We pursue the perspective of Reiter that in the situation calculus one can formalize primitive, determinate actions with axioms which, among others, include two disjoint sets: a set of successor state axioms and a set of action precondition axioms. We posed ourselves the problem of automatically generating successor state axioms, given only a set of effect axioms and a set of state constraints. This is a special version of what has been traditionally called the ramification problem. To our surprise, we found that there are state constraints whose role is not to yield indirect effects of actions. Rather, they are implicit axioms about action preconditions. As such, they are intimately related to the classical qualification problem. We also discovered that other kinds of state constraints arise; these are related to the formalization of strategic or control information. This paper is devoted to describing our results along these lines, focusing on ramification and qualification state con...

This paper considers the problem of specifying the effects of actions in the situation calculus using domain constraints. We argue that normal state constraints that refer to only the truth values of fluents are not strong enough for this purpose, and that a notion of causation needs to be employed explicitly. Technically, we introduce a new ternary predicate Caused into the situation calculus: Caused(p; v; s) if the proposition p is caused (by something unspecified) to have the truth value v in the state s. Using this predicate, we can represent not only action-triggered causal statements such as that the action load causes the gun to be loaded, but also fluent-triggered ones such as that the fact that the switch is in the up position causes the lamp to be on. The former is convenient for representing the direct effects of actions, and the latter the indirect effects. 1 Introduction We consider the problem of formalizing the effects of actions in the situation calculus [ McCarthy a...

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We define and study a high-level language for describing actions, more expressive than the action language A introduced by Gelfond and Lifschitz. The new language, AR, allows us to describe actions with indirect effects (ramifications), nondeterministic actions, and actions that may be impossible to execute. It has symbols for nonpropositional fluents and for the fluents that are exempt from the commonsense law of inertia. Temporal projection problems specified using the language AR can be represented as nested abnormality theories based on the situation calculus.

this paper we extend the language A and its translation to allow reasoning about the effects of concurrent actions. The logic programming formalization of situation calculus with concurrent actions presented in the paper is of independent interest and may serve as a test bed for the investigation of various transformations and logic programming inference mechanisms. ! 1. INTRODUCTION

We extend the ontology of the situation calculus to provide for the representation of time and event occurrences. We do this by defining a time line corresponding to a sequence of situations (called actual situations) beginning with the initial situation. Actual situations are totally ordered and the actions that lead to different actual situations are said to have occurred. This exension to the situation calculus permits one to express truths about the state of the world at different times. For example, we can state that at some point in the future certain fluent will be true. We can also express constraints on the occurrences of events, for example, that after releasing a cup, it will eventually hit the floor. Our version of the situation calculus subsumes other temporal logics. In particular, we show that the modal Temporal Logic of Concurrency [4] can be embedded in the extended situation calculus. Our extension can also realize the essential features of other first ord...

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Natural language generation (NLG) is first and foremost a reasoning task. In this reasoning, a system plans a communicative act that will signal key facts about the domain to the hearer. In generating action descriptions, this reasoning draws on characterizations both of the causal properties of the domain and the states of knowledge of the participants in the conversation. This dissertation shows how such characterizations can be specified declaratively and accessed efficiently in NLG. The heart of this dissertation is a study of logical statements about knowledge and action in modal logic. By investigating the proof-theory of modal logic from a logic programming point of view, I show how many kinds of modal statements can be seen as straightforward instructions for computationally manageable search, just as Prolog clauses can. These modal statements provide sufficient expressive resources for an NLG system to represent the effects of actions in the world or to model an addressee whose knowledge in some respects exceeds and in other respects falls short of its own. To illustrate the use of such statements, I describe how the SPUD sentence planner exploits a modal knowledge base to

We propose a modification L 1 of the action description language A. The language L 1 allows representation of hypothetical situations and hypothetical occurrence of actions (as in A) as well as representation of actual occurrences of actions and observations of the truth values of fluents in actual situations. The corresponding entailment relation formalizes various types of common-sense reasoning about actions and their effects not modeled by previous approaches. As an application of L 1 we also present an architecture for intelligent agents capable of observing, planning and acting in a changing environment based on the entailment relation of L 1 and use logic programming approximation of this entailment to implement a planning module for this architecture. We prove the soundness of our implementation and give a sucient condition for its completeness.

A knowledge representation problem can be sometimes viewed as an element of a family of problems, with parameters corresponding to possible assumptions about the domain under consideration. When additional assumptions are made, the class of domains that are being described becomes smaller, so that the class of conclusions that are true in all the domains becomes larger. As a result, a satisfactory solution to a parametric knowledge representation problem on the basis of some nonmonotonic formalism can be expected to have a certain formal property, that we call restricted monotonicity. We argue that it is important to recognize parametric knowledge representation problems and to verify restricted monotonicity for their proposed solutions. Introduction This paper is about the methodology of representing knowledge in nonmonotonic formalisms. A knowledge representation problem can be sometimes viewed as an element of a family of problems, with parameters corresponding to possible assumpt...