In this paper, we review recent work aimed at the application of declarative logic programming to knowledge representation in artificial intelligence. We consider exten- sions of the language of definite logic programs by classical (strong) negation, disjunc- tion, and some modal operators and show how each of the added features extends the representational power of the language.

Recently, Gelfond and Lifschitz presented a formal language for representing incomplete knowledge on actions and states, and a sound translation from this language to extended logic programming. We present an alternative translation to abductive logic programming with integrity constraints and prove the soundness and completeness. In addition, we show how an abductive procedure can be used, not only for explanation, but also for deduction and proving satisfiability under uncertainty. From a more general perspective, this work can be viewed as a-successfulexperiment in the declarative representation of and automated reasoning on incomplete knowledge using abductive logic programming. 1

data types are facilitated in Godel by its type and module systems. Thus, in order to describe the meta-programming facilities of Godel, a brief account of these systems is given. Each constant, function, predicate, and proposition in a Godel program must be specified by a language declaration. The type of a variable is not declared but inferred from its context within a particular program statement. To illustrate the type system, we give the language declarations that would be required for the program in Figure 1. BASE Name. CONSTANT Tom, Jerry : Name. PREDICATE Chase : Name * Name; Cat, Mouse : Name. Note that the declaration beginning BASE indicates that Name is a base type. In the statement Chase(x,y) !- Cat(x) & Mouse(y). the variables x and y are inferred to be of type Name. Polymorphic types can also be defined in Godel. They are constructed from the base types, type variables called parameters, and type constructors. Each constructor has an arity 1 attached to it. As an...

The consequences of a logic program depend in general upon both the rules of the program and its language. However the consequences of some programs are independent of the choice of language, while others depend on the language of the program in only a restricted way. In this paper, we define notions of language independence and language tolerance corresponding to these two cases. Furthermore, we show that there are syntactically-defined classes of programs that are language independent and language tolerant. A primary application of these results is to guarantee that for some programs it is permissible to ignore the fact that the language of the program is manysorted. This is useful to know, since query evaluation procedures generally take no account of sorts. 1 Introduction The consequences of a logic program depend in general upon both the rules of the program and its language. For instance, consider the program P 1 whose only rule is p(X) / : If the language of P 1 is unsorted ...

Declarative meta-programming is vital, since it is the most promising means by which programs can be made to reason about other programs. A metaprogram is a program that takes another program, called the object program, as data. A declarative programming language is a programming language based on a logic that has a model theory. A meta-program operates on a representation of an object...

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