Showing papers by "James Bailey published in 2001"

Transaction oriented computational models for multi-agent systems

Abstract: BDI (Belief, Desire, Intention) is a mature and commonly adopted architecture for intelligent agents. However, the current computational model adopted by BDI has a number of problems with concurrency control, recoverability and predictability. This has hindered the construction of agents having robust and predictable behaviour. Indeed the conceptual and practical tools needed for building dependable agent systems, resilient to faults and other unexpected situations, are still at an early stage of research. To this end, we propose to use ideas from established database technology as an adjunct to BDI agent systems. In the long term, we envisage a two layer model for distributed system development. The upper layer, called "behavioural" in our scheme, consists of concepts and techniques coming from agent research. The lower layer, called "control", is based on more traditional computer technologies and implements the actions decided by the upper layer. The emphasis of the upper behavioural layer is on flexibility of the software development process, in order to be effective in application domains that are difficult to analyse or rapidly changing. By contrast, the main focus of the lower control layer is rigorous and efficient implementation within wellknown boundaries. We discuss the development of an agent system having a computational model with well-defined correctness criteria. Instead of hardwiring robustness and fault-tolerant behaviour into agent plans, well defined notions of correctness exist at the semantic level. Verification can then be undertaken at the desired level of abstraction.

Expressiveness issues and decision problems for active database event queries

Abstract: A key facility of active database management systems is their ability to detect and react to the occurrence of events. Such events can be either atomic in nature, or specified using an event algebra to form complex events. An important role of an event algebra is to define the semantics of when events become invalid (event consumption). In this paper, we examine a simple event algebra and provide a logical framework for specification of various consumption policies. We then study the problems of equivalence and implication, identifying a powerful class of complex events for which equivalence is decidable. We then demonstrate how extensions of this class lead to undecidability.

Expressiveness Issues and Decision Problems for Active Database Event Queries

Abstract: A key facility of active database management systems is their ability to detect and react to the occurrence of events. Such events can be either atomic in nature, or specified using an event algebra to form complex events. An important role of an event algebra is to define the semantics of when events become invalid (event consumption). In this paper, we examine a simple event algebra and provide a logical framework for specification of various consumption policies. We then study the problems of equivalence and implication, identifying a powerful class of complex events for which equivalence is decidable. We then demonstrate how extensions of this class lead to undecidability.

Optimising Active Database Rules by Partial Evaluation and Abstract Interpretation

Abstract: A key issue for active databases is optimising the execution event-condition-action rules. In this paper we show how partial evaluation provides a formal and general route to optimising such rules. We produce a specialised version of the rule execution semantics for each possible sequence of actions that may execute from the current database state. This gives the opportunity to optimise rule execution for each particular sequence of actions. We obtain information about possible sequences of rule executions actions by applying abstract interpretation to the rule execution semantics. Our techniques are applicable both statically, i.e. at rule compilation time, and dynamically, during rule execution.