Abstract
The Resource Description Framework (RDF) is a language for
representing information about resources in the World Wide Web. RDF
Schema provides a data-modelling vocabulary for RDF data. RDF Schema
is an extension of the basic RDF vocabulary.
Status of This Document
This section describes the status of this document at the time of its publication.
Other documents may supersede this document. A list of current W3C publications and the
latest revision of this technical report can be found in the W3C technical reports index at
http://www.w3.org/TR/.
This document is an edited version of the 2004 RDF
Schema Recommendation. The purpose of this revision is to make this
document available as part of the RDF 1.1 document set. Changes are
limited to errata, revised references, terminology updates, and adaptations to
the introduction. The title of the document was changed from "RDF
Vocabulary Description Language 1.0: RDF Schema" to "RDF Schema 1.1".
The technical content of the document is unchanged. Details of the changes
are listed in the Changes section.
Since the edits to this document do not constitute a technical
change the Director decided no new implementation report was required.
This document was published by the RDF Working Group
as a Proposed Edited Recommendation. This document is
intended to become a W3C Recommendation.
The W3C
Membership and other interested parties are invited to review
the document and send comments to
public-rdf-comments@w3.org
(subscribe,
archives)
through 09 February 2014. Advisory Committee Representatives should consult their
WBS questionnaires.
All comments are welcome.
Publication as a Proposed Edited Recommendation does not
imply endorsement by the W3C
Membership. This is a draft document and may be updated, replaced or obsoleted by other
documents at any time. It is inappropriate to cite this document as other than work in
progress.
This document was produced by a group operating under the
5 February 2004 W3C Patent
Policy.
W3C maintains a public list of any patent
disclosures
made in connection with the deliverables of the group; that page also includes
instructions for disclosing a patent. An individual who has actual knowledge of a patent
which the individual believes contains
Essential
Claim(s) must disclose the information in accordance with
section
6 of the W3C Patent Policy.
1. Introduction
The Resource Description Framework (RDF) is a general-purpose language
for
representing information in the Web.
RDF Schema provides a data-modelling vocabulary for RDF data.
It is complemented by several companion documents which
describe the basic concepts and abstract stntax of RDF
[RDF11-CONCEPTS], the formal semantics of RDF [RDF11-MT], and
various concrete syntaxes for RDF, such as Turtle [TURTLE],
TriG, [TRIG], and JSON-LD [JSON-LD]. The RDF Primer
[RDF11-PRIMER] provides an informal introduction and
examples of the use of the concepts specified in this document.
This document is intended to provide a clear specification of RDF
Schema to those who find the formal semantics
specification [RDF11-MT]
daunting. Thus, this document duplicates material also specified in the
RDF
Semantics specification. Where there is disagreement between this
document
and the RDF Semantics specification, the RDF Semantics specification
should
be taken to be correct.
RDF Schema is a semantic
extension of RDF. It provides mechanisms for describing groups of
related resources and the relationships between these resources. RDF
Schema is written in RDF
using the terms described in this document. These resources are used to
determine characteristics of other resources, such as the domains
and ranges of properties.
The RDF Schema class and property system is similar to the type
systems of object-oriented programming languages such as Java. RDF
Schema differs from many such systems in that instead of defining a
class in
terms of the properties its instances may have, RDF Schema
describes properties in terms of the classes of
resource to which they apply. This is the role of the domain
and range
mechanisms described in this specification. For example, we could
define the eg:author property to have a domain of eg:Document
and a range of
eg:Person, whereas a classical object oriented system might
typically define a class eg:Book with an attribute called
eg:author of type eg:Person. Using the RDF
approach, it is easy for others to subsequently define additional
properties with a domain of eg:Document or a range of
eg:Person. This can be done without the need to re-define
the original description of
these classes. One benefit of the RDF property-centric approach is that
it
allows anyone to extend the description of existing resources, one of
the
architectural principles of the Web [BERNERS-LEE98].
This specification does not attempt to enumerate all the possible forms
of
representing the meaning of RDF
classes and properties. Instead, the RDF Schema strategy is
to acknowledge that there are many techniques through which the meaning
of
classes and properties can be described. Richer vocabulary or 'ontology'
languages such as OWL [OWL2-OVERVIEW], inference rule
languages and other formalisms (for example temporal logics) will each
contribute to our ability to capture meaningful generalizations about
data in
the Web.
The language defined in this specification consists of a collection of
RDF resources that can be used to describe other RDF resources in
application-specific RDF vocabularies. The core vocabulary is defined in
a namespace informally called rdfs here. That namespace is
identified by the IRI
http://www.w3.org/2000/01/rdf-schema#
and is conventionally associated with the prefix rdfs:. This
specification also uses the prefix
rdf: to refer to the RDF namespace
http://www.w3.org/1999/02/22-rdf-syntax-ns#
For convenience and readability, this specification uses an abbreviated
form to represent IRIs. A name of the form prefix:suffix should be
interpreted as a IRI consisting of the IRI associated
with the prefix concatenated with the suffix.
2. Classes
Resources may be divided into groups called classes. The members of a
class are known as instances of the class. Classes are
themselves
resources. They are often identified by IRIs
and
may be described using RDF properties. The rdf:type
property may be used to state that a
resource is an instance of a class.
RDF distinguishes between a class and the set of its instances.
Associated
with each class is a set, called the class extension of the class, which
is
the set of the instances of the class. Two classes may have the same set
of
instances but be different classes. For example, the tax office may
define
the class of people living at the same address as the editor of this
document. The Post Office may define the class of people whose address
has
the same zip code as the address of the author. It is possible for these
classes to have exactly the same instances, yet to have different
properties.
Only one of the classes has the property that it was defined by the tax
office, and only the other has the property that it was defined by the
Post
Office.
A class may be a member of its own class extension and may be an
instance of itself.
The group of resources that are RDF Schema classes is itself a class
called rdfs:Class.
If a class C is a subclass of a class C', then all instances
of C will
also be instances of C'. The rdfs:subClassOf
property may be used to state that one class is a subclass of another.
The term super-class is used as the inverse of subclass. If a class C'
is a super-class of a class C, then all instances of C are also
instances of C'.
The RDF Concepts and Abstract Syntax [RDF11-CONCEPTS] specification
defines the RDF concept of an RDF
datatype. All datatypes are classes. The instances of a class that
is a
datatype are the members of the value space of the datatype.
2.1 rdfs:Resource
All things described by RDF are called resources, and are
instances of the class rdfs:Resource. This is the class
of
everything. All other classes are subclasses
of
this class. rdfs:Resource is an instance of rdfs:Class.
2.2 rdfs:Class
This is the class of resources that are RDF classes.
rdfs:Class is an instance of rdfs:Class.
2.3 rdfs:Literal
The class rdfs:Literal is the class of literal
values such as strings and integers. Property values such as textual
strings are examples of RDF literals.
rdfs:Literal is an instance of rdfs:Class.
rdfs:Literal is a subclass of rdfs:Resource.
2.4 rdfs:Datatype
rdfs:Datatype is the class of datatypes. All instances
of
rdfs:Datatype correspond to the RDF
model
of a datatype described in the RDF Concepts specification
[RDF11-CONCEPTS].
rdfs:Datatype is
both an instance of and a subclass of rdfs:Class. Each instance of rdfs:Datatype
is a subclass of rdfs:Literal.
2.8 rdf:Property
rdf:Property is the class of RDF properties.
rdf:Property is an instance of rdfs:Class.
3. Properties
The RDF Concepts and Abstract Syntax specification [RDF11-CONCEPTS]
describes the concept of an RDF property as a relation between subject
resources and object resources.
This specification defines the concept of subproperty. The rdfs:subPropertyOf
property may be used to state that one property is a subproperty of
another.
If a property P is a subproperty of property P', then all pairs of
resources which are related by P are also related by P'. The term
super-property is often
used as the inverse of subproperty. If a property P' is a super-property
of a property P, then all pairs of resources which are related by P are
also related by P'. This specification does not define a top
property that is the super-property of all properties.
Note
The basic facilities provided by rdfs:domain
and rdfs:range do not provide any
direct way to indicate property restrictions that are local to a class.
Although it is possible to combine use rdfs:domain
and rdfs:range with sub-property
hierarchies, direct support for such declarations are provided by richer
Web Ontology languages such as OWL [OWL2-OVERVIEW].
3.1 rdfs:range
rdfs:range is an instance of rdf:Property
that is used to state that
the values of a property are instances of one or more classes.
The triple
P rdfs:range C
states that P is an instance of the class rdf:Property,
that C is an instance of the class rdfs:Class
and that the resources denoted by the objects of triples whose
predicate is P are instances of the class C.
Where P has more than one rdfs:range property, then the resources
denoted by the objects of triples with predicate P are instances of
all the classes stated by the rdfs:range properties.
The rdfs:range property can be applied to itself. The
rdfs:range of rdfs:range is the class rdfs:Class.
This states that any resource
that is the value of an rdfs:range property is an
instance of rdfs:Class.
The rdfs:range property is applied to properties. This
can be represented in RDF using the rdfs:domain
property. The rdfs:domain of rdfs:range
is
the class rdf:Property. This
states
that any resource with an rdfs:range property is an
instance of
rdf:Property.
3.2 rdfs:domain
rdfs:domain is an instance of rdf:Property
that is used to state that
any resource that has a given property is an instance of one or more
classes.
A triple of the form:
P rdfs:domain C
states that P is an instance of the class rdf:Property,
that C is a instance of the class rdfs:Class
and that the resources denoted by the subjects of triples whose
predicate is P are instances of the class C.
Where a property P has more than one rdfs:domain property, then the
resources denoted by subjects of triples with predicate P are
instances of all the classes stated by the rdfs:domain
properties.
The rdfs:domain property may be applied to itself. The
rdfs:domain of rdfs:domain is the class rdf:Property.
This states that any
resource with an rdfs:domain property is an instance of
rdf:Property.
The rdfs:range of
rdfs:domain is the class rdfs:Class.
This states that any resource that is the value of an rdfs:domain
property is an
instance of rdfs:Class.
3.4 rdfs:subClassOf
The property rdfs:subClassOf is an instance of rdf:Property that is used to state
that all the instances of one class are instances of another.
A triple of the form:
C1 rdfs:subClassOf C2
states that C1 is an instance of rdfs:Class,
C2 is an instance of rdfs:Class
and C1 is a subclass of C2. The rdfs:subClassOf
property is transitive.
The rdfs:domain of
rdfs:subClassOf is rdfs:Class.
The rdfs:range of rdfs:subClassOf
is rdfs:Class.
3.5 rdfs:subPropertyOf
The property rdfs:subPropertyOf is an instance of rdf:Property that is used to state
that all resources related by one property are also related by
another.
A triple of the form:
P1 rdfs:subPropertyOf P2
states that P1 is an instance of rdf:Property,
P2 is an instance of rdf:Property
and P1 is a subproperty of P2. The
rdfs:subPropertyOf property is transitive.
The rdfs:domain of
rdfs:subPropertyOf is rdf:Property.
The rdfs:range of
rdfs:subPropertyOf is rdf:Property.
3.6 rdfs:label
rdfs:label is an instance of rdf:Property
that may be used to provide a human-readable version of a resource's
name.
A triple of the form:
R rdfs:label L
states that L is a human readable label for R.
The rdfs:domain of
rdfs:label is rdfs:Resource.
The rdfs:range of rdfs:label is
rdfs:Literal.
Multilingual labels are supported using the language
tagging facility of RDF literals.
4. Using the Domain and Range vocabulary
This section is non-normative.
This specification introduces an RDF vocabulary for describing the
meaningful use of properties and classes in RDF data. For example, an
RDF
vocabulary might describe limitations on the types of values that are
appropriate for some property, or on the classes to which it makes sense
to
ascribe such properties.
RDF Schema provides a mechanism for describing this information, but
does not say whether or how an application should use it. For example,
while an RDF vocabulary can assert that an author property
is used to
indicate resources that are instances of the class Person,
it
does not say whether or how an application should act in processing that
range information. Different applications will use this information in
different ways. For example, data checking tools might use this to help
discover errors in some data set, an interactive editor might suggest
appropriate values, and a reasoning application might use it to infer
additional information from instance data.
RDF vocabularies can describe relationships between vocabulary items
from
multiple independently developed vocabularies. Since IRIs are used
to identify classes and properties on the Web, it is possible to create
new
properties that have a domain or range whose
value
is a class defined in another namespace.
5. Other vocabulary
Additional classes and properties, including constructs for
representing
containers and RDF statements, and for deploying RDF vocabulary
descriptions
in the World Wide Web, are defined in this section.
5.4 Utility Properties
The following utility classes and properties are defined in the RDF
core
namespaces.
5.4.1 rdfs:seeAlso
rdfs:seeAlso is an instance of rdf:Property
that is used to indicate a
resource that might provide additional information about the subject
resource.
A triple of the form:
S rdfs:seeAlso O
states that the resource O may provide additional information about
S. It
may be possible to retrieve representations of O from the Web, but
this is
not required. When such representations may be retrieved, no
constraints are
placed on the format of those representations.
The rdfs:domain of
rdfs:seeAlso is rdfs:Resource.
The rdfs:range of rdfs:seeAlso
is
rdfs:Resource.
5.4.2 rdfs:isDefinedBy
rdfs:isDefinedBy is 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.
A triple of the form:
S rdfs:isDefinedBy O
states that the resource O defines S. It may be possible to
retrieve
representations of O from the Web, but this is not required. When
such
representations may be retrieved, no constraints are placed on the
format of
those representations. rdfs:isDefinedBy is a subproperty
of rdfs:seeAlso.
The rdfs:domain of
rdfs:isDefinedBy is rdfs:Resource.
The rdfs:range of rdfs:isDefinedBy
is
rdfs:Resource.
5.4.3 rdf:value
rdf:value is an instance of rdf:Property
that may be used in
describing structured values.
rdf:value has no meaning on its own. It is provided as a piece of
vocabulary that may be used in idioms such as illustrated
in example below:
Example 1
<http://www.example.com/2002/04/products#item10245>
<http://www.example.org/terms/weight> [
rdf:value 2.4 ;
<http://www.example.org/terms/units> <http://www.example.org/units/kilograms>
] .Despite
the lack of formal specification of the meaning of this property,
there is
value in defining it to encourage the use of a common idiom in
examples of
this kind.
The rdfs:domain of
rdf:value is rdfs:Resource.
The rdfs:range of rdf:value
is rdfs:Resource.
A. Acknowledgments
This section is non-normative.
The RDF Schema design was originally produced by the RDF Schema Working
Group (1997-2000). The current specification is largely an editorial
clarification of that design, and has benefited greatly from the hard
work of
the RDF Core Working Group
members, and
from
implementation feedback from many members of the RDF
Interest Group. In
2013-2014 Guus Schreiber edited this document on behalf of the RDF
Working Group
to bring it in line with the RDF 1.1 specifications.
David Singer of IBM was the chair of the original RDF Schema group
throughout most of the development of this specification; we thank David
for
his efforts and thank IBM for supporting him and us in this endeavor.
Particular thanks are also due to Andrew Layman for his editorial work
on
early versions of this specification.
The original RDF Schema Working Group membership included:
Nick Arnett (Verity), Dan Brickley (ILRT / University of Bristol),
Walter
Chang (Adobe), Sailesh Chutani (Oracle), Ron Daniel (DATAFUSION),
Charles
Frankston (Microsoft), Joe Lapp (webMethods Inc.), Patrick Gannon
(CommerceNet), RV Guha (Epinions, previously of Netscape
Communications), Tom
Hill (Apple Computer), Renato Iannella (DSTC), Sandeep Jain (Oracle),
Kevin
Jones, (InterMind), Emiko Kezuka (Digital Vision Laboratories), Ora
Lassila
(Nokia Research Center), Andrew Layman (Microsoft), John McCarthy
(Lawrence
Berkeley National Laboratory), Michael Mealling (Network Solutions),
Norbert
Mikula (DataChannel), Eric Miller (OCLC), Frank Olken (Lawrence Berkeley
National Laboratory), Sri Raghavan (Digital/Compaq), Lisa Rein
(webMethods
Inc.), Tsuyoshi Sakata (Digital Vision Laboratories), Leon Shklar
(Pencom Web
Works), David Singer (IBM), Wei (William) Song (SISU), Neel Sundaresan
(IBM),
Ralph Swick (W3C), Naohiko Uramoto (IBM), Charles Wicksteed (Reuters
Ltd.),
Misha Wolf (Reuters Ltd.)