Losslessness and semantic correctness of database schema transformation: Another look of schema equivalence (Q1072724)

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.