2.6 Extending the Description Schema of MPEG-7

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The DDL of MPEG-7 defines the syntax of the MPEG-7 description tools. The description tools are instantiated as descriptions in textual format (XML), thanks to the DDL (based on XML Schema). Binary format of descriptions is obtained by means of the BiM defined in the Systems part (see Section 2.7).

Some applications, however, require a more detailed description framework than that proposed by MPEG-7. For instance, consider an application for the annotation of sport videos. It would be desirable to distinguish semantic entities, like players and referees, and detail their relationship and the soccer events (e.g., goal, penalty). For this purpose, MPEG-7 proposes mechanisms for the creation of specialized classification schemes. Moreover, it allows the creation of new description schemes and, possibly, descriptors. it also allows the extension and modification of existing description schemes.

The simplest extension is the creation of a new classification scheme. As stated in Section 2.1, the MPEG-7 CS defines a list of typical terms used in many applications together with their meanings. For instance, it allows the definition of the file formats in a standard way. Note that the publication of a newly created or extended CS is subject to a registration. More information on registration may be obtained from the MPEG homepage at http://www.chiariglione.org/mpeg/.

2.6.1 Creation of a New CE

Let us assume that we want to create a new CS for the parental rating specific to national standards. MPEG-7 supplies terms that are compliant to the ICRA (Internet Content Rating Association) Parental Rating Classification (http://www.icra.org/), which is an international, well-recognized classification of violence, nudity, and so forth, in multimedia material. However, most countries also support national standards for broadcasted material. For instance, the SPIO (Spitzenorganisation der Filmwirtschaft e.V.) organization (http://www.spio.de/) provides, for German-speaking countries, a CS, known as FSK, that is based on age. A total of five terms are introduced:

Released for general public
Released for persons older than 6 years of age
Released for persons older than 12 years of age
Released for persons older than 16 years of age
Not released for persons younger than 18 years of age

To establish the new CS, we have first to define a new identification URI (Uniform Resource Identifier). In accordance with the ICRA Rating, the URI urn:mpeg:mpeg7:cs:FSKParentalRatingCS:2003 is proposed. Second, we have to provide the domain to which this new CS applies. Obviously, it applies to the same domain as the ICRA does: "//CreationInformation/Classification/ParentalGuidance/ParentalRating."

The following XML fragment shows the declaration of the new CS identified by urn:mpeg:mpeg7:cs:FSKParentalRatingCS:2003:

 <ClassificationScheme uri="urn:mpeg:mpeg7:cs:FSKParentalRatingCS:2003" domain="//CreationInformation/Classification/ParentalG uidance/ParentalRating">   <Header xsi:type="DescriptionMetadataType">     <Comment>       <FreeTextAnnotation xml:lang="en">         Thesaurus for Parental Rating according the FSK             of SPIO       </FreeTextAnnotation>     </Comment>   </Header>   <Term term>     <Name xml:lang="en">released for general         public</Name>   </Term>   <Term term>     <Name xml:lang="en">released for persons older than         6 years</Name>   </Term>   <Term term>     <Name xml:lang="en">released for persons older than         12 years</Name>   </Term>   <Term term>     <Name xml:lang="en">released for persons older than         16 years</Name>   </Term>   <Term term>     <Name xml:lang="en">not released for persons         younger than 18 years</Name>   </Term>   <Term term>     <Name xml:lang="en">not rated</Name>   </Term> </ClassificationScheme>

2.6.2 Extending Existing Descriptors and Creating New Ones

MPEG-7 provides a standardized set of technologies for describing multimedia content. This is especially true for multimedia content such as images, video, and audio. However, for applications using specialized entities, for instance, for soccer games, a PlayerType as an extension of the PersonType might be of interest.

MPEG-7 provides in the DDL a mechanism for introducing new descriptors/description schemes without changing the definition of the DDL of each part. The proposed extensions are put into its own file, for example, named here <myMPEG-7.xsd>. The following modifications to the schema files of MPEG-7 have to be made: add the file name—<myMPEG-7.xsd>—to Mpeg7-2001.xsd by adding the line

 <! - my own definitions - > <include schemaLocation="./myMPEG7.xsd"/>

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