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Abstract. The logic programming language Datalog has been extensively researched as a query language for deductive databases. Although similar to Prolog, the Datalog operational mechanisms are more intricate, leading to computations quite hard to debug by traditional approaches. In this paper, we present a theoretical framework for debugging Datalog programs based on the ideas of declarative debugging. In our setting, a debugging session starts when the user detects an unexpected answer for some query, and ends with the debugger pointing to either an erroneous predicate or to a set of mutually recursive predicates as the cause of the unexpected answer. Instead of representing the computations by means of trees, as usual in declarative debugging, we propose graphs as a more convenient structure in the case of Datalog, proving formally the soundness and completeness of the debugging technique. We also present a debugging tool implemented in the publicly available deductive database system DES following this theoretical framework.

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In this paper, we present our proposal to Constraint Functional Logic Programming over Finite Domains (CF LP (FD) ) with a lazy functional logic programming language which seamlessly embodies finite domain (FD) constraints. This proposal increases the expressiveness and power of constraint logic programming over finite domains (CLP (FD) ) by combining functional and relational notation, curried expressions, higher-order functions, patterns, partial applications, non-determinism, lazy evaluation, logical variables, types, domain variables, constraint composition, and finite domain constraints.We describe the syntax of the language, its type discipline, and its declarative and operational semantics. We also describe T OY(FD), an implementation for CF LP (FD) , and a comparison of our approach with respect to CLP (FD) from a programming point of view, showing the new features we introduce. And, finally, we show a performance analysis which demonstrates that our implementation is competitive with respect to existing CLP (FD) systems and that clearly outperforms the closer approach to CF LP (FD) .

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Abstract. This paper presents a debugging technique for diagnosing errors in SQL views. The debugger allows the user to specify the error type, indicating if there is either a missing answer (a tuple was expected but it is not in the result) or a wrong answer (the result contains an unexpected tuple). This information is employed for slicing the associated queries, keeping only those parts that might be the cause of the error. The validity of the results produced by sliced queries is easier to determine, thus facilitating the location of the error. Although based on the ideas of declarative debugging, the proposed technique does not use computation trees explicitly. Instead, the logical relations among the nodes of the trees are represented by logical clauses that also contain the information extracted from the specific questions provided by the user. The atoms in the body of the clauses correspond to questions that the user must answer in order to detect an incorrect relation. The resulting logic program is executed by selecting at each step the unsolved atom that yields the simplest question, repeating the process until an erroneous relation is detected. Soundness and completeness results are provided. The theoretical ideas have been implemented in a working prototype included in the Datalog system DES.

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