It is known that there is an eqmvalence between functional dependencies m a relatmonal database and a certain fragment of proposmonal logic Thins eqmvalence is extended to include both functional and multivalued dependencmes. Thus, for each dependency there is a corresponding statement m proposmonal logic. It ms then shown that a dependency (funcuonal or multivalued) is a consequence of a set of dependencies ff and only ff the corresponding proposiuonal statement ~s a consequence of the corresponding set of proposmonal statements. Examples are given to show that these techniques are valuable mn provmdmg much shorter proofs of theorems about dependencies than have been obtained by more tradmonal means It is shown that this eqmvalence cannot be extended to include either join dependencies or embedded multmvalued dependencies.KEY WORDS AND PHRASES. relational database, functmonal dependency, multmvalued dependency, embedded multivalued dependency, join dependency, proposmUonal logmc CR CATEGORIES: 4.33, 5 21
Due to the development of the World Wide Web, the integration of heterogeneous data sources has become a major concern of the database community. Appropriate architectures and query languages have been proposed. Yet, the problem of data conversion which is essential for the development of mediators/wrappers architectures has remained largely unexplored.In this paper, we present the YAT system for data conversion. This system provides tools for the specification and the implementation of data conversions among heterogeneous data sources. It relies on a middleware model, a declarative language, a customization mechanism and a graphical interface.The model is based on named trees with ordered and labeled nodes. Like semistructured data models, it is simple enough to facilitate the representation of any data. Its main originality is that it allows to reason at various levels of representation. The YAT conversion language (called YATL) is declarative, rule-based and features enhanced pattern matching facilities and powerful restructuring primitives It allows to preserve or reconstruct the order of collections. The customization mechanism relies on program instantiations:an existing program may be instantiated into a more specific one, and then easily modified. We also present the architecture, implementation and practical use of the YAT prototype, currently under evaluation within the OPAL* project.
The purpose of this paper is to present a new approach to the conceptual design of logical schemata for relational databases. One-to-one, one-to-many, and many-to-many relationships between the attributes of database relations are modeled by means of functional dependencies and multivalued dependencies. A new type of dependency is introduced: first-order hierarchical decomposition. The properties of this new type of dependency are studied and related to the normalization process of relations. The relationship between the concept of first-order hierarchical decomposition and the notion of hierarchical organization of data is discussed through the normalization process.
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