Techreport,
Open and Closed Reasoning in the Semantic Web
Centro de Inteligncia Artificial da Universidade Nova de Lisboa, 2005. Available from http://centria. di. fct. unl. pt/cd, (2005)
Abstract
The Semantic Web brings new problems for the knowledge representation community, due to its distributed and world-wide character. At the time of the start of the Semantic Web Initiative it was clearly marked that the globalization of Knowledge Representation introduces new challenges: The Semantic Web is what we will get if we perform the same globalization process to Knowledge Representation that the Web initially did to Hypertext. We remove the centralized concepts of absolute truth, total knowledge, and total provability, and see what we can do with limited knowledge. 8 In the same set of documents 6, the following fundamental theoretical problems have been identified (besides other ones): • Negation, Contradiction and Inconsistencies • Open World versus Closed World assumptions • Rule Systems in the Semantic Web For the time being, the first two issues have been circumvented by discarding the facilities to introduce them, namely classical negation and closed world assumptions in RDF(S) 20. The widely recognized need of having rules in the Semantic Web 23, 32 restarted the discussion of the fundamentals of closedworld reasoning in the Semantic Web, and the appropriate mechanisms in Rule Systems to implement it, and in particular “negation as failure.” The RDF(S) recommendation 20 has been a major breakthrough, and provides solid ground to discuss the issues. We defend that partial logics 2, 38, 36, 29, 30, 27, 28, 22 are a step through, and a necessary one, for a powerful and expressive Semantic Web. Furthermore, we claim that semantics like the ones proposed in the logic programming and deductive databases communities 17, 18, 36, 24, 30, 1, 33, 11, 13, 14, 28, 5 can be immediately used for specifying Rule Systems in the Semantic Web, in particular the one we have adopted in this paper 22.
