On the Expressive Power of Concurrent Constraint Programming Languages

Abstract

The tcc paradigm is a formalism for timed concurrent constraint programming. Several tcc languages differing in their way of expressing infinite behaviour have been proposed in the literature. In this paper we study the expressive power of some of these languages. In particular, we show that:

(1)

recursive procedures with parameters can be encoded into parameterless recursive procedures with dynamic scoping, and vice-versa.

(2)

replication can be encoded into parameterless recursive procedures with static scoping, and vice-versa.

(3)

the languages from (1) are strictly more expressive than the languages from (2).

Furthermore, we show that behavioural equivalence is undecidable for the languages from (1), but decidable for the languages from (2). The undecidability result holds even if the process variables take values from a fixed finite domain.