Constraint Logic Programming (CLP) is a merger of two declarative paradigms: constraint solving and logic programming. Although a relatively new field, CLP has progressed in several quite different directions. In particular, the early fundamental concepts have been adapted to better serve in different areas of applications. In this survey of CLP, a primary goal is to give a systematic description of the major trends in terms of common fundamental concepts. The three main parts cover the theory, implementation issues, and programming for applications.

Machine or WAM. Section 5 describes some optimizations and shows how Mercury handles I/O. Section 6 gives the current state of the Mercury system while section 7 presents performance results. 2. The Mercury language Syntactically, Mercury is similar to Prolog with additional declarations, partly because Prolog syntax is standard in the logic programming community and partly because this made it simple to execute Mercury programs using Prolog systems early in our project. Semantically, however, Mercury is very different from Prolog. Mercury is a pure logic programming language with a well-defined declarative semantics. Like Godel [14], Mercury provides declarative replacements for Prolog 's non-logical features. Unlike Godel, Mercury does not retain any non-logical features; in Mercury even I/O is declarative. Mercury is designed to appeal to at least two groups of programmers. One group is those with backgrounds in imperative languages such as C who are looking for a higher level an...

We present the clp(FD) system: a Constraint Logic Programming language with finite domain constraints...

CFT is a new constraint system providing records as logical data structure for constraint (logic) programming. It can be seen as a generalization of the rational tree system employed in Prolog II, where finer-grained constraints are used, and where subtrees are identified by keywords rather than by position. CFT is defined by a first-order structure consisting of so-called feature trees. Feature trees generalize the ordinary trees corresponding to first-order terms by having their edges labeled with field names called features. The mathematical semantics given by the feature tree structure is complemented with a logical semantics given by five axiom schemes, which we conjecture to comprise a complete axiomatization of the feature tree structure. We present a decision method for CFT, which decides entailment / disentailment between possibly existentially quantified constraints. Since CFT satisfies the independence property, our decision method can also be employed for checking the sat...

: This paper provides a mathematical analysis of the Warren Abstract Machine for executing Prolog and a correctness proof for a general compilation scheme of Prolog for the WAM. Starting from an abstract Prolog model which is close to the programmer's intuition, we derive the WAM methodically by stepwise refinement of Prolog models, proving correctness and completeness for each refinement step. Along the way we explicitely formulate, as proof assumptions, a set of natural conditions for a compiler to be correct, thus making our proof applicable to a whole class of compilers. The proof method provides a rigorous mathematical framework for the study of Prolog compilation techniques. It can be applied in a natural way to extensions and variants of Prolog and related WAMs allowing for parallelism, constraint handling, types, functional components---in some cases it has in fact been successfully extended. Our exposition assumes only a general understanding of Prolog. We reach full mathemati...

This paper presents the constraint system FT, which we feel is an intriguing alternative to Herbrand both theoretically and practically. As does Herbrand, FT provides a universal data structure based on trees. However, the trees of FT (called feature trees) are more general than the trees of Herbrand (called constructor trees), and the constraints of FT are finer grained and of different expressivity. The basic notion of FT are functional attributes called features, which provide for record-like descriptions of data avoiding the overspecification intrinsic in Herbrand's constructor-based descriptions. The feature tree structure fixes an algebraic semantics for FT. We will also establish a logical semantics, which is given by three axiom schemes fixing the first-order theory FT. FT is a constraint system for logic programming, providing a test for unsatisfiability, and a test for entailment between constraints, which is needed for advanced control mechanisms. The two major technical con...

SLG resolution uses tabling to evaluate nonfloundering normal logic programs according to the well-founded semantics. The SLG-WAM, which forms the engine of the XSB system, can compute in-memory recursive queries an order of magnitude faster than current deductive databases. At the same time, the SLG-WAM tightly integrates Prolog code with tabled SLG code, and executes Prolog code with minimal overhead compared to the WAM. As a result, the SLG-WAM brings to logic programming important termination and complexity properties of deductive databases. This article describes the architecture of the SLG-WAM for a powerful class of programs, the class of fixed-order dynamically stratified programs. We offer a detailed description of the algorithms, data structures, and instructions that the SLG-WAM adds to the WAM, and a performance analysis of engine overhead due to the extensions.

The paper provides a mathematical yet simple model for the full programming language Prolog, as apparently intended by the ISO draft standard proposal. The model includes all control constructs, database operations, solution collecting predicates and error handling facilities, typically ignored by previous theoretical treatments of the language. We add to this the ubiquitous box-model debugger. The model directly reflects the basic intuitions underlying the language and can be used as a primary mathematical definition of Prolog. The core of the model has been applied for mathematical analysis of implementations, for clarification of disputable language features and for specifying extensions of the language in various directions. The model may provide guidance for extending the established theory of logic programming to the extralogical features of Prolog. Introduction One of the original aims of mathematical semantics was to provide the programmer with a set of mathematical models and...

Since the early days of logic programming, researchers in the field realized the potential for exploitation of parallelism present in the execution of logic programs. Their high-level nature, the presence of non-determinism, and their referential transparency, among other characteristics, make logic programs interesting candidates for obtaining speedups through parallel execution. At the same time, the fact that the typical applications of logic programming frequently involve irregular computations, make heavy use of dynamic data structures with logical variables, and involve search and speculation, makes the techniques used in the corresponding parallelizing compilers and run-time systems potentially interesting even outside the field. The objective of this paper is to provide a comprehensive survey of the issues arising in parallel execution of logic programming languages along with the most relevant approaches explored to date in the field. Focus is mostly given to the challenges emerging from the parallel execution of Prolog programs. The paper describes the major techniques used for shared memory implementation of Or-parallelism, And-parallelism, and combinations of the two. We also explore some related issues, such as memory

Architecture The Alma Abstract Architecture (AAA) is the virtual architecture used during the intermediate code generation phase of the Alma-0 compiler. The AAA combines the features of the abstract machines for imperative languages and for logic programming languages. The compiler compiles the Alma-0 programs into AAA programs. In a second phase the AAA instructions are translated into C statements. As the Alma-0 language itself, the AAA aims to combine the best of both worlds; elements were taken from virtual machines used to compile imperative languages (in particular the RISC architecture described in Wirth [1996, pp. 55--59], and from the WAM machine used to compile a logical language (see Ait-Kaci [1991]). Still, the AAA resembles most the virtual machines used in the compilation of imperative languages. The additions made to provide for the extensions of the Alma-0 language are ---the failure handling instructions ONFAIL, FAIL, 40 \Delta Krzysztof R. Apt et al ---the log ...