Viviana E. Ferraggine

Elicitation and conversion of hidden objects and restrictions in a database schema

Mapping a database schema from one model into another, with a higher semantic capacity, is a current research subject with application in several development fields, such as schema integration and translation, migration from legacy systems and reengineering of poor quality or no-longer accurate data models. Inclusion dependencies are one of the most important concepts in relational databases and they are the key to perform some reengineering of database schemas. Referential integrity restrictions (rir), a particular case of an inclusion constraint, requires that the set of distinct values occurring in some specified column, simple or composite (foreign key), must be a subset of the set of distinct primary key values drawn from the same domain. Pure inclusion dependencies (id), however, may apply between other pairs of attributes also (alternate keys or non-keys). Database schemas containing ids frequently reveal the presence of hidden objects and misrepresented relationships and, as a consequence, increase the effort to develop program applications and maintain the integrity. This work presents a heuristics for the conversion of schemas with ids into equivalent schemas with only rirs. In case some irreducible ids remain, a semantic interpretation of their necessity and maintenance is given.