Notes by Lex Toumbourou

RDFS or RDF Schema is an extension to the RDF document model that provides the basic structures for describing data structures and inheritance.

Classes and Inheritance

For example, we can declare classes using rdfs:Class type:

@prefix rdfs: <http://www.w3.org/2000/01/rdf-schema#> .
@prefix ex: <http://example.org/> .

ex:DomesticatedMammal rdfs:type rdfs:Class .

We can support inheritance relationships through rdfs:subClassOf type, to create hierarchical taxonomies:

ex:Dog rdfs:subClassOf ex:DomesticatedMammal .
ex:Poodle rdfs:subClassOf ex:Dog .

Therefore, every Dog is also a Domesticated Mammal, and every Poodle is both a Dog and a Domesticated Mammal. You can even subclass from multiple parent classes to create rich, interconnected vocabularies.

Established Vocabularies

RDFS uses prefixes to make URIs more readable and leverages existing ontologies. For example, FOAF (Friend of a Friend) is a well-established ontology for describing social networks and contact details.

@prefix foaf: <http://xmlns.com/foaf/0.1/> .

ex:lex rdfs:type foaf:Person .
ex:lex foaf:name "Lex Toumbourou"
ex:lex foaf:mbox <mailto:lextoumbourou@gmail.com>

Properties and Relationships

Properties in RDFS define the relationship between resources and can serve as predicates in RDF triples. RDFS provides a powerful way to constrain and organise these properties.

Properties can specific their domain (what type of subject they can have) and range (what type of object they can have):

ex:teaches rdfs:type rdf:Property .
ex:teaches rdfs:domain ex:Professor .
ex:teaches rdfs:range ex:Course .

ex:enrolledIn rdfs:type rdf:Property .
ex:enrolledIn rdfs:domain ex:Student .
ex:enrolledIn rdfs:range ex:Course .

Here only Professors can use the teaches property, and they can only teach Courses. Similarly, only Studnets can be enrolledIn something, and they can only be enrolled in Courses.

Properties can support inheritance through rdfs:subPropertyOf:

ex:supervises rdfs:type rdf:Property .
ex:supervises rdfs:subPropertyOf ex:teaches .

This means that if a Professor supervises a student, they also teach that student in a broader sense.