Alexandre Tessier

Declarative Diagnosis in the CLP Scheme

When a result is computed but it is considered as incorrect because it is not expected, we consider that we have a symptom (of error). The symptom may be a wrong answer or a missing answer. The role of diagnosis is to locate an error, that is a limited program fragment responsible for the symptom. The notions of symptom and error have a meaning only w.r.t. some notion of expected semantics. We consider only declarative semantics. The user does not need to understand the operational behaviour of the CLP system. Symptom and error are connected via some kind of tree and the diagnosis amounts to search for a kind of minimal symptom in this tree. Several search strategies are possible. The principles of an implementation are described, with a diagnosis session.

Declarative Debugging in Constraint Logic Programming

This paper is motivated by the declarative insufficiency diagnosis of constraint logic programs, but focuses only on theoretical viewpoints. Constraint logic program semantics is redefined in terms of proof trees using a cover relation. We give a theoretical framework where declarative diagnosis method can be studied thanks to the inductive nature of the semantics. We define the notions of symptoms and errors and prove that if there exists a symptom then there exists an error.

Theoretical Foundations of Value Withdrawal Explanations for Domain Reduction

Solvers on finite domains use local consistency notions to remove values from the domains. This paper defines value withdrawal explanations. Domain reduction is formalized with chaotic iterations of monotonic operators. To each operator is associated its dual which will be described by a set of rules. For classical consistency notions, there exists a natural such system of rules. They express value removals as consequences of other value removals. The linking of these rules inductively defines proof trees. Such a proof tree clearly explains the removal of a value (the root of the tree). Explanations can be considered as the essence of domain reduction.