Reasoning on the Web with Open and Closed Predicates

SQL, Prolog, RDF and OWL are among the most prominent and most widely used computational logic languages. However, SQL, Prolog and RDF do not allow the representation of negative information, only OWL does so. RDF does not even include any negation concept. While SQL and Prolog only support reasoning with closed predicates based on negation-as-failure, OWL supports reasoning with open predicates based on classical negation, only. However, in many practical application contexts, one rather needs support for reasoning with both open and closed predicates. To support this claim, we show that the well-known Web vocabulary FOAF includes all three kinds of predicates i.e. closed, open and partial predicates. Therefore, reasoning with FOAF data, as a typical example of reasoning on the Web, requires a formalism that supports the distinction between open and closed predicates. We argue that ERDF, an extension of RDF, offers a solution to deal with this problem.