The nature of a referenced resource is a property of 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 default value is http://www.rddl.org/#resource.
When a referenced resource is XML and its nature can be inferred from the namespace URI of the root element, this namespace URI is the
nature of the referenced resource. 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.isi.edu/in-notes/iana/assignments/media-types/.
The nature of a resource can be as simple as being a defined term.
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 URI http://www.isi.edu/in-notes/iana/assignments/media-types/text/css is well-known URI for CSS.
This URI is a well-known URI for the content-type text/css and is used as the nature of CSS. This URI
itself resolves to a text/plain document.
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]
A URI which describes the nature of a DTD is http://www.isi.edu/in-notes/iana/assignments/media-types/application/xml-dtd.
This 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.
HTML provides an interesting case study for the discussion of natures given its range of incarnations.
The MIME content-type The nature of HTML 4 is http://www.w3.org/TR/html4/. This URI also refers to the HTML 4 specification.
The nature of something is not typically the specification, but this URI is also the root URI for the DTDs which define HTML 4 Strict, Transitional and Frameset.
The nature of HTML 4 Strict is http://www.w3.org/TR/html4/strict. This URI resolves to the DTD for HTML 4 Strict.
Here we define this nature to derive from the nature of HTML 4.
The nature of HTML 4 Transitional is http://www.w3.org/TR/html4/transitional. This URI resolves to the DTD for HTML 4 Transitional.
Here we define this nature to derive from the nature of HTML 4.
The nature of HTML 4 Frameset is http://www.w3.org/TR/html4/frameset. This URI resolves to the DTD for HTML 4 Frameset.
Here we define this nature to derive from the nature of HTML 4.
The nature of XHTML is http://www.w3.org/1999/xhtml. This URI is the namespace of XHTML.
Here we define this nature to derive from the nature of HTML 4.
The nature of XHTML 1.0 Strict is http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict. This URI resolves to the DTD for XHTML 1.0 Strict.
Here we define this nature to derive from the nature of XHTML.
The nature of XHTML 1.0 Transitional is http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional. This URI resolves to the DTD for XHTML 1.0 Transitional.
Here we define this nature to derive from the nature of XHTML.
Generic HTML
text/html denotes the most general or generic type of HTML. It could be
HTML 1,2,3,4 or XHTML and can be strict, transitional, frameset etc. Its nature derives from text/sgml and is refered to by the
canonical URI for text/html namely http://www.isi.edu/in-notes/iana/assignments/media-types/text/htmlHTML 4
HTML 4 Strict
HTML 4 Transitional
HTML 4 Frameset
XHTML
XHTML 1.0 Strict
XHTML 1.0 Transitional
An RDF Schema is a language which describes vocabularies using the Resource Description Framework.
The RDF Schema namespace URI is http://www.w3.org/2000/01/rdf-schema#. The nature
of an RDF Schema is http://www.w3.org/2000/01/rdf-schema#
The RDF Schema specification is a W3C Candidate 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 URI which is used as the nature of a RELAX Core grammar.
This is the namespace URI of a RELAX core grammar.
http://www.xml.gr.jp/xmlns/relaxNamespace is the URI which is used as the nature of a RELAX Namespace grammar.
This is the namespace URI of a RELAX namespace grammar.
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. This URI is used as the nature of a Schematron schema.
An OASIS Open Catalog Format document mapps Public Identifiers to System Identifiers.
The URI http://www.rddl.org/natures#SOCAT can be used as a well known URI for an OASIS Open Catalog.
The XML Schema Definition Language is a formal language for which to describe XML grammars.
The well known URI for XSD is: http://www.w3.org/2000/10/XMLSchema which defines the nature of an XML Schema
module. This is the namespace URI of the root element of an XSD schema.
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.]
An IETF RFC is known by the URI http://www.ietf.org/rfc/rfc2026.txt.
An ISO standard is known by the URI http://www.iso.ch/.