RDF Schema (Resource Description Framework Schema, variously abbreviated as RDFS, , RDF-S, or RDF/S) is a set of classes with certain properties using the RDF extensible

knowledge representation Knowledge representation and reasoning (KRR, KR&R, KR²) is the field of artificial intelligence (AI) dedicated to representing information about the world in a form that a computer system can use to solve complex tasks such as diagnosing a medic ...

data model, providing basic elements for the description of

ontologies In computer science and information science, an ontology encompasses a representation, formal naming, and definition of the categories, properties, and relations between the concepts, data, and entities that substantiate one, many, or all domains ...

. It uses various forms of RDF vocabularies, intended to structure RDF

resource Resource refers to all the materials available in our environment which are technologically accessible, economically feasible and culturally sustainable and help us to satisfy our needs and wants. Resources can broadly be classified upon thei ...

s. RDF and RDFS can be saved in a

triplestore A triplestore or RDF store is a purpose-built database for the storage and retrieval of triples through semantic queries. A triple is a data entity composed of subject–predicate–object, like "Bob is 35" or "Bob knows Fred". Much like a rel ...

, then one can extract some knowledge from them using a query language, like

SPARQL SPARQL (pronounced " sparkle" , a recursive acronym for SPARQL Protocol and RDF Query Language) is an RDF query language—that is, a semantic query language for databases—able to retrieve and manipulate data stored in Resource Description ...

. The first version was published by the World-Wide Web Consortium (W3C) in April 1998, and the final

W3C recommendation The World Wide Web Consortium (W3C) is the main international standards organization for the World Wide Web. Founded in 1994 and led by Tim Berners-Lee, the consortium is made up of member organizations that maintain full-time staff working t ...

was released in February 2014. Many RDFS components are included in the more expressive

Web Ontology Language The Web Ontology Language (OWL) is a family of knowledge representation languages for authoring ontologies. Ontologies are a formal way to describe taxonomies and classification networks, essentially defining the structure of knowledge for vario ...

(OWL).

Terminology

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

Classes

; : Represents the class of everything. All things described by RDF are resources. ; : An ''rdfs:Class'' declares a resource as a

class Class or The Class may refer to: Common uses not otherwise categorized * Class (biology), a taxonomic rank * Class (knowledge representation), a collection of individuals or objects * Class (philosophy), an analytical concept used differently ...

for other resources. A typical example of an rdfs:Class is in the Friend of a Friend (

FOAF FOAF (an acronym of friend of a friend) is a machine-readable ontology describing persons, their activities and their relations to other people and objects. Anyone can use FOAF to describe themselves. FOAF allows groups of people to describe s ...

) vocabulary. An instance of is a resource that is linked to the class using the

property Property is a system of rights that gives people legal control of valuable things, and also refers to the valuable things themselves. Depending on the nature of the property, an owner of property may have the right to consume, alter, share, r ...

, 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 is recursive: 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: ; : literal values such as strings and integers. Property values such as textual strings are examples of RDF literals. Literals may be plain or typed. ; : the class of datatypes. is both an instance of and a subclass of . Each instance of is a subclass of . ; : the class of XML literal values. is an instance of (and thus a subclass of ). ; : the class of properties.

Properties

Properties are instances of the class and describe a relation between subject resources and object resources. When used as such a property is a

predicate Predicate or predication may refer to: * Predicate (grammar), in linguistics * Predication (philosophy) * several closely related uses in mathematics and formal logic: **Predicate (mathematical logic) **Propositional function **Finitary relation, o ...

(see also RDF: reification). ; : the ''rdfs:domain'' of an declares the class of the ''subject'' in a

triple Triple is used in several contexts to mean "threefold" or a " treble": Sports * Triple (baseball), a three-base hit * A basketball three-point field goal * A figure skating jump with three rotations * In bowling terms, three strikes in a row * ...

whose predicate is that property. ; : the ''rdfs:range'' of an 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 relates a subject, which is of type , to an object, which is of type :

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 is a , and is a . ; : a property used to state that a resource is an instance of a class. A commonly accepted

QName A QName, or qualified name, is the fully qualified name of an element, attribute, or identifier in an XML document. A QName concisely associates the URI of an XML namespace with the ''local name'' of an element, attribute, or identifier in that na ...

for this property is "a". ; : 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. ; : an instance of that is used to state that all resources related by one property are also related by another. ; : an instance of that may be used to provide a human-readable version of a resource's name. ; : an instance of that may be used to provide a human-readable description of a resource.

Utility properties

; : an instance of that is used to indicate a resource that might provide additional information about the subject resource. ; : an instance of 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

entailment Logical consequence (also entailment) is a fundamental concept in logic, which describes the relationship between statements that hold true when one statement logically ''follows from'' one or more statements. A valid logical argument is one ...

regime defines, by using RDFS (or 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 relation in the semantic web. For example, the following declares that 'Dog1 is an animal', 'Cat1 is a cat', 'zoos host animals' and 'Zoo1 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

The graph is not well-formed because the system can not guess that a cat is an animal. To make a well-formed graph, the statement 'Cats are animals' can be added:

ex:cat		rdfs:subClassOf		ex:animal

Here is a correct example: If the

(or RDF database) implements the regime

of RDF and RDFS, the

query as follows (the keyword "a" is equivalent to rdf:type in SPARQL): PREFIX ex: SELECT ?animal WHERE The following gives the result with ''cat1'' in it, because the Cat's type inherits of Animal's type:

Examples of RDF vocabularies

RDF vocabularies represented in RDFS include: *

: the source of the FOAF Vocabulary Specification is RDFS written in the RDFa syntax. *

Dublin Core 220px, Logo image of DCMI, which formulates Dublin Core The Dublin Core, also known as the Dublin Core Metadata Element Set (DCMES), is a set of fifteen "core" elements (properties) for describing resources. This fifteen-element Dublin Core has ...

: RDFS source is available in several syntaxes *

Schema.org Schema.org is a reference website that publishes documentation and guidelines for using structured data mark-up on web-pages (called microdata). Its main objective is to standardize HTML tags to be used by webmasters for creating rich results (di ...

: the source of their schema was originally RDFS written in the RDFa syntax until July 2020. * Simple Knowledge Organization System (SKOS) developed the RDF schema titled as SKOS XL Vocabulary, which is an OWL ontology for the SKOS vocabulary that uses the OWL RDF/XML syntax, and hence makes use of a number of classes and properties from RDFS. * The

Library of Congress The Library of Congress (LOC) is the research library that officially serves the United States Congress and is the ''de facto'' national library of the United States. It is the oldest federal cultural institution in the country. The libra ...

defines an RDF schema titled Metadata Authority Description Schema in RDF, or MADS/RDF for short. From the abstract, it is intended to use for within their library and "information science (LIS) community". It allows for annotating special relational data, such as if an individual within a family is well-known via . * The

UniProt UniProt is a freely accessible database of protein sequence and functional information, many entries being derived from genome sequencing projects. It contains a large amount of information about the biological function of proteins derived from ...

database has an RDF schema for describing

biochemical Biochemistry or biological chemistry is the study of chemical processes within and relating to living organisms. A sub-discipline of both chemistry and biology, biochemistry may be divided into three fields: structural biology, enzymology an ...

data, and is specialized towards describing

proteins Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, respo ...

References

External links

W3C RDFS Specification

W3C RDF 1.1 Primer

W3C SPARQL 1.1 Entailment Regimes Specification

W3C RDFS Entailment

Map OWL-RDF/S ontologies and XML Schemas. Transform XML Schema to OWL. {{DEFAULTSORT:Rdf Schema Resource Description Framework Knowledge representation languages Semantic Web World Wide Web Consortium standards