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relating rss namespace(s) to other vocabulary

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  • Dan Brickley
    replying to a point raised on Ben s weblog: [ Another question for everyone I guess. In both RSS 1.0 and the Userland proposal for RSS 2.0, you can have
    Message 1 of 1 , Sep 16, 2002
      replying to a point raised on Ben's weblog:

      Another question for everyone I guess. In both RSS 1.0 and the Userland
      proposal for RSS 2.0, you can have duplicate semantics. For example:

      <dc:title>ANOTHER TITLE<dc:title>

      Which of these takes precedence? This is mostly an issue with RSS 2.0, as
      there is a lot of overlap between the core elements and available modules.
      (and RSS 1.0 has only one possible overlap, the title/dc:title one.) This
      is one reason why I'd like to see the core elements become fewer in

      Posted by Ben Hammersley at 05:04 PM

      This is one of the reasons why _namespaces alone aren't enough_. (a
      concern re RSS 0.94/2.0 btw)

      We need rules for using and understanding XML namespaces, if they're going
      to help us share, aggregate and exploit namespace'd data.

      Here are some of the rules we wrote in the
      RDF schema for http://purl.org/rss/1.0/

      <rdf:Property rdf:about="http://purl.org/rss/1.0/description"
      rdfs:comment="A short text description of the subject.">
      <rdfs:subPropertyOf rdf:resource="http://purl.org/dc/elements/1.1/description" />
      <rdfs:isDefinedBy rdf:resource="http://purl.org/rss/1.0/" />

      <rdf:Property rdf:about="http://purl.org/rss/1.0/title"
      rdfs:comment="A descriptive title for the channel.">
      <rdfs:subPropertyOf rdf:resource="http://purl.org/dc/elements/1.1/title" />
      <rdfs:isDefinedBy rdf:resource="http://purl.org/rss/1.0/" />

      This means, roughly, that the relationship we call rss:title (between
      something and its rss:title....) is a specialised case of the more general
      relationship dc:title. Similarly with rss:description and dc:description.
      This means that whenever we see someone claiming that "blah" is the
      rss:title of something, and if we hold them to undersand the meaning of
      rss:title under the rules of RDF, we can hold them to also be claiming
      that the dc:title of that thing is also "blah". Same for dc:description.

      If someone builds a tool for searching Web documents based on their
      dc:title and/or dc:description, the rules associated with RSS 1.0 and RDF
      (and RDF Schema) make it ok for them to use rss:title and rss:description
      data instead of the more general Dublin Core versions. This is good; it
      means the Dublin Core and RSS 1.0 communities can, for the most part, get
      on with their lives without having to worry too much about interop. The fact
      that both communities have bought into RDF means that a certain amount of
      interop is acquired for free. Or for the cost of the syntactic burden of
      RDF in the RSS 1.0 XML syntax, ie. the rdf:RDF and rdf:Seq bits that are
      needed to allow RDF tools to understand an RSS 1.0 feed.

      So to answer Ben's question. Neither as such takes precendence. But we
      should realise that, since dc:title is defined as more general than
      rss:title (the latter is an rdfs:subPropertyOf the former),

      <dc:title>ANOTHER TITLE<dc:title>

      ...in RSS 1.0 should be taken to imply:

      <dc:title>ANOTHER TITLE<dc:title>

      since the rss title of something is always a DC title of it too. This
      constraint helps fix the meaning of RSS title. For example, we
      inherit the work done in the DC world for translating property defintions
      into multiple languages. Unless we care to duplicate that work on RSS-DEV,
      this sort of thing seems to be rather a good deal...


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