For many years, the non-monotonic reasoning commu-nity has focussed on highly expressive logics. Such logics have tumed out to be computationally expensive, and have given little support to the practical use of non-monotonic reasoning. In this work we discuss defeasible logic, a less-expressive but more efficient non-monotonic logic. We report on two new implemented systems for defeasible logic: a query answering system employing a backward-chaining approach, and a forward-chaining implementation that computes all conclusions. Our experimental evaluation demonstrates that the systems can deal with large theories (up to hundreds of thousands of rules). We show that defea-sible logic has linear complexity, which contrasts markedly with most other non-monotonic logics and helps to explain the impressive experimental results. We believe that defea-sible logic, with its eficiency and simplicity, is a good can-didate to be used as a modelling language for practical ap-plications, including modelling of regulations and business rules. 1

Defeasible logic is a rule-based nonmonotonic logic, with both strict and defeasible rules, and a priority relation on rules. We show that inference in the propositional form of the logic can be performed in linear time. This contrasts markedly with most other propositional nonmonotonic logics, in which inference is intractable. 1 Introduction Mostwork in non-monotonicreasoning has focussed on languages for whichpropositional inference is not tractable. Sceptical default reasoning is \Pi p 2 -hard, even for very simple classes of default rules, as is sceptical autoepistemic reasoning and propositional circumscription. The complexity of sceptical inference from logic programs with negation-as-failure varies according to the semantics of negation. For both the stable model semantics and the Clark completion, sceptical inference is co-NPhard. See [13, 9] for more details. Although such languages are very expressive, and this expressiveness has been exploited in answer-set progra...

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Abstract. We propose a computationally oriented non-monotonic multi-modal logic arising from the combination of agency, intention and obligation. We argue about the defeasible nature of these notions and then we show how to represent and reason with them in the setting of defeasible logic. 1

Abstract. In this paper we provide a formal framework for developing the idea of normative co-ordination. We argue that this idea is based on the assumption that agents can achieve flexible co-ordination by conferring normative positions to other agents. These positions include duties, permissions, and powers. In particular, we introduce the idea of declarative power, which consists in the capacity of the power-holder of creating normative positions, involving other agents, simply by “proclaiming” such positions. In addition, we account also for the concepts of representation, consisting in the representative’s capacity of acting in the name of his principal, and of mandate, which corresponds the mandatee’s duty to act as the mandator has requested. 1

Defeasible logic is an efficient logic for defeasible reasoning.

We propose a formal and executable framework for expressing protocols and strategies for automated (legal) negotiation. In this framework a party involved in a negotiation is represented through a software agent composed of four modules: (i) a communication module which manages the interaction with the other agents; (ii) a control module; (iii) a reasoning module specified as a defeasible theory; and (iv) a knowledge base which bridges the control and the reasoning modules, while keeping track of past decisions and interactions. The choice of defeasible logic is justified against a set of desirable criteria for negotiation automation languages. Moreover, the suitability of the framework is illustrated through two case studies.

The development of the Semantic Web proceeds in layers. Currently the most advanced layer that has reached maturity is the ontology layer, in the form of the DAML+OIL language which corresponds to a rich description logic.

Abstract. Management, execution and maintenance of Service Level Agreements (SLAs) in the upcoming service oriented IT landscape need new levels of flexibility and automation not available with the current technology. In this paper we evolve a rule based approach to SLA representation and management which allows a clean separation of concerns, i.e. the contractual business logic are separated from the application logic. We make use of sophisticated, logic based knowledge representation (KR) concepts and combine adequate logical formalisms in one expressive logic based framework called ContractLog. ContractLog underpins a declarative rule based SLA (RBSLA) language with which to describe SLAs in a generic way as machine readable and executable contract specifications. Based on ContractLog and the RBSLA we have implemented a high level architecture for the automation of electronic contracts- a rule-based Service Level Management tool (RBSLM) capable of maintaining, monitoring and managing large amounts of complex contract rules. 1 Why declarative rule-based SLA representation? Our studies of a vast number of SLAs currently used throughout the industry have revealed that today’s prevailing contracts are plain natural language documents. Consequently,