Patent Publication Number: US-2009231968-A1

Title: Recording medium storing management information for content attribute and recording device and playback device for the recording medium

Description:
TECHNICAL FIELD 
     The present invention relates to a recording medium that records digital data content, and more particularly to a recording medium that stores management information on content attributes. In addition, the present invention relates to a device that reproduces content from such a recording medium and a device that records content in such a recording medium. 
     BACKGROUND ART 
     For recording media that record various digital data (hereinafter, referred to as “content”) such as music content, moving image content, and still image content, there exist various types of media such as semiconductor recording media, magnetic disks, optical disks, and magneto-optical disks. 
     Among them, particularly, the semiconductor recording media have their features including small size and lightweight. Further, improvement of capacity and speed, and price reduction thereof have been rapidly achieved in recent years. Thus the semiconductor recording media can be used in various apparatuses such as digital cameras, mobile phones, portable music players, television sets, and DVD recorders. Typical semiconductor recording media include memory cards such as SD memory cards (registered trademark). Among these semiconductor recording media, there is a medium, as represented by an SD memory card, that has a copyright protection function and is capable of recording contents that require copyright protection. 
     An example of a content recording method that can be implemented by such a copyright protection function of a semiconductor recording medium is shown below. 
     A semiconductor recording medium has a protected area that can be accessed only when the semiconductor recording medium and a host device which is a playback device or a recording device have authorized each other, and a normal area that can be accessed without authorization. Encrypted content is recorded in the normal area, and a content key for encrypting the content is recorded in the protected area. 
     The content which is recorded in a semiconductor recording medium using such a copyright protection function cannot be reproduced by an unauthorized apparatus that cannot make mutual authorization with the semiconductor recording medium. In addition, just copying only the content recorded in the normal area to another memory card does not enable playback of the content because there is no content key. In this manner, it is possible to prevent illegal copy or the like of the content that requires copyright protection. 
     For a case of using the content, which requires copyright protection, there is a case in which a user rips content from a music CD bought by the user him/herself to a PC (personal computer) and records the ripped content in a semiconductor recording medium. Furthermore, there is a case in which content, such as music, a moving image, or a book, is downloaded from a content provider to a terminal, such as a PC or mobile phone, via the Internet or a mobile phone network by paying fee, the downloaded content is recorded in a semiconductor recording medium, and the content is reproduced using the semiconductor recording medium storing the content and a small semiconductor player. In addition, it is also possible to buy content not only through a PC or mobile phone connected to the Internet or a mobile phone network but also through an electronic terminal (KIOSK terminal) installed in specific places such as convenience stores, predetermined stores, and stations. Such expansion of a digital content distribution environment increases convenience for users and expands various sales networks for providers, and thus, it is expected that various content types and use environments continuously proliferate. 
     Meanwhile, upon recording content that requires copyright protection as described above in a semiconductor recording medium, recording standards as a recording method are determined according to characteristics of various semiconductor media and contents. Thus a recording device needs to record content in a semiconductor recording medium according to the recording standard. Accordingly, any apparatus can perform recording and playback as long as the apparatus complies with the recording standard. 
     For example, in an exemplary case of a music application, content corresponding to a song is encrypted with a content key and the encrypted content and the content key are recorded in a predetermined folder in a semiconductor recording medium in a predetermined file format. Patent Document 1 describes a semiconductor recording medium in which a plurality of encryption keys are recorded in a predetermined order to a protected area that can be accessed by successful authorization between the semiconductor recording medium and a host device, and the encrypted content and management information on the encrypted content are recorded in a normal area. The semiconductor recording medium achieves high convenience such as changing of the playback order of songs and capability of deleting a song, while preventing unauthorized decryption of music content. 
     Patent Document 1: JP-A-2001-249695 
     DISCLOSURE OF INVENTION 
     Problems to be Solved by the Invention 
     However, the above-described conventional art has the following problem. With an increase in the capacity of the semiconductor recording medium, the number of pieces of recordable content also increases. In order to obtain user&#39;s target content in a semiconductor recording medium having recorded therein many pieces of contents, an apparatus (e.g., a playback device) that installs the semiconductor recording medium needs to read and search all management information files related to all pieces of content recorded in the semiconductor recording medium. However, reading and searching all management information files by the apparatus for the user&#39;s target content while holding the management information files in the apparatus dramatically increases its overhead along with the increase in the number of pieces of content. This is a problem on practical use. 
     Particularly, when the maximum number of pieces of content to be managed which is specified according to the data recording standard for a semiconductor recording medium is very large, a process of reading management information files for all pieces of content and holding information in the management information files in the apparatus is an excessive load to an apparatus whose hardware performance is not relatively high, such as a playback-dedicated apparatus. Thus the apparatus cannot handle the process. 
     In view of the above-described problem, an object of the present invention is therefore to provide a recording medium having a mechanism that enables an apparatus having not so high hardware performance, such as a playback-dedicated apparatus, to easily perform a narrowing-down extraction of content, and a playback device and a recording device for such a recording medium. 
     Means for Solving the Problems 
     In the present invention, in order that even an apparatus whose throughput is not so high, such as a playback-dedicated apparatus, can easily implement a narrowing-down search of content (particularly, audio content), attribute management files are provided for respective pieces of attribution information (genre, composer, artist, album, title, and so on) on the content. Furthermore, in order that while easily implementing an update of the attribute management files, sorted information in each attribute management file can be displayed, only sort information for the case in which information in each attribute management file is sorted is managed by a different file. 
     According to a first aspect of the present invention, there is provided a recording medium that records content. The recording medium includes plural pieces of attribute management information, each piece of attribute management information managing each of various pieces of attribute information on the content for each of various predetermined items, and sort management information that manages information on sort order when the information managed by the attribute management information is sorted by a predetermined procedure. The attribute management information includes text data indicating an item to be managed thereby, and pointer information indicating a link relationship between pieces of attribute management information. The sort management information includes, for each piece of attribute management information, information on a sort order when all entries in each piece of attribute management information are sorted by a predetermined procedure. 
     According to a second aspect of the present invention, there is provided a recording device that records content in a recording medium. The recording device includes an input unit that inputs content and pieces of various attribute information on the content, and a data recording unit that records the inputted content to the recording medium. The data recording unit generates pieces of attribute management information and sort management information based on the attribute information inputted from the input unit, each piece of attribute management information managing each of various pieces of attribute information on the content for each of various predetermined items, the sort management information managing information on sort order when the information managed by the attribute management information is sorted by a predetermined procedure. The data recording unit records the generated attribute management information and sort management information together with the content to the recording medium. 
     According to a third aspect of the present invention, there is provided a playback device that reproduces content recorded in a recording medium. The recording medium stores plural pieces of attribute management information, each piece of attribute management information managing each of various pieces of attribute information on the content for each of various predetermined items, and sort management information that manages information on sort order when the information managed by the attribute management information is sorted by a predetermined procedure. The attribute management information includes text data indicating an item to be managed thereby, and pointer information indicating a link relationship between pieces of attribute management information. The sort management information includes, for each piece of attribute management information, information on a sort order when all entries in each piece of attribute management information are sorted by a predetermined procedure. 
     The playback device includes a content reader. The content reader reads out the attribute management information and the sort management information from the recording medium, and identifies desired content data according to a user selection by referring to the read attribute management information and sort management information. 
     According to a fourth aspect of the present invention, there is provided a recording medium that stores a program for recording content in the recording medium. The program causes a computer to execute the procedures of: inputting content and pieces of various attribute information on the content; generating pieces of attribute management information and sort management information based on the inputted attribute information, each piece of attribute management information managing each of various pieces of attribute information on the content for each of various predetermined items, the sort management information managing information on sort order when the information managed by the attribute management information is sorted by a predetermined procedure; and recording the generated attribute management information and sort management information together with the content to a recording medium. 
     According to a fifth aspect of the present invention, there is provided a recording medium that stores a program for reproducing content from the recording medium. The recording medium stores plural pieces of attribute management information, each piece of attribute management information managing each of various pieces of attribute information on the content for each of various predetermined items, and sort management information that manages information on sort order when the information managed by the attribute management information is sorted by a predetermined procedure. The attribute management information includes text data indicating an item to be managed thereby, and pointer information indicating a link relationship between pieces of attribute management information. The sort management information includes, for each piece of attribute management information, information on a sort order when all entries in each piece of attribute management information are sorted by a predetermined procedure. The program causes a computer to execute the procedures of: reading out the attribute management information and the sort management information from the recording medium; sorting the information managed by each piece of attribute management information according to the sort management information, and displaying the sorted information on a selection screen; and identifying content to be reproduced, according to information selected by a user on the selection screen. 
     EFFECTS OF THE INVENTION 
     According to the present invention, pieces of attribute management information that respectively manage attributes (genre, artist, composer, album, title, etc.) of content are hierarchically linked to one another, and information on the links (pointers) is managed by each piece of attribute management information. Hence a narrowing-down extraction of desired content can be performed with a simple configuration. In addition, sort management information that manages sort information on the pieces of attribute management information is separately provided. With this configuration, while suppressing an increase in complication of a process for updating the attribute management information, caused by content addition, content deletion, or the like, facilitation of a search based on the attributes of content recorded in a semiconductor recording medium is achieved. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a diagram showing a configuration of a semiconductor recording medium in a first embodiment of the present invention. 
         FIG. 2  is a diagram showing configurations of a search information recording area and a data area in the semiconductor recording medium. 
         FIG. 3  is a diagram describing encryption of content and content keys. 
         FIG. 4  is a diagram showing directory/file configurations in a recording medium of the first embodiment of the present invention. 
         FIG. 5  is a diagram showing a configuration of navigation files in the first embodiment of the present invention. 
         FIG. 6  shows diagrams showing examples of attribute information on audio content. 
         FIG. 7  is a diagram showing a configuration of a genre management file in the first embodiment of the present invention. 
         FIG. 8  is a diagram showing a configuration of a composer management file in the first embodiment of the present invention. 
         FIG. 9  is a diagram showing a configuration of an artist management file in the first embodiment of the present invention. 
         FIG. 10  is a diagram showing a configuration of an album management file in the first embodiment of the present invention (first example). 
         FIG. 11  is a diagram showing a configuration of a title management file in the first embodiment of the present invention. 
         FIG. 12  is a diagram showing a configuration of an album management file in the first embodiment of the present invention (second example). 
         FIG. 13  is a diagram showing a configuration of an album management file in the first embodiment of the present invention (third example). 
         FIG. 14  is a diagram showing configurations of a genre management file and a sort information management file in the first embodiment of the present invention (first example). 
         FIG. 15  is a diagram showing configurations of a genre management file and a sort information management file in the first embodiment of the present invention (second example). 
         FIG. 16  is a diagram showing a configuration of a recording device in the present invention. 
         FIG. 17  is a flowchart showing a recording process of the recording device in the first embodiment of the present invention. 
         FIG. 18  is a flowchart showing a navigation file generation method in the first embodiment of the present invention. 
         FIG. 19  is a diagram showing a configuration of a playback device in the first embodiment of the present invention. 
         FIG. 20  is a flowchart showing a process of the playback device in the first embodiment of the present invention. 
         FIGS. 21A and 21B  are diagrams showing exemplary displays of selection menus on the playback device in the first embodiment of the present invention. 
         FIGS. 22C and 22D  are diagrams showing exemplary displays of selection menus on the playback device in the first embodiment of the present invention. 
         FIG. 23  is a flowchart showing a process of the playback device when a selection is made by a user in an initial menu. 
         FIG. 24  is a flowchart showing a process of the playback device to be performed when a “genre list” is selected in the initial menu. 
         FIG. 25  is a flowchart showing a process of the playback device to be performed when a “composer (artist) list” is selected in the initial menu. 
         FIG. 26  is a flowchart showing a process of the playback device to be performed when an “album list” is selected in the initial menu. 
         FIG. 27  is a flowchart showing a process of the playback device to be performed when a “title list” is selected in the initial menu. 
         FIG. 28  is an illustrative diagram showing a configuration of navigation files in a second embodiment of the present invention. 
         FIG. 29  is a diagram showing a configuration of a genre management file in the second embodiment of the present invention. 
         FIG. 30  is a flowchart showing a process of the recording device in the second embodiment of the present invention. 
         FIG. 31  is a flowchart showing a process of the playback device in the second embodiment of the present invention. 
         FIG. 32  is an illustrative diagram showing a configuration of navigation files in a third embodiment of the present invention. 
         FIG. 33  is a diagram showing a configuration of a genre management file in the third embodiment of the present invention. 
         FIG. 34  is a flowchart showing a process when content is recorded in the third embodiment of the present invention. 
         FIG. 35  is a flowchart showing a process when content is deleted in the third embodiment of the present invention. 
         FIG. 36  is an illustrative diagram showing configurations of a title management file and a sort information management file in a fourth embodiment of the present invention. 
         FIG. 37  is a diagram showing an exemplary display of the playback device in the fourth embodiment of the present invention. 
     
    
    
     DESCRIPTION OF REFERENCE NUMERALS 
     
         
         
           
               100  SEMICONDUCTOR RECORDING MEDIUM 
               110  HOST INTERFACE 
               120  CONTROLLER 
               130  RECORDING AREA 
               131  SPECIAL AREA 
               132  PROTECTED AREA 
               133  NORM AREA 
               201  and  201   b  COMPOSER MANAGEMENT FILE 
               203  and  203   b  ARTIST MANAGEMENT FILE 
               205  and  205   b  ALBUM MANAGEMENT FILE 
               207  TITLE MANAGEMENT FILE 
               209  SORT INFORMATION MANAGEMENT FILE 
               211  and  211   b  SORT INFORMATION MANAGEMENT FILE 
               1600  RECORDING DEVICE 
               1601  DATA RECORDING UNIT 
               1602  ENCODER 
               1603  ENCRYPTOR 
               1604  CONTENT KEY GENERATOR 
               1605  NAVIGATION FILE GENERATOR 
               1606  CONTENT INFORMATION GENERATOR 
               1607  DATA INPUT I/F UNIT 
               1608  CONTENT READER/WRITER 
               1609  CONTENT KEY READER/WRITER 
               1610  and  1808  MEDIUM ACCESS UNIT 
               1611  INPUT UNIT 
               1612  and  1909  DISPLAY UNIT 
               1800  PLAYBACK DEVICE 
               1801  OUTPUT UNIT 
               1802  CONTENT PLAYBACK UNIT 
               1803  ENCODER 
               1804  DECRYPTOR 
               1805  CONTENT KEY READER 
               1806  CONTENT READER 
               1807  CONTENT SEARCH UNIT 
           
         
       
    
     BEST MODE FOR CARRYING OUT THE INVENTION 
     Embodiments of the present invention will be described below with reference to the accompanying drawings. 
     First Embodiment 
     1. Semiconductor Recording Medium 
       FIG. 1  is a diagram showing an example of the configuration of a semiconductor recording medium according to the embodiment of the present invention. A semiconductor recording medium  100  includes a host interface  110 , a controller  120 , and a recording area  130 . 
     The host interface  110  has a function of transferring/receiving information to/from a host device (a playback device, a recording device, and so on) that accesses the semiconductor recording medium  100 . 
     The controller  120  has a function of controlling the semiconductor recording medium  100 . The controller  120  interprets a read or write command received from the host device and accesses the recording area  130 . The controller  120  notifies the host device through the host interface  110 , of the access result, if necessary. 
     The recording area  130  has a function of storing digital data and is physically composed of a non-volatile memory such as a flash memory. The recording area  130  has a special area  131 , a protected area  132 , and a normal area  133 . 
     The special area  131  is an area having recorded therein digital data to be used therein by the semiconductor recording medium  100  and is an area that cannot be directly accessed by the host device. In the special area  131 , upon manufacturing the semiconductor recording medium  100 , a medium unique key which has a value specific to each semiconductor recording medium  100 . 
     The protected area  132  is an area that can be accessed only when the host device and the semiconductor recording medium  100  successfully authorize each other. That is, only a host device that has succeeded in mutual authorization can read and write arbitrary digital data in the protected area  132 . 
     The normal area  133  is an area from and to which the host device can read and write arbitrary digital data. That is, the normal area  133  is an area in which read and write can be performed without mutual authorization of the host device and the semiconductor recording medium  100 . 
     Each of the protected area  132  and the normal area  133  includes a search information recording area  135  and a data area  137 . 
     The data area  137  is an area for recording arbitrary digital data. The search information recording area  135  is an area for recording information (an address, a size, etc.) required when the host device takes out digital data recorded in the data area  137 . 
     In the present embodiment, it is assumed that each digital data is managed by a FAT file system and information (file system management information) required by the FAT file system is recorded in a corresponding search information recording area  135 . 
       FIG. 2  shows exemplary configurations of the search information recording area  135  and the data area  137  for the case of adopting a FAT file system. In  FIG. 2 , the search information recording area  135  is composed of a master boot record partition table that records information for dividing the data area  137  into a plurality of areas called partitions and managing the partitions; a partition boot sector that records management information in one partition; a FAT table  1  and a FAT table  2  that show recording positions of data included in files; and a root directory entry that records information on a file and a directory present immediately under a root directory. The data area  137  is managed in a unit called a cluster. The details of the FAT file system is omitted. 
     1.1 Recording of Content to a Semiconductor Recording Medium 
     A method of recording content to the semiconductor recording medium  100  in the present embodiment will be described using  FIGS. 3 and 4 . 
       FIG. 3  is a diagram describing an example of the method of recording content in the semiconductor recording medium  100 . The content is digital data, such as video data, music data, audio data, and text data, that is distributed via various networks such as the Internet and a mobile phone network, or recorded on a CD, an MD, a DVD, or the like, or recorded on an HDD of a PC as a file. 
     In  FIG. 3 , N pieces of content (content # 1 , . . . content #N) are respectively encrypted with N content keys (content key # 1 , . . . content key #N), whereby N pieces of encrypted content (encrypted content # 1 , . . . encrypted content #N) are generated. The pieces of encrypted content (encrypted content # 1 , . . . encrypted content #N) are recorded in the normal area  133  of the semiconductor recording medium  100 , together with navigation files (the details of which will be described later) that manage attributes, and so on, of the content. 
     The N content keys (content key # 1 , . . . content key #N) are encrypted with a medium unique key recorded in the special area  131  of the semiconductor recording medium  100 . The N encrypted content keys (content key # 1 , . . . content key #N) are recorded in the protected area  132  of the semiconductor recording medium  100  as a second-format encrypted content key # 1 , . . . a second-format encrypted content key #N. 
       FIG. 4  is a diagram specifically showing the data structure of directories and files of encrypted content data and management files which are recorded in the normal area  133  of the semiconductor recording medium  100 . In the drawing, an oval block represents a directory and a rectangular block represents a file. A directory “SD_AUD2” is located immediately under a “Root” directory. “Navigation files” represented by a dashed line (the detail of which will be described later) are recorded immediately under the directory “SD_AUD2”. Furthermore, a directory “PLAYLIST” and a directory “AUDxxx” (xxx=001 to 999) are provided immediately under the directory “SD_AUD2”. In the directory “PLAYLIST”, a user playlist management file represented by “UPLyyy.PLM” (yyy=001 to 099) can be recorded. In the directory “AUDxxx”, a management file represented by “SD_AUDIO.TKM” and an encrypted content file (audio object) represented by “AOBzzz.SA1” (zzz=001 to 999) are recorded. Thus, 998,001 (=999×999) tracks can be recorded at most. 
     In  FIG. 4 , the navigation files include a plurality of files which are used for extracting content recorded in the semiconductor recording medium  100 , and manage attribute information (meta-information) on various content in a consolidated manner. A detailed exemplary configuration will be described later. 
     The user playlist management file (UPLyyy.PLM) is a file for registering desired content selected by a user and can be accessed by a playback device that complies with a predetermined regulation (standard) such as in the present embodiment. 
     A management file represented by “SD_AUDIO.TK4” records information on a file “AOBzzz.SA1” which is content recorded in the same folder. The management file “SD_AUDIO.TKM” contains a codec, a time management table for a bit rate, a sampling frequency, and special playback, and text information. 
     The “AOBzzz.SA1” is audio content data. In the configuration in  FIG. 4 , various content, such as an image file and a text information file, that is associated with an audio content file may be further included. 
     As such, content to be recorded in the semiconductor recording medium  100  is recorded and managed together with various information by a recording device in predetermined folders and predetermined files, according to a predetermined regulation (standard). Therefore, an apparatus such as a playback device that complies with the regulation (standard) can read and reproduce data. 
     1.2 Navigation Files 
     The navigation files will be described with reference to  FIGS. 5 to 15 .  FIG. 5  is a diagram showing a relationship between the navigation files and a content file. A content file  250  contains audio objects. 
     The navigation files include various attribute management files  201 ,  203 , . . . , each of which manages attribute information (genre, composer, artist, album, and title) on content for each item, and a sort information management file  209  that manages a sort order for the case in which information managed by an attribute management file is sorted by a predetermined procedure. 
     An attribute management file contains a plurality of pieces of management information (entries). Each attrite management file contains text information indicating the type of an attribute managed thereby, and information on pointers to other attribute management files. The attribute management files specifically include a genre management file  201 , an artist management file  203 , an album management file  205 , a title management file  207 , and a composer management file  211 , and the sort information management file  209 . 
     The genre management file  201  contains information required to manage audio content stored in the recording medium by genre (classical, jazz, pop, rock, and so on.). The artist management file  203  contains information required to manage audio content stored in the recording medium by artist. The album management file  205  contains information required to manage audio content stored in the recording medium by album. The title management file  207  contains information required to manage audio content stored in the recording medium by title (song title). The composer management file  211  contains information required to manage audio content stored in the recording medium by composer. 
     Each of the attribute management files including the genre management file  201 , the artist management file  203 , the album management file  205 , the title management file  207 , and the composer management file  211 , contains a plurality of entries. Each entry (management information) includes text information and information on pointers to other attribute management files. More specifically, management information in the genre management file  201  includes the name of a genre and pointers to other attribute management files related to content belonging to the genre. 
     For example, in  FIG. 5 , the management information # 1  contained in the genre management file  201  includes information on pointers to management information # 1  and # 3  in the artist management file  203  and pointers to management information # 1  and # 2  in the composer management file  211 . Note that in  FIG. 5  an arrow indicates a destination pointed by the pointer information. 
     Similarly, the management information in the artist management information file  203  includes information on pointers to the management information in the album management file  205 . The management information in the album management file  205  includes information on pointers to the management information in the title management file  207 . The management information in the title management file  207  includes information on a pointer relating to a recording location in the content  250  by which a content file can be identified. 
     As described above, the navigation files have a hierarchical structure in order of the genre management file  201 →the artist management file  203 →the composer management file  211 →the album management file  205 →the title management file  207 , according to information accompanying the content. 
     The sort information management file  209  manages a state of management information (entry) that have been subjected to sorting in each of the attribute management files including the genre management file  201 , the composer management file  211 , the artist management file  203 , the album management file  205 , and the title management file  207 . In  FIG. 5 , the dashed-line arrows indicate that information on a sorted state of management information in each of the attribute management files  201 ,  203  . . . , is recorded in the sort information management file. Thus, when management information in the genre management file  201  need to be obtained with the management information being sorted, it can be achieved by referring to sort information (management information) regarding the “genre management file” in the sort information management file  209 . 
     A further detailed exemplary configuration of the navigation files will be described.  FIG. 6  is a diagram showing an example of information associated with audio content. 
       FIG. 6(   a ) shows an example of information associated with audio content A. The audio content A has accompanying information including “POPS (pop)” as genre information, “AAA” as composer information, “Name A” as artist information, “Album A” as album information, and “Title A” as title information. Audio content B shown in  FIG. 6(   b ) has accompanying information including genre information “CLASSIC (classical)”, composer information “BBB”, artist information “Name B”, album information “Album B”, and title information “Title B”. Such accompanying information assigned to each content is available from a content holder (content provider) or WEB site for providing information via a network such as the Internet, or may be generated by a user. 
     1.2.1 Genre Management File 
       FIG. 7  is a diagram showing an example of recording of information to the genre management file  201  for the recording of the audio content shown in  FIG. 6 . 
     As shown in  FIG. 7 , each piece of management information in the genre management file  201  has 512 bytes length and includes text information indicating a genre name, a pointer to management information in the artist management file  203 , a pointer to management information in the composer management file  211 , and other information indicating the usage status of the management information. 
     The area of management information # 2  which is the second entry is used for the audio content A shown in  FIG. 6(   a ) and the genre name “POPS” is recorded as text information. In addition, in the management information # 2 , “1” is recorded as a pointer to the artist management file  203 . This indicates that information on an artist of the audio content A belongs to the first entry, i.e., management information # 1 , in the artist management file  203 . Similarly, “2” is recorded as a pointer to the composer management file  211 . This indicates that information on a composer of the audio content A belongs to management information # 2  which is the second entry in the composer management file  211 . Information “used” indicating the usage status of the second entry is recorded in the “other information”. 
     The same also applies to the audio content B shown in  FIG. 6(   b ). “CLASSIC” as text information, “2” as a pointer to the artist management file  203 , “1” as a pointer to the composer management file  211 , and information “used” as other information are recorded in management information # 1 . 
     Note that in the example of  FIG. 7  management information # 3  and management information # 4  are not used and thus “unused” is recorded as other information. Namely,  FIG. 7  indicates that although an area for recording information itself is reserved, it is not yet used as management information. There are no particular limitations as to which management information (entry) is used for content, in the attribute management file. 
     1.2.2 Composer Management File 
       FIG. 8  shows exemplary recording of information in the composer management file  211  for the audio content shown in  FIG. 6 . Each piece of management information in the composer management file  211  includes text information indicating a composer name, a pointer to the album management file  205 , a pointer to the genre management file  201 , and the other information, having a total of 512 bytes length. 
     Composer information of the audio content A shown in  FIG. 6(   a ) is “AAA” and “2” as a pointer to the composer management file is recorded in the management information # 2  of the genre management file  201  shown in  FIG. 7 . Thus, “AAA” is recorded as text information in the area of management information # 2  which is the second entry of management information in the composer management file  211 . “3” as a pointer to the album management file  205  is recorded in the management information # 2 . This indicates that album information of the audio content A belongs to management information # 3  in the album management file  205 . In addition, “2” is recorded as a pointer to the genre management file  201 , which indicates that genre information of the audio content A belongs to management information # 2  which is the second management information in the genre information management file  201 . In addition, information “used” indicating the usage state of the entry is recorded as other information. 
     The same also applies to the audio content B shown in  FIG. 6(   b ). Composer information of the audio content B is “BBB”, and “1” as a pointer to the composer management file  211  is recorded in the management information # 1  in the genre management file  201  shown in  FIG. 7 . Thus, in the area of management information # 1  which is the first entry in the composer management file  211 , “BBB” is recorded as its composer&#39;s name (text information), “1” is recorded as a pointer to the album management file  205 , “1” is recorded as a pointer to the genre management file  201 , and “used” is recorded as other information. 
     In management information # 3  and management information # 4 , information “unused” is recorded as other information, which indicates that although an area for recording information itself is reserved, it is not used as management information. 
     1.2.3 Artist Management File 
       FIG. 9  shows exemplary recording of information in the artist management file  203  for the audio content shown in  FIG. 6 . Each piece of management information in the artist management file  203  includes text information indicating an artist name, a pointer to the album management file  205 , a pointer to the genre management file  201 , and other information, having a total of 512 bytes length. 
     Artist information of the audio content A shown in  FIG. 6(   a ) is “Name A”, and “1” as a pointer to the artist management file  203  is recorded in the management information # 2  in the genre management file  201  shown in  FIG. 7 . Thus, “Name A” is recorded as text information in the area of management information # 1  which is the first entry of management information in the artist management file  203 . In the management information # 1 , “3” is recorded as a pointer to the album management file  205 . This indicates that album information of the audio content A belongs to management information # 3  in the album management file  205 . In addition, “2” is recorded as a pointer to the genre management file  201 . This indicates that genre information of the audio content A belongs to the management information # 2  which is the second management information in the genre information management file  201 . In addition, “used” indicating the usage status of the entry is recorded as other information. 
     The same also applies to the audio content B shown in  FIG. 6(   b ). Artist information of the audio content B is “Name B”, and “1” is recorded as a pointer to the composer management file  211  in the management information # 1  in the genre management file  201  shown in  FIG. 7 . Thus, in the area of management information # 1  which is the first entry of management information in the artist management file  203 , “Name B” is recorded as its artist&#39;s name (text information), “1” is recorded as a pointer to the album management file  205 , “1” is recorded as a pointer to the genre management file  201 , and “used” is recorded as other information. 
     In management information # 3 , “unused” is recorded as other information, which indicates that although an area for recording information itself is reserved, it is not used as management information. 
     1.2.4 Album Management File 
       FIG. 10  shows exemplary recording of information in the album management file  205  for the audio content shown in  FIG. 6 . Each piece of management information in the album management file  205  includes text information indicating an album name, a pointer to the title management file  207 , a pointer to the genre management file  201 , a pointer to the artist management file  203 , a pointer to the composer management file  211 , and other information, having a total of 512 bytes length. 
     Album information of the audio content A shown in  FIG. 6(   a ) is “Album A”, and “3” as a pointer to the album management file  205  is recorded in the management information # 1  in the artist management file  203  shown in  FIG. 9 . Thus, in the area of management information # 3  which is the third entry of management information in the album management file  205 , “Album A” is recorded as an album name (text information). In the management information # 3 , “4” is recorded as a pointer to the title management file  207 . This indicates that a title of the audio content A belongs to management information # 4  in the title management file  207 . In addition, “2” is recorded as a pointer to the genre management file  201 . This indicates that genre information of the audio content A belongs to the management information # 2  which is the second management information in the genre management file  201 . In addition, “2” is recorded as a pointer to the composer management file  211 . This indicates that composer information of the audio content A belongs to the management information # 2  which is the second management information in the composer management file  211 . “1” is recorded as a pointer to the artist management file  203 . This indicates that artist information of the audio content A belongs to the management information # 1  which is the first management information in the artist management file  203 . In addition, “used” indicating the usage status of the entry is recorded as other information. 
     The same also applies to the audio content B shown in  FIG. 6(   b ). Album information of the audio content B is “Album B”, and “1” is recorded as a pointer to the album management file  205  in the management information # 2  in the artist management file  203  shown in  FIG. 9 . Thus, in the area of management information # 1  which is the first entry of management information in the album management file  205 , “Album B” is recorded as an album name (text information), “2” is recorded as a pointer to the title management file  207 , “1” is recorded as a pointer to the genre management file  201 , “1” is recorded as a pointer to the composer management file  211 , “2” is recorded as a pointer to the artist management file  203 , and “used” is recorded as other information. 
     In management information # 2 , management information # 4 , and management information # 5 , information “unused” is recorded as other information, which indicates that although an area for recording information itself is reserved, it is not used as management information. 
     1.2.5 Title Management File 
       FIG. 11  shows exemplary recording of information in the title management file  207  for the audio content shown in  FIG. 6 . Each piece of management information in the title management file  207  includes text information indicating a title, a pointer to a content recording location, a pointer to the genre management file  201 , a pointer to the composer management file  211 , a pointer to the artist management file  203 , a pointer to the album management file  205 , and other information, having a total of 512 bytes length. 
     Title information of the audio content A shown in FIG.  6 (A) is “Title A”, and “4” as a pointer to the title management file is recorded in the management information # 3  in the album management file  205  shown in  FIG. 10 . Thus, in the area of management information # 4  which is the fourth entry of management information in the title management file  207 , “Title A” is recorded as a title (text information). “DIR:3 and FILE:5” is recorded as a pointer to a content recording location. This indicates that the audio content A is a file “AOB005.SA1” in a directory “AUD003”. “2” is recorded as a pointer to the genre management file  201 . This indicates that a genre of the audio content A belongs to the management information # 2  which is the second management information in the genre management file  201 . “2” is recorded as a pointer to the composer management file  211 . This indicates that composer information of the audio content A belongs to the management information # 2  which is the second management information in the composer management file  211 . “1” is recorded as a pointer to the artist management file  203 . This indicates that artist information of the audio content A belongs to the management information # 1  in the artist management file  203 . “3” is recorded as a pointer to the album management file  205 . This indicates that album information of the audio content A belongs to the management information # 3  in the album management file  205 . In addition, “used” indicating the usage status of the entry is recorded as other information. 
     The same also applies to the audio content B shown in  FIG. 6(B) . Title information of the audio content B is “Title B” and “2” is recorded as a pointer to the title management file  207  in the management information # 1  in the album management file  205  shown in  FIG. 10 . Thus, in the area of management information # 2  which is the second entry in the title management file  207 , “Title B” is recorded as a title (text information), “DIR:2 and FILE:4” are recorded as a pointer to a content recording location, “1” is recorded as a pointer to the genre management file  201 , “1” is recorded as a pointer to the composer management file  211 , “2” is recorded as a pointer to the artist management file  203 , “1” is recorded as a pointer to the album management file  205 , and “used” is recorded as other information. In management information # 1 , management information # 3 , and management information # 5 , information “unused” is recorded as other information, which indicates that although an area for recording information itself is reserved, it is not used as management information. 
     The configuration of each attribute management file as described above is described with reference to the content shown in  FIG. 6 . When in each attribute management file new management information needs to be added upon recording new content, for example, management information (entry) can be added. Hence, the size of each attribute management file is a variable length. On the other hand, when management information becomes unnecessary with the deletion of content, it can be handled by changing a flag in the other information indicating a usage status to “unused”, for example, without deleting the area of the management information (entry). The above example shows that the flag indicating a usage status is held in individual management information. Instead of it, as an example, an area for managing integrally the entire usage status of the file is provided at a head portion of one piece of management file, or the entire usage status may be managed using another file. 
     Note that a single type of text information is shown as text information in each attribute management file. However a plurality of pieces of text information may be recorded in the same management information, so that character codes of different types can be simultaneously handled and the text information is not limited to that described above. For example, it may be configured that a plurality of areas, each capable of storing text information, are provided in each piece of management information and a dedicated area determined according to a character code such as a 1-byte character code or a 2-byte character code is used. 
     For simplicity of description, the case in which there is only one pointer in each of the genre management file  201 , the composer management file  211 , the artist management file  203 , and the album management file  205  is described as an example. However, it may be configured, as shown in  FIG. 5 , that individual management information can store a plurality of pointers and can record pointers to management information in a plurality of attribute management files. In such a case, pointers to be recorded in one piece of management information may be recorded in a predetermined sequence. Further, in such a case, when the number of pointers which need to be recorded is more than the number of pieces of management information which can be recorded in one entry, the pointers to management information may be recorded by using a plurality of entries with link information. 
       FIG. 12  is a diagram showing an exemplary configuration in which a large number of pointers are managed by using a plurality of pieces of management information (entries). In the drawing, it is assumed that three pointers to the title management file  207  can be registered in one piece of management information in the album management file  205  at most. When it needs to record three or more of pointers to the title management file  207  for the “Album B”, link information is recorded in the “other information”, so that management information # 1  and management information # 2  can be used as management information of the “Album B”. 
     In each attribute management file, information to be recorded as other information is not limited to information indicating the usage status of an entry and link information on the entry. In addition to them, as shown in  FIG. 13 , flag information indicating whether an album is a compilation album, information indicating a location at which image data (picture data) for the album is recorded, and the like, may be recorded. 
     The size of management information in each attribute management file is not limited to 512 bytes and may be a variable length. Although the description is made that the configuration of each attribute management file itself has a variable length, it may be a fixed length. Although the attribute management files are configured as different files, it may be configured that information in the attribute management files is consolidated in one or several files. 
     1.2.6 Sort Information Management File 
     The sort information management file  209  that manages a sort status of management information (entry) in each attribute management file is described below with reference to  FIG. 14 . 
       FIG. 14  is a diagram showing exemplary configurations of the genre management file  201  and the sort information management file  209  for the genre management file  201 . 
     The sort information management file  209  stores information indicating the order of management information having been subjected to sorting, for the case in which management information in the genre management file  201 , the composer management file  211 , the artist management file  203 , the album management file  205 , and the title management file  207  are sorted by text information managed by the respective attribute management files, i.e., by genre, composer, artist, album, and title, under a predetermined condition (procedure). Thus, the sort information management file  209  has areas for storing order of respective pieces of information sorted by each of genre, composer, artist, album, and title. 
     In an area of the sort information management file  209  which stores sort information for the genre, sort order of pieces of management information in the genre management file  201  for the case in which management information is sorted by a predetermined condition is recorded, using index number of management information in the genre management file  201 . 
     For example, the case is considered, in which management information # 1 , management information # 2 , and management information # 4  are used in the genre management file  201  and “CLASSIC”, “POPS”, and “JAZZ” are recorded as their respective genre names (text information). When the management information in the genre management file  201  is sorted alphabetically by genre name (text information), the order is the management information # 1 , the management information # 4 , and the management information # 2 . Hence, in the area of the sort information management file  209  where sort information on the genre is to be recorded, index numbers are recorded in the manner such as # 1 , # 4 , and # 2 . In this way, a status of management information in each attribute management file which is sorted by a predetermined condition is managed with index numbers, in the sort information management file  209 . Thus, there is no need to actually sort management information in each attribute management file, making it possible to easily manage the order of management information having been subjected to sorting. 
     It becomes possible for a playback device to easily display a list in which genres are sorted in a predetermined order, by referring to the sort information management file  209 . For composer, artist, album, and title, similarly, sort order information obtained after sorting management information in each attribute management file by a predetermined condition is managed in the sort information management file  209  using index numbers. As in the case described above, when each attribute management file is variable in length according to the number of pieces of management information to be recorded, an area of the sort information management file  209  that manages sort information on each piece of management information also becomes variable in length. 
     As shown in  FIG. 15 , the sort information management file  209  may store Used information  223  which is flag information indicating usage status of the respective management information entries in each attribute management file, in addition to index information  221  obtained after sorting. In the example of  FIG. 15 , in the genre management file  201 , management information # 1 , management information # 2 , management information # 3 , and management information # 4  are respectively “used”, “used”, “unused”, and “used”. Thus, the flag information “1”, “1”, “0”, and “1” is recorded as Used information  223  on genre information. 
     Although the above shows the configuration in which the sort information management file  209  is variable in length, the sort information management file  209  may be a fixed-length file. Although the example is shown in which the status of pieces of management information in the respective management information files which are sorted by a predetermined condition are collectively managed in one file, a file that manages sort information may be provided for each attribute management file. Namely, as long as a sorting status of management information in each attribute management file which is sorted by a predetermined condition can be managed, any configuration can be employed. 
     2. Recording Device 
     The configuration and operation of a recording device for the above-described semiconductor recording medium  100  will be described. 
     2.1 Configuration 
     The configuration of a recording device is shown in  FIG. 16 . A recording device  1600  obtains content from a CD, a DVD, a file, or the like, or via various networks such as the Internet and a mobile phone network, and records the content in a semiconductor recording medium  100 . The recording device  1600  is, for example, a PC (personal computer), a mobile (cellular) phone, a PDA (Personal Digital Assistant), a portable apparatus, a television, or the like. 
     The recording device  1600  includes a data input I/F unit  1607 , a data recording unit  1601 , a content reader/writer  1608 , a content key reader/writer  1609 , a medium access unit  1610 , an input unit  1611 , and a display unit  1612 . 
     The data input I/F unit  1607  has a function of reading out a content file such as a CD, a DVD, or a file, and a network I/F function. The data input I/F unit  1607  has a function of receiving content and various information accompanying the content, such as genre, artist name, album name, composer&#39;s name, and song title, from a dedicated delivery server connected to the same network. 
     The data recording unit  1601  has a function of generating a content key, content information, and navigation information for the inputted content. The data recording unit  1601  includes an encoder  1602 , an encryptor  1603 , a content key generator  1604 , a navigation file generator  1605 , and a content information generator  1606 . 
     The encoder  1602  has a function of encoding and compressing the content inputted through the data input I/F unit  1607 , as required. Although the encoder  1602  is not necessarily required, in the present embodiment the inputted content is compressed by the encoder  1602  and then the compressed content is encrypted by the encryptor  1603 . 
     The encryptor  1603  has a function of encrypting content with a content key generated by the content key generator  1604  to generate the encrypted content. 
     The content key generator  1604  has a function of generating a content key to be used for encrypting local content inputted from the data input I/F unit  1607 . In the present embodiment, the content key generator  1604  has a random number generator and generates a content key using random numbers. 
     The content information generator  1606  has a function of processing attribute information on content, such as genre, artist, composer, album, and title, received from a delivery server  300  through the data input I/F unit  1607  to generate content information. The content information generator  1606  can also receive attribute information on content which is inputted by a user, through the input unit  1611  such as an input apparatus such as a keyboard or buttons. 
     The navigation file generator  1605  has a function of analyzing navigation files recorded in the semiconductor recording medium  100  and generating new navigation files based on the content information generated by the content information generator  1606 . 
     The content reader/writer  1608  has a function of writing encrypted content together with navigation files to the semiconductor recording medium  100  through the medium access unit  1610  or reading navigation files and/or encrypted content recorded in the semiconductor recording medium  100 . 
     The content key reader/writer  1609  has a function of writing or reading an encrypted content key generated by the data recording unit  1601 , in the semiconductor recording medium  100  through the medium access unit  1610 . 
     The medium access unit  1610  is loaded with the semiconductor recording medium  100  and has a function of accessing the loaded semiconductor recording medium  100 . The medium access unit  1610  further has a function of reading out a medium unique key recorded in a special area  131  of the semiconductor recording medium  100  or performing authorization required for reading and writing of arbitrary digital data recorded in a protected area  132 . 
     The input unit  1611  has a keyboard, various buttons, or the like through which a user can perform input of text information, and so on. 
     The display unit  1612  has a function of providing a screen or the like, capable of displaying various text information accompanying the content, and the like, such as genre, artist, composer, album, and title. 
     2.2 Recording Operation 
       FIG. 17  is a flowchart showing an example of an operation sequence for the recording device  1600  which records content obtained through the data input I/F unit  1607  in the semiconductor recording medium  100 . 
     First, the data input I/F unit  1607  of the recording device  1600  obtains content from a recording medium having source data recorded therein, such as a CD or DVD, or from an input apparatus such as a camera and a microphone, or via the Internet or a mobile phone network (S 1700 ). The obtained content is sent to the data recording unit  1601 . 
     The data recording unit  1601  generates a content key, content information, and encrypted content (S 1701 ). Specifically, the data recording unit  1601  performs compression by encoding of local content with the encoder  1602 . Furthermore, the content key generator  1604  generates a content key. The encryptor  1603  encrypts the encoded local content with the aforementioned content key to generate encrypted content. Furthermore, attribute information on the content, such as genre, composer, artist, album, and title, is obtained from the delivery server through the data input I/F unit  1607 . Alternatively the attribute information on the content is generated by displaying data on the display unit  1612  of the recording device and receiving an input from the user through the input unit  1611  such as a keyboard or buttons, in response to a data change request or the like from a user. 
     Then, navigation files are generated (S 1702 ). Navigation files (attribute management files such as a genre management file, an artist management file, a composer management file, an album management file, and a title management file, and a sort information management file) are read out from the semiconductor recording medium  100 . Then the read navigation files are added with information based on the content information generated in step S 1701  and stored in the data recording unit  1601 . A specific operation of this will be described later. 
     The content reader/writer  1608  records the content encrypted by the encryptor  1603  in the data recording unit  1601  and the navigation files held inside in a normal area  133  of the semiconductor recording medium  100  through the medium access unit  1610  (S 1703 ). 
     The content key reader/writer  1609  records the content key generated by the data recording unit  1601  in a protected area  132  of the semiconductor recording medium  100  through the medium access unit  1610  with the content key being encrypted with a medium unique key specific to the semiconductor recording medium  100  (S 1704 ). Note that the write to the protected area  132  of the semiconductor recording medium  100  is enabled by mutual authorization of the medium access unit  1610  and the semiconductor recording medium  100 . 
     2.2.1 Generation of Navigation Files 
     A detailed process of the aforementioned navigation files generation step (S 1702 ) will be described with reference to a flowchart in  FIG. 18 . 
     First, by referring to a genre management file  201  recorded in the semiconductor recording medium  100 , it is checked whether the same genre information as that on the content to be recorded now is contained in the genre management file  201  (S 1800 ). 
     If the genre information on the content to be recorded is not contained in the genre management file  201 , then management information is newly generated for the genre information (S 1801 ). 
     Subsequently, management information in an artist management file  203  and a composer management file  211  is read out from the semiconductor recording medium  100 . By referring to the read management information, it is checked whether the same artist information and composer information as those on the content to be recorded are already contained in the files (S 1802 ). 
     If the artist information and composer information on the content to be recorded are not contained in the artist management file  203  and the composer management file  211 , respectively, then management information is newly generated (S 1803 ). 
     In the above-described step, in the artist management file  203  and the composer management file  211 , management information (i.e., pointers) related to the content to be recorded is determined. A pointer to the artist management file  203  and a pointer to the composer management file  211  are recorded in management information in the genre management file  201 , which is related to the content to be recorded (S 1804 ). 
     Thereafter, management information in an album management file  205  is read out from the semiconductor recording medium  100 . By referring to the read management information, it is checked whether the same album information as that on the content to be recorded is contained in the album management file  205  (S 1805 ). 
     If the album information on the content to be recorded is not contained in the management information in the album management file  205 , then management information is newly generated (S 1806 ). 
     In the above-described step, in the album management file  205 , management information including information related to the content to be recorded is determined. Subsequently, a pointer to the album management file is recorded in management information in the artist management file  203  and the composer management file  211  (S 1807 ). 
     Then, based on title management information on the content to be recorded, management information in a title management file  207  is newly generated (S 1808 ). 
     In the above-described step, in the title management file  207 , management information including information related to the content to be recorded is determined. A pointer to the title management file  207  is recorded in management information in the album management file  205  (S 1809 ). 
     Note that after completion of the steps (S 1801 , S 1803 , S 1806 , and S 1808 ) of newly generating management information, sort information indicating a sort order for the case in which management information in each attribute management file is sorted by a predetermined condition is generated. Then the sort information management file  209  is updated based on the sort information. For example, when the management information in the genre management file  201  is sorted for the “genre” fields by a predetermined condition (e.g., alphabetical order) after adding management information to the genre management file  201  in step S 1801 , the order of sorted management information is recorded in the sort information management file  209 . 
     As described above, the recording device  1600  can update and record navigation files and content in the semiconductor recording medium  100 , according to the recording method shown in  FIG. 3  and the directory configuration shown in  FIG. 4 . 
     3. Playback Device 
     The configuration and operation of a playback device for the above-described semiconductor recording medium  100  will be described. 
     3.1 Configuration 
     An example of the configuration of a playback device of the present embodiment is shown in  FIG. 19 . A playback device  1900  includes an output unit  1901 , a content playback unit  1902 , a content key reader  1905 , a content reader  1906 , a medium access unit  1908 , and a display unit  1909 . 
     The content reader  1906  has a function of reading out content, navigation files, or a playlist file from a semiconductor recording medium  100 . The content reader  1906  includes a content search unit  1907  and the content search unit  1907  has a function of reading out navigation files or a playlist file which are recorded in the semiconductor recording medium  100  and displaying information thereof on the display unit  1909  mounted on the playback device  1900 . The content reader  1906  also searches for hierarchical navigation files or a playlist file and performs a narrowing-down selection of content, according to information selected by a user, and eventually searches the semiconductor recording medium  100  for content that the user desires. The searched content is encrypted and is sent to the content playback unit  1902 . In addition, the content reader  1906  holds information indicating recording locations of content keys in the semiconductor recording medium  100  and has a function of outputting the information. 
     The content key reader  1905  has a function of reading out an encrypted content key recorded in the semiconductor recording medium  100  through the medium access unit  1908  based on the information indicating the recording locations of the content keys which is received from the content reader  1906 , decrypting the read encrypted content key to generate a plaintext content key, and outputting the plaintext content key to the content playback unit  1902 . 
     The content playback unit  1902  has a function of decrypting the content (encrypted content) received from the content reader  1906  with the content key received from the content key reader  1905 , performing a decompression process, and reproducing the content. A decryptor  1904  performs a process of decrypting the encrypted content with a content key. The content playback unit  1902  includes the decryptor  1904  and a decoder  1903 . When the content decrypted by the decryptor  1904  is compressed, the decoder  1903  performs a process of decompressing the content to restore the content to a state before compression. Note that the decoder  1903  may not need to be provided when the content is not compressed. 
     The output unit  1901  has a function of outputting content data decrypted by the content playback unit  1902 . For example, the output unit  1901  corresponds to a speaker when the content data is audio data, and corresponds to a display when the content data is video data or character data. When a display or speaker provided external to the playback device  1900  is used, the output unit  1901  corresponds to an output terminal such as AV-OUT. 
     The medium access unit  1908  is loaded with the semiconductor recording medium  100  and has a function of accessing the loaded semiconductor recording medium  100 . The medium access unit  1908  has a function of reading out a medium unique key recorded in a special area  131  of the semiconductor recording medium  100  or performing authorization process required for reading and writing arbitrary digital data for a protected area  132 . 
     The display unit  1909  includes a liquid crystal display device (LCD), for example, and has a function of displaying information on content, navigation files, or a playlist file, which are read by the content reader  1906 . 
     3.2 Playback Operation 
       FIG. 20  is a flowchart showing an exemplary operation sequence for the playback device  1900  which reproduces content recorded in the semiconductor recording medium  100 . 
     First, the content reader  1906  of the playback device  1900  reads out navigation files or a playlist file recorded in the semiconductor recording medium  100 , through the medium access unit  1908  (S 2000 ). 
     Then, a content file is read out according to an instruction from a user (S 2001 ). Specifically, based on information in the read navigation files or playlist file, a selection menu is displayed on the display unit  1909  of the playback device  1900  and the user is allowed to select desired content through the selection menu. According to the selection by the user, the content search unit  1907  searches for the navigation files, the playlist file, and the content file. Thus obtained content data and attribute information on content are sent to the content playback unit  1902  and the content key reader  1905 . A detail of this process and exemplary displays on the display unit  1909  will be described later. 
     Subsequently, a content key (encrypted content key) for decrypting the encrypted content is read out (S 2002 ). The content key reader  1905  identifies a recording location of the encrypted content key based on information received from the content reader  1905  and reads out the encrypted content key from the semiconductor recording medium  100  through the medium access unit  1908 . The content key read out from the semiconductor recording medium  100  is being encrypted with a medium unique key which is specific to the semiconductor recording medium  100 . Thus, first, it needs to read out the medium unique key from the semiconductor recording medium  100  and calculate a plaintext content key from the read content key using the medium unique key. 
     The thus obtained content key is sent to the content playback unit  1902 . Note that the reading of the content key is enabled by mutual authorization between the medium access unit  1909  and the semiconductor recording medium  100 . 
     Finally, by using the content and content key read out from the semiconductor recording medium  100 , the content is decrypted and reproduced (S 2003 ). The decryptor  1904  in the content playback unit  1902  decrypts the content received from the content reader  1905  using the content key received from the content key reader  1905 . The decoder  1903  performs a decompression process on the decrypted content and transmits the decompressed content to the output unit  1901 . This implements the playback of the content. 
       FIGS. 21A ,  21 B,  22 C, and  22 D show exemplary displays of selection menus on the display unit  1909  of the playback device  1900 , based on navigation information read out from the semiconductor recording medium  100  at the aforementioned step S 2001 . The displays transition as follows: FIG.  21 A→FIG.  21 B→FIG.  22 A→ FIG. 22B . 
       FIG. 21A  is a diagram showing an example of an initial menu to be displayed first on the display unit  1909  of the playback device  1900 . The user can select one item from selection items including “genre list”, “composer list”, “artist list”, “album list”, “title list”, and “user playlist”.  FIG. 21B  shows an exemplary display when the “genre list” is selected in the selection menu shown in  FIG. 21A . In the selection menu at this time, genres managed by the genre management file  201  are displayed according to a sort order managed by the sort information management file  209 . 
       FIG. 22C  shows an exemplary display when “CLASSIC” is selected in the selection menu shown in  FIG. 21B . At this time, a screen for confirming whether the selection is made from “artist” or “composer” is further displayed. That is, management information in the genre management file  201  recorded in the semiconductor recording medium  100  has a pointer to the artist management file  203  and a pointer to the composer management file  211 , and thus the user can select one of the management files of which information is to be displayed. 
       FIG. 22D  shows an exemplary display for the case in which “artist” is selected in the selection menu in  FIG. 22C . Based on the pointer to the artist management file which is recorded in the genre management file  201 , artist information is displayed. At that time, the display order follows a sort order managed by the sort information management file  209 . After this, a user&#39;s selection hierarchically proceeds from album to title. Selection items are displayed based on pointer information in each attribute management file recorded in the recording medium  100  and sort information managed by the sort information management file  209 . 
     Note that the display of screens is not limited to the aforementioned examples and an arbitrary display format is possible. For example, in an initial selection menu, only a list of a user playlist may be displayed, and when a specific action (e.g., pressing a button) is taken, the operation may shift to a narrowing-down operation of content. 
     As described above, by effectively using navigation files in the playback device  1900 , content that the user desires can be effectively narrowed down from numbers of pieces of content and reproduced. 
     3.2.1 Detail of Content Playback Process 
     A detail of the content file read-out process in step S 2001  will be described using  FIGS. 23 to 27 . 
     (a) Initial Menu Process 
       FIG. 23  shows the flow of a display of an initial menu (initial selection screen) in  FIG. 21A  and a process for the selection made by the user in the initial menu. First, an initial menu (“Menu List”) shown in  FIG. 21A  is displayed on the display unit  1909  (S 21 ). If the item “genre list” is selected by the user in the initial menu (YES at S 22 ), then a process on selection of “genre list” is performed (S 28 ). If the item “composer list” is selected (YES at S 23 ), then a process on selection of the “composer list” is performed (S 29 ). If the item “artist list” is selected (YES at S 24 ), then a process on selection of the “artist list” is performed (S 30 ). If the item “album list” is selected (YES at S 25 ), then a process on selection of the “album list” is performed (S 31 ). If the item “title list” is selected (YES at S 26 ), then a process on selection of the “title list” is performed (S 32 ). If the item “playlist display” is selected (YES at S 27 ), then a process on selection of the “playlist display” is performed (S 33 ). 
     (b) Process on Selection of Genre List 
     The process on Selection of genre list will be described with reference to a flowchart in  FIG. 24 . If the “genre list” is selected in the initial menu shown in  FIG. 21A , then the genre management file  201  is referred to and a list of genre items (text information on management information) such as that shown in  FIG. 21B  is displayed (S 221 ). Specifically, information (genre names) described in the “genre” fields of respective pieces of management information in the genre management file  201  is obtained and the genre names are sorted according to a sort order recorded in the sort information management file  209  and then displayed. 
     The user can select a desired genre from a list of genre items as shown in  FIG. 21B . If a selection of one genre is made by the user (YES at S 222 ), then a screen for selecting either “artist” or “composer” as shown in  FIG. 22A  is displayed (S 223 ). 
     If the “artist” is selected by the user (S 224 ), then the artist management file  203  is referred to, artists (artist names), such as those in  FIG. 22B  belonging to the selected genre are searched for, and a list thereof is displayed (S 232 ). At this time, the artists (artist names) are displayed in a predetermined sort order. For example, the artists are sorted according to a sort order recorded in the sort information management file  209  and then displayed. When pointers registered in the “pointer to the artist” in the genre management file  201  are already sorted, the sort information management file  209  does not need to be referred to for sorting and the artists may be displayed in the order shown by the registered pointers (which also applies to the case in which information in other attribute management files is displayed in a list). 
     Information (artist names) on the artists belonging to the selected genre can be obtained as follows. In the genre management file  201 , management information relating to the selected genre is identified. By referring to the “pointer to the artist management file” in the identified management information, management information on the artists related to the selected genre in the artist management file  203  is identified. Then, from the identified management information in the artist management file  203 , artist names belonging to the selected genre are obtained. 
     After displaying the artist list, if a selection of one artist is made by the user (YES at S 233 ), then the album management file  205  is referred to, albums of the selected artist are searched for, and a list thereof is displayed (S 234 ). At this time, information on the searched albums is sorted according to a sort order recorded in the sort information management file  209 , for example, and then displayed. 
     Information (album names) on the albums of the selected artist can be obtained as follows. In the artist management file  203 , management information relating to the selected artist is identified. By referring to the “pointer to the album management file” in the identified management information, management information on the albums related to the selected artist in the album management file  205  is identified. Then, from the identified management information in the album management file  205 , information on the albums related to the selected artist is obtained. 
     On the other hand, if in step S 224  the “composer” is selected by the user, then the composer management file  211  is referred to, composers belonging to that genre are searched for, and a list thereof is displayed (S 225 ). At this time, information on the searched composers is sorted according to a sort order recorded in the sort information management file  209 , for example, and then displayed. 
     After displaying the composer list, if a selection of one composer is made by the user (YES at S 226 ), then the album management file  205  is referred to, albums of the selected composer are searched for, and a list thereof is displayed (S 227 ). As with step S 234 , by referring to the “pointer to the album management file” in the composer management file  211 , information on albums related to the selected composer can be obtained. 
     After displaying the album list, if one album is selected by the user (YES at S 228 ), then the title management file  207  is referred to, titles included in the selected album are searched for, and a list thereof is displayed (S 229 ). At this time, information on the searched titles is sorted according to a sort order recorded in the sort information management file  209 , for example, and then displayed. 
     Specifically, in the album management file  205 , management information relating to the selected album is identified. By referring to the “pointer to the title management file” in the identified management information, management information on titles related to the selected album in the title management file  207  is identified. Then, from the identified management information in the title management file  207 , information on the titles related to the selected album is obtained. 
     After displaying the title list, if one title is selected by the user (YES at S 230 ), then content of the selected title is read out from the semiconductor recording medium  100  (S 231 ). A recording location of the content can be recognized by referring to the “pointer to the content recording location” in the title management file  207 . 
     (c) Process on Selection of Composer (Artist) List 
     The process on selection of composer list (or the process on selection of artist list) will be described with reference to a flowchart in  FIG. 25 . 
     If the “composer list” (or the “artist list”) is selected by the user in the initial menu, then the composer management file  211  (or the artist management file  203 ) is referred to, composers (or artists) are searched for, and a list thereof is displayed (S 241 ). At this time, the searched composers (or artists) are sorted according to a sort order recorded in the sort information management file  209  and then displayed. 
     After displaying the composer (or artist) list, if a selection of one composer (or one artist) is made by the user (YES at S 242 ), then the album management file  205  is referred to, albums of the selected composer (or artist) are searched for, and a list thereof is displayed (S 243 ). 
     After displaying the album list, if one album is selected by the user (YES at S 244 ), then the title management file  207  is referred to, titles included in the selected album are searched for, and a list thereof is displayed (S 245 ). 
     After displaying the title list, if one title is selected by the user (YES at S 246 ), then content of the selected title is read out from the semiconductor recording medium  100  (S 247 ). 
     (d) Process on Selection of Album List 
     The process on selection of album list will be described with reference to a flowchart in  FIG. 26 . 
     If the “album list” is selected by the user in the initial menu, then the album management file  205  is referred to and a list thereof is sorted and then displayed (S 251 ). At this time, information on the albums is sorted according to a sort order recorded in the sort information management file  209 , for example, and then displayed. 
     After displaying the album list, if one album is selected by the user (YES at S 252 ), then the title management file  207  is referred to, titles included in the selected album are searched for, for example, and a list thereof is sorted and then displayed (S 253 ). 
     After displaying the title list, if one title is selected by the user (YES at S 254 ), then content of the selected title is read out from the semiconductor recording medium  100  (S 255 ). 
     (e) Process on Selection of Title List 
     The process on selection of title list will be described with reference to a flowchart in  FIG. 27 . 
     If the “title list” is selected by the user in the initial menu, then the title management file  207  is referred to, titles are searched for, and a list thereof is sorted, for example, and then displayed (S 261 ). 
     After displaying the title list, if one title is selected by the user (YES at S 262 ), then content of the selected title is read out from the semiconductor recording medium  100  (S 263 ) Note that, although here a detailed description is omitted, when the “playlist” is selected by the user in the initial menu and the user selects the content, the selected content which is registered in the playlist is read out from the semiconductor recording medium  100 . 
     In the above-described manner, in the present embodiment, management files (attribute management files)  201 ,  203  . . . , are provided for respective attributes (genre, artist, composer, album, title, etc.) relating to the content. The attribute management files  201 ,  203  . . . , are hierarchically linked to one another. The link information (pointer) is managed by each attribute management file. Thus, a narrowing-down extraction of desired content is enabled with a simple configuration. In addition, information on a sort order to be obtained in the case where information managed by each attribute management file is sorted by a predetermined condition, is managed by a file (sort information management file  209 ) which is different from the attribute management files. By thus providing the sort information management file  209 , there is no need to sort entries in the attribute management files upon addition or deletion of content and while suppressing an increase in the cumbersomeness of an update process for the attribute management files, facilitation of a search based on the attributes of content recorded in a semiconductor recording medium  100  is implemented. 
     Second Embodiment 
     A second embodiment of the present invention will be described below. The present embodiment is different from the first embodiment in a method of storing information on a pointer to management information in each attribute management file in navigation files. Other configuration and operation are the same as basic points. The configurations of a recording device and a playback device of the present embodiment are the same as those in the first embodiment. 
       FIG. 28  is a diagram showing a relationship between navigation files and a content file containing audio objects in the present embodiment. The navigation files include a genre management file  201   b , a composer management file  211   b , an artist management file  203   b , an album management file  205   b , a title management file  207 , and a sort information management file  209 . 
     Each of the attribute management files, including the genre management file  201   b , the composer management file  211   b , the artist management file  203   b , the album management file  205   b , and the title management file  207 , contains text information and information on a pointer to the title management file. 
     For example, in  FIG. 28 , pointers to management information # 1  and management information # 3  of the title management file  207  are recorded in management information # 1  contained in the genre management file  201   b . In the drawing, an arrow indicates a destination pointed by pointer information. Similarly, pointers to the title management file  207  are recorded in management information in the other attribute management files too. A pointer relating to a recording location of content is recorded in management information in the title management file  207 . By referring to the pointer, a content file  250   b  can be identified. 
     As with the first embodiment, the sort information management file  209  manages a sort order for the case in which management information in each of the attribute management files, including the genre management file  201   b , the composer management file  211   b , the artist management file  203   b , the album management file  205   b , and the title management file  207 , is sorted. In the drawing, dashed-line arrows indicate that sort information on each attribute management file is recorded in the sort information management file  209 . 
       FIG. 29  is a diagram showing exemplary recording of information in the genre management file  201   b . Each management information in the genre management file  201   b  includes “genre (text information)”, “pointer to the title management file”, and “other information”, having a total of 512 bytes length. In management information # 1 , “1” and “2” are recorded as pointers to the title management file  207 . This indicates that titles belonging to the genre “CLASSIC” belong to management information # 1  and management information # 2  in the title management file  207 . 
     Similarly, in management information # 2  in the genre management file  201   b, “ 3, 5, and 6” are recorded as pointers to the title management file  207 . This indicates that titles belonging to the genre “POPS” belong to management information # 3 , management information # 5 , and management information # 6  in the title management file  207 . In management information # 3  and management information # 4 , “unused” is recorded as other information. This indicates that although an area for recording information itself is reserved, it is not used as management information. Here, there are no particular limitations on what number of management information is used for genre information. Note that although in the aforementioned example a flag indicating a usage status is held in individual management information, as another example, a method may be employed in which in a starting portion of a management file is provided an area for performing overall management of the entire usage status in the file, or a method may be employed in which management is performed using another file. 
     The configuration of the composer management file  211   b , the artist management file  203   b , and the album management file  205   b  in the present embodiment is also the same as that of the genre management file  201   b  and thus a detailed description thereof is omitted. The configuration of the title management file  207  is the same as that in the first embodiment shown in  FIG. 11 . 
       FIG. 30  is a flowchart showing navigation files generation process. The process is performed by a recording device  1600 . The flowchart shows a generation process for attribute management files including a genre management file  201   b , a composer management file  211   b , an artist management file  203   b , and an album management file  205   b.    
     First, by referring to attribute management files (a genre management file  201   b , a composer management file  211   b , an artist management file  203   b , and an album management file  205   b ) recorded in a semiconductor recording medium  100 , it is checked whether the same genre information as that on content to be recorded now is included in management information in the respective attribute management files  201   b , . . . (S 2500 ). 
     If the information on the content to be recorded is not included in the management information in the respective attribute management files  201   b , . . . , then management information on the genre information is newly generated (S 2501 ). 
     Then, management information is newly generated in the title management file  207  (S 2502 ). 
     By the aforementioned step, in the title management file  207 , management information (i.e., pointers) related to the content to be recorded is determined. Then, pointers to the title management file  207  are recorded in management information in the respective attribute management files  201   b , . . . (S 2503 ). 
     Sort information indicating a sort order for the case in which management information in each attribute management file is sorted by a predetermined condition when management information is newly generated in each of the aforementioned steps, is generated and recorded in the sort information management file  209 . 
       FIG. 31  is a flowchart showing an operation of a playback device  1900  on selection of playback content. The flowchart shows an operation of the playback device  1900  to be performed when a user selection is made in the manner shown in  FIGS. 21A ,  21 B,  22 C, and  22 D. Note that a dashed line in  FIG. 31  indicates an input to the playback device, i.e., an operation by a user. 
     If one genre is selected by the user from a genre list in the selection menu shown in  FIG. 21B , then information on the selection is inputted to the playback device  1900  (S 2601 ). Thereafter, a menu for selecting a “composer” or an “artist” as shown in  FIG. 22C , is displayed. In the present example, it is assumed that the “artist” is selected by the user. 
     In the playback device  1900 , based on the “pointer to the title management file” registered in management information in the genre management file  201   b  for the selected genre, management information in the title management file  207  is obtained. From the “pointer to the artist management file” included in the obtained management information, information on artists is searched for and search results are displayed as an artist list (S 2602 ). Accordingly, the artist list as shown in  FIG. 22D  is displayed. 
     Then, if one artist is selected by the user from the artist list shown in  FIG. 22D , then information on the selection is inputted to the playback device  1900  (S 2603 ). 
     Based on the “pointer to the title management file” registered in management information in the artist management file  203   b  for the selected artist, management information in the title management file  207  is obtained. From the “pointer to the album management file” included in the obtained management information, album information is searched for and search results are displayed as an album list (S 2604 ). 
     If one album is selected by the user from the album list, then information on the selection is inputted to the playback device  1900  (S 2605 ). 
     Based on the “pointer to the title management file” registered in management information in the album management file  205   b  for the selected album, management information in the title management file  207  is obtained. Obtained results are displayed as a title list (S 2606 ). 
     If one title is selected by the user from the title list, then information on the selection is inputted to the playback device  1900  (S 2607 ). 
     Based on the “pointer to the content recording location” registered in management information in the title management file  207  for the selected title, content data is obtained (S 2608 ). Thereafter, the obtained content data is subjected to decryption and decompression processes and then reproduced. 
     In this way, according to the present embodiment, all management files in the navigation files other than the title management file  207  store pointers to the title management file. With this configuration, addition or deletion of an attribute management file itself can be easily and flexibly handled. 
     Third Embodiment 
     A third embodiment of the present invention will be described below. The present embodiment is different from the first and second embodiments in a method of storing management information in each attribute management file in navigation files. Other configuration and operation are the same as basic points. The configurations of a recording device and a playback device of the present embodiment are the same as those in the first embodiment. 
       FIG. 32  is a diagram showing a relationship between navigation files and a content file containing audio objects in the present embodiment. The navigation files include a genre management file  201   c , a composer management file  211   c , an artist management file  203   c , an album management file  205   c , a title management file  207 , and a sort information management file  209 . 
     Each of attribute management files, including the genre management file  201   c , the composer management file  211   c , the artist management file  203   c , the album management file  205   c , and the title management file  207 , contains text information indicating content of an attribute and reference count information indicating the number of pieces of management information related to the attribute which are registered in the other attribute management files. In the present embodiment, the attribute management files  201   c , . . . , do not contain information on pointers to other management files. 
     In management information in the title management file  207 , as with the first embodiment, a pointer relating to a recording location of content is recorded. By referring to the pointer, a content file  250  can be identified. 
     As with the first embodiment, the sort information management file  209  manages a sort order for the case in which management information in each of the attribute management files including the genre management file  201   c , the composer management file  211   c , the artist management file  203   c , the album management file  205   c , and the title management file  207 , is sorted. In the drawing, dashed-line arrows indicate that sort information on each attribute management file is recorded in the sort information management file  209 . 
       FIG. 33  is a diagram showing exemplary recording of information in the genre management file  201   c . Each piece of management information in the genre management file  201   c  includes “genre (text information)”, “reference count”, and “other information”, having a total of 512 bytes length. In management information # 1 , “2” is recorded as a reference count. This indicates that titles belonging to the genre “CLASSIC” are used in two of all pieces of management information in the title management file  207 . 
     Similarly, in management information # 2  in the genre management file  201   c, “ 1” is recorded as a reference count. This indicates that a title belonging to the genre “POPS” is used in one of all pieces of management information in the title management file  207 . In management information # 3  and management information # 4 , “unused” is recorded as other information. This indicates that although an area for recording information itself is reserved, it is not used as management information. Here, there are no particular limitations on what number of management information is used for genre information. The example is shown in which a flag indicating the usage status is held in individual management information. However, as another example, a method may be employed in which in a starting portion of a management file is provided an area for performing overall management of the entire usage status in the file, or a method may be employed in which management is performed using another file. 
     The configuration of the composer management file  211   c , the artist management file  203   c , and the album management file  205   c  in the present embodiment is also the same as that of the genre management file  201   c  and thus a detailed description thereof is omitted. The configuration of the title management file  207  is the same as that in the first embodiment shown in  FIG. 11 . 
       FIG. 34  is a flowchart showing navigation files generation process in the present embodiment. The process is performed by a recording device  1600 . The flowchart shows a generation process for attribute management files including a genre management file  201   c , a composer management file  211   c , an artist management file  203   c , and an album management file  205   c.    
     First, by referring to attribute management files (a genre management file  201   c , a composer management file  211   c , an artist management file  203   c , and an album management file  205   c ) recorded in a semiconductor recording medium  100 , it is checked whether the same genre information as that on content to be recorded now is included in management information in the respective attribute management files  201   c , . . . (S 300 ). 
     If the information on the content to be recorded is not included in the management information in the respective attribute management files  201   c , . . . , then management information on the genre information is newly generated (S 301 ). 
     Then, management information is newly generated in the title management file  207  (S 302 ). 
     By the aforementioned step, in the title management file  207 , management information (i.e., pointers) related to the content to be recorded is determined. Then, a value (“1” for the case of new generation) obtained by counting up reference counts in management information in the respective attribute management files  201   c , . . . , is recorded (S 303 ). 
     Note that sort information indicating a sort order for the case in which management information in each attribute management file is sorted by a predetermined condition when management information is newly generated in each of the aforementioned steps, is generated and recorded in the sort information management file  209 . 
     An operation of a playback device  1900  on selection of content to be reproduced of the present embodiment will be described with reference to  FIG. 31 . Here, an operation of the playback device  1900  to be performed when a user selection is made in the manner shown in  FIGS. 21A ,  21 B,  22 C, and  22 D is shown. Note that, as described above, a dashed line in  FIG. 31  indicates an input to the playback device, i.e., an operation by a user. 
     If one genre is selected by the user from a genre list in a selection menu shown in  FIG. 21B  with the genres sorted according to a sort order recorded in the sort information management file  209 , then information on the selection is inputted to the playback device  1900  (S 2601 ). Thereafter, a menu for selecting a “composer” or an “artist” as shown in  FIG. 22C , is displayed. In the present example it is assumed that the “artist” is selected by the user. 
     In the playback device  1900 , management information related to the selected genre is obtained from the title management file  207 . Specifically, in the genre management file  201   c , management information (entry number thereof) including the same genre information as that on the selected genre is identified. For example, in the example of  FIG. 33 , when the selected genre is “POPS”, management information # 2  is identified (the entry number is “2”). Then, in the tile management file  207 , management information whose value of the “pointer to the genre management file” matches the entry number of the identified management information is identified. By using the “pointer to the artist management file” included in the identified management information, information on artists is searched for through the artist management file  203   c  and the search results are displayed as a artist list (S 2602 ). At this time, the information on artists is displayed according to a predetermined sort order. The artist list such as shown in  FIG. 22D  may be displayed. 
     Then, if one artist is selected by the user from the artist list shown in  FIG. 22D , then information on the selection is inputted to the playback device  1900  (S 2603 ). 
     Management information on the selected artist is obtained from management information in the title management file  207 . Album information is searched for from the “pointer to the album management file” included in the obtained management information, and the search results are displayed as an album list (S 2604 ). At this time, the albums may be sorted according to a predetermined sort order and then displayed. 
     If one album is selected by the user from the album list, then information on the selection is inputted to the playback device  1900  (S 2605 ). 
     Management information on the selected album is obtained from management information in the title management file  207  and the obtained results are displayed as a title list (S 2606 ). At this time, the titles may be sorted according to a predetermined sort order and then displayed. 
     If one title is selected by the user from the title list, then information on the selection is inputted to the playback device  1900  (S 2607 ). 
     Based on the “pointer to the content recording location” registered in management information in the title management file  207  for the selected title, content data is obtained (S 2608 ). Thereafter, the obtained content data is subjected to decryption and decompression processes and then reproduced. 
     As such, for the navigation files of the present embodiment, each management file can be searched through on the basis of the title management file  207 . With this configuration, addition or deletion of an attribute management file itself can be more easily and flexibly handled over the configuration in the second embodiment. 
     Next, an update process for each attribute management file for the case in which content is deleted will be described with reference to  FIG. 35 . The process is performed by a data recording unit  1601  of a recording device  1600 . 
     If content to be deleted is specified by the user, then data on the specified content is deleted from a recording medium  100  (S 321 ). The content key for the content is also deleted together with the content. In each of the attribute management files  201   c ,  203   c , . . . , for the content, the reference count in management information related to the deleted content is counted down (S 322 ). In each of the attribute management files  201   c ,  203   c , . . . , it is determined whether the value of the counted down reference count is 0. If the value is 0, then the management information is deleted (S 323 ). Here, the deletion of management information refers to a process of clearing all information other than “other information” in the management information and changing the value of the other information (management information usage status) from “used” to “unused”. Note that when management information is deleted in the aforementioned step, information on pointers to relevant management information is also deleted from the sort information management file  209 . 
     By referring to a reference count in the above-described manner, management information on attributes that becomes unnecessary with the deletion of content can be easily recognized and deleted. 
     Fourth Embodiment 
     A fourth embodiment of the present invention will be described below. The present embodiment is different from the first, second, and third embodiments in the configuration of a sort information management file. Other configuration and operation are the same basically. 
       FIG. 36  is a diagram showing an exemplary configuration of a sort information management file in the present embodiment. The sort information management file  209  in the first, second, and third embodiments stores sort information for the case in which sorting is performed by only one procedure. On the other hand, in the present embodiment, a sort information management file  209   c  stores sort information for each procedure in a plurality of sorting procedures. 
     It is assumed that a sorting procedure A is a procedure in which sorting is performed alphabetically and a sorting procedure B is a procedure in which sorting is performed by date of title. Sort information for the case in which a title management file  207  is sorted by the sorting procedure A is recorded in title information (A) in a manner such as # 2 , # 4 , and # 1 , as shown in  FIG. 36 . Sort information for the case in which the title management file  207  is sorted by the sorting procedure B is recorded in title information (B) in a manner such as # 1 , # 2 , and # 4 . To manage sort information by another sorting procedure C, it is also possible to record sort information in title information (C) in a manner such as # 4 , # 1 , and # 2 . 
     For example, an exemplary display of a playback device for the case in which such sort information is used is shown in FIG.  37 . When the titles are sorted alphabetically, chronologically, and in order of degree of fun of song and managed in the sort information management file  209   c , it is also possible to display lists of titles according to the types of sorting procedures as shown in  FIG. 37 , allowing the user to make a selection. 
     As such, by managing states in which sorting is performed in a plurality of procedures, a playback device can increase variation in terms of displaying content information. 
     Note that although the aforementioned example shows a configuration in which sort information by three sorting procedures can be managed for the title management file  207 , the number and type of sorting procedures are not limited thereto. A sorting procedure and information indicating whether information according to the procedure is recorded or not may be managed, so that the sorting procedure and the information according to the procedure can be relatively freely expanded. Namely, each pieces of information on genre, composer, artist, album, and title may be sorted by different procedure so that there are plural sorting statuses. Alternatively, a configuration may be such that the pieces of sorted information are managed as different files. 
     Variation 
     Although the concepts of the present invention have been described based on the first to fourth embodiments, needless to say, the concepts of the present invention are not limited to the above-described specific embodiments. Various changes and modifications can be made without departing from the sprit and scope of the present invention. For example, the following variant is also included in the scope of the present invention throughout the first to third embodiments. 
     (1) In the above-described embodiments, a semiconductor recording medium is described as an example of a medium for recording content and navigation files. However, needless to say, the concepts of the present invention can also be applied to the other recording medium (e.g., hard disk and optical disk such as DVD and CD) different from the semiconductor recording medium. A recording device or a playback device may incorporate therein a recording medium (e.g., a hard disk or semiconductor recording medium) for storing content, and record navigation files in the incorporated recording medium. 
     (2) Although in the above-described embodiments a FAT file system is used as a file system, other file systems such as FAT32 and UDF may be used. A data size, recording address, and so on may be managed without using a file system. 
     (3) Although in the above-described embodiments a key that encrypts a content key is a medium unique key, the present invention is not limited thereto. A content key can be recorded freely regardless of format. Similarly, content can also be recorded freely regardless of format. For example, if security can be secured by other methods, a plaintext content key which is not encrypted may be recorded. If there is no need to encrypt and mange content, plaintext content data may be recorded as it is without using a content key. 
     (4) In the above-described embodiments, information managed by navigation files include information (genre, composer, artist, album, and title) accompanying music content and sort information for each attribute management file. However the types of information to be managed and a link relationship between pieces of management information are not limited to the examples in the above-described embodiments. For example, it may be configured that a file with a specific name (e.g., a “lyric writer management file”) may be reserved in advance and only a predetermined apparatus can generate the file with a specific name. The types of information to be managed are not limited to those described above. The types of information to be managed may be changed according to the type of content data. For example, content data which is not music data may be managed by the other accompanying information. 
     (5) In the above-described embodiments, navigation files are composed of management files for attribute information associated with each piece of content, such as genre and composer, and a sort information management file that manages sort information on each piece of management information in the management files. The present invention is not limited to this configuration. It may be configured that a sort information management file is not included. 
     (6) The above-described embodiments show an example of the configuration of navigation files and a content file in a semiconductor recording medium. Thus, configuration, numbers, and names of folders and files are not limited to those in the above-described example. The configuration, and so on of folders and files can be determined freely as long as effective management of various information accompanying content and effective narrowing-down search of content can be achieved. 
     (7) The functions of the recording device and the playback device in the above-described embodiments may be implemented by a predetermined control program to be executed by a CPU, MPU, or the like. 
     Please note that the application of the present invention is related to Japanese Patent Application No. 2005-251154 (filed on Aug. 31, 2005), the content of which is incorporated herein by reference. 
     INDUSTRIAL APPLICABILITY 
     The present invention is effective for a content data management method in which music data (audio content) encrypted for copyright protection is recorded together with a key thereto in a semiconductor recording medium. Particularly, according to the present invention, a narrowing-down search function for selecting content recorded in a recording medium can be implemented with a simple configuration. Accordingly, the present invention is useful for a playback device for content recorded in a recording medium.