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Annexes
and attributes from more than one DTD that may have identical names and different
semantics in the different DTDs. The mechanism for achieving this is to use qualified names for both XML elements and attributes. A qualified name consists of a
namespace prefix, a single colon as separator, followed by the local name. Here is an
example ofthe use ofthe XML namespace mechanism:
234445 150
23 55
Here we see x contain two elements named point. The local point element is defined in the DTD of the XML document, but the gis:point element is defined in a
DTD located at URI ''http://www.example.org/shema/spatial.dtd''. The special purpose attribute xmlns:gis in element x defines gis as a namespace prefix of the declarations defined in the target DTD.
The Resource Description Framework (RDF) is a result of the W3C Metadata
Activity. RDF is the foundation for processing and exchanging machineunderstandable metadata on the Web using XML as the exchange format. It can be
used in a variety of application areas: in resource discovery, in cataloguing for describing the content and content relationships available at a particular Web site, in
content rating, in describing collections of pages that represent a single logical
document, for describing intellectual property rights of Web pages, and for expressing the privacy preferences of a user as well as the privacy policies of a Web site.
The RDF Model and Syntax Specification (RDF99 1999) document defines a data
model for representing named properties and property values. The data model consists of three object types: Resource, Property and Statement. Instances of the RDF
data model are called a RDF Schema. RDF resources are things of interest, e.g. an
entire Web page, an XML element or an entire Web site. An RDF property is a specific aspect, characteristic, attribute or relation used to describe aresource, whereas
an RDF statement is a specific RDF resource in combination with a named RDF
property for that resource. RDF can be used to express a wide variety of data models,
e.g. Entity-Relationship models. The RDF Schema Specification (RDFOO 2000)
document defines a schema specification language that pro vi des a basic type system
for use in RDF models. lt defines resources and properties such as class and subclass-of constructs that can be used in application specific schemas. RDF Schemas
can be compared with XML DTDs, but unlike an XML DTD, which gives specific
constraints on the structure of an XML document, a RDF Schema provides information about the interpretation ofthe statements given in an RDF data model.
XMI (XMI03 2003) is an XML based exchange standard for exchange of objectoriented metadata models. The purpose of XMI is to facilitate UML model data interchange between different modelling tools in a vendor neutral way. It is based on
OMG's Meta Object Facility and on CORBA data types. XMI can in theory be used
to exchange data based on UML models, but are not primarily designed for this purpose.
Annexes
and attributes from more than one DTD that may have identical names and different
semantics in the different DTDs. The mechanism for achieving this is to use qualified names for both XML elements and attributes. A qualified name consists of a
namespace prefix, a single colon as separator, followed by the local name. Here is an
example ofthe use ofthe XML namespace mechanism:
Here we see x contain two elements named point. The local point element is defined in the DTD of the XML document, but the gis:point element is defined in a
DTD located at URI ''http://www.example.org/shema/spatial.dtd''. The special purpose attribute xmlns:gis in element x defines gis as a namespace prefix of the declarations defined in the target DTD.
The Resource Description Framework (RDF) is a result of the W3C Metadata
Activity. RDF is the foundation for processing and exchanging machineunderstandable metadata on the Web using XML as the exchange format. It can be
used in a variety of application areas: in resource discovery, in cataloguing for describing the content and content relationships available at a particular Web site, in
content rating, in describing collections of pages that represent a single logical
document, for describing intellectual property rights of Web pages, and for expressing the privacy preferences of a user as well as the privacy policies of a Web site.
The RDF Model and Syntax Specification (RDF99 1999) document defines a data
model for representing named properties and property values. The data model consists of three object types: Resource, Property and Statement. Instances of the RDF
data model are called a RDF Schema. RDF resources are things of interest, e.g. an
entire Web page, an XML element or an entire Web site. An RDF property is a specific aspect, characteristic, attribute or relation used to describe aresource, whereas
an RDF statement is a specific RDF resource in combination with a named RDF
property for that resource. RDF can be used to express a wide variety of data models,
e.g. Entity-Relationship models. The RDF Schema Specification (RDFOO 2000)
document defines a schema specification language that pro vi des a basic type system
for use in RDF models. lt defines resources and properties such as class and subclass-of constructs that can be used in application specific schemas. RDF Schemas
can be compared with XML DTDs, but unlike an XML DTD, which gives specific
constraints on the structure of an XML document, a RDF Schema provides information about the interpretation ofthe statements given in an RDF data model.
XMI (XMI03 2003) is an XML based exchange standard for exchange of objectoriented metadata models. The purpose of XMI is to facilitate UML model data interchange between different modelling tools in a vendor neutral way. It is based on
OMG's Meta Object Facility and on CORBA data types. XMI can in theory be used
to exchange data based on UML models, but are not primarily designed for this purpose.