| Current Status | Published |
|---|---|
| Year Started | 1998 |
| Editors | Dan Brickley, Ramanathan V. Guha |
| Base Standards | RDF |
| Related Standards | OWL |
| Domain | Semantic Web |
| Abbreviation | RDFS |
| Website | RDF Schema |
RDF Schema (variously abbreviated as RDFS, RDF(S), RDF-S, or RDF/S) is a set of classes with certain properties using the RDF extensible knowledge representation language, providing basic elements for the description of ontologies, otherwise called RDF vocabularies, intended to structure RDF resources. These structured elements with RDFS in a triplestore, you can use the query language SPARQL to reach them.
The first version[1] was published by the World-Wide Web Consortium (W3C) in April 1998, and the final[2] W3C recommendation was released in February 2004. Many RDFS components are included in the more expressive language Web Ontology Language (OWL).
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RDFS constructs are the RDFS classes, associated properties and utility properties built on the limited vocabulary of RDF.
A typical example of an rdfs:Class is foaf:Person in the Friend of a Friend (FOAF) vocabulary. An instance of foaf:Person is a resource that is linked to the class foaf:Person using the rdf:type property, such as in the following formal expression of the natural language sentence : 'John is a Person'.
ex:John rdf:type foaf:Person
The definition of rdfs:Class is recursive: rdfs:Class is the rdfs:Class of any rdfs:Class.
The other classes described by the RDF and RDFS specifications are:
Properties are instances of the class rdf:Property and describe a relation between subject resources and object resources. When used as such a property is a predicate (see also RDF: reification).
For example, the following declarations are used to express that the property ex:employer relates a subject, which is of type foaf:Person, to an object, which is of type foaf:Organization:
ex:employer rdfs:domain foaf:Person
ex:employer rdfs:range foaf:Organization
Given the previous two declarations, the following triple requires that ex:John is necessarily a foaf:Person, and ex:CompanyX is necessarily a foaf:Organization:
ex:John ex:employer ex:CompanyX
For example, the following declares that 'Every Person is an Agent':
foaf:Person rdfs:subClassOf foaf:Agent
Hierarchies of classes support inheritance of a property domain and range (see definitions in next section) from a class to its subclasses.
An entailment regime defines by RDFs (,OWL, etc.) not only which entailment relation is used, but also which queries and graphs are well-formed for the regime. The RDFS entailment is a standard entailment relations in the semantic web.
For example, the following declares that 'Dog is an animal','Cat1 is a cat', 'Zoos host animals' and 'Zoo hosts the Cat2' :
ex:dog1 rdf:type ex:animal ex:cat1 rdf:type ex:cat zoo:host rdfs:range ex:animal ex:zoo1 zoo:host ex:cat2
But this graph is not well formed because the system can not guess that a cat is an animal. We have to add 'Cats are animals' to do a well-formed graph with :
ex:cat rdfs:subClassOf ex:animal
Voila, the correct example:
| In english | The graph |
|---|---|
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| En RDF/turtle | |
@prefix rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#> . @prefix rdfs: <http://www.w3.org/2000/01/rdf-schema#> . @prefix ex: <http://example.org/> . @prefix zoo: <http://example.org/zoo/> . ex:dog1 rdf:type ex:animal . ex:cat1 rdf:type ex:cat . ex:cat rdfs:subClassOf ex:animal . zoo:host rdfs:range ex:animal . ex:zoo1 zoo:host ex:cat2 . |
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If your triplestore (or RDF database) implements the regime entailment of RDF and RDFS, the SPARQL query as follows (the keyword "a" is equivalent to rdf:type in SPARQL):
PREFIX ex: <http://example.org/> SELECT ?animal WHERE { ?x a ex:animal . }
Give the following result with cat2 because the Cat's type inherits of Animal's type:
| animal |
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| <http://example.org/dog1> |
| <http://example.org/cat1> |
| <http://example.org/cat2> |
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