RDF Vocabulary Description Language 1.0: RDF Schema

Abstract

The Resource Description Framework (RDF) is a general-purpose language for representing information in the Web. This specification describes how to use RDF to describe RDF vocabularies. This specification defines a vocabulary for this purpose and defines other built-in RDF vocabulary initially specified in the RDF Model and Syntax Specification.

Contents

1. Introduction
2. Classes
    2.1 rdfs:Resource
    2.2 rdfs:Class
    2.3 rdfs:Literal
    2.4 rdfs:Datatype
    2.5 rdf:XMLLiteral
    2.6 rdf:Property
3. Properties
    3.1 rdfs:range
    3.2 rdfs:domain
    3.3 rdf:type
    3.4 rdfs:subClassOf
    3.5 rdfs:subPropertyOf
    3.6 rdfs:label
    3.7 rdfs:comment
4. Using the Domain and Range vocabulary (Informative)
5. Other vocabulary
    5.1 Container Classes and Properties
       5.1.1 rdfs:Container
       5.1.2 rdf:Bag
       5.1.3 rdf:Seq
       5.1.4 rdf:Alt
       5.1.5 rdfs:ContainerMembershipProperty
       5.1.6 rdfs:member
    5.2 RDF Collections
       5.2.1 rdf:List
       5.2.2 rdf:first
       5.2.3 rdf:rest
       5.2.4 rdf:nil
    5.3 Reification Vocabulary
       5.3.1 rdf:Statement
       5.3.2 rdf:subject
       5.3.3 rdf:predicate
       5.3.4 rdf:object
    5.4 Utility Properties
       5.4.1 rdfs:seeAlso
       5.4.2 rdfs:isDefinedBy
       5.4.3 rdf:value
6. RDF Schema summary (Informative)
    6.1 Classes
    6.2 Properties
7. References
    7.1 Normative References
    7.2 Informational References
8. Acknowledgments
Appendix A RDF Schema as RDF/XML

1. Introduction

The Resource Description Framework (RDF) is a general-purpose language for representing information in the Web.

This specification is one of several [RDF-PRIMER] [RDF-SYNTAX] [RDF-CONCEPTS] [RDF-SEMANTICS] [RDF-TESTS] related to RDF. The reader is referred to the RDF schema chapter in the RDF Primer [RDF-PRIMER] for an informal introduction and examples of the use of the concepts specified in this document.

This specification introduces RDF's vocabulary description language, RDF Schema. It is complemented by several companion documents which describe RDF's XML encoding [RDF-SYNTAX], mathematical foundations [RDF-SEMANTICS] and Resource Description Framework (RDF): Concepts and Abstract Syntax [RDF-CONCEPTS]. The RDF Primer [RDF-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 the RDF vocabulary description language to those who find the formal semantics specification, RDF Semantics [RDF-SEMANTICS] 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 properties may be thought of as attributes of resources and in this sense correspond to traditional attribute-value pairs. RDF properties also represent relationships between resources.

RDF however, provides no mechanisms for describing these properties, nor does it provide any mechanisms for describing the relationships between these properties and other resources. That is the role of the RDF vocabulary description language, RDF Schema. RDF Schema defines classes and properties that may be used to describe classes, properties and other resources.

This document does not specify a vocabulary of descriptive properties such as "author". Instead it specifies mechanisms that may be used to name and describe properties and the classes of resource they describe.

RDF's vocabulary description language, RDF Schema, is a semantic extension (as defined in [RDF-SEMANTICS]) of RDF. It provides mechanisms for describing groups of related resources and the relationships between these resources. RDF Schema vocabulary descriptions are 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 vocabulary description language class and property system is similar to the type systems of object-oriented programming languages such as Java. RDF differs from many such systems in that instead of defining a class in terms of the properties its instances may have, the RDF vocabulary description language 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 vocabulary description that are useful for representing the meaning of RDF classes and properties. Instead, the RDF vocabulary description 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 DAML+OIL, W3C's [OWL] language, 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. RDF vocabulary designers can create and deploy Semantic Web applications using the RDF vocabulary description language 1.0 facilities, while exploring richer vocabulary description languages that share this general approach.

The language defined in this specification consists of a collection of RDF resources that can be used to describe properties of other RDF resources (including properties) in application-specific RDF vocabularies. The core vocabulary is defined in a namespace informally called 'rdfs' here. That namespace is identified by the URI-Reference http://www.w3.org/2000/01/rdf-schema# and is 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 URI-References. A name of the form prefix:suffix should be interpreted as a URI-Reference consisting of the URI-Reference 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 RDF URI References 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 [RDF-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. Literals may be plain or typed. A typed literal is an instance of a datatype class. This specification does not define the class of plain 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 [RDF-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.

2.5 rdf:XMLLiteral

The class rdf:XMLLiteral is the class of XML literal values. rdf:XMLLiteral is an instance of rdfs:Datatype and a subclass of rdfs:Literal.

2.6 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 [RDF-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].

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.

3.3 rdf:type

rdf:type is an instance of rdf:Property that is used to state that a resource is an instance of a class.

A triple of the form:

R rdf:type C

states that C is an instance of rdfs:Class and R is an instance of C.

The rdfs:domain of rdf:type is rdfs:Resource. The rdfs:range of rdf:type is 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.

3.7 rdfs:comment

rdfs:comment is an instance of rdf:Property that may be used to provide a human-readable description of a resource.

A triple of the form:

R rdfs:comment L

states that L is a human readable description of R.

The rdfs:domain of rdfs:comment is rdfs:Resource. The rdfs:range of rdfs:comment is rdfs:Literal.

A textual comment helps clarify the meaning of RDF classes and properties. Such in-line documentation complements the use of both formal techniques (Ontology and rule languages) and informal (prose documentation, examples, test cases). A variety of documentation forms can be combined to indicate the intended meaning of the classes and properties described in an RDF vocabulary. Since RDF vocabularies are expressed as RDF graphs, vocabularies defined in other namespaces may be used to provide richer documentation.

Multilingual documentation is supported through use of the language tagging facility of RDF literals.

4. Using the Domain and Range Vocabulary (Informative)

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.

The RDF Vocabulary Description language 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 URI-References are used to identify classes and properties in 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.

5.1 Container Classes and Properties

RDF containers are resources that are used to represent collections. An introduction to RDF containers with examples may be found in the RDF Primer [RDF-PRIMER]. The same resource may appear in a container more than once. Unlike containment in the physical world, a container may be contained in itself.

Three different kinds of container are defined. Whilst the formal semantics [RDF-SEMANTICS] of all three classes of container are identical, different classes may be used to indicate informally further information. An rdf:Bag is used to indicate that the container is intended to be unordered. An rdf:Seq is used to indicate that the order indicated by the numerical order of the container member ship properties of the container is intended to be significant. An rdf:Alt container is used to indicate that typical processing of the container will be to select one of the members.

Just as a hen house may have the property that it is made of wood, that does not mean that all the hens it contains are made of wood, a property of a container is not necessarily a property of all of its members.

RDF containers are defined by the following classes and properties.

5.1.1 rdfs:Container

The rdfs:Container class is a super-class of the RDF Container classes, i.e. rdf:Bag, rdf:Seq, rdf:Alt.

5.1.2 rdf:Bag

The rdf:Bag class is the class of RDF 'Bag' containers. It is a subclass of rdfs:Container. Whilst formally it is no different from an rdf:Seq or an rdf:Alt, the rdf:Bag class is used conventionally to indicate to a human reader that the container is intended to be unordered.

5.1.3 rdf:Seq

The rdf:Seq class is the class of RDF 'Sequence' containers. It is a subclass of rdfs:Container. Whilst formally it is no different from an rdf:Bag or an rdf:Alt, the rdf:Seq class is used conventionally to indicate to a human reader that the numerical ordering of the container membership properties of the container is intended to be significant.

5.1.4 rdf:Alt

The rdf:Alt class is the class of RDF 'Alternative' containers. It is a subclass of rdfs:Container. Whilst formally it is no different from an rdf:Seq or an rdf:Bag, the rdf:Alt class is used conventionally to indicate to a human reader that typical processing will be to select one of the members of the container. The first member of the container, i.e. the value of the rdf:_1 property, is the default choice.

5.1.5 rdfs:ContainerMembershipProperty

The rdfs:ContainerMembershipProperty class has as instances the properties rdf:_1, rdf:_2, rdf:_3 ... that are used to state that a resource is a member of a container. rdfs:ContainerMembershipProperty is a subclass of rdf:Property. Each instance of rdfs:ContainerMembershipProperty is an rdfs:subPropertyOf the rdfs:member property.

Given a container C, a triple of the form:

C rdf:_nnn O

where nnn is the decimal representation of an integer greater than 0 with no leading zeros, states that O is a member of the container C.

Container membership properties may be applied to resources other than containers.

5.1.6 rdfs:member

rdfs:member is an instance of rdf:Property that is a super-property of all the container membership properties i.e. each container membership property has an rdfs:subPropertyOf relationship to the property rdfs:member.

The rdfs:domain of rdfs:member is rdfs:Resource. The rdfs:range of rdfs:member is rdfs:Resource.

5.2 RDF Collections

RDF containers are open in the sense that the core RDF specifications define no mechanism to state that there are no more members. The RDF Collection vocabulary of classes and properties can describe a closed collection, i.e. one that can have no more members. The reader is referred to the collections section of the RDF primer for an informal introduction to collections with examples.

A collection is represented as a list of items, a representation that will be familiar to those with experience of Lisp and similar programming languages. There is a shorthand notation in the RDF/XML syntax specification [RDF-SYNTAX] for representing collections.

Note: RDFS does not require that there be only one first element of a list-like structure, or even that a list-like structure have a first element.

5.2.1 rdf:List

rdf:List is an instance of rdfs:Class that can be used to build descriptions of lists and other list-like structures.

5.2.2 rdf:first

rdf:first is an instance of rdf:Property that can be used to build descriptions of lists and other list-like structures.

A triple of the form:

L rdf:first O

states that there is a first-element relationship between L and O.

The rdfs:domain of rdf:first is rdf:List. The rdfs:range of rdf:first is rdfs:Resource.

5.2.3 rdf:rest

rdf:rest is an instance of rdf:Property that can be used to build descriptions of lists and other list-like structures.

A triple of the form:

L rdf:rest O

states that there is a rest-of-list relationship between L and O.

The rdfs:domain of rdf:rest is rdf:List. The rdfs:range of rdf:rest is rdf:List.

5.2.4 rdf:nil

The resource rdf:nil is an instance of rdf:List that can be used to represent an empty list or other list-like structure.

A triple of the form:

L rdf:rest rdf:nil

states that L is an instance of rdf:List that has one item; that item can be indicated using the rdf:first property.

5.3 Reification Vocabulary

The original RDF Model and Syntax Specification [RDFMS] defined a vocabulary for describing RDF statements without stating them. [RDFMS] did not provide a formal semantics for this vocabulary, and the informal definition that was provided was somewhat inconsistent. The current RDF specification does not assign a normative formal semantics to this vocabulary. However, an intended meaning of this vocabulary (which generally clarifies the intent of the [RDFMS] definition) is described here. An informal introduction to the reification vocabulary, with examples, may be found in the RDF Primer [RDF-PRIMER].

5.3.1 rdf:Statement

rdf:Statement is an instance of rdfs:Class. It is intended to represent the class of RDF statements. An RDF statement is the statement made by a token of an RDF triple. The subject of an RDF statement is the instance of rdfs:Resource identified by the subject of the triple. The predicate of an RDF statement is the instance of rdf:Property identified by the predicate of the triple. The object of an RDF statement is the instance of rdfs:Resource identified by the object of the triple. rdf:Statement is in the domain of the properties rdf:predicate, rdf:subject and rdf:object. Different individual rdf:Statement instances may have the same values for their rdf:predicate, rdf:subject and rdf:object properties.

5.3.2 rdf:subject

rdf:subject is an instance of rdf:Property that is used to state the subject of a statement.

A triple of the form:

S rdf:subject R

states that S is an instance of rdf:Statement and that the subject of S is R.

The rdfs:domain of rdf:subject is rdf:Statement. The rdfs:range of rdf:subject is rdfs:Resource.

5.3.3 rdf:predicate

rdf:predicate is an instance of rdf:Property that is used to state the predicate of a statement.

A triple of the form:

S rdf:predicate P

states that S is an instance of rdf:Statement, that P is an instance of rdf:Property and that the predicate of S is P.

The rdfs:domain of rdf:predicate is rdf:Statement and the rdfs:range is rdfs:Resource.

5.3.4 rdf:object

rdf:object is an instance of rdf:Property that is used to state the object of a statement.

A triple of the form:

S rdf:object O

states that S is an instance of rdf:Statement and that the object of S is O.

The rdfs:domain of rdf:object is rdf:Statement. The rdfs:range of rdf:object is rdfs:Resource.

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 16 of the RDF primer [RDF-PRIMER]. 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.

6. RDF Schema summary (Informative)

This table presents an overview of the vocabulary of RDF, drawing together vocabulary originally defined in the RDF Model and Syntax specification with classes and properties that originate with RDF Schema.

6.1 RDF classes

6.2 RDF properties

In addition to these classes and properties, RDF also uses properties called rdf:_1, rdf:_2, rdf:_3... etc., each of which is both a sub-property of rdfs:member and an instance of the class rdfs:ContainerMembershipProperty. There is also an instance of rdf:List called rdf:nil that is an empty rdf:List.

7.References

7.1 Normative References

[RDF-CONCEPTS]

Resource Description Framework (RDF): Concepts and Abstract Syntax, Graham Klyne and Jeremy J. Carroll, Editors, W3C Recommendation, 10 February 2004, http://www.w3.org/TR/2004/REC-rdf-concepts-20040210/ . Latest version available at http://www.w3.org/TR/rdf-concepts/ .

[RDF-SEMANTICS]

RDF Semantics, Patrick Hayes, Editor, W3C Recommendation, 10 February 2004, http://www.w3.org/TR/2004/REC-rdf-mt-20040210/ . Latest version available at http://www.w3.org/TR/rdf-mt/ .

[RDF-SYNTAX]

RDF/XML Syntax Specification (Revised), Dave Beckett, Editor, W3C Recommendation, 10 February 2004, http://www.w3.org/TR/2004/REC-rdf-syntax-grammar-20040210/ . Latest version available at http://www.w3.org/TR/rdf-syntax-grammar/ .

[RDF-TESTS]

RDF Test Cases, Jan Grant and Dave Beckett, Editors, W3C Recommendation, 10 February 2004, http://www.w3.org/TR/2004/REC-rdf-testcases-20040210/ . Latest version available at http://www.w3.org/TR/rdf-testcases/ .

[RDFMS]

Resource Description Framework (RDF) Model and Syntax, W3C Recommendation, 22 February 1999
http://www.w3.org/TR/1999/REC-rdf-syntax-19990222/

[XMLNS]

Namespaces in XML; W3C Recommendation, 14 January 1999
http://www.w3.org/TR/1999/REC-xml-names-19990114/

7.2 Informational References

[RDF-PRIMER]

RDF Primer, Frank Manola and Eric Miller, Editors, W3C Recommendation, 10 February 2004, http://www.w3.org/TR/2004/REC-rdf-primer-20040210/ . Latest version available at http://www.w3.org/TR/rdf-primer/ .

[BERNERS-LEE98]

What the Semantic Web can represent, Tim Berners-Lee, 1998
http://www.w3.org/DesignIssues/RDFnot.html

[EXTWEB]

Web Architecture: Extensible Languages, Tim Berners-Lee and Dan Connolly, 1998
http://www.w3.org/TR/1998/NOTE-webarch-extlang-19980210

[DCMI]

Dublin Core Metadata Initiative
http://www.dublincore.org/

[OWL]

OWL Web Ontology Language Reference, Mike Dean and Guus Schreiber, Editors, W3C Recommendation, 10 February 2004, http://www.w3.org/TR/2004/REC-owl-ref-20040210/ . Latest version available at http://www.w3.org/TR/owl-ref/ .

[SCHEMA-ARCH]

The Cambridge Communiqué, W3C NOTE, 7 October 1999, Swick and Thompson
http://www.w3.org/TR/1999/NOTE-schema-arch-19991007

[XML]

Extensible Markup Language (XML) 1.0, W3C Recommendation, 10-February-1988, Section 3.2 Element Type Declarations
http://www.w3.org/TR/1998/REC-xml-19980210.html#elemdecls

8. Acknowledgments

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.

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.)

Changes

The following is an outline of the main changes made to this specification, latest first, since the Last Call Working Draft of 23 January 2003. See the Last Call issue tracking document for details of the specific issues raised regarding this specification.

• Amended Appendix A to note that the RDF/XML description of RDF and RDFS terms is not directly published at the RDFS namespace, but split between the 'rdf:' and 'rdfs:' namespace documents. Also removed the pre-REC warning that the WG might choose to change the namespace URI prior to Recommendation.
• Amended rdfs:range specification for rdf:predicate for consistency with the Semantics document (previously rdf:Property; now, rdfs:Resource)
• Removed reference to RDF mimetypes doc, as the IETF draft has expired and is 404 missing on their site.
• Reification vocabulary redescribed (details).
• Reworded rdfs:comment for rdfs:member, changing "container" to "resource"
• Reworded lead-in to Appendix A per 0170.html.
• OWL references now go to OWL specs rather than WebOnt homepage. Fixed minor typos per 0373.html)
• Reworded rdf:nil to tone down the imperative style.
• Added note to Properties section warning about over-use of sub-property, and referencing OWL, an editorial suggestion from Bijan Parsia. (details).
• Regarding pfps-12, discussion led to rdf:first/rest/List/nil rewritten per Peter Patel-Schneider's suggestion.
• Change to description of subProperty and subClass, to match changes to RDF Semantics. See discussion for details.
• Edits closing 'what is rdf schema' issue by clarifying that RDFS is a semantic extension of RDF, as defined in the RDF Semantics document. This closes rdfcore last call issue pfps-24.

Appendix A: RDF Schema as RDF/XML

An RDFS description of the RDF vocabulary and RDFS vocabulary is given here in RDF/XML syntax. It includes statements describing RDF resources originally introduced by the 1999 RDF Model and Syntax specification, as well as definitions for resources introduced in the RDF Core Schema vocabulary.

This material is also available as a separate RDF/XML document. It does not necessarily match the content published at the RDF namespace URI or the RDFS namespace URI, which may evolve over time.

<rdf:RDF
  xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
  xmlns:rdfs="http://www.w3.org/2000/01/rdf-schema#"
  xmlns:owl="http://www.w3.org/2002/07/owl#">

<owl:Ontology rdf:about="http://www.w3.org/2000/01/rdf-schema#"/>

<rdfs:Class rdf:about="http://www.w3.org/2000/01/rdf-schema#Resource">
  <rdfs:isDefinedBy rdf:resource="http://www.w3.org/2000/01/rdf-schema#"/>
  <rdfs:label>Resource</rdfs:label>
  <rdfs:comment>The class resource, everything.</rdfs:comment>
</rdfs:Class>

<rdf:Property rdf:about="http://www.w3.org/1999/02/22-rdf-syntax-ns#type">
  <rdfs:isDefinedBy rdf:resource="http://www.w3.org/1999/02/22-rdf-syntax-ns#"/>
  <rdfs:label>type</rdfs:label>
  <rdfs:comment>The subject is an instance of a class.</rdfs:comment>
  <rdfs:range rdf:resource="http://www.w3.org/2000/01/rdf-schema#Class"/>
  <rdfs:domain rdf:resource="http://www.w3.org/2000/01/rdf-schema#Resource"/>
</rdf:Property>

<rdfs:Class rdf:about="http://www.w3.org/2000/01/rdf-schema#Class">
  <rdfs:isDefinedBy rdf:resource="http://www.w3.org/2000/01/rdf-schema#"/>
  <rdfs:label>Class</rdfs:label>
  <rdfs:comment>The class of classes.</rdfs:comment>
  <rdfs:subClassOf rdf:resource="http://www.w3.org/2000/01/rdf-schema#Resource"/>
</rdfs:Class>

<rdf:Property rdf:about="http://www.w3.org/2000/01/rdf-schema#subClassOf">
  <rdfs:isDefinedBy rdf:resource="http://www.w3.org/2000/01/rdf-schema#"/>
  <rdfs:label>subClassOf</rdfs:label>
  <rdfs:comment>The subject is a subclass of a class.</rdfs:comment>
  <rdfs:range rdf:resource="http://www.w3.org/2000/01/rdf-schema#Class"/>
  <rdfs:domain rdf:resource="http://www.w3.org/2000/01/rdf-schema#Class"/>
</rdf:Property>

<rdf:Property rdf:about="http://www.w3.org/2000/01/rdf-schema#subPropertyOf">
  <rdfs:isDefinedBy rdf:resource="http://www.w3.org/2000/01/rdf-schema#"/>
  <rdfs:label>subPropertyOf</rdfs:label>
  <rdfs:comment>The subject is a subproperty of a property.</rdfs:comment>
  <rdfs:range rdf:resource="http://www.w3.org/1999/02/22-rdf-syntax-ns#Property"/>
  <rdfs:domain rdf:resource="http://www.w3.org/1999/02/22-rdf-syntax-ns#Property"/>
</rdf:Property>

<rdfs:Class rdf:about="http://www.w3.org/1999/02/22-rdf-syntax-ns#Property">
  <rdfs:isDefinedBy rdf:resource="http://www.w3.org/1999/02/22-rdf-syntax-ns#"/>
  <rdfs:label>Property</rdfs:label>
  <rdfs:comment>The class of RDF properties.</rdfs:comment>
  <rdfs:subClassOf rdf:resource="http://www.w3.org/2000/01/rdf-schema#Resource"/>
</rdfs:Class>

<rdf:Property rdf:about="http://www.w3.org/2000/01/rdf-schema#comment">
  <rdfs:isDefinedBy rdf:resource="http://www.w3.org/2000/01/rdf-schema#"/>
  <rdfs:label>comment</rdfs:label>
  <rdfs:comment>A description of the subject resource.</rdfs:comment>
  <rdfs:domain rdf:resource="http://www.w3.org/2000/01/rdf-schema#Resource"/>
  <rdfs:range rdf:resource="http://www.w3.org/2000/01/rdf-schema#Literal"/>
</rdf:Property>

<rdf:Property rdf:about="http://www.w3.org/2000/01/rdf-schema#label">
  <rdfs:isDefinedBy rdf:resource="http://www.w3.org/2000/01/rdf-schema#"/>
  <rdfs:label>label</rdfs:label>
  <rdfs:comment>A human-readable name for the subject.</rdfs:comment>
  <rdfs:domain rdf:resource="http://www.w3.org/2000/01/rdf-schema#Resource"/>
  <rdfs:range rdf:resource="http://www.w3.org/2000/01/rdf-schema#Literal"/>
</rdf:Property>

<rdf:Property rdf:about="http://www.w3.org/2000/01/rdf-schema#domain">
  <rdfs:isDefinedBy rdf:resource="http://www.w3.org/2000/01/rdf-schema#"/>
  <rdfs:label>domain</rdfs:label>
  <rdfs:comment>A domain of the subject property.</rdfs:comment>
 <rdfs:range rdf:resource="http://www.w3.org/2000/01/rdf-schema#Class"/>
  <rdfs:domain rdf:resource="http://www.w3.org/1999/02/22-rdf-syntax-ns#Property"/>
</rdf:Property>

<rdf:Property rdf:about="http://www.w3.org/2000/01/rdf-schema#range">
  <rdfs:isDefinedBy rdf:resource="http://www.w3.org/2000/01/rdf-schema#"/>
  <rdfs:label>range</rdfs:label>
  <rdfs:comment>A range of the subject property.</rdfs:comment>
  <rdfs:range rdf:resource="http://www.w3.org/2000/01/rdf-schema#Class"/>
  <rdfs:domain rdf:resource="http://www.w3.org/1999/02/22-rdf-syntax-ns#Property"/>
</rdf:Property>

<rdf:Property rdf:about="http://www.w3.org/2000/01/rdf-schema#seeAlso">
  <rdfs:isDefinedBy rdf:resource="http://www.w3.org/2000/01/rdf-schema#"/>
  <rdfs:label>seeAlso</rdfs:label>
  <rdfs:comment>Further information about the subject resource.</rdfs:comment>
  <rdfs:range rdf:resource="http://www.w3.org/2000/01/rdf-schema#Resource"/>
  <rdfs:domain   rdf:resource="http://www.w3.org/2000/01/rdf-schema#Resource"/>
</rdf:Property>

<rdf:Property rdf:about="http://www.w3.org/2000/01/rdf-schema#isDefinedBy">
  <rdfs:isDefinedBy rdf:resource="http://www.w3.org/2000/01/rdf-schema#"/>
  <rdfs:subPropertyOf rdf:resource="http://www.w3.org/2000/01/rdf-schema#seeAlso"/>
  <rdfs:label>isDefinedBy</rdfs:label>
  <rdfs:comment>The defininition of the subject resource.</rdfs:comment>
  <rdfs:range rdf:resource="http://www.w3.org/2000/01/rdf-schema#Resource"/>
  <rdfs:domain rdf:resource="http://www.w3.org/2000/01/rdf-schema#Resource"/>
</rdf:Property>

<rdfs:Class rdf:about="http://www.w3.org/2000/01/rdf-schema#Literal">
  <rdfs:isDefinedBy rdf:resource="http://www.w3.org/2000/01/rdf-schema#"/>
  <rdfs:label>Literal</rdfs:label>
  <rdfs:comment>The class of literal values, eg. textual strings and integers.</rdfs:comment>
  <rdfs:subClassOf rdf:resource="http://www.w3.org/2000/01/rdf-schema#Resource"/>
</rdfs:Class>

<rdfs:Class rdf:about="http://www.w3.org/1999/02/22-rdf-syntax-ns#Statement">
  <rdfs:isDefinedBy rdf:resource="http://www.w3.org/1999/02/22-rdf-syntax-ns#"/>
  <rdfs:label>Statement</rdfs:label>
  <rdfs:subClassOf rdf:resource="http://www.w3.org/2000/01/rdf-schema#Resource"/>
  <rdfs:comment>The class of RDF statements.</rdfs:comment>
</rdfs:Class>

<rdf:Property rdf:about="http://www.w3.org/1999/02/22-rdf-syntax-ns#subject">
  <rdfs:isDefinedBy rdf:resource="http://www.w3.org/1999/02/22-rdf-syntax-ns#"/>
  <rdfs:label>subject</rdfs:label>
  <rdfs:comment>The subject of the subject RDF statement.</rdfs:comment>
  <rdfs:domain rdf:resource="http://www.w3.org/1999/02/22-rdf-syntax-ns#Statement"/>
  <rdfs:range rdf:resource="http://www.w3.org/2000/01/rdf-schema#Resource"/>
</rdf:Property>

<rdf:Property rdf:about="http://www.w3.org/1999/02/22-rdf-syntax-ns#predicate">
  <rdfs:isDefinedBy rdf:resource="http://www.w3.org/1999/02/22-rdf-syntax-ns#"/>
  <rdfs:label>predicate</rdfs:label>
  <rdfs:comment>The predicate of the subject RDF statement.</rdfs:comment>
  <rdfs:domain rdf:resource="http://www.w3.org/1999/02/22-rdf-syntax-ns#Statement"/>
  <rdfs:range rdf:resource="http://www.w3.org/2000/01/rdf-schema#Resource"/>
</rdf:Property>

<rdf:Property rdf:about="http://www.w3.org/1999/02/22-rdf-syntax-ns#object">
  <rdfs:isDefinedBy rdf:resource="http://www.w3.org/1999/02/22-rdf-syntax-ns#"/>
  <rdfs:label>object</rdfs:label>
  <rdfs:comment>The object of the subject RDF statement.</rdfs:comment>
  <rdfs:domain rdf:resource="http://www.w3.org/1999/02/22-rdf-syntax-ns#Statement"/>
  <rdfs:range rdf:resource="http://www.w3.org/2000/01/rdf-schema#Resource"/>
</rdf:Property>

<rdfs:Class rdf:about="http://www.w3.org/2000/01/rdf-schema#Container">
  <rdfs:isDefinedBy rdf:resource="http://www.w3.org/2000/01/rdf-schema#"/>
  <rdfs:label>Container</rdfs:label>
  <rdfs:subClassOf rdf:resource="http://www.w3.org/2000/01/rdf-schema#Resource"/>
  <rdfs:comment>The class of RDF containers.</rdfs:comment>
</rdfs:Class>

<rdfs:Class rdf:about="http://www.w3.org/1999/02/22-rdf-syntax-ns#Bag">
  <rdfs:isDefinedBy rdf:resource="http://www.w3.org/1999/02/22-rdf-syntax-ns#"/>
  <rdfs:label>Bag</rdfs:label>
  <rdfs:comment>The class of unordered containers.</rdfs:comment>
  <rdfs:subClassOf rdf:resource="http://www.w3.org/2000/01/rdf-schema#Container"/>
</rdfs:Class>

<rdfs:Class rdf:about="http://www.w3.org/1999/02/22-rdf-syntax-ns#Seq">
  <rdfs:isDefinedBy rdf:resource="http://www.w3.org/1999/02/22-rdf-syntax-ns#"/>
  <rdfs:label>Seq</rdfs:label>
  <rdfs:comment>The class of ordered containers.</rdfs:comment>
  <rdfs:subClassOf rdf:resource="http://www.w3.org/2000/01/rdf-schema#Container"/>
</rdfs:Class>

<rdfs:Class rdf:about="http://www.w3.org/1999/02/22-rdf-syntax-ns#Alt">
  <rdfs:isDefinedBy rdf:resource="http://www.w3.org/1999/02/22-rdf-syntax-ns#"/>
  <rdfs:label>Alt</rdfs:label>
  <rdfs:comment>The class of containers of alternatives.</rdfs:comment>
  <rdfs:subClassOf rdf:resource="http://www.w3.org/2000/01/rdf-schema#Container"/>
</rdfs:Class>

<rdfs:Class rdf:about="http://www.w3.org/2000/01/rdf-schema#ContainerMembershipProperty">
  <rdfs:isDefinedBy rdf:resource="http://www.w3.org/2000/01/rdf-schema#"/>
  <rdfs:label>ContainerMembershipProperty</rdfs:label>
  <rdfs:comment>The class of container membership properties, rdf:_1, rdf:_2, ...,
                    all of which are sub-properties of 'member'.</rdfs:comment>
  <rdfs:subClassOf rdf:resource="http://www.w3.org/1999/02/22-rdf-syntax-ns#Property"/>
</rdfs:Class>

<rdf:Property rdf:about="http://www.w3.org/2000/01/rdf-schema#member">
  <rdfs:isDefinedBy rdf:resource="http://www.w3.org/2000/01/rdf-schema#"/>
  <rdfs:label>member</rdfs:label>
  <rdfs:comment>A member of the subject resource.</rdfs:comment>
  <rdfs:domain rdf:resource="http://www.w3.org/2000/01/rdf-schema#Resource"/>
  <rdfs:range rdf:resource="http://www.w3.org/2000/01/rdf-schema#Resource"/>
</rdf:Property>

<rdf:Property rdf:about="http://www.w3.org/1999/02/22-rdf-syntax-ns#value">
  <rdfs:isDefinedBy rdf:resource="http://www.w3.org/1999/02/22-rdf-syntax-ns#"/>
  <rdfs:label>value</rdfs:label>
  <rdfs:comment>Idiomatic property used for structured values.</rdfs:comment>
  <rdfs:domain rdf:resource="http://www.w3.org/2000/01/rdf-schema#Resource"/>
  <rdfs:range rdf:resource="http://www.w3.org/2000/01/rdf-schema#Resource"/>
</rdf:Property>

<!-- the following are new additions, Nov 2002 -->

<rdfs:Class rdf:about="http://www.w3.org/1999/02/22-rdf-syntax-ns#List">
  <rdfs:isDefinedBy rdf:resource="http://www.w3.org/1999/02/22-rdf-syntax-ns#"/>
  <rdfs:label>List</rdfs:label>
  <rdfs:comment>The class of RDF Lists.</rdfs:comment>
  <rdfs:subClassOf rdf:resource="http://www.w3.org/2000/01/rdf-schema#Resource"/></rdfs:Class>

<rdf:List rdf:about="http://www.w3.org/1999/02/22-rdf-syntax-ns#nil">
  <rdfs:isDefinedBy rdf:resource="http://www.w3.org/1999/02/22-rdf-syntax-ns#"/>
  <rdfs:label>nil</rdfs:label>
  <rdfs:comment>The empty list, with no items in it. If the rest of a list is nil then the list has no more items in it.</rdfs:comment>
</rdf:List>

<rdf:Property rdf:about="http://www.w3.org/1999/02/22-rdf-syntax-ns#first">
  <rdfs:isDefinedBy rdf:resource="http://www.w3.org/1999/02/22-rdf-syntax-ns#"/>
  <rdfs:label>first</rdfs:label>
  <rdfs:comment>The first item in the subject RDF list.</rdfs:comment>
  <rdfs:domain rdf:resource="http://www.w3.org/1999/02/22-rdf-syntax-ns#List"/>
  <rdfs:range rdf:resource="http://www.w3.org/2000/01/rdf-schema#Resource"/>
</rdf:Property>

<rdf:Property rdf:about="http://www.w3.org/1999/02/22-rdf-syntax-ns#rest">
  <rdfs:isDefinedBy rdf:resource="http://www.w3.org/1999/02/22-rdf-syntax-ns#"/>
  <rdfs:label>rest</rdfs:label>
  <rdfs:comment>The rest of the subject RDF list after the first item.</rdfs:comment>
  <rdfs:domain rdf:resource="http://www.w3.org/1999/02/22-rdf-syntax-ns#List"/>
  <rdfs:range rdf:resource="http://www.w3.org/1999/02/22-rdf-syntax-ns#List"/>
</rdf:Property>

<rdfs:Class rdf:about="http://www.w3.org/2000/01/rdf-schema#Datatype">
  <rdfs:isDefinedBy rdf:resource="http://www.w3.org/2000/01/rdf-schema#"/>
  <rdfs:label>Datatype</rdfs:label>
  <rdfs:comment>The class of RDF datatypes.</rdfs:comment>
  <rdfs:subClassOf rdf:resource="http://www.w3.org/2000/01/rdf-schema#Class"/>
</rdfs:Class>
	
<rdfs:Datatype rdf:about="http://www.w3.org/1999/02/22-rdf-syntax-ns#XMLLiteral">
  <rdfs:subClassOf rdf:resource="http://www.w3.org/2000/01/rdf-schema#Literal"/> 
  <rdfs:isDefinedBy rdf:resource="http://www.w3.org/1999/02/22-rdf-syntax-ns#"/>
  <rdfs:label>XMLLiteral</rdfs:label>
  <rdfs:comment>The class of XML literal values.</rdfs:comment>
</rdfs:Datatype>

<rdf:Description rdf:about="http://www.w3.org/2000/01/rdf-schema#">
  <rdfs:seeAlso rdf:resource="http://www.w3.org/2000/01/rdf-schema-more"/>
</rdf:Description>

</rdf:RDF>