Losslessness and semantic correctness of database schema transformation: another look at schema equivalence

Kobayashi, I
Kobayashi, I
Information Systems
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Kobayashi1986Losslessnessandsemanticcorrectnessofdatabaseschema.pdf0 bytes

Transformations between two groups of relation schemata play important roles in a database environment. These transformations are used for obtaining normal form relation schemata, generating certain view schemata and deciding appropriate internal schemata. They are also related to the data translation between distinct data models and hence between distinct database management systems. Relations belonging to one group of schemata are usually maintained in computer storage, while those belonging to another group of schemata can be virtual. It is always possible to retrieve data from virtual relations as if they are existing relations. However, if one would like to update virtual relations, the transformation between two groups of schemata must be a bijection. This paper presents four basic schema transformations and rules (constraints) which the two groups of relation schemata should obey for each transformation to be a bijection. Two of them are algebraic transformations and two others are functional transformations. On one group of schemata, some additional rules (constraints) may be imposed, against which database updates must be validated. Only the updates which transform one group of relations consistent with respect to the given rules into another group of relations also consistent with respect to them, are allowed. When the subject group of relation schemata is transformed into another group of relation schemata, these rules should also be transformed into those imposed on the latter group of relation schemata. Rule-transforming procedures associated with the four transformations are also discussed in this paper. The subject issue may provide foundations of normal form theory, view support problems, and physical representation of database relations. Also the rule transformation procedures can be applied to query transformation problems. Several extensions of the issue are also presented.