science

RDF Schema

RDF Schema is a science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand RDF Schema rather than just read about it. In short: 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.

Key takeaways

RDF Schema belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect RDF Schema to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of RDF Schema from memory before moving on to harder problems.

Reference excerpt

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 was published by the World-Wide Web Consortium (W3C) in April 1998, and the final W3C recommendation was released in February 2014. Many RDFS components are included in the more expressive Web Ontology Language (OWL).

Terminology RDFS constructs are the RDFS classes, associated properties and utility properties built on the vocabulary of RDF.

Classes rdfs:Resource Represents the class of everything. All things described by RDF are resources. rdfs:Class An rdfs:Class declares a resource as a class for other resources. 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 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:Literal literal values such as strings and integers. Property values such as textual strings are examples of RDF literals. Literals may be plain or typed. rdfs:Datatype the class of datatypes. rdfs:Datatype is both an instance of and a subclass of rdfs:Class. Each instance of rdfs:Datatype is a subclass of rdfs:Literal. rdf:XMLLiteral the class of XML literal values. rdf:XMLLiteral is an instance of rdfs:Datatype (and thus a subclass of rdfs:Literal). rdf:Property the class of properties.

Properties 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).

rdfs:domain the rdfs:domain of an rdf:Property declares the class of the subject in a triple whose predicate is that property. rdfs:range the rdfs:range of an rdf: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:type a property used to state that a resource is an instance of a class. A commonly accepted QName for this property is "a". rdfs:subClassOf allows declaration of hierarchies of classes. 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 the next section) from a class to its subclasses.

rdfs:subPropertyOf an instance of rdf:Property that is used to state that all resources related by one property are also related by another. rdfs:label an instance of rdf:Property that may be used to provide a human-readable version of a resource's name. rdfs:comment an instance of rdf:Property that may be used to provide a human-readable description of a resource.

Utility properties rdfs:seeAlso an instance of rdf:Property that is used to indicate a resource that might provide additional information about the subject resource. rdfs:isDefinedBy an instance of rdf: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.

RDFS entailment An entailment regime defines whether the triples in a graph are logically contradictory or not. RDFS entailment 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.

… excerpt ends here. Continue reading the full article.

Worked examples

Example 1 — a first encounter with RDF Schema

Start with the simplest possible case. Write down what RDF Schema claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to RDF Schema before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about RDF Schema ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of RDF Schema

In research: RDF Schema appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses RDF Schema in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: RDF Schema is common in secondary-school and first-year university syllabi. It links to neighbouring topics Knowledge representation languages, Resource Description Framework, Semantic Web, so understanding it makes those chapters shorter.
In everyday life: Look for RDF Schema outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study RDF Schema in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what RDF Schema means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain RDF Schema out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is RDF Schema in simple terms?

Why does RDF Schema matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study RDF Schema?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on RDF Schema.