WD-smil-boston-19991115

8. The SMIL Metadata Module

Editors:: Thierry Michel (tmichel@w3.org), W3C

8.1 Introduction

The World Wide Web was originally built for human consumption, and although everything on it is machine-readable, this data is not machine-understandable. It is very hard to automate anything on the Web, and because of the volume of information the Web contains, it is not possible to manage it manually. Metadata is "data about data" (for example, a library catalog is metadata, since it describes publications) or specifically in the context of this specification "data describing Web resources".
The solution proposed here is to use metadata to describe SMIL documents published on the Web.

The earlier SMIL 1.0 specification allowed authors to describe documents with a very basic vocabulary using the "meta" element.
The SMIL Metadata module defined in this specification fully supports the use this "meta" element from SMIL 1.0 but it also introduces new capabilities for describing metadata using the Resource Description Framework Model and Syntax [RDFsyntax], a powerful metadata language for providing information about resources.

8.2 Compatibility with SMIL 1.0 using the meta Element

To insure backward compatibility with SMIL 1.0, the <meta> element as specified in the SMIL 1.0 [SMIL10] Recommendation can be used to define properties of a document (e.g., author/creator, expiration date, a list of key words, etc.) and assign values to those properties.
Each <meta> element specifies a single property/value pair in the name and content attributes, respectively.

8.3 Extensions to SMIL 1.0 Metadata.

RDF provides a more general treatment of metadata. RDF is a declarative language and provides a standard way for using XML to represent metadata in the form of statements about properties and relationships of items on the Web. Such items, known as resources, can be almost anything, provided it has a Web address. This means that you can associate metadata with a SMIL documents, but also a graphic, an audio file, a movie clip, and so on.

RDF is the appropriate language for metadata. The specifications for RDF can be found at:

Resource Description Framework (RDF) Model and Syntax [RDFsyntax], a W3C Recommendation 22 February 1999
Resource Description Framework (RDF) Schema [RDFschema], a W3C Proposed Recommendation 03 March 1999

Metadata within an SMIL document should be expressed in the appropriate RDF namespaces [XML-NS] and should be placed within the <metadata> child element to the document's <smil> root element. (See example below.)

8.3.1 Using multiple description schemes simultaneously

RDF appears to be the ideal approach for supporting descriptors from multiple description schemes simultaneously.

Here are some suggestions for content creators regarding metadata:

Content creators should refer to W3C Metadata Recommendations and activities when deciding which metadata schema to use in their documents.
Content creators should refer to the Dublin Core Metadata Initiative [DC], which is a set of generally applicable core metadata properties (e.g., Title, Creator, Subject, Description, etc.).
Content creators should refer to the Video Metadata Representation, which extends Dublin Core properties to cope with video content metadata requirements (e.g., Type, Relation, Format, Coverage, etc.).
Additionally, the SMIL Metadata Schema (below) contains a set of additional metadata properties that are common across most uses of multimedia.

Individual industries or individual content creators are free to define their own metadata schema, but everyone is encouraged to follow existing metadata standards and use standard metadata schema wherever possible to promote interchange and interoperability. If a particular standard metadata schema does not meet your needs, then it is usually better to define an additional metadata schema in RDF that is used in combination with the given standard metadata schema than to totally avoid the standard schema.

8.4 The SMIL Metadata Schema

(This schema has not yet been defined. Here are some candidate attributes for the schema: LevelAccessibilityGuidelines, ListOfImagesUsed, ListOfAudioUsed, ListOfTextUsed, ListOfTextstreamUsed, ListOfRefUsed, ListOfCodecUsed, etc)

8.5 An Example

Here is an example of how metadata can be included in an SMIL document. The example uses the Dublin Core version 1.0 Schema [DC] and the SMIL Metadata Schema:

<?xml version="1.0" ?>
<smil xmlns = "http://www.w3.org/TR/.../SMIL-Boston.dtd">
 <head>
 <meta id="meta-smil1.0-a" name="Publisher" content="W3C" />
 <meta id="meta-smil1.0-b" name="Date" content="1999-10-12" />
 <meta id="meta-smil1.0-c" name="Rights" content="Copyright 1999 John Smith" />

  <metadata id="meta-rdf">
   <rdf:RDF
       xmlns:rdf = "http://www.w3.org/1999/02/22-rdf-syntax-ns#"
       xmlns:rdfs = "http://www.w3.org/TR/1999/PR-rdf-schema-19990303#"
       xmlns:dc = "http://purl.org/metadata/dublin_core#"
       xmlns:smilmetadata = "http://www.w3.org/AudioVideo/.../smil-ns#" >

<!-- Metadata about the SMIL presentation -->
   <rdf:Description about="http://www.foo.com/meta.smi"
       dc:Title="An Introduction to the Resource Description Framework"
       dc:Description="The Resource Description Framework (RDF) enables the encoding, exchange and reuse of structured metadata"
       dc:Publisher="W3C"
       dc:Date="1999-10-12"
       dc:Rights="Copyright 1999 John Smith"
       dc:Format="text/smil" >                
       <dc:Creator>
          <rdf:Seq ID="CreatorsAlphabeticalBySurname">
             <rdf:li>Mary Andrew</rdf:li>
             <rdf:li>Jacky Crystal</rdf:li>
          </rdf:Seq>
       </dc:Creator>
       <smilmetadata:ListOfVideoUsed>
          <rdf:Seq ID="VideoAlphabeticalByFormatname">
              <rdf:li Resource="http://www.foo.com/videos/meta-1999.mpg"/>
              <rdf:li Resource="http://www.foo.com/videos/meta2-1999.mpg"/> 
          </rdf:Seq>
       </smilmetadata:ListOfVideoUsed>
       <smilmetadata:Access LevelAccessibilityGuidelines="AAA"/>
   </rdf:Description>

<!-- Metadata about the video -->
   <rdf:Description about="http://www.foo.com/videos/meta-1999.mpg"
        dc:Title="RDF part one"
        dc:Creator="John Smith"
        dc:Subject="Metadata,RDF"
        dc:Description="RDF basic fonctionalities"
        dc:Publisher="W3C Press Service"
        dc:Format="video/mpg"
        dc:Language="en"
        dc:Date="1999-10-12"
        smilmetadata:Duration="60 secs"
        smilmetadata:VideoCodec="MPEG2" >
        <smilmetadata:ContainsSequences>
           <rdf:Seq ID="ChronologicalSequences">
             <rdf:li Resource="http://www.foo.com/videos/meta-1999.mpg#scene1"/>
             <rdf:li Resource="http://www.foo.com/videos/meta-1999.mpg#scene2"/> 
           </rdf:Seq>
         </smilmetadata:ContainsSequences>
   </rdf:Description>

<!-- Metadata about a scene of the video -->
   <rdf:Description about="#scene1"
        dc:Title="RDF intro"
        dc:Description="Introduction to RDF fonctionalities"
        dc:Language="en"
        smilmetadata:Duration="30 secs"
        smilmetadata:Presenter="David Jones" >
        <smilmetadata:ContainsShots>
           <rdf:Seq ID="ChronologicalShots">
             <rdf:li>Panorama-shot</rdf:li>
             <rdf:li>Closeup-shot</rdf:li>
           </rdf:Seq>
        </smilmetadata:ContainsShots>
   </rdf:Description>
  </rdf:RDF>
 </metadata>

<!-- SMIL presentation -->
 <layout>
    <region id="a" top="5" />
 </layout>
 </head>
 <body>
 <seq>
   <video region="a" src="/videos/meta-1999.mpg" >
     <area id="scene1" begin="0" end ="30"/>
     <area id="scene2" begin="30" end ="60"/>
   </video>
   <video region="a" src="/videos/meta2-1999.mpg"/>
 </seq>
 </body>
</smil>

Note:Validate the above RDF description with SiRPAC; a Simple RDF Parser and Compiler, written by Janne Saarela (W3C).

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