Schema mappings define relationships between schemas in a declarative way. We demonstrate MVT, a mapping validation tool that allows the designer to ask whether the mapping has certain desirable properties. The answers to these questions will provide information on whether the mapping adequately matches the intended needs and requirements. MVT is able to deal with a highly expressive class of mappings and database schemas, which allows the use of negations, order comparisons and null values. The tool does not only provide a Boolean answer as test result, but also a feedback for that result. Depending on the tested property and on the test result, the provided feedback can be in the form of example schema instances, or in the form of an explanation, that is, highlighting the mapping assertions and schema constraints responsible for getting such a result.

In this paper we present LEARN-SQL, a system conforming to the IMS QTI specification that allows on-line learning and assessment of students on SQL skills in an automatic, interactive, informative, scalable and extensible manner.

A query is unlively if it always returns an empty answer. Debugging a database schema requires not only determining unlively queries, but also fixing them. To the best of our knowledge, the existing methods do not provide the designer with an explanation of why a query is not lively. In this paper, we propose a method for computing explanations that is independent of the particular method used to determine liveliness. It provides three levels of search: one explanation, a maximal set of non-overlapping explanations, and all explanations. The first two levels require only a linear number of calls to the underlying method. We also propose a filter to reduce the number of these calls, and experimentally compare our method with the best known method for finding unsatisfiable subsets of constraints.

We show that database schema validation and update processing problems such as view updating, materialized view maintenance, integrity constraint checking, integrity constraint maintenance or condition monitoring can be classified as problems of either abductive or deductive nature, according to the reasoning paradigm that inherently suites them. This is done by performing abductive and deductive reasoning on the event rules (Olivé 1991), a set of rules that define the difference between consecutive database states. In this way, we show that it is possible to provide methods able to deal with all these problems as a whole. We also show how some existing general deductive and abductive procedures may be used to reason on the event rules. In this way, we show that these procedures can deal with all database schema validation and update processing problems considered in this paper.

We propose two interpretations of the event rules which provide a common framework for classifying and specifying deductive database updating problems such as view updating, materialized view maintenance, integrity constraints checking, integrity constraints maintenance, repairing inconsistent databases, integrity constraints satisfiability or condition monitoring. Moreover, these interpretations allow us to identify and to specify some problems that have received little attention up to now like enforcing or preventing condition activation. By considering only a unique set of rules for specifying all these problems, we want to show that it is possible to provide general methods able to deal with all these problems as a whole.>