Semantics in Wiki - Community-Built Databases: Research and Development - page 243

l RDF Schema : a simple type modelling language for describing classes of
resources and properties between them in the basic RDF model. It provides a
simple reasoning framework for inferring types of resources.
l Ontologies : a richer language for providing more complex constraints on the
types of resources and their properties.
l Logic and Proof : an (automatic) reasoning system provided on top of the
ontology structure to make new inferences. Thus, using such a system, a
software agent can make deductions as to whether a particular resource satisfies
its requirements (and vice versa).
l Trust : The final layer of the stack addresses issues of trust that the Semantic Web
can support. This component has not progressed further than a vision of allowing
people to ask questions about the trustworthiness of the information on the Web
in order to receive an assurance of its quality.
10.3.1 Resource Description Framework
A language for representing information about resources in the World Wide Web is
known as a RDF. It is used to represent metadata about Web resources, such as the
title, author and modification date of a Web page, copyright and licensing informa-
tion about a Web document or the availability schedule for some shared resource.
RDF can also be used to represent information about things that can be identified on
the Web, even when they cannot be directly retrieved on the Web. Examples include
information about items available from online shopping facilities (e.g. information
about specifications, prices and availability), or the description of a Web user's
preferences for information delivery.
RDF is a graph-centric approach which builds on the intuition that the funda-
mental aspects of a domain of interest can be modelled as binary relationships
between objects. This linking structure forms a directed, labelled graph, where the
edges represent the named link between two resources, represented by the graph
nodes. This graph view is the easiest possible mental model for RDF and is often
used in easy-to-understand visual explanations [ 8 ].
RDF is based on the idea of identifying things using Web identifiers (called
Uniform Resource Identifiers ,or URIs ) and describing resources in terms of simple
properties and property values. This enables RDF to represent simple statements
about resources as a graph of nodes and arcs representing the resources, and their
properties and values. For example, “there is a Person identified by http://www.w3.
org/People/EM/contact#me , whose name is Eric Miller, whose email address is
[e-mail], and whose title is Dr”, could be represented as the RDF graph in
Fig. 10.2 [ 13 ].
RDF extends the linking structure of the Web to use URIs to name the relation-
ship between things and the two ends of the link (this is usually referred to as a
“triple”). This simple model allows structured and semi-structured data to be mixed,
exposed and shared across different applications [ 12 ]. RDF provides a common