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Text to be included to resolve LC-2389

From: Bailer, Werner <werner.bailer@joanneum.at>
Date: Tue, 11 Jan 2011 18:01:13 +0100
To: Thierry MICHEL <tmichel@w3.org>
CC: "public-media-annotation@w3.org" <public-media-annotation@w3.org>
Message-ID: <CD9846F872C7874BB4E0FDF2A61EF09F965BC8DBC6@RZJC1EX.jr1.local>
Dear Thierry,

As discussed today, here is the text for two subsections to be included in the usage examples section of the ontology document. The text is based on the response to this LC comment.

Best regards,

1) Subtitles and the ontology for media resources

Concerning external subtitles, using ma:relation is the recommended approach. The identifier attribute contains the URL of the subtitle file, and the relation type qualifies it as a subtitle relation. The value should be a URI, but could also be a string. It is recommended to use a controlled vocabulary for the type of the relation.

Embedding of subtitles is not a use case that has been considered, however it is possible. The mechanism used to specify timed metadata is to specify fragments identified by Media Fragment URIs [1] and then describe annotations of these fragments.

To summarize, there are three options for dealing with subtitles:

- Link to external subtitle file using ma:fragment, with type subtitle and a Timed Text Markup Language (TTML) [2] or WebSRT [3] file as target.
- Subtitles can be embedded in a media file, in which case they can be described as a track media fragment using ma:fragment and Media Fragment URIs [1].
- Subtitles could be embedded by using ma:title with a type qualifier for subtitle. A list of time media fragments is defined and each fragment is annotated using ma:title.

Although the last option is a way of embedding subtitles it is not recommended. Instead, a dedicated format such as TTML or WebSRT should be used for the subtitles and referenced.

2) Semantic annotation

Time based annotations are a possible and the following two cases are covered by the specification:

- use ma:description for a textual description of the media resource (or a fragment)
- use ma:relation to link to a RDF file or named graph containing the annotation for the media resource (or fragment)

At the time of writing this specification, there no solution for embedding a set of triples into one of the properties of the ontology for media resources. The summary of a discussion with the Semantic Web Coordination Group is that named graphs could be a solution to this issue, but there is no standard syntax for expressing them, to which this specification could refer. Such a syntax might find its way into RDF 2.0. Thus the embedding of triples into media annotation elements is excluded until a standard syntax for named graphs is available. 

[1] http://www.w3.org/TR/2010/WD-media-frags-20100624
[2] http://www.w3.org/TR/2010/CR-ttaf1-dfxp-20100223/
[3] http://www.whatwg.org/specs/web-apps/current-work/#websrt-0

  Werner Bailer
  Audiovisual Media Group
  DIGITAL - Institute of Information and Communication Technologies
  JOANNEUM RESEARCH Forschungsgesellschaft mbH
  Steyrergasse 17, A-8010 Graz, AUSTRIA
  phone:  +43-316-876-1218            personal fax: +43-316-876-91218             
  mobile: +43-699-1876-1218            general fax: +43-316-876-1191  
  web:    http://www.joanneum.at/digital        
  e-mail: mailto:werner.bailer@joanneum.at
Received on Tuesday, 11 January 2011 17:01:45 UTC

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