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ACTION-469,470: Draft text concerning missing/multiple identifiers

From: Bailer, Werner <werner.bailer@joanneum.at>
Date: Tue, 27 Mar 2012 15:39:53 +0200
To: "public-media-annotation@w3.org" <public-media-annotation@w3.org>
Message-ID: <CD9846F872C7874BB4E0FDF2A61EF09FEE76912932@RZJC1EX.jr1.local>
Dear all,

please find below a draft text concerning the issue of missing/multiple identifiers to be included as informative text in the API document.

Looking at the API document, I suggest adding it as a section "Implementation Notes" after the current section 5 (Usage examples).

Best regards,


This section contains recommendations for implementators for handling missing or multiple identifiers of media resources/fragments.

x.1 Multiple identifiers of media resources or fragements

In some source formats, it could be possible to identify the resource or one of its fragments in multiple ways, e.g. by one or more identifiers, fragment name or temporal/spatial fragment URIs. For example, there could be a temporal media fragment, which can be addressed by the time range, that also has an assigned ID.
In the RDF representation of the Ontology for Media Resources, this can be represented (as recommended in the guidelines) by using owl:sameAs. To ensure a similar behaviour in the API, an implementation SHOULD return all such identifiers in a response. If queries to properties of a fragment with multiple are made, the implementation SHOULD accept each of the alternative identifiers and return the same response for each of them.

x.2 Missing fragment identifiers

There are source formats, which may contain metadata about a fragment (e.g. a track) without specifying any kind of identifier for it. For the RDF representation this is not a problem, as blank nodes can be used. In an API implementation, a client requesting the list of fragments cannot query properties of a fragment in case there is no identifier.
An implementation SHOULD generate an identifier for the fragment in such a case and SHOULD ensure that it is valid for a sufficiently long time so that the client can use it in subsequent queries to properties of fragments. The identifier is not guaranteed to remain permanently valid.
This can be implemented in different ways, including the following:
- In a session-aware environment (e.g., in the user agent, in a web service environment with session handling), the identifier could be bound to the session and remain valid at least for the duration of the session.
- In a stateless environment, the identifier could be the same for all clients and remain valid a defined time after it is last used (i.e., part of a query or response).
- The identifier could be defined to be unique and permanent. In that case the implementation has to manage the assignment of identifiers to metadata sources.

  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, 27 March 2012 13:40:23 UTC

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