View text source at Wikipedia
| Resource Description Framework Schema | |
| Abbreviation | RDFS |
|---|---|
| Status | W3C Recommendation |
| Year started | January 5, 1999[1][2] |
| First published | April 30, 2002[2] |
| Latest version | 1.1 (Recommendation) February 25, 2014[3] |
| Organization | |
| Editors |
|
| Base standards | RDF |
| Related standards | |
| Domain | |
| Website | www |
RDF Schema (Resource Description Framework 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 data model, providing basic elements for the description of ontologies. It uses various forms of RDF vocabularies, intended to structure RDF resources. RDF and RDFS can be saved in a triplestore, then one can extract some knowledge from them using a query language, like SPARQL.
The first version[1][4] was published by the World-Wide Web Consortium (W3C) in April 1998, and the final W3C recommendation was released in February 2014.[3] Many RDFS components are included in the more expressive Web Ontology Language (OWL).
RDFS constructs are the RDFS classes, associated properties and utility properties built on the vocabulary of RDF.[5][6][7]
rdfs:Resourcerdfs:ClassA typical example of an rdfs:Class is foaf:Person in the Friend of a Friend (FOAF) vocabulary.[8] 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 class of classes, and so it is an instance of itself.
rdfs:Class rdf:type rdfs:Class
The other classes described by the RDF and RDFS specifications are:
rdfs:Literalrdfs:Datatyperdfs:Datatype is both an instance of and a subclass of rdfs:Class. Each instance of rdfs:Datatype is a subclass of rdfs:Literal.rdf:XMLLiteralrdf:XMLLiteral is an instance of rdfs:Datatype (and thus a subclass of rdfs:Literal).rdf:PropertyProperties 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).
rdfs:domainrdf:Property declares the class of the subject in a triple whose predicate is that property.rdfs:rangerdf:Property declares the class or datatype of the object in a triple whose predicate is that property.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, from the triple:
ex:John ex:employer ex:CompanyX
can be inferred (resp. follows) that ex:John is a foaf:Person, and ex:CompanyX is a foaf:Organization.
rdf:typerdfs:subClassOfFor 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 the next section) from a class to its subclasses.
rdfs:subPropertyOfrdf:Property that is used to state that all resources related by one property are also related by another.rdfs:labelrdf:Property that may be used to provide a human-readable version of a resource's name.rdfs:commentrdf:Property that may be used to provide a human-readable description of a resource.rdfs:seeAlsordf:Property that is used to indicate a resource that might provide additional information about the subject resource.rdfs:isDefinedByrdf:Property that is used to indicate a resource defining the subject resource. This property may be used to indicate an RDF vocabulary in which a resource is described.An entailment regime defines whether the triples in a graph are logically contradictory or not. RDFS entailment [11]is not very restrictive, i.e. it does not contain a large amount of rules (compared, for example, to OWL) limiting what kind of statements are valid in the graph. On the other hand it is also not very expressive, meaning that the semantics that can be represented in a machine-interpretable way with the graph is quite limited.
Below in a simple example of the capabilities and limits of RDFS entailment, we start with a graph containing the following explicit triples:
foo:SomeGiraffe rdf:type bar:Animal. foo:SomeElephant rdf:type bar:Elephant. foo:SomeZoo rdf:type bar:Zoo. bar:livesInZoo rdfs:domain bar:Animal. bar:livesInZoo rdfs:range bar:Zoo. foo:SomeElephant bar:livesInZoo foo:SomeZoo.
Without enabling inferencing with RDFS entailment, the data we have does not tell us whether foo:SomeElephant is a bar:Animal. When we do RDFS-based inferencing, we will get the following extra triple:
foo:SomeElephant rdf:type bar:Animal.
The rdfs:domain statement dictates that any subject in triples where bar:livesInZoo is the predicate is of type bar:Animal. What RDFS entailment is not able to tell us is the relationship between bar:Animal and bar:Elephant. Due to inferencing we now know that foo:SomeElephant is both bar:Animal and bar:Elephant so these classes do intersect but there is no information to deduce whether they merely intersect, are equal or have a subclass relationship.
In RDFS 1.1, the domain and range statements do not carry any formal meaning and their interpretation is left up to the implementer. On the other hand in the 1.2 Working draft they are used as entailment rules for inferencing the types of individuals. Nevertheless in both versions, it is very clearly stated that the expected functionality of range is "the values of a property are instances of one or more classes" and domain "any resource that has a given property is an instance of one or more classes".
The example above demonstrated some of the limits and capabilities of RDFS entailment, but did not show an example of a logical inconsistency (which could in layman terms be interpreted as a "validation error"), meaning that the statements the triples make are in conflict and try to express contradictory states of affairs. An example of this in RDFS would be having conflicting datatypes for objects (e.g. declaring a resource to be of type xsd:integer and being also declared to be xsd:boolean when inferencing is enabled).
RDF vocabularies represented in RDFS include:[10]
madsrdf:prominentFamilyMember.[16]{{cite web}}: Missing or empty |title= (help)