Descriptions

An RDF document is a list of descriptions. Each description applies usually to one resource, and contains a list of properties. Property values are either URIs, literals or others Descriptions.

In XML, RDF meta-data are embedded in an element named rdf:RDF. This element contains a sequence of elements named rdf:Description. Those elements can have one of the two attributes rdf:about or rdf:ID (but not both).

• rdf:about is used to describe any resource ; its value is either an absolute or a relative URI.

  <rdf:Description about="http://rama.cpe.fr/index.html">
    ...
  </rdf:Description>
  

• rdf:ID is used to define a resource ; its value is a fragment identifier (without the "#" character) to be added to the XML document URI. A resource may not be defined more than once.

  <rdf:Description ID="foo">
    ...
  </rdf:Description>
  

• a description without rdf:about nor rdf:ID is said to describe an anonymous resource.

  <rdf:Description>
    ...
  </rdf:Description>
  

An element rdf:Description contains a sequence of XML elements. Those elements are interpreted as properties, whose predicate's URI is the expanded name of the element. If the element is empty, it must have an attribute rdf:resource whose value is the object's URI (see $1^{st}$ dc:Creator in fig.3). Else, it can contain plain text (then interpreted as a literal - see dc:Title in fig.3) or a single embedded rdf:Description element (see $2^{nd}$ dc:Creator in fig.3).

Figure 3: XML syntax simple example

<?xml version="1.0" encoding="UTF-8" ?>
<rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
         xmlns:dc="http://purl.org/DC/"
         xmlns:os="http://somesite.org/Schema/">
  <rdf:Description about="http://rama.cpe.fr/index.html">
    <dc:Creator rdf:resource="mailto:am@cpe.fr"/>
    <dc:Title> Index of my web site </dc:Title>
    <dc:Creator>
      <rdf:Description about="mailto:champin@cpe.fr">
        <os:worksWith rdf:resource="mailto:am@cpe.fr"/>
      </rdf:Description>
    </dc:Creator>
  </rdf:Description>
</rdf:RDF>

In case of ambiguity, the attribute rdf:parseType can be used in property elements with "Resource" or "Literal" value. The later can be used when a literal contains XML tags, to prevent their being parsed as a description.

The syntax may also be abbreviated in two ways:

• the description element name may be replaced by any URI. It is interpreted as an additional rdf:type property, valued by the named resource. Note that the context always allows to differ a typed description element from a property element.
• properties with literal values may be written as attributes of the description element rather than an embedded elements.

For example, the following description:

  <rdf:Descritpion ID="fatherOf">
    <rdf:type rdf:resource=
       "http://www.w3.org/1999/02/22-rdf-syntax-ns#Property"/>
    <rdf:label> father of </rdf:label>
    <rdfs:subPropertyOf rdf:resource="#parentOf">
  </rdf:Descritpion>

may be abbreviated into

  <rdf:Property ID="fatherOf" rdfs:label="father of">
    <rdfs:subPropertyOf rdf:resource="#parentOf">
  </rdf:Descritpion>