Yves Lespérance

Golog: A logic programming language for dynamic domains

Abstract This paper proposes a new logic programming language called GOLOG whose interpreter automatically maintains an explicit representation of the dynamic world being modeled, on the basis of user supplied axioms about the preconditions and effects of actions and the initial state of the world. This allows programs to reason about the state of the world and consider the effects of various possible courses of action before committing to a particular behavior. The net effect is that programs may be written at a much higher level of abstraction than is usually possible. The language appears well suited for applications in high level control of robots and industrial processes, intelligent software agents, discrete event simulation, etc. It is based on a formal theory of action specified in an extended version of the situation calculus. A prototype implementation in Prolog has been developed.

ConGolog , a concurrent programming language based on the situation calculus

Abstract As an alternative to planning, an approach to high-level agent control based on concurrent program execution is considered. A formal definition in the situation calculus of such a programming language is presented and illustrated with some examples. The language includes facilities for prioritizing the execution of concurrent processes, interrupting the execution when certain conditions become true, and dealing with exogenous actions. The language differs from other procedural formalisms for concurrency in that the initial state can be incompletely specified and the primitive actions can be user-defined by axioms in the situation calculus. Some mathematical properties of the language are proven, for instance, that the proposed semantics is equivalent to that given earlier for the portion of the language without concurrency.

Iterated belief change in the situation calculus

John McCarthys situation calculus has left an enduring mark on artificial intelligence research. This simple yet elegant formalism for modelling and reasoning about dynamic systems is still in common use more than forty years since it was first proposed. The ability to reason about action and change has long been considered a necessary component for any intelligent system. The situation calculus and its numerous extensions as well as the many competing proposals that it has inspired deal with this problem to some extent. In this paper, we offer a new approach to belief change associated with performing actions that addresses some of the shortcomings of these approaches. In particular, our approach is based on a well-developed theory of action in the situation calculus extended to deal with belief. Moreover, by augmenting this approach with a notion of plausibility over situations, our account handles nested belief, belief introspection, mistaken belief, and handles belief revision and belief update together with iterated belief change.

Al models for business process reengineering

Most models fail to capture the rationale behind processes, making business reengineering less effective. The authors describe their I* framework, which views organizations as collections of actors with strategic interests, and interdependencies involving goals, tasks, and resources. The authors discuss the ConGolog framework, which supports reasoning about the dynamics of processes under incomplete knowledge.

The cognitive agents specification language and verification environment for multiagent systems

The Cognitive Agents Specification Language (CASL) is a frame-work for specifying multiagent systems. It has a mix of declarative and procedural components to facilitate the specification and verification of complex multiagent systems. In this paper, we describe CASL and a verification environment (CASLve) for it based on the PVS verification system. We give an example of a multiagent meeting scheduler application specified with CASL. To illustrate the verification system, we discuss a proof we carried out in it, namely, that all bounded-loop CASL specifications terminate.

On the Semantics of Deliberation in Indigolog—from Theory to Implementation

We develop an account of the kind of deliberation that an agent that is doing planning or executing high-level programs under incomplete information must be able to perform. The deliberators job is to produce a kind of plan that does not itself require deliberation to interpret. We characterize these as epistemically feasible programs: programs for which the executing agent, at every stage of execution, by virtue of what it knew initially and the subsequent readings of its sensors, always knows what step to take next towards the goal of completing the entire program. We formalize this notion and characterize deliberation in the situation calculus based IndiGolog agent programming language in terms of it. We also show that for certain classes of problems, which correspond to those with bounded solutions and those with solutions without sensing, the search for epistemically feasible programs can be limited to programs of a simple syntactic form. Finally, we discuss implementation issues and execution monitoring and replanning too.

IndiGolog: a high-level programming language for embedded reasoning agents

IndiGolog isaprogramming languagefor autonomousagentsthat sense their environment anddo planning astheyoperate. Insteadof classical planning, it supports high-level program execution. The programmer provides a high-level nondeterministicprograminvolving domain-speci? c actions andteststo perform the agent’s tasks. The IndiGolog interpreterthenreasons aboutthepreconditions andeffectsofthe actionsintheprogramtonda legalterminatingexecution.To support this, the programmer provides a declarative specication of the domain (i.e.,primitive actions,preconditions andeffects, whatis known aboutthe initial state)inthe situation calculus. Theprogrammer can controlthe amountof non-determinism in the program and how muchof it is searched over. The language isrichand supports concurrentprogramming.Programsareexecuted onlinetogether withsensingthe environment and monitoringforevents,thus supporting thedevelopmentofreactiveagents.We discussthe language, itsimplementation, and applicationsthathave beenrealized withit.

Ability and knowing how in the situation calculus

Most agents can acquire information about their environments as they operate. A good plan for such an agent is one that not only achieves the goal, but is also executable, i.e., ensures that the agent has enough information at every step to know what to do next. In this paper, we present a formal account of what it means for an agent to know how to execute a plan and to be able to achieve a goal. Such a theory is a prerequisite for producing specifications of planners for agents that can acquire information at run time. It is also essential to account for cooperation among agents. Our account is more general than previous proposals, correctly handles programs containing loops, and incorporates a solution to the frame problem. It can also be used to prove programs containing sensing actions correct.

A Situation Calculus Approach to Modeling and Programming Agents

The notion of computational agents has become very fashionable lately [24, 32]. Building such agents seems to be a good way of congenially providing services to users in networked computer systems. Typical applications are information retrieval over the internet, automation of common user activities, smart user interfaces, integration of heterogenous software tools, intelligent robotics, business and industrial process modeling, etc. The term “agent” is used in many different ways, so let us try to clarify what we mean by it. We take an agent to be any active entity whose behavior is usefully described through mental notions such as knowledge, goals, abilities, commitments, etc. (This is pretty much the standard usage in artificial intelligence, in contrast to the common view of agents as scripts that can execute on remote machines). Moreover, we will focus on the approach to building applications that involves designing a system as a collection of interacting agents.

Modeling Dynamic Domains with ConGolog

In this paper, we describe the process specification language ConGolog and show how it can be used to model business processes for requirements analysis. In ConGolog, the effects of actions in a dynamic domain are specified in a logical framework. This supports modeling even in the absence of complete information. The behavior of agents in the domain is specified in a concurrent process language, whose semantics is defined in the same logical framework. We then describe a simulation tool implemented in terms of logic programming technology. As well, we discuss a verification tool which is being developed based on theorem proving technology.