Semantic Web Technologies
43
Subject
Object
property
Fig. 2 A graph of RDF statement
Resource Identifier (URI) reference. A property may also be treated as a resource
but it is used to define the relationship between two resources. RDF statement is a
fundamental unit of RDF. It is represented in the form of (subject, property, object).
A simple graph connecting two nodes (subject and object) via directed arc (property) models the RDF statement (Fig. 2). Directed Labelled Graph (DLG), which
comprises set of such graphs is used to extract the domain knowledge. RDF model
as a graph is insensitive both to syntax and semantics. Yet in either XML or N3
syntax, or even a specialized graphical notation language such as direct labelled
graph (DLG2), a RDF model can be serialized. At the other hand, the semantics of
an RDF model is obtained by relation to RDF schema language (RDFS) and ontology
web language (OWL). Two other semantic web technologies are RDFS and OWL.
Both languages are layered on top of RDF to provide inference and axiom support for
two features that render semantic web technologies a step from data representation
to information representation [7].
3.4 RDF Schema
The RDF Schema specifies the terminology used in RDF data models. RDF Schema
includes simple modeling for expressing the information of RDF like classes,
properties, hierarchies etc. A number of modeling primitives are used to organize
RDF vocabularies in typed hierarchies. RDFS extends RDF to include “schema
vocabulary”, e.g. Class, Property, type, subClassOf, subPropertyOf, range, domain
etc.
3.5 OWL
Web Ontology Language (OWL) offers more modeling primitives compared to RDF
Schema. It is a Semantic Web language with clean, formal semantics. It reflects rich
and diverse knowledge of things, groups of things and interrelationships. OWL is a
language which is based on computational logic. Computer programs can leverage
information expressed in OWL. Three species of OWL (1) OWL full is union of
OWL syntax and RDF (2) OWL DL restricted to FOL (First Order Logic) fragment
(3) OWL Lite is ‘easier to execute’ OWL DL subset.
43
Subject
Object
property
Fig. 2 A graph of RDF statement
Resource Identifier (URI) reference. A property may also be treated as a resource
but it is used to define the relationship between two resources. RDF statement is a
fundamental unit of RDF. It is represented in the form of (subject, property, object).
A simple graph connecting two nodes (subject and object) via directed arc (property) models the RDF statement (Fig. 2). Directed Labelled Graph (DLG), which
comprises set of such graphs is used to extract the domain knowledge. RDF model
as a graph is insensitive both to syntax and semantics. Yet in either XML or N3
syntax, or even a specialized graphical notation language such as direct labelled
graph (DLG2), a RDF model can be serialized. At the other hand, the semantics of
an RDF model is obtained by relation to RDF schema language (RDFS) and ontology
web language (OWL). Two other semantic web technologies are RDFS and OWL.
Both languages are layered on top of RDF to provide inference and axiom support for
two features that render semantic web technologies a step from data representation
to information representation [7].
3.4 RDF Schema
The RDF Schema specifies the terminology used in RDF data models. RDF Schema
includes simple modeling for expressing the information of RDF like classes,
properties, hierarchies etc. A number of modeling primitives are used to organize
RDF vocabularies in typed hierarchies. RDFS extends RDF to include “schema
vocabulary”, e.g. Class, Property, type, subClassOf, subPropertyOf, range, domain
etc.
3.5 OWL
Web Ontology Language (OWL) offers more modeling primitives compared to RDF
Schema. It is a Semantic Web language with clean, formal semantics. It reflects rich
and diverse knowledge of things, groups of things and interrelationships. OWL is a
language which is based on computational logic. Computer programs can leverage
information expressed in OWL. Three species of OWL (1) OWL full is union of
OWL syntax and RDF (2) OWL DL restricted to FOL (First Order Logic) fragment
(3) OWL Lite is ‘easier to execute’ OWL DL subset.