Glossary

From RDF Data Shapes Working Group
Jump to: navigation, search

RDF graph, and other RDF terminology

See RDF 1.1 Concepts and Abstract Syntax for definitions of various terminology related to RDF graphs, including "RDF graph", "subject", "predicate", "object", "node", "RDF term", "IRI", "blank node", "literal", "resource", and "statement". This terminology is formally defined in either RDF 1.1 Concepts and Abstract Syntax or RDF 1.1 Semantics.

RDF graphs may be accessible via one or more URLs by dereferencing the URL and parsing the resultant document.

Closed Shape

A Shape that is satisfied only if there no other remaining triples than the ones specified by it in the RDF Node.

For example, a closed shape that declares that a node must have a "rdfs:label" property with a literal value of type "xsd:string" would be satisfied by node :luke below but would not be satisfied by node :darth.

:luke rdfs:label "Luke" .
:darth rdfs:label "Darth", foaf:age 23 .

Constraint

A constraint is a component of a schema that says what needs to be satisfied. It may or may not include a scope (see below).

Constraint Condition/ShEx Rule

A component of a constraint that carries a condition that needs to be evaluated as part of validation, e.g., a ShEx rule, or an OWL description, or clause in a SPIN SPARQL query.

Example: At least one name and all names are strings

Example: At least one name that is a string

Example: Between two and four children who are married

Decoration

Additional information associated with a constraint, e.g, SPIN CONSTRUCT constructs or annotations on OWL axioms. This information may for example provide severity or other information about constraint violations.

Example: This is the person name constraint

Example: Violations produce a warning for person name constraint violation

Example: Return violating object and any of its names that are not strings

Document

A container for a sequence of Unicode characters available, which may or not be the accessible via URL dereferencing.

Entailment

An RDF triple is said to be entailed by a set of RDF triples if it is a consequence of the semantics of that set of triples. The meaning of consequence is defined by specifications such as RDF, RDFS, OWL, and RIF. These specifications define entailment relations between sets of triples, i.e. each entailment relation defines how a given set of triples entails another set of triples.

Example: Consider the following triples:

ex:Luke ex:hasFather ex:Darth .
ex:hasFather rdfs:range ex:Male .

Then this triple is entailed:

ex:Darth rdf:type ex:Male .

Here the entailment relation used is defined by the semantics of RDFS.

Entailment Regime

The term entailment regime is used in RDF 1.1 Semantics and SPARQL 1.1 Entailment Regimes. The SPARQL specification provides this definition of entailment regime:

An entailment regime defines not only which entailment relation is used, but also which queries and graphs are well-formed for the regime, how the entailment is used (since there are potentially different meaningful ways to use the same entailment relation), and what kinds of errors can arise.

The SPARQL specification defines URIs to identify several important entailment regimes, e.g. http://www.w3.org/ns/entailment/RDFS identifies the RDFS entailment regime.

A SPARQL endpoint may advertise the entailment regime is uses by providing a service description document, see SPARQL 1.1 Service Description.

Inferencing

'Inferencing' is the process of applying an entailment relation to an input set of triples to compute an output set of entailed triples. Software components that perform inferencing are also referred to as reasoners.

Ontology

Something that provides information about classes and properties. RDF graphs containing RDFS properties like rdfs:subClassOf can be considered to be ontologies. OWL documents containing class and property axioms are ontologies. It should be possible to transform the ontology into an RDF graph in a standard way. Ontologies may be accessible via one or more URLs, but it may require more than URL dereferencing and parsing of the resultant document into an ontology, for example importing may have to be performed.

Open Shape

A Shape that is satisfied even if there are other remaining triples than the ones specified by it in the RDF Node.

For example, an open shape that declares that a node must have a "rdfs:label" property with a literal value of type "xsd:string", would be satisfied if the node contained another triple with property "foaf:age" and any other value.

RDF node shape

An RDF node shape is a set of constraints over the triples that involve a given RDF node.

For example, an RDF node shape can be that one RDF node can have a "rdfs:label" property with a literal value of type "xsd:string" and a "foaf:age" property with a value of type "xsd:integer"

Recognition Constraint

A constraint that introduces vocabulary, e.g., a labeled ShEx expression or an OWL axiom defining a new class.

Example: Named things are those things that have at least one name and all their names are strings

Example: Named people are those people that have at least one known name that is a string.

Recursive Recognition Constraints

A recognition constraint that refers to itself, either directly or indirectly.

Example: Nicely named things are those things that have at least one name and all their parts are nicely named things

Example: Uniquely named things are those things that have at least one name and some of their parts are not uniquely named things

Shape

A Shape is a constraint or set of constraints over RDF graphs.

Shapes can also be considered Unscoped constraints.

Schema

Something that provides a set of constraints that can be applied to a target, e.g., a SPIN document, a ShEx document, or an ontology. It should be possible to transform the schema into an RDF graph in a standard way. Schemas may be accessible via one or more URLs, but it may require more than URL dereferencing and parsing of the resultant document into a schema, for example importing may have to be performed.

A document can contain both an ontology and a schema, but documents might also contain only an ontology or only a schema.

Scoped Constraint

A constraint that indicates where it is to be satisfied on an RDF graph, e.g., a SPIN constraint (with both subject and object) or an OWL axiom.

Example: Every person has at least one name that is a string. Here the scope is instances of person.

Example: Every person without a social security number has nobody that they are a dependent of who is a US citizen. Here the scope is instances of person who do not have social security numbers.

Unscoped Constraint/Shape

A constraint that cannot be validated against an RDF graph without some extra information on where it is to be satisfied, e.g., a labelled ShEx shape expression or SPIN ask or OWL description.

Example: Named things are those things that have at least one name and all their names are strings

Example: Things with at least one name that is a string

Example: Things with between two and four children who are married.

Validation

The process of taking a schema and an RDF graph (or several RDF graphs or an RDF dataset) and maybe some other information, such as an ontology or some scoping information, and at least determining whether the RDF graph (or ...) satisfies (does not violate) the schema. Validation may produce more than just a boolean result if the constraints of the schema have decorations.