Besik Dundua

A rule-based approach to XML processing and web reasoning

We illustrate the potential of conditional hedge transformations in Web-related applications on the example of PρLog: an extension of logic programming with advanced rule-based programming features for hedge transformations, strategies, and regular constraints.

Constraint Logic Programming for Hedges: A Semantic Reconstruction

We describe the semantics of CLP(H): constraint logic programming over hedges. Hedges are finite sequences of unranked terms, built over variadic function symbols and three kinds of variables: for terms, for hedges, and for function symbols. Constraints involve equations between unranked terms and atoms for regular hedge language membership. We give algebraic semantics of CLP(H) programs, define a sound, terminating, and incomplete constraint solver, and describe some fragments of constraints for which the solver returns a complete set of solutions.

CLP(H): Constraint logic programming for hedges

CLP(H) is an instantiation of the general constraint logic programming scheme with the constraint domain of hedges. Hedges are finite sequences of unranked terms, built over variadic function symbols and three kinds of variables: for terms, for hedges, and for function symbols. Constraints involve equations between unranked terms and atoms for regular hedge language membership. We study algebraic semantics of CLP(H) programs, define a sound, terminating, and incomplete constraint solver, investigate two fragments of constraints for which the solver returns a complete set of solutions, and describe classes of programs that generate such constraints.

An Overview of P\(\rho \)Log

This paper describes P\(\rho \)Log: a tool that combines Prolog with the \(\rho \)Log calculus. Such a combination brings strategy-controlled conditional transformation rules into logic programming. They operate on sequences of terms. Transformations may lead to several results, which can be explored by backtracking. Strategies provide a control on rule applications in a declarative way. They are programmable: users can construct complex strategies from simpler ones by special combinators. Different types of first- and second-order variables provide flexible control on selecting parts from sequences or terms. As a result, the obtained code is usually pretty compact and declaratively clear. In programs, P\(\rho \)Log-specific code can be intermixed with the standard Prolog code. The tool is implemented and tested in SWI-Prolog.

Lambda Calculus with Regular Types

In this paper we introduce λR: A foundational calculus for sequence processing with regular expression types. Its term language is the lambda calculus extended with sequences of terms and its types are regular expressions over simple types. We provide a flexible notion of subtyping based on the semantic notion of nominal interpretation of a type. Then we prove that types are preserved by reduction (subject reduction), and that there exist no infinite reduction sequences starting at typed terms (strong normalization).

Unranked tableaux calculus for web related applications

In the present paper unranked tableaux calculus is discussed, which extends the classical first order tableaux calculus for formulas over unranked terms. The correctness and completeness theorems of the calculus are proved and its expressive power in Web-related applications are illustrated.

P-rho-Log: Combining Logic Programming with Conditional Transformation Systems

P-rho-Log extends Prolog by conditional transformations that are controlled by strategies. We give a brief overview of the tool and illustrate its capabilities.

A Constraint Solver for Equations over Sequences and Contexts

In this paper we propose a solving algorithm for equational constraints over unranked terms, contexts, and sequences. Unranked terms are constructed over function symbols which do not have fixed arity. For some function symbols, the order of the arguments matters (ordered symbols). For some others, this order is irrelevant (unordered symbols). Contexts are unranked terms with a single occurrence of hole. Sequences consist of unranked terms and contexts. Term variables stand for single unranked terms, sequence variables for sequences, context variables for contexts, and function variables for function symbols. We design an terminated and incomplete constraint solving algorithm, and indicate a fragment for which the algorithm is complete.

Strategies in PRholog

PRholog is an experimental extension of logic programming with strategic conditional transformation rules, combining Prolog with Rholog calculus. The rules perform nondeterministic transformations on hedges. Queries may have several results that can be explored on backtracking. Strategies provide a control on rule applications in a declarative way. With strategy combinators, the user can construct more complex strategies from simpler ones. Matching with four different kinds of variables provides a flexible mechanism of selecting (sub)terms during execution. We give an overview on programming with strategies in PRholog and demonstrate how rewriting strategies can be expressed.