the MPV filed being parsed. 
     FIG. 10  is a flowchart of the steps performed by a method to solve cyclic referencing according to the present invention. 
   Referring to  FIG. 10 , first, the MPV parser  82  determines whether or not an MPV file to be parsed complies with an XML file rule in operation  101 . If the MPV file to be parsed does not comply with the XML file rule, the MPV parser  82  finishes parsing. 
   Next, the MPV parser  82  determines whether or not the MPV file to be parsed complies with an MPV file rule in operation  102 . If the MPV file to be parsed does not comply with the MPV file rule, the MPV parser  82  finishes parsing. 
   When the MPV file to be parsed complies with both the XML file rule and MPV file rule, the MPV parser  82  parses the entire MPV asset in operation  103 . 
   When the MPV file is parsed, the cyclic referencing management unit  83 , in particular, determines whether or not the MPV file has cyclic referencing in operation  104 . If the MPV file does not have cyclic referencing, the parsing is finished. 
   When the MPV file has cyclic referencing, the cyclic referencing management unit  83  performs processing to ignore the asset generating the cyclic referencing in operation  105 , and finishes parsing. 
     FIG. 11  is a detailed flowchart of the method to solve cyclic referencing shown in  FIG. 10 . 
   Referring to  FIG. 11 , first, the cyclic referencing capable asset detection unit  91  determines whether or not there is a direct child asset of AssetList (DCA) not parsed in operation  111 . If the determination result indicates that there is not DCA, it means that all parsing is performed, and the parsing is finished. 
   If there is a DCA not parsed, the cyclic referencing capable asset detection unit  91  determines whether or not the DCA is &lt;mpv:Seq&gt; asset or &lt;mpv:Par&gt; asset in operation  112 . If the determination result indicates that the DCA is neither &lt;mpv:Seq&gt; nor &lt;mpv:Par&gt;, there is no possibility of occurrence of cyclic referencing, and accordingly, the operation  111  is performed to parse a next asset. 
   When the DCA is &lt;mpv:Seq&gt; or &lt;mpv:Par&gt;, the ID insertion unit stores mpv:id that is the ID of the DCA in RefIDSet in operation  113 . 
   Next, the cyclic referencing capable asset detection unit  91  determines whether or not there is a child asset in which the DCA is not parsed in operation  114 . 
   If the determination result indicates that there is no child asset in which the DCA is not parsed, there is no possibility of occurrence of cyclic referencing from the DCA, and accordingly, the operation  111  is performed to parse a next asset. 
   However, if there is a child asset in which the DCA is not parsed, it is determined whether or not the child asset refers to another asset in operation  115 . That is, it is determined whether or not the child asset has mpv:idRef. If the determination result indicates that it is not an asset referring to another asset, there is no possibility of occurrence of cyclic referencing, and accordingly the operation  114  is performed to parse a next child asset. 
   If the child asset refers to another asset, that is, if the child asset has pv:idref, the ID comparison unit  93  determines whether or not RefIDSet has mpv:idRef of this child asset in operation  116 . In other words, it is determined whether or not an ID identical to mpv:idRef of the child asset being currently parsed is stored in the RefIDSet. 
   If the determination result indicates that an ID identical to mpv:idref of the child asset being currently parsed is stored in the RefIDSet, the ID comparison unit  93  determines that cyclic referencing occurs, and ignores the child asset generating the cyclic referencing in operation  119 . In order to perform the operation  119 , the cyclic referencing processing unit  96  may generate reproduction control information to prevent the child asset generating the cyclic referencing from being reproduced, and provide the information to the MPV parser  82 . Then, the operation  114  is performed to parse a next child asset. 
   If the determination result indicates that the ID is not stored in the RefIDSet, the cyclic referencing capable asset detection unit  91  determines whether or not the child asset to be parsed currently refers to a DCA that is &lt;mpv:Seq&gt; or &lt;mpv:Par&gt; in operation  117 . If the determination result indicates that this child asset does not refer to &lt;mpv:Seq&gt; or &lt;mpv:Par&gt;, the operation  114  is performed to parse a next child asset. 
   If the determination result indicates that this child asset refers to &lt;mpv:Seq&gt; or &lt;mpv:Par&gt;, parsing the DCA referred to by this child asset is started in operation  118 , and the operation  113  is performed to store mpv:id that is the ID of the DCA referred to by this child asset, in RefIDSet. 
   If it is determined in the operation  114  that the DCA does not have a child asset not parsed, the ID deletion unit  94  clears RefIDSet in operation  120 . 
   The cyclic referencing solving method according to the present embodiment will now be explained with an example of an MPV file in which actual cyclic referencing occurs as shown in  FIG. 6A . 
   First, since the type of the first child asset  61  is &lt;mpv:Seq&gt; and the ID of the first child asset  61  is “seq001”, “seq001”  121  is stored in the ID storage unit  95  as shown in  FIG. 12A  in operation  113 . 
   Next, the child asset of the first child asset  61  is detected. Since this child asset has &lt;mpv:idRef&gt;, it is determined whether or not this mpv:idRef “seq002” is an ID stored in the ID storage unit  95  shown in  FIG. 12A  in operation  116 . Since the ID storage  95  does not have “seq002”, the next operation  117  is performed. Since this child asset refers to DCA that is &lt;mpv:Seq&gt;, the operation  118  is performed to start parsing the DCA referred to by this child asset, and the operation  113  is performed to store the DCA referred to by this child asset, that is, “seq002”, in the ID storage unit  95  in operation  113 . Thus, seq001  121  and seq002  122  are stored in the ID storage unit  95  as shown in  FIG. 12B . 
   Next, the child asset of this second child asset  62  is detected. Since this child asset has mpv:idRef, it is determined whether or not this mpv:idRef “seq003” is an ID stored in the ID storage unit  95  in operation  116 . Since the ID storage  95  does not have “seq003”, the next operation  117  is performed. Since this child asset refers to DCA that is &lt;mpv:Seq&gt; in the operation  117 , the operation  118  is performed to start parsing the DCA referred to by this child asset, and the operation  113  is performed to store the DCA referred to by this child asset, that is, “seq003”, in the ID storage unit  95  in operation  113 . Thus, seq001  121 , seq002  122 , and seq003  123  are stored in the ID storage unit  95  as shown in  FIG. 12C . 
   Next, the child asset of this third child asset  63  is detected. Since this child asset has mpv:idRef, it is determined whether or not this mpv:idRef “seq001” is an ID stored in the ID storage unit  95  in operation  116 . Since the ID storage  95  stores “seq001”, it can be found that cyclic referencing occurs, and the operation  119  is performed to ignore this child asset. That is, &lt;mpv:SeqRef mpv:idRef=“seq001”&gt; that is the child asset of the third child asset  63  is ignored. In the example of the MPV file shown in  FIG. 6A , all the child assets of the AssetList and their child assets are formed with only &lt;mpv:Seq&gt; and &lt;mpv:SeqRef&gt; in order to show cyclic referencing, and accordingly, it is difficult to apply this example to actual reproduction. However, if there is another child asset in front of &lt;mpv:SeqRef mpv:idRef=“seq001”&gt; that is the child asset of the third child asset  63 , reproduction can be performed to the former child asset and the reproduction of &lt;mpv:SeqRef mpv:idRef=“seq001”&gt; can be prohibited. 
   Then, the operation  114  is performed and since there is no child asset to be parsed any more, the operation  120  is performed to clear the ID storage unit. 
   Though applying the cyclic referencing management method according to the present invention mainly to the MPV file and the apparatus parsing the MPV file is explained in the above embodiments, application of the cyclic referencing management according to the present invention is not limited to this MPV and can include any applications generating and using a playlist for asset control, which will be easily understood by a person skilled in the art of the present invention. 
   The cyclic referencing management method as described above can also be embodied as computer readable codes on a computer readable recording medium. The computer readable recording medium is any data storage device that can store data which can be thereafter read by a computer system. Examples of the computer readable recording medium include read-only memory (ROM), random-access memory (RAM), CD-ROMs, magnetic tapes, floppy disks, optical data storage devices, and carrier waves (such as data transmission through the Internet). The computer readable recording medium can also be distributed over network coupled computer systems so that the computer readable code is stored and executed in a distributed fashion. (Also, functional programs, codes, and code segments for accomplishing the present invention can be easily construed by programmers skilled in the art to which the present invention pertains.) 
   While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the following claims. The preferred embodiments should be considered in descriptive sense only and not for purposes of limitation. Therefore, the scope of the invention is defined not by the detailed description of the invention but by the appended claims, and all differences within the scope will be construed as being included in the present invention. 
   According to the present invention as described above, cyclic referencing that can occur in an MPV file can be detected and processed such that the system can be prevented from entering an indefinite loop or causing an erroneous operation.