This paper investigates transformations and normal forms in the context of Defeasible Logic, a simple but efficient formalism for nonmonotonic reasoning based on rules and priorities. The transformations described in this paper have two main benefits: on one hand they can be used as a theoretical tool that leads to a deeper understanding of the formalism, and on the other hand they have been used in the development of an efficient implementation of defeasible logic

Default reasoning comprises methods of reasoning with uncertain and incomplete information which share the idea of using default rules to represent plausible conclu-sions. Even though the applicational scope of default reasoning was clear right from the beginning, research focussed heavily on theoretical aspects and neglected for a long time pragmatic and applicational questions. This, coupled with a presentation that is usually too technical for potential applicants of this technology, has led to the impression that default reasoning �and other forms of nonmonotonic reasoning � have very lit-tle relevance to practice. This paper seeks to counter this view. It describes the basic advantages of using defaults in the representation of information and in reasoning with information. And then it presents ap-plications of default reasoning in various areas, such as software engineering, information retrieval, law, graph-ics design etc.

Policy-based access control is nowadays a common mechanism to protect data in distributed environments. However, the word policy has been given many different meanings and is used in different contexts. This chapter gives an overview of the existing approaches to logic- and rule-based system behavior specification in the light of the peculiar needs of business and security rules.