Tuesday, 13 March 2018

The World of Meaningful Web: Semantic Web

The Semantic Web is an initiative by the W3C in a collaborative effort with a number of scientists with the goal of providing machine-readable Web intelligence that would come from hyperlinked dictionaries, enabling Web authors to explicitly define their words and concepts. The idea allows software agents to analyze the Web on our behalf, making smart inferences that go beyond the simple linguistic analysis performed by today’s search engines.

The Semantic Web is an extension of the World Wide Web through standards by the World Wide Web Consortium (W3C). The standards promote common data formats and exchange protocols on the Web, most fundamentally the Resource Description Framework (RDF). According to the W3C, "The Semantic Web provides a common framework that allows data to be shared and reused across application, enterprise, and community boundaries". The Semantic Web is therefore regarded as an integrator across different content, information applications and systems.

The Semantic Web takes the solution further. It involves publishing in languages specifically designed for data: Resource Description Framework (RDF), Web Ontology Language (OWL), and Extensible Markup Language (XML). HTML describes documents and the links between them. RDF, OWL, and XML, by contrast, can describe arbitrary things such as people, meetings, or airplane parts.

These technologies are combined in order to provide descriptions that supplement or replace the content of Web documents. Thus, content may manifest itself as descriptive data stored in Web-accessible databases, or as markup within documents (particularly, in Extensible HTML (XHTML) interspersed with XML, or, more often, purely in XML, with layout or rendering cues stored separately). The machine-readable descriptions enable content managers to add meaning to the content, i.e., to describe the structure of the knowledge we have about that content. In this way, a machine can process knowledge itself, instead of text, using processes similar to human deductive reasoning and inference, thereby obtaining more meaningful results and helping computers to perform automated information gathering and research.

An example of a tag that would be used in a non-semantic web page:

Encoding similar information in a semantic web page might look like this:
<item rdf:about="http://example.org/semantic-web/">Semantic Web</item>

Tim Berners-Lee calls the resulting network of Linked Data the Giant Global Graph, in contrast to the HTML-based World Wide Web. Berners-Lee posits that if the past was document sharing, the future is data sharing.

Conceptually the SW represents a layered Architecture (Fig 1), where each level provides different degree of expressiveness.

Figure 1: Layered Structure of Semantic Web

The bottom most layer allow user to provide a controlled vocabulary and namespaces. Next layer, Resource Description Framework (RDF) represents information about resources in the World Wide Web. It consists of a triplet – resource, property and value. Ontology vocabulary, the next upper layer, adds more semantics to RDF by allowing a better specification of constraints on concepts. The rules for explicit inference are established by Logic layer which are then executed by the Proof layer. The top most layer, Trust provide mechanisms to imbibe trust in a given proof [13]. The semantic web as whole, acts as a decentralized knowledge bank that provides meaning to a learner's search and thus allows extracting most appropriate learning material.

Puja Munjal
Assistant Professor
Dept of Information Technology

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