Swoogle
The Sematic web is the extension of World Wide Web which is known as WWW shortly. Semantic web is the next generation of online content representation where the web documents are represented in a language that is not only easy for humans but is machine readable as well. The main elements of the semantic web include data model description formats such as Resource Description Framework (RDF), a variety of data interchange formats (e.g. RDF/XML, Turtle, N-Triples), and notations such as RDF Schema (RDFS), the Web Ontology Language (OWL), all of which are intended to provide a formal description of concepts, terms, and relationships within a given knowledge domain. Swoogle is also an important element in Sematic Web, which is an attempt to mine and index this new set of web documents.
Swoogle is a crawler-based indexing and retrieval system for the Semantic Web. It extracts metadata for each discovered document, and computes relations between documents.The engine performs crawling of semantic documents like most web search engines and the search is available as web service too. The engine is primarily written in Java with the PHP used for the front-end and MySQL for database. Swoogle is capable of searching over 10,000 ontologies and indexes more that 1.3 million web documents. It also computes the importance of a Semantic Web document. The techniques used for indexing are the more google-type page ranking and also mining the documents for inter-relationships that are the basis for the semantic web.
Swoogle uses an adaptive crawler to discover documents with RDF content. The RDF and document metadata are analyzed and stored in a database and indexed in an information retrieval system. Custom algorithms are used to rank ontologies, data documents and terms. Services are provided to both humans and programs.
The architecture of Swoogle comprised of four components namely Discovery,Indexing,Analysis and Services.
Discovery
The Discovery component collects candidate URLs to find and cache SWDs using four mechanisms.
(i) Submitted URLs of SWDs and sites
(ii) A web crawler that explores promising sites
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(iii) Acustomized meta-crawler that discovers likely URLs using conventional search engines
(iv) The SwoogleBot Semantic Web crawler which validates and analyses SWDs to produce new candidates.
Indexing
The Indexing component analyzes the discovered SWDs and generates the bulk of Swoogle’s metadata about the Semantic Web. The metadata not only characterizes the features associated with individual SWDs and SWTs, but also tracks the relations among them, e.g., “how SWDs use/define/populate a given SWT” and “how two SWTs are associated by instantiating ‘rdfs:domain’ relation”.
Analysis
The Analysis component analyzes the generated metadata and hosts the modular ranking mechanisms.Swoogle uses two custom ranking algorithms OntoRank and TermRank to order a collection of SWDs or terms, respectively. These algorithms are based on an abstract “surfing” model that captures how an agent might access Semantic Web knowledge.
Services
The Services module provides search services to agents, allowing them to access the metadata and navigate the Semantic Web. It is highlighted by the “Swoogle Search” service that searches SWDs using constraints on URLs, the SWTs being used or defined, etc.; and the “Ontology Dictionary” service that searches ontologies at the term level and offers more navigational paths.
Several techniques are used for Ranking by Swoogle inspired by the Google’s PageRank algorithm.Swoogle uses two custom ranking algorithms OntoRank and TermRank to order a collection of SWDs or terms, respectively. These algorithms are based on an abstract “surfing” model that captures how an agent might access Semantic Web knowledge.
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