The nature of a referenced resource applies to the referenced resource itself, whereas the purpose
is a property of the link. In many cases the purpose of a referenced resource can be inferred from its nature.
All resources have a nature, and when not specified the implicit value is http://www.rddl.org/#resource.
When a referenced resource is XML its nature may in some circumstances be inferred from the namespace URI of the root element. The relationship between a nature and namespace URI is indicated by the property http://www.rddl.org/properties#namespace. When a referenced resource is not XML and its nature can be inferred from its MIME content-type,
the nature of the referenced resource is obtained by appending the content-type to the prefix http://www.rddl.org/natures/media-types/. The use of the URI prefix
http://www.isi.edu/in-notes/iana/assignments/media-types/ is deprecated.
A nature is a class of resources which share a characteristic. For example, the nature of an XML Schema is identified by the URI http://www.rddl.org/natures#XMLSchema. All XML Schema documents have this common nature. Another way to say this is that the nature http://www.rddl.org/natures#XMLSchema is defined as the class of XML Schema documents.
The nature of a resource can be as simple as being a defined Term. In many cases the nature of a resource is a method for the author of a namespace document to indicate the class of a namespace related resource. The use of a namespace name as a nature is deprecated because a namespace name properly identifies a class of namespace related names.
The nature of a namespace is http://www.rddl.org/natures#Namespace.
From W3C CSS1: CSS1 is a simple style sheet mechanism that allows authors and readers to attach style (e.g. fonts, colors and spacing) to HTML documents. The CSS1 language is human readable and writable, and expresses style in common desktop publishing terminology.
The nature of theW3C CSS1 Recommendation is http://www.rddl.org/natures/html#V4.01.
The URI http://www.isi.edu/in-notes/iana/assignments/media-types/text/css provides a brief text/plain description of CSS. The nature of CSS is identified by the URI http://www.rddl.org/natures/content-type/text/css.
Natures of media types are obtained by appending the media type to the URI prefix http://www.rddl.org/natures/media-type/ in the same way that simple text descriptions can be obtained by appending the media type to the prefix http://www.isi.edu/in-notes/iana/assignments/media-types/.
We define http://www.rddl.org/natures#CSS as being equivalent to http://www.rddl.org/natures/media-type/text/css.
From XML 1.0: The XML document type declaration contains or points to markup declarations that provide a grammar for a class of documents. This grammar is known as a document type definition, or DTD. The document type declaration can point to an external subset (a special kind of external entity) containing markup declarations, or can contain the markup declarations directly in an internal subset, or can do both. The DTD for a document consists of both subsets taken together. [1]
The nature of a DTD is identified by the URI http://www.rddl.org/natures#DTD. This is equivalent to the nature http://www.rddl.org/natures/media-types/application/xml-dtd which is the content-type of a DTD according to RFC 3023.
A URI which can be used to describe the nature of a mailbox is http://www.rddl.org/natures#mailbox.
The nature of HTML is described in this RDDL document.
An RDF Schema is a language which describes vocabularies using the Resource Description Framework.
The nature
of an RDF Schema is http://www.rddl.org/natures#RDFSchema.
http://www.w3.org/2000/01/rdf-schema#. Use of the namespace URI as a nature for RDF Schemas is deprecated.
The RDF Schema/RDF Vocabulary Description Language specification is a W3C Recommendation.
OWL is an ontology definition language.
The nature
of OWL is http://www.rddl.org/natures#OWL.
http://www.w3.org/2002/07/owl#. The Ontology on the Web Language (OWL) specification is a W3C Recommendation.
RELAX: Regular Language Description for XML, is An XML Structure Validation Language using Patterns in Trees
The RELAX specification is available at http://www.xml.gr.jp/relax.
http://www.xml.gr.jp/xmlns/relaxCore is the namespace URI of a RELAX core grammar.
http://www.xml.gr.jp/xmlns/relaxNamespace is the namespace URI of a RELAX namespace grammar.
The nature of RELAX is http://www.rddl.org/natures#RELAX.
RELAXNG: Regular Language Description for XML, is An XML Structure Validation Language using Patterns in Trees
The RELAXNG specification is available at http://www.oasis-open.org/committees/relax-ng/spec-20011203.html.
http://relaxng.org/ns/structure/1.0 is the namespace URI of a RELAXNG namespace grammar.
The nature of RELAXNG is http://www.rddl.org/natures#RELAXNG.
Schematron is An XML Structure Validation Language using Patterns in Trees.
The schematron spec
The well known URI for Schematron is http://www.ascc.net/xml/schematron. This URI is the namespace URI for the root
element of a Schematron schema. This URI resolves to a RDDL document which describes the Schematron namespace. The nature of a Schematron schema is http://www.rddl.org/natures#Schematron.
An OASIS Open Catalog Format document mapps Public Identifiers to System Identifiers.
The URI http://www.rddl.org/natures#SOCAT identifies the nature of an OASIS Open Catalog.
The XML Schema Definition Language is a formal language for which to describe XML grammars.
The namespace URI for XSD is: http://www.w3.org/2001/XMLSchema. This is the namespace URI of the root element of an XSD schema.
The nature of an XML Schema is http://www.rddl.org/natures#XMLSchema. Use of the namespace URI as the nature of an XML Schema is deprecated.
The URI http://www.w3.org/TR/REC-xml.html#dt-chardata. From XML 1.0 [Definition: All text that is not markup constitutes the character data of the document.]
The URI http://www.w3.org/TR/REC-xml.html#dt-escape. From XML 1.0 [Definition: Entity and character references can both be used to escape the left angle bracket, ampersand, and other delimiters. A set of general entities (amp, lt, gt, apos, quot) is specified for this purpose. Numeric character references may also be used; they are expanded immediately when recognized and must be treated as character data, so the numeric character references "<" and "&" may be used to escape < and & when they occur in character data.]
The URI http://www.w3.org/TR/REC-xml.html#dt-unparsed. From XML 1.0 [Definition: An unparsed entity is a resource whose contents may or may not be text, and if text, may be other than XML. Each unparsed entity has an associated notation, identified by name. Beyond a requirement that an XML processor make the identifiers for the entity and notation available to the application, XML places no constraints on the contents of unparsed entities.]
A RDDL directory can be referenced from within a RDDL directory. This RDDL document describes the nature of software related resources.
An IETF RFC has a nature http://www.rddl.org/natures#RFC.
An ISO standard has a nature http://www.rddl.org/natures#ISO.