International Journal of Web & Semantic Technology (IJWesT) Vol.3, No.1, January 2012 DOI : 10.5121/ijwest.2012.3103 23          M .Hemalatha 1 , V. Uma 2 and Dr . G. Aghila 3 1 Department of Computer Science, Pondicherry University, India hemalathamohanraj@gmail.com 2 Assistant Professor, Department of Computer Science, Pondicherry University, India umabskr@gmail.com 3 Professor, Department of Computer Science, Pondicherry University, India aghilaa@yahoo.com ABSTRACT: Ontology of time is gaining importance as it is necessary to realize the Semantic Web. They play an important role in Natural Language Processing applications, data mining, decision support systems etc. Existing time ontologies have been represented using DAML, OWL, KSL, KIF and Cyc. In time ontology, events are concepts and topological temporal relations between events are either Point based or Interval based. Allen has proposed temporal interval relations which have been represented in the existing time ontologies. Among the Allen’s 13 temporal relations the ‘before’ relation is ambiguous as it is context dependent. In this work, the ‘before’ relation has been augmented with 3 more specific relative event based temporal relations which increases the efficiency of temporal reasoning. A temporal ontology when created for medical domain using Protégé OWL can be an efficient decision support system when the additional temporal relations RETR are incorporated. KEY WORDS: Semantic web,ontology, time ontology, temporalrelations, referenceevent 1. INTRODUCTION: The semantic web is a weave of information interlinked with each other in such a way that it can be easily understood by the machines and the information available can be easily handled globally on a large scale. So, it can also be represented efficiently as a globally linked database. Now the semantic web is playing a major role and the researchers are trying to incorporate this upcoming semantic web concept into the existing web. This semantic web is built using ontologies. Gruber [1] stated that ontology is the explicit specification of conceptualization. It describes the knowledge of a specific domain in an abstract and simplified view which can be further used for different purposes. The ontology can either be built afresh or can reuse the existing ontology. The domain can be explicitly explained with the help of ontology which involves concepts,objects,entities and relationships existing among them [1].Ontologies are used