What is RDF

• A language for representing propositional information (classification facts and property facts) on the Web.
• A lightweight ontology system to support the exchange of knowledge on the Web
• RDF is the basis of the Semantic Web.

The RDF Jargon

• Entities/things are called "resources"
• Properties are special resources
• Property facts are called "subject-predicate-object triples":

For example, foaf:name( http://www.informatik.tu-cottbus.de/~agiurca, Giurca) is represented as the triple

http://www.informatik.tu-cottbus.de/~agiurca foaf:name "Giurca"^^xs:string

where

the subject is http://www.informatik.tu-cottbus.de/~agiurca

the predicate is http://xmlns.com/foaf/0.1/name

the object is the typed literal "Giurca"^^xs:string

A set (conjunction) of property facts is called a graph, because such a set can be visualized as a graph.

RDF Terms

URI References as Individual Names

RDF uses URI References as globally unique names for resources Examples: btu-teachers:AG = "http://www.BTU.de/teachers#AG"

rdf:type = "http://www.w3.org/1999/02/22-rdf-syntax-ns#type"

Plain Literals

Typed Literals

Blank Nodes

An RDF Graph

Expressing Facts

Data-Valued Property Facts

The data-valued property fact course:modNo( SemWeb, "12-4-39") is expressed in RDF/XML as

<rdf:Description rdf:about="course:SemWeb">
  <course:modNo>12-4-39</course:modNo>
</rdf:Description>

Object-Valued Property Facts

The object-valued property fact course:teacher( sem:SemWeb, btu-teachers:AG) is expressed in RDF/XML as

<rdf:Description rdf:about="sem:SemWeb">
  <course:teacher rdf:resource="btu-teachers:AG"/>
</rdf:Description>

Classification Facts

Classification facts, such as uni:Seminar(sem:SemWeb), are expressed in the form of special property facts using the pre-defined property rdf:type:

<rdf:Description rdf:ID="sem:SemWeb">
  <rdf:type rdf:resource="uni:Seminar"/>
</rdf:Description>

Or, equivalently (short syntax), using the class name as XML element name:

<uni:Seminar rdf:ID="sem:SemWeb"/>

Several facts about the same object/resource

The following facts (conjunction)

uni:Seminar(sem:SemWeb) ∧ course:teacher( sem:SemWeb, btu-teachers:AG) ∧ course:modNo( sem:SemWeb, "12-4-39")

can be aggregated in an object description fact:

<uni:Seminar rdf:ID="sem:SemWeb">
  <course:modNo>12-4-39</course:modNo>
  <course:teacher rdf:resource="btu-teachers:AG"/>
</uni:Seminar>

An RDF Graph as a set of sentences

RDF Graph without blank nodes is

• Set of variable-free triples
• Conjunction of property facts

RDF Graph with blank nodes is:

• Set of triples
• Existentially quantified conjunction of property atoms

The following graph

corresponds to the logical formula

∃ x ( foaf:topic(webTech:RDF_Tutorial, webTech:Category:Semantic Web) ∧ dc:creator(webTech:RDF_Tutorial, x)∧ foaf:homePage( x, btu-teachers:AG) ∧ foaf:name( x, "Adrian Giurca") )

What is the triple representation of this ?

<rdf:Description rdf:about="http://hydrogen.informatik.tu-cottbus.de/wiki/index.php/RDF_Tutorial"> 
 <foaf:topic rdf:resource="http://hydrogen.informatik.tu-cottbus.de/wiki/index.php/Category:Semantic_Web"/>
 <dc:creator> 
   <foaf:Person>
      <foaf:homePage rdf:resource="btu-teachers:AG" /> 
      <foaf:name>Adrian Giurca</foaf:name> 
   </rdf:Person> 
 </dc:creator> 
</rdf:Description>

Answer:

// to be completed