A timed concurrent constraint language
Information and Computation
Well-structured transition systems everywhere!
Theoretical Computer Science
CONCUR '90 Proceedings of the Theories of Concurrency: Unification and Extension
General decidability theorems for infinite-state systems
LICS '96 Proceedings of the 11th Annual IEEE Symposium on Logic in Computer Science
The Munich Rent Advisor: A success for logic programming on then Internet
Theory and Practice of Logic Programming
The computational power and complexity of constraint handling rules
ACM Transactions on Programming Languages and Systems (TOPLAS)
Expressiveness of Multiple Heads in CHR
SOFSEM '09 Proceedings of the 35th Conference on Current Trends in Theory and Practice of Computer Science
Constraint Handling Rules
CLP projection for constraint handling rules
Proceedings of the 13th international ACM SIGPLAN symposium on Principles and practices of declarative programming
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We study the decidability of termination for two CHR dialects which, similarly to the Datalog like languages, are defined by using a signature which does not allow function symbols (of arity 0). Both languages allow the use of the = built-in in the body of rules, thus are built on a host language that supports unification. However each imposes one further restriction. The first CHR dialect allows only range-restricted rules, that is, it does not allow the use of variables in the body or in the guard of a rule if they do not appear in the head. We show that the existence of an infinite computation is decidable for this dialect. The second dialect instead limits the number of atoms in the head of rules to one. We prove that in this case, the existence of a terminating computation is decidable. These results show that both dialects are strictly less expressive1 than Turing Machines. It is worth noting that the language (without function symbols) without these restrictions is as expressive as Turing Machines.