The CLP( ℛ ) language and system

Abstract

The CLP( ℛ ) programming language is defined, its underlying philosophy and programming methodology are discussed, important implementation issues are explored in detail, and finally, a prototype interpreter is described. CLP( ℛ ) is designed to be an instance of the Constraint Logic Programming Scheme, a family of rule-based constraint programming languages defined by Jaffar and Lassez. The domain of computation ℛ of this particular instance is the algebraic structure consisting of uninterpreted functors over real numbers. An important property of CLP( ℛ )is that the constraints are treated uniformly in the sense that they are used to specify the input parameters to a program, they are the only primitives used in the execution of a program, and they are used to describe the output of a program. Implementation of a CLP language, and of CLP( ℛ ) in particular, raises new problems in the design of a constraint-solver. For example, the constraint solver must be incremental in the sense that solving additional constraints must not entail the resolving of old constraints. In our system, constraints are filtered through an inference engine, an engine/solver interface, an equation solver and an inequality solver. This sequence of modules reflects a classification and prioritization of the classes of constraints. Modules solving higher priority constraints are isolated from the complexities of modules solving lower priority constraints. This multiple-phase solving of constraints, together with a set of associated algorithms, gives rise to a practical system.

A Reasoning Method for Timed CSP Based on Constraint Solving

“…The practical implication is that we may then use powerful constraint solver like CLP(R) [10] to do various proving over systems modelled using Timed CSP. Both the operational semantics and denotational semantics are encoded.…”

“…The relation tos defines a transition system interpretation of a Timed CSP process, where the state is identified by the combination of the process expression and the time variable. Using tabling mechanism offered in some of the constraint solvers like CLP(R) [10] or XSB [19], the termination of the derivation sequence based on relation tos depends on the finiteness of the reachable process expressions from the initial one. Therefore, if a process is irregular (i.e.…”

“…We then go beyond by allowing useful extensions to Timed CSP, for example, the concept of signal as in [4] for specifying broadcast communication and some liveness conditions, and integration of Timed CSP and state-based specification languages, so that we may specify and verify systems with non-trivial data structures. The practical implication of our translation of Timed CSP to CLP is that powerful constraint solvers like CLP(R) [10] can be used to prove properties over systems modelled using Timed CSP. We investigate ways of proving traditional safety properties and beyond, for example reachability, deadlock-freeness, refinement relationship,lower or upper bound of a time interval and etc.…”

Coordination of Many Agents

“…Rather than using a tailor-made CLP system, our prototype for simplicity integrates the CLP(R) system [9] with a server registry explained in Section 2.3 that manages a collection of reactors especially to handle triggering and communicates with external agents. The multi-threaded registry was implemented in C++.…”

A Fully Formalized Theory for Describing Visual Notations

“…CTL uses constraint logic programming (CLP) systems that can cope with systems of (in)equalities over (non)linear polynomials (e.g. CLP( ) [18]). The above mentioned concepts SmallCircle and VerySmallCircle can be easily specified in CTL as defined concepts.…”