What role do ontologies and/or rules have on the Semantic Web?
On the Semantic Web both ontologies and rules are used to express extra constraints and logical relationships among resources. An example for their usage is to help data integration when, for example, different terms are used to describe the same thing in different data sets, or when a bit of extra knowledge may lead to the discovery of new relationships. Ontologies and rules refer to two different traditions stemming from logic, as developed in the past decades. Whereas ontologies are more closely related to knowledge representation, and particularly to description logic, rules rely more on the advances of logic programming and rule based systems. See the separate questions on Ontologies and on Rules.
On the Semantic Web both ontologies and rules are used to express extra constraints and logical relationships among resources. An example for their usage is to help data integration when, for example, different terms are used to describe the same thing in different data sets, or when a bit of extra knowledge may lead to the discovery of new relationships. Ontologies and rules refer to two different traditions stemming from logic, as developed in the past decades. Whereas ontologies are more closely related to classification systems, and particularly to description logic, rules rely more on the advances of logic programming and rule based systems. See the separate questions on Ontologies and on Rules.
