Understanding RDF

[John Cowan]

Paul Prescod wrote:

> I keep thinking I understand RDF and then I look at DCD and think "I
> guess I don't." DCD is supposed to be an RDF vocabulary, right?

Well, sort of.  It is Microsoft RDF, not W3C RDF.  :-)

> So what are the properties of the DCD node? Just ElementDef and
> AttributeDef?
> Am I to understand that these are vector-valued properties?

Multivalued rather than vector (Sequence, in RDF terms) valued.
A property may have more than one value (in current RDF terms,
there may be multiple sentences with a common subject and
predicate), as you'd expect.
 
> People complain about SGML minimization, but RDF abbreviation is much
> more complicated. Perhaps someone can walk me through the expansion of
> A DCD document into completely described nodes and properties.

I'll try.  Here's the example from clause 1.1:

 <DCD>
  <ElementDef Type="Booking" Model="Elements" Content="Closed">
    <Description>Describes an airline reservation</Description>
    <Group RDF:Order="Seq">
      <Element>LastName</Element> <Element>FirstInitial</Element>
      <Element>SeatRow</Element> <Element>SeatLetter</Element>
      <Element>Departure</Element> <Element>Class</Element>
    </Group>
  </ElementDef>

  <!-- example omits boring field declarations -->
  <ElementDef Type="SeatRow" Model="Data" Datatype="i1" Min="1" Max="72" />
  <ElementDef Type="SeatLetter" Model="Data" Datatype="char" Min="A" Max="K"/>
  <ElementDef Type="Class" Model="Data" Datatype="char" Default="1"/>
 </DCD>

And here's my attempt to make unabbreviated correct RDF:

<RDF:RDF xmlns:RDF="http://w3.org/TR/1999/PR-rdf-syntax-19990105#"
	xmlns="http://w3.org/TR/1998/NOTE-dcd-19980731#">
 <RDF:Description>
 <RDF:type resource="http://w3.org/TR/1998/NOTE-dcd-19980731#DCD"/>
  <RDF:li>
   <RDF:Description>
    <RDF:type resource="http://w3.org/TR/1998/NOTE-dcd-19980731#ElementDef"/>
    <Type>Booking"</Type>
    <Model>Elements</Model>
    <Content>Closed</Content>
    <Description>Describes an airline reservation</Description>
    <Group>
     <Element>LastName</Element> <Element>FirstInitial</Element>
     <Element>SeatRow</Element> <Element>SeatLetter</Element>
     <Element>Departure</Element> <Element>Class</Element>
    </Group>
   </RDF:Description>
  </RDF:li>
  <RDF:li>
   <!-- example omits boring field declarations -->
   <RDF:Description>
    <RDF:type resource="http://w3.org/TR/1998/NOTE-dcd-19980731#ElementDef"/>
    <Type>SeatRow</Type>
    <Model>Data</Model>
    <Datatype>i1</Datatype>
    <Min>1</Min>
    <Max>72</Max>
   </RDF:Description>
  </RDF:li>
  <RDF:li>
   <RDF:Description>
    <RDF:type resource="http://w3.org/TR/1998/NOTE-dcd-19980731#ElementDef"/>
    <Type>SeatLetter</Type>
    <Model>Data</Model>
    <Datatype>char</Datatype>
    <Min>A</Min>
    <Max>K</Max>
   </RDF:Description>
  </RDF:li>
  <RDF:li>
   <RDF:Description>
    <RDF:type>http://www.w3.org/namespaces/DCD#ElementDef</RDF:type>
    <Type>Class</Type>
    <Model>Data</Model>
    <Datatype>char</Datatype>
    <Default>1</Default>
   </RDF:Description>
  </RDF:li>
 </RDF:Description>
<RDF:RDF>

-- 
John Cowan	http://www.ccil.org/~cowan		cowan at ccil.org
	You tollerday donsk?  N.  You tolkatiff scowegian?  Nn.
	You spigotty anglease?  Nnn.  You phonio saxo?  Nnnn.
		Clear all so!  'Tis a Jute.... (Finnegans Wake 16.5)

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