Carles Farré

Containment of conjunctive queries over databases with null values

We study containment of conjunctive queries that are evaluated over databases that may contain tuples with null values. We assume the semantics of SQL for single block queries with a SELECT DISTINCT clause. This problem (“null containment” for short) is different from containment over databases without null values and sometimes more difficult. We show that null-containment for boolean conjunctive queries is NP-complete while it is

Validation of mappings between schemas

\mathit\Pi^{\rm P}_{2}

AuRUS: automated reasoning on UML/OCL schemas

-complete for queries with distinguished variables. However, if no relation symbol is allowed to appear more than twice, then null-containment is polynomial, as it is for databases without nulls. If we add a unary test predicate IS NULL, as it is available in SQL, then containment becomes

Providing Explanations for Database Schema Validation

\mathit\Pi^{\rm P}_{2}

SVTe: a tool to validate database schemas giving explanations

-hard for boolean queries, while it remains in

A Survey on Software Release Planning Models

\mathit\Pi^{\rm P}_{2}

SVT: schema validation tool for microsoft SQL-server

for arbitrary queries.

A New Approach for Checking Schema Validation Properties

Mappings between schemas are key elements in several contexts such as data exchange, data integration and peer data management systems. In all these contexts, the mapping design process requires the participation of a mapping designer, who needs to be able to validate the mapping that is being defined, i.e., check whether the mapping is in fact what the designer intended. However, to date very little work has directly focused on the effective validation of schema mappings. In this paper, we present a new approach for validating schema mappings that allows the mapping designer to ask whether they have certain desirable properties. We consider four properties of mappings: mapping satisfiability, mapping inference, query answerability and mapping losslessness. We reformulate these properties in terms of the problem of checking whether a query is lively over a database schema. A query is lively if there is a consistent instance of the database for which the query gives a non-empty answer. To show the feasibility of our approach, we use an implementation of the CQC method and provide some experimental results.

AuRUS: explaining the validation of UML/OCL conceptual schemas

To ensure the quality of an information system, the conceptual schema that represents its domain must be semantically correct. We present a prototype to automatically check whether a UML schema with OCL constraints is right in this sense. It is well known that the full expressiveness of OCL leads to undecidability of reasoning. To deal with this problem, our approach finds a compromise between expressiveness and decidability, thus being able to handle very expressive constraints guaranteeing termination in many cases.

Computing explanations for unlively queries in databases

We propose a new method for database schema validation that provides an explanation when it determines that a certain desirable property of a database schema does not hold. Explanations are required to give the designer a hint about the changes of the schema that are needed to fix the problem identified. Our method is an extension of the CQC method, which has been shown successful for testing such properties.