**Description Logic Programs under Probabilistic Uncertainty and Fuzzy Vagueness**

In International Journal of Approximate Reasoning, 2009

This paper is directed towards an infrastructure for handling both uncertainty and vagueness in the Rules, Logic, and Proof layers of the Semantic Web. More concretely, we present probabilistic fuzzy description logic programs, which combine fuzzy description logics, fuzzy logic programs (with stratified default-negation), and probabilistic uncertainty in a uniform framework for the Semantic Web. We define important concepts dealing with both probabilistic uncertainty and fuzzy vagueness, such as the expected truth value of a crisp sentence and the probability of a vague sentence. Furthermore, we describe a shopping agent example, which gives evidence of the usefulness of probabilistic fuzzy~description logic programs in realistic web applications. We also provide algorithms for query processing in probabilistic fuzzy description logic programs, and we delineate a special case where~query processing~can be done in polynomial time in the data complexity.