Abstract:
A method for processing content data includes the steps of, when content data is transmitted from a data provider, adding usage rule information prescribing a rule of usage of the content data to the content data and transmitting the content data with the usage rule information; receiving the transmitted content data; extracting the usage rule information from the received content data; and notifying a user of the content data of the extracted usage information.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a method of processing content data, an apparatus for providing content data, and an apparatus for processing content data. More particularly, the present invention relates to a method of processing content data on the basis of usage rule information, an apparatus for supplying content data on the basis of usage rule information, and an apparatus for processing content data on the basis of usage rule information. 
   2. Description of the Related Art 
   In recent years, a great reduction in price for Internet connection service has been achieved. This has made it possible for ordinary people to always get access to the Internet via a high-speed line. As a result of such an improvement in the Internet connection environment, it has become very popular to distribute content data via the Internet. 
   In the present invention, the term “content data” is intended to describe a wide variety of information which is provided for use by users from an information provider, such as music information, moving picture information, book information, and game programs. 
   For example, in a music content distribution service using the Internet, such as EMD (Electronic Music Distribution), dedicated software is generally preinstalled in personal computers of users to perform necessary processing such as access to a content providing server on the Internet, downloading of music content data, and accounting. This allows users to easily purchase music content data via the Internet. 
   Not only such content data which need fee payment but also a great number of charge-free content data such as those produced personally for fun are distributed via the Internet. 
   In general, content data does not include information explicitly indicating whether or not fee payment is needed. Therefore, when a user receives content data via the Internet, the user cannot know, directly from the content data itself, whether it needs payment or it is free. 
   In the present environment in which a great number of contents which need payment and also those which are free are distributed, users have a mixture of purchased content data and charge-free content data. Once purchased content data and charge-free content data are mixed together, content data which are not free of charge are used without paying the fee thereof because the content data do not have a mechanism for easily indicating whether or not fee payment is needed, unless additional usage restriction processing by means of, for example, encryption is performed on the content data. 
   In some cases, in addition to the usage rule in terms of whether fee payment is needed, a usage rule in terms of whether copying is permitted is also specified by a copyright holder. However, also in such content data, the lack of mechanism for indicating the usage rule can cause even those users, who have intention to use content data in valid manners, to illegally copy content data against their intention. 
   SUMMARY OF THE INVENTION 
   It is therefore an object of the present invention to provide a content data processing method, which resolves the above-mentioned problem. 
   It is another object of the present invention to provide a content data providing apparatus, which resolves the above-mentioned problem. 
   It is further object of the present invention to provide a content data processing apparatus, which resolves the above-mentioned problem. 
   According to the present invention, there is provided a content data processing method including the steps of, when content data is transmitted from a data provider, adding usage rule information prescribing a rule of usage of the content data to the content data and transmitting the content data with the usage rule information; receiving the transmitted content data; extracting the usage rule information from the received content data; and notifying a user of the content data of the extracted usage information. 
   According to the present invention, there is provided a content data providing apparatus including a storage unit, an adding unit, and a transmitting unit. In the storage unit, a plurality of content data are stored. The adding unit adds usage rule information to content data read from the storage unit. The transmitting unit transmits the content data with the usage rule information added thereto by the adding unit. 
   According to the present invention, there is provided a content data processing apparatus including a communication unit, an extractor, a notifying unit, an input unit, and a processing unit. The communication unit receives transmitted content data. The extractor extracts the usage rule information from the content data received by the communication unit. The notifying unit notifies a user of the content data of the extracted usage rule information. The input unit is used by the user to input a command, data, or the like in accordance with the usage rule information notified by the notifying unit. The processing unit processes the content data received in accordance with a command/data input via the input unit. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a block diagram schematically showing an example of a construction of a content providing apparatus according to a first embodiment of the present invention; 
       FIG. 2  is a block diagram schematically showing an example of a construction of a content processing apparatus according to the first embodiment of the present invention; 
       FIG. 3  is a flow chart showing a content data transmission process performed by the content providing apparatus shown in  FIG. 1 ; 
       FIG. 4  is a flow chart showing a process performed on content data by the content processing apparatus shown in  FIG. 2 ; 
       FIGS. 5A to 5C  are diagrams showing examples of usage rule information displayed; 
       FIG. 6  is a block diagram schematically showing an example of a construction of a content processing apparatus according to a second embodiment of the present invention; 
       FIG. 7  is a flow chart showing a process performed on content data by the content processing apparatus shown in  FIG. 6 ; 
       FIG. 8  is a block diagram schematically showing an example of a construction of a content providing apparatus according to a third embodiment of the present invention; 
       FIG. 9  is a block diagram schematically showing an example of a construction of a content processing apparatus according to the third embodiment of the present invention; 
       FIG. 10  is a flow chart showing a content data transmission process performed by the content providing apparatus shown in  FIG. 8 ; 
       FIG. 11  is a flow chart showing a process performed on content data by the content processing apparatus shown in  FIG. 9 ; 
       FIG. 12  is a block diagram schematically showing an example of a construction of a content providing apparatus according to a fourth embodiment of the present invention; 
       FIG. 13  is a block diagram schematically showing an example of a construction of a content processing apparatus according to the fourth embodiment of the present invention; 
       FIG. 14  is a flow chart showing a process performed on content data by the content processing apparatus shown in  FIG. 12 ; and 
       FIG. 15  is a flow chart showing a process performed on content data by the content processing apparatus shown in  FIG. 13 . 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   The present invention are described in further detail below with reference to four embodiments in conjunction with the accompanying drawings. 
   First Embodiment 
     FIG. 1  is a block diagram schematically showing an example of a construction of a content providing apparatus according to a first embodiment of the present invention. 
   As shown in  FIG. 1 , this content providing apparatus  10  for providing content data includes a content database  101 , a content manager  102 , an information adder  103 , and a communication unit  104 . 
   The content database  101  is a database in which a plurality of content data to be provided to users are recorded or stored. Various kinds of content data such as music data, image data, document data of books, and game programs may be stored in the content database  101 . 
   The content manager  102  manages usage rule information prescribing the rule of usage of contents stored in the content database  101 . For example, the content manager  102  manages information indicating whether or not content data needs payment for usage thereof and/or information indicating whether or not copying of content data is permitted by copyright holders. 
   The information adder  103  reads content data to be provided to a user from the content database  101  and adds usage rule information S 1 , associated with the content data and received from the content manager  102 , to the content data read from the content database  101 . The usage rule information S 1  added to the content data by the information adder  103  indicates, for example, whether or not the content data needs payment for usage thereof and/or whether or not copying of the content data is permitted. 
   One manner in which the information adder  103  adds information to content data is to produce a usage rule information file separately from a content file and attach the usage rule information file to the content file. Another manner is to describe usage rule information in a header of a single content file. 
   The information added by the information adder  103  may be code data indicating a usage rule or image data to be displayed on a display unit of a content processing apparatus, which will be described later. 
   Alternatively, the information adder  103  may form a content file and determine its file name so as to indicate a usage rule. 
   In this case, for example, the file name may consist of a first part indicating a unique name of a file and a second part (extension) indicating the type of the file, wherein those two parts are separated by a dot “.” such as “unique name”+“.”+“extension”, which is a form generally employed in the art. In such a format, “unique name” or “extension” may be determined so as to indicate usage rule information. 
   First Example of a Manner of Setting File Names 
   For music data in the MP3 (MPEG1 Audiolayer 3) format, “mpc” is employed as the extension of file names for data which needs fee payment, while “mpf” is employed as the extension of file names for free data. 
   That is, a file name for data which needs payment is given as “********.mpc”, and a file name for data which is free is given as “********.mpf”, wherein “********” is an arbitrary string of characters. 
   Second Example of a Manner of Setting File Names 
   A code “_c” is used to indicate that content data needs payment, and a code “_f” is sued to indicate that content data is free, and either one of codes is added at the end of a unique name. 
   For example, a file name for data which needs payment is given as “******_c.mp3”, and a file name for data which is free is given as “******_f.mp3”, wherein “******” is an arbitrary string of characters indicating a unique name. 
   Third Example of a Manner of Setting File Names 
   For music data in the WAVE format, “wav” is employed as the extension of file names for data permitted to be copied, while “waw” is employed as the extension of file names for data not permitted to be copied. 
   For example, a file name for a WAVE file permitted to be copied is given as “********.wav”, while a file name for a WAVE file not permitted to be copied is given as “********.waw”, wherein “********” is an arbitrary string of characters. 
   The information adder  103  has been described above. 
   The communication unit  104  converts the content data with the usage rule information added thereto by the information adder  103  into a signal in a format adapted to a transmission line and transmits it to a content processing apparatus. In the example shown in  FIG. 1 , content data is transmitted via a network  1  serving as the transmission line. 
     FIG. 2  is a block diagram schematically showing an example of a construction of a content processing apparatus according to the first embodiment of the present invention. 
   The content processing apparatus  20  shown in  FIG. 2  includes a communication unit  201 , an information extractor  202 , a display unit  203 , an input unit  204 , and a processing unit  205 . 
   The communication unit  201  receives a content signal transmitted from the content providing apparatus  10  via the network  1  and reproduces content data in the form of digital data. 
   The information extractor  202  extracts the usage rule information S 2  from the content data received by the communication unit  201 . For example, in a case in which usage rule information in the form of image data is included, the information extractor  202  extracts that image data. In a case in which a file name of a content file includes usage rule information, the information extractor  202  extracts the usage rule information from the file name. 
   The display unit  203  is a block for displaying the usage rule information S 2  extracted by the information extractor  202  so that a user of content data can view the usage rule information. The usage rule information S 2  may be presented to users in various ways via a display device such as a liquid crystal display or an audio speaker. 
   In a case in which the usage rule information is given in the form of data which can be reproduced by the display unit  203 , the data may be reproduced and displayed. For example, in a case in which usage rule information is given in the form of image data added to content data, an image may be displayed on the display unit  203  in accordance with the image data. 
   In response to an inputting operation performed by a user, the input unit  204  generates a process request signal S 3  indicating a request for processing of content data. More specifically, the input unit  204  includes various types of input devices such as a keyboard, a mouse, and/or a microphone, and the input unit  204  generates a process request signal S 3  in response to an inputting operation performed on the input devices. 
   The processing unit  205  processes the content data received by the communication unit  201  in accordance with the process request signal S 3 . More specifically, the processing unit  205  performs various kinds of processing depending on the given content data, such as reproducing or recording of music content data, image content data, or a book content data, or executing of a program/content, in accordance with the process request signal S 3 . 
   The operation of the content providing system including the content providing apparatus  10  and the content processing apparatus  20  is described below with reference to flow charts shown in  FIGS. 3 and 4 . 
     FIG. 3  is a flow chart showing a content data transmission process performed by the content providing apparatus shown in  FIG. 1 . 
     FIG. 4  is a flow chart showing a process performed on content data by the content processing apparatus shown in  FIG. 2 . 
   In the content providing apparatus  10 , content data to be provided to the content processing apparatus  20  is read from the content database  101 , and usage rule information S 1  associated with the content data read from the content database  101  is output from the content manager  102  (step ST 101 ). The information adder  103  adds the usage rule information S 1  to the read content data (step ST 102 ). The communication unit  104  converts the resultant data into a signal in a predetermined format and transmits it to the content processing apparatus  20  connected to the network  1  (step ST 103 ). 
   The content signal transmitted over the network  1  is received by the communication unit  201  of the content processing apparatus  20  and reproduced into content data in the form of digital data (step ST 201 ). 
   Thereafter, the information extractor  202  extracts the usage rule information S 2  added to the received content data (step ST 202 ). 
   In the case in which the usage rule information is included in a file name, the usage rule information S 2  is extracted from the file name. 
   The extracted usage rule information S 2  is input to the display unit  203 , which displays an image and/or generates a voice/sound in accordance with the usage rule information S 2  thereby informing a user of the usage rule (step ST 203 ). 
   For example, image data added as the usage rule information S 2  to the content data is reproduced and displayed on the display unit  203 . Alternatively, image data corresponding to the usage rule information S 2  may be selected from image data prestored in the content processing apparatus  10 , and the selected image data may be displayed. 
   Examples of usage rule information S 2  displayed on the display unit  203  are shown in  FIGS. 5A to 5C . 
   In the example shown in  FIG. 5A , a list of received content data is displayed in such a manner that a mark indicating whether content data needs payment or is free is displayed at the left end of each line in which a content name is displayed. In the example shown in  FIG. 5A , “CONTENT 1” and “CONTENT 3” need payment, and “CONTENT 2” is free. 
   In the example shown in  FIG. 5B , a mark indicating whether or not copying of content data is permitted is displayed. In this example, “CONTENT 2” is permitted to be copied, while “CONTENT 1” and “CONTENT 3” are not permitted to be copied. 
   In the example shown in  FIG. 5C , a combination of a mark employed in  FIG. 5A  to indicate whether content data needs payment or is free and a mark employed in  FIG. 5B  to indicate whether content data is permitted to copied is displayed. In the example shown in  FIG. 5C , “CONTENT 1” and “CONTENT 3” need payment and are not permitted to be copied, while “CONTENT 2” is free and is permitted to be copied. 
   After displaying the usage rule information on the display unit  203 , the process goes into a state in which the process waits until an inputting operation is performed by the user on the input unit  204 , and it is determined whether processing of content data is performed in response to an inputting operation performed by the user (step ST 204 ). In a case in which in step ST 204 , a command indicating that processing of the content data should be cancelled is input to the processing unit  205  via the input unit  204 , the process is cancelled. On the other hand, in step ST 204 , if a command indicating that processing of the content should be executed is input as the process request signal S 3  to the processing unit  205 , processing corresponding to the process request signal S 3  is performed on the received content data (step ST 205 ). 
   In the content providing system shown in  FIGS. 1 and 2 , as described above, usage rule information prescribing the usage rule is added in advance to content data to be provided, and the usage rule information is presented in an explicit fashion to users who want to use the content data. This lets users easily know whether provided content data needs payment and/or whether copying of the content data is permitted, and thus users can easily decide whether to use the content data without any worry. Furthermore, because usage rule information is presented in an explicit fashion when a user tries to use content data, the content data is prevented from being used in a unauthorized manner. 
   Second Embodiment 
   A second embodiment of the present invention is described below. 
   In this second embodiment, the processing operation of the content processing apparatus is restricted in accordance with usage rule information. 
     FIG. 6  is a block diagram schematically showing a construction of a content processing apparatus according to the second embodiment of the present invention. 
   The content processing apparatus  20   a  shown in  FIG. 6  includes a communication unit  201 , an information extractor  202 , a display unit  203 , an input unit  204 , and a processing unit  205   a . In  FIG. 6 , similar parts to those in  FIG. 2  are denoted by similar reference numerals, and they are not described in further detail herein. 
   The processing unit  205   a  processes the content data received via the communication unit  201  in accordance with the process request signal S 3 , while processing of the received content data is restricted in accordance with the usage rule information S 2  extracted by the information extractor  202 . 
   For example, in the processing unit  205   a  including, as shown in  FIG. 6 , a playback unit  2051  for playing back received content data in response to the process request signal S 3  and a recording unit  2052  for recording received content data in response to the process request signal S 3 , the playback unit  2051  performs playing back without encountering any restriction, but recording performed by the recording unit  2052  is restricted in accordance with the usage rule information S 2 . 
   More specifically, if the usage rule information S 2  includes information indicating that recording of content data is permitted, the recording unit  2052  records the received content data in response to the process request signal. However, if the usage rule information S 2  includes information indicating that recording of content data is not permitted, the recording unit  2052  does not record the received content data. 
   Referring to  FIG. 7 , the operation of a content providing system including the content processing apparatus  20   a  is described below. As for the content providing apparatus, the construction and the transmission operation thereof are similar to those described above with reference to  FIG. 1 , and thus a further detailed description thereof is not given herein. 
     FIG. 7  is a flow chart showing a content data recording process performed by the content processing apparatus  20   a  shown in  FIG. 6 . In  FIG. 7 , similar steps to those in  FIG. 4  are denoted by similar step numbers. 
   The content signal transmitted over the network  1  is received by the communication unit  201  of the content processing apparatus  20  and reproduced into content data in the form of digital data (step ST 201 ). Thereafter, the information extractor  202  extracts the usage rule information S 2  added to the received content data (step ST 202 ). The extracted usage rule information S 2  is input to the display unit  203 , which displays an image and/or generates a voice/sound in accordance with the usage rule information S 2  thereby informing a user of the usage rule (step ST 203 ). 
   Thereafter, on the basis of the extracted usage rule information S 2 , it is determined whether copying of the content data is permitted (step ST 206 ). If copying is not permitted, the recording process is terminated. On the other hand, if it is determined in step ST 206  that copying is permitted, the process goes into a state in which the process waits until an inputting operation is performed by a user on the input unit  204 , and if inputting via the input unit  204  is performed, it is determined whether recording of the content data should be performed in response to the inputting operation (step ST 207 ). If, in step ST 207 , a command indicating that recording of the content data should be cancelled is input to the processing unit  205   a  via the input unit  204 , recording of the content data is cancelled. If, in step ST 207 , a record request command is input as the record request signal S 2  to the processing unit  250   a , the recording unit  2052  performs recording of the content data such that the received content is recorded on a recording apparatus (not shown) included in the recording unit  2052  (step ST 208 ). 
   As described above, also in the content providing system including the content processing apparatus  20   a  shown in  FIG. 6 , as with the content providing system according to the first embodiment described earlier, the usage rule information associated with the provided content data is explicitly presented to users so as to let users easily know the usage rule associated with the content data. Furthermore, processing on the content data is restricted in accordance with the usage rule information, and thus the content data is prevented from being used against the usage rule. 
   Third Embodiment 
   A third embodiment of the present invention is described below. 
   In this third embodiment, the processing operation of the content processing apparatus is restricted in accordance with usage rule information, and content data is encrypted in accordance with the usage rule information before it is provided to users thereby ensuring that usage of content data is restricted if the usage rule information is tampered with. 
     FIG. 8  is a block diagram schematically showing a construction of a content providing apparatus according to the third embodiment of the present invention. 
   The content providing apparatus  10   b  shown in  FIG. 8  includes a content database  101 , a content manager  102 , an information adder  103 , a communication unit  104 , and an encryptor  105 . In  FIG. 8 , similar parts to those in  FIG. 1  are denoted by similar reference numerals. 
   The encryptor  105  encrypts content data read from the content database in accordance with usage rule information S 1  supplied from the content manager  102  and supplies the encrypted content data to the information adder  103 . 
   The information adder  103  adds usage rule information S 1  to the content data encrypted by the encryptor  105 . 
     FIG. 9  is a block diagram schematically showing a construction of a content processing apparatus according to the third embodiment of the present invention. 
   The content processing apparatus  20   b  shown in  FIG. 9  includes a communication unit  201 , an information extractor  202 , a display unit  203 , an input unit  204 , and a processing unit  205   b . In  FIG. 9 , similar parts to those in  FIG. 2  are denoted by similar reference numerals and they are not described in further detail herein. 
   The processing unit  205   b  decrypts the content data received by the communication unit  201 , in accordance with the usage rule information S 2  extracted by the information extractor  202  and processes the decrypted content data in accordance with the process request signal S 3 . The processing unit  205   b  restricts processing on the content data in accordance with the usage rule information S 2 . 
   For example, as shown in  FIG. 9 , the processing unit  205   b  includes a playback unit  2051  for playing back received content data in response to the process request signal S 3 , a recording unit  2052  for recording received content data in response to the process request signal S 3 , and a decryptor  2053  for decrypting the received content data in accordance with the usage rule information S 2 . 
   The decryptor  2053  decrypts the content data encrypted by the encryptor  105  of the content providing apparatus  10   b  in accordance with the extracted usage rule information S 2  thereby reproducing the unencrypted original content data. The playback unit  2051  and the recording unit  2052  can perform playing back or recording of content data decrypted by the decryptor  2053 , but they cannot perform playing back or recording of content data in an undecrypted form. 
   The operation of the content providing system including the content providing apparatus  10   b  and the content processing apparatus  20   b  is described below with reference to flow charts shown in  FIGS. 10 and 11 . 
     FIG. 10  is a flow chart showing a content data transmission process performed by the content providing apparatus  10   b  shown in  FIG. 8 . In  FIG. 10 , similar steps to those in  FIG. 3  are denoted by similar step numbers. 
     FIG. 11  is a flow chart showing a content recording process performed by the content processing apparatus  20   b  shown in  FIG. 9 . In  FIG. 11 , similar steps to those in  FIG. 7  are denoted by similar step numbers. 
   In the content providing apparatus  10   b , content data to be provided to the content processing apparatus  20   b  is read from the content database  101 , and usage rule information S 1  associated with the read content data is output from the content manager  102  (step ST 101 ). The read content data is encrypted in accordance with the usage rule information S 1  (step ST 104 ), and the usage rule information S 1  is added, by the information adder  103 , to the encrypted content data (step ST 102 ) The communication unit  104  converts the encrypted content data into a signal in a predetermined format and transmits it to the content processing apparatus  20  connected to the network  1  (step ST 103 ). 
   The content signal transmitted over the network  1  is received by the communication unit  201  of the content processing apparatus  20   c  and reproduced into content data in the form of digital data (step ST 201 ) Thereafter, the information extractor  202  extracts the usage rule information S 2  added to the received content data (step ST 202 ) The extracted usage rule information S 2  is input to the display unit  203 , which displays an image and/or generates a voice/sound in accordance with the usage rule information S 2  thereby informing a user of the usage rule (step ST 203 ). 
   Thereafter, on the basis of the extracted usage rule information S 2 , it is determined whether copying of the content data is permitted (step ST 206 ). If copying is not permitted, the recording process is terminated. On the other hand, if it is determined in step ST 206  that copying is permitted, the process goes into a state in which the process waits until an inputting operation is performed by a user on the input unit  204 , and if inputting via the input unit  204  is performed, it is determined whether recording of the content data should be performed in response to the inputting operation (step ST 207 ). 
   If it is determined in step ST 207  that a command indicating that recording of the content data should be cancelled is input to the processing unit  205   b  via the input unit  204 , recording of the content data is cancelled. On the other hand, if it is determined in step ST 207  that a record request command has been input as the record request signal S 2  to the processing unit  205   b , the decryptor  2053  decrypts the received content data (step ST 209 ), and the recording unit  2052  records the decrypted content data (step ST 210 ). 
   However, in a case in which the usage rule information S 2  added to the content data input to the processing unit  205   b  has been tampered with, for example, such that the content data, which actually needs payment, looks as if it were free, it becomes impossible for the decryptor  2053  to decrypt the content data, and thus recording of the content data is not performed against the intention of the user. 
   As described above, also in the content providing system constructed as shown in  FIGS. 9 and 10 , as with the content providing system according to the second embodiment described earlier, the usage rule information associated with the provided content data is explicitly presented to users so as to let users easily know the usage rule associated with the content data. Furthermore, processing on the content data is restricted in accordance with the usage rule information, and thus the content data is prevented from being used against the usage rule. Furthermore, because encrypted content data with tampered usage rule information cannot be decrypted, the content data is prevented from being used against the usage rule. 
   Fourth Embodiment 
   A fourth embodiment of the present invention is described below. 
   In this fourth embodiment, when usage rule information includes information indicating that the content data needs fee payment, a content processing apparatus performs processing only if valid payment information has been input. 
     FIG. 12  is a block diagram schematically showing an example of a construction of a content providing apparatus according to the fourth embodiment of the present invention. 
   The content providing apparatus  10   c  shown in  FIG. 12  includes a content database  101 , a content manager  102 , an information adder  103 , a communication unit  104 , and a content usage restrictor  106 , and an accounting unit  107 . In  FIG. 12 , similar parts to those in  FIG. 1  are denoted by similar reference numerals, and they are not described in further detail herein. 
   The content usage restrictor  106  performs a usage restriction process to impose a restriction on content data read from the content database in accordance with usage rule information S 1 . 
   For example, when content data needs payment, the processing unit  106  encrypts the content data using a private key, while the content data is not encrypted if the content data is free. 
   The processing unit  106  may encrypt content data using a public key possessed by a user who has issued a request for the content data. This prevents the content data from being illegally used by unauthorized users other than the user who issued the request for that content data. 
   Content data may be encrypted using the usage rule information S 1 , as with the encryptor  105  shown in  FIG. 8 , to prevent the usage rule information S 1  from being tampered with. 
   In response to receiving a restriction release request signal, requesting for restriction release information associated with content data, from the content processing apparatus  20   c  to which the content data has been provided, the accounting unit  107  compares pre-registered user authentication information with user authentication information received together with the request signal. If, the comparison indicates that the user is an authorized user, the restriction release information needed to release the restriction imposed by the content usage restrictor  106  is transmitted to the content processing apparatus  20   c  of that user, and information indicating the price of the content data purchased by the user is added to account information managed for each user. If the user is determined as not being an authorized user, the accounting unit  107  transmits a message, indicating that the restriction release information request has been refused, to the content processing apparatus  20   c  of that user. 
     FIG. 13  is a block diagram schematically showing an example of a construction of a content processing apparatus according to the fourth embodiment of the present invention. 
   The content processing apparatus  20   c  shown in  FIG. 13  includes a communication unit  201 , an information extractor  202 , a display unit  203 , an input unit  204 , and a processing unit  205   c . In  FIG. 13 , similar parts to those in  FIG. 2  are denoted by similar reference numerals, and they are not described in further detail herein. 
   When a process request signal is input via the input unit  204  to request processing of content data, if usage rule information S 2  includes information indicating that use of the content data needs payment, the processing unit  205   c  transmits a restriction release request signal to the content providing apparatus  10   c  to request the content providing apparatus  10   c  to provide restriction release information. If the processing unit  205   c  receives the restriction release information transmitted in response to the restriction release request signal, the processing unit  205   c  releases the restriction on the usage of the content data using the received restriction release information and performs processing, such as recording or playing back, on the content data. 
   As shown in  FIG. 13 , the processing unit  205   c  includes an accounting unit  2054 , a usage restrictor releaser  2055 , and a record/playback unit  2056 . 
   When a process request signal S 3  is input via the input unit  204  to request processing of content data, if the usage rule information S 2  includes information indicating that use of the content data needs payment, the accounting unit  2054  transmits a restriction release request signal to the content providing apparatus  10   c  to request the content providing apparatus  10   c  to provide restriction release information. When the restriction release request signal is transmitted, user authentication information input together with the process request signal S 3  is also transmitted to the content providing apparatus  10   c . If the accounting unit  2054  receives the restriction release information transmitted, in response to the request signal S 3 , from the content providing apparatus  10   c , the accounting unit  2054  transfers the received restriction release information to the usage restriction releaser  2055 . However, if a message indicating that the restriction release request has been refused is returned, processing of the content data is terminated. 
   Using the restriction release information supplied from the accounting unit  2054 , the usage restriction releaser  2055  releases the usage restriction imposed on the content data received by the communication unit  201 . For example, in a case in which the content data has been encrypted by the content usage restrictor  106  using a private key, the usage restriction releaser  2055  decrypts the encrypted content data using the private key as the restriction release information. 
   In a case in which the content data has been encrypted using a public key possessed by the content processing apparatus  20   c , the usage restriction releaser  2055  decrypts the content data using a private key corresponding to the public key. On the other hand, in a case in which the content data has been encrypted using usage rule information, the usage restriction releaser  2055  decrypts the content data using the usage rule information S 2  extracted by the information extractor  202 . 
   The record/playback unit  2056  records or plays back the content data whose usage restriction has been released by the usage restriction releaser  2055 . 
   The operation of the content providing system including the content providing apparatus  10   c  and the content processing apparatus  20   c  is described below with reference to flow charts shown in  FIGS. 14 and 15 . 
     FIG. 14  is a flow chart showing a content data transmission process performed by the content providing apparatus  10   c  shown in  FIG. 12 , wherein In  FIG. 14 , similar steps to those in  FIG. 3  are denoted by similar step numbers. 
     FIG. 15  is a flow chart showing a process performed on content data by the content processing apparatus  20   c  shown in  FIG. 13 , wherein In  FIG. 15 , similar steps to those in  FIG. 4  are denoted by similar step numbers. 
   In the content providing apparatus  10   c , content data to be provided to the content processing apparatus  20   c  is read from the content database  101 , and usage rule information S 1  associated with the content data read from the content database  101  is output from the content manager  102  (step ST 101 ). In the content usage restrictor  106 , information indicating usage restriction is added to the read content data, in accordance with the usage rule information S 1  (step ST 105 ) Thereafter, the usage rule information S 1  is added, by the information adder  103 , to the encrypted content data (step ST 102 ). The communication unit  104  converts the content data restricted in terms of usage into a signal in a predetermined format and transmits it to the content processing apparatus  20  connected to the network  1  (step ST 103 ). 
   The content signal transmitted over the network  1  is received by the communication unit  201  of the content processing apparatus  20   c  and reproduced into content data in the form of digital data (step ST 201 ). Thereafter, the information extractor  202  extracts the usage rule information S 2  added to the received content data (step ST 202 ). The extracted usage rule information S 2  is input to the display unit  203 , which displays an image and/or generates a voice/sound in accordance with the usage rule information S 2  thereby informing a user of the usage rule (step ST 203 ). 
   It is determined whether the extracted usage rule information S 2  indicates that the content data needs payment or is free of charge (step ST 211 ). If the content data is free of charge, steps ST 212  and ST 214  are performed. However, if the content needs payment, steps ST 214  to ST 219  are performed. 
   In step ST 212 , the process goes into a state in which the process waits until an inputting operation is performed by a user on the input unit  204 , and it is determined whether processing should be performed. If it is determined in step ST 212  that a command, indicating that processing of the content data should be cancelled, has been input, processing of the content data is cancelled. However, if it is determined in step ST 212  that a command to perform a process on the content data has been input to the processing unit  205   c , the record/playback unit  2056  performs a process specified by the user on the content data (step ST 213 ). 
   In step ST 214 , the process goes into a state in which the process waits until an inputting operation is performed by the user on the input unit  204 , and it is determined whether processing should be performed. If it is determined in step ST 214  that a command indicating that processing of the content data should be cancelled has been input, processing of the content data is cancelled. However if it is determined in step ST 214  that a command to perform a process on the content data has been input to the processing unit  205   c , the accounting unit  2054  transmits a restriction release request signal to the content providing apparatus  10   c  to request the content providing apparatus  10   c  to provide restriction release information (step ST 215 ). When the restriction release request signal is transmitted in step ST 215 , user authentication information input via the input unit  204  is also transmitted together. 
   If the content providing apparatus  10   c  receives the request for the restriction release information, the content providing apparatus  10   c  compares pre-registered user authentication information with the user authentication information received together with the request signal. If the comparison indicates that the user is an authorized user, the restriction release information needed to release the restriction imposed by the content usage restrictor  106  is transmitted to the content processing apparatus  20   c  of the user who has issued the request. If the user is determined as not being an authorized user, a message indicating that the restriction release information request has been refused is returned to the content processing apparatus  20   c  (step ST 216 ). 
   In the case in which the message indicating refusal to provide the restriction release information was returned from the content providing apparatus  10   c , processing on the content data by the content processing apparatus  20   c  is cancelled. On the other hand, if the content processing apparatus  20   c  receives the restriction release information, the usage restriction releaser  2055  of the content processing apparatus  20   c  release the usage restriction imposed on the content data using the received restriction release information (step ST 218 ). After the restriction imposed on the content data has been released, the record/playback unit  2056  performs a process specified by the user on the content data (step ST 219 ). 
   As described above, also in the content providing system shown in  FIGS. 12 and 16 , as with the content providing system according to the first embodiment described earlier, the usage rule information associated with the provided content data is explicitly presented to users so as to let users easily know the usage rule associated with the content data. 
   As described above, when a user purchases content data, information explicitly indicating whether the content data needs payment or is free of charge is displayed in accordance with the usage rule information added to the content data, and thus the user can easily know whether or not content data stored on the content processing apparatus is free. Therefore, even in the case in which a large number of content data are stored in the content processing apparatus, it is possible to quickly determine whether or not each content data is free. 
   It will be apparent to those skilled in the art that the present invention is not limited to the details of the embodiments described above but various modifications are possible. 
   For example, although in the embodiments described above, content data is provided via a network, the network may be a wireless network or a cable network. The present invention may also be applied to a system in which information is provided by means of a one-way transmission from a content providing apparatus to a content processing apparatus, as with broadcasting. 
   Furthermore, the accounting method for charging a content fee is not limited to that employed in the content providing system described above with reference to  FIGS. 12 and 13 , but other various accounting methods may also be employed. For example, accounting may be performed in conjunction with prepaid cards. In this case, both the accounting process and the generation of restrict release information may be performed in the accounting unit disposed in the content processing apparatus rather than in the content providing apparatus. This makes unnecessary for the content providing apparatus to include the accounting unit. 
   Although all parts of the content providing apparatus and the content processing apparatus described in the respective embodiments may be formed by means of hardware, at least some parts may also be realized by a processing apparatus such as a computer which performs a process in accordance with a preinstalled program.