Semantic Web:
Layered Architecture
Semantic Web is the new generation Web that tries to
represent information such that it can be used by machines, not just for
display purposes, but for automation, integration, and reuse across
applications. Furthermore, semantic Web is about explicitly declaring the
knowledge embedded in many Web based applications, integrating information in
an intelligent way, providing semantic based access to the Internet, and
extracting information from texts. Traditionally,
HTML provides the standard of structured document published on the Internet.
Though the simplicity of HTML promotes the growth of the web, it seriously
hampered advanced applications such as processing, understanding and semantic
interoperability of information contained in several documents. It enables
intelligent services such as information brokers, search agents and information
filters, and also offers greater functionality and interoperability. It
promotes web based applications with both semantic and syntactic
interoperability. The explicit representation of meta-information, accompanied
by domain theories (i.e. ontologies), will enable a web to provide a
qualitatively new level of service. This process may ultimately create
extremely knowledgeable systems with various specialized reasoning services. The
semantic Web technologies offer a new approach to managing information and
processes, the fundamental principle of which is the creation and use of
semantic metadata.
In building one layer of the Semantic web on
top of another, two principles should be followed:
• Downward compatibility: Agents fully
aware of a layer, that should also be able to interpret and use information
written at lower levels.
• Upward partial understanding: The
design should be such that agents fully aware of a layer that should be able to
take at least partial advantage of information at higher levels.
(i) URI
A universal resource identifier (URI) is a formatted
string that serves as a means of identifying abstract or physical resource.
(ii) Unicode
Unicode provides a unique number for every character,
independently of the underlying platform, program, or language.
(iii)XML and XML Namespace
XML (eXtensible markup language) with XML namespace
and XML schema definitions makes sure that there is a common syntax used in the
semantic Web.
(iv) RDF and RDF Schema
On top of XML is the Resource Description Framework
(RDF), for representing information about resources in a graph form. RDF is
based on triples O-A-V that form a graph data with a relation among object (a
resource), an attribute (a property), and a value (a resource).
(v) Ontology
Ontology comprises a set of knowledge terms, including
the vocabulary, the semantic interconnections, simple rules of inference and
logic for some particular topic. Ontologies applied to the Web are creating the
semantic Web.
(vi) Logic, Proof, Trust and Digital Signature
The logic layer is used to enhance the ontology
language further and to allow the writing of application-specific declarative
knowledge.
The proof layer involves the actual deductive process
as well as the representation of proofs in Web languages and proof validation.
Finally, the Trust layer will emerge through the use
of digital signatures and other kinds of knowledge, based on recommendations by
trusted agents or on rating and certification agencies and consumer bodies.
For the semantic Web to become more expressive enough
to help in a wide range of situations, it will become necessary to construct a
powerful logic language for making inferences. The next step in the
architecture is ‘Trust’ and ‘Proof’. Very little is written about these layers
though they will become important in future.
by
R. Suganya,M.Sc.,M.Phil.,
Asst.professor,Dept of Computer Science
Marudhar kesari Jain College For Women
Vaniyambadi
