Specifying Database Updates Using A Subschema

The notion of a subschema, as a formal and abstract definition of data, constraints, and database update activities that are needed to make a transaction program, is introduced in the paper. Subschema is a component of a transaction program specification. It is designed using a user request and an existing relational database schema. The principles of a database update using subschema concepts are introduced at the abstraction level of instances to express the fact that a subschema and the corresponding database schema must satisfy certain conditions to allow safe database updates using a program made in accordance with subschema concepts. The conditions of the formal subschema and database schema consistency are introduced at the schema abstraction level, as well. It is shown that formal consistency implies database update principles, which leads to the conclusion that a subschema design process should adhere to formal consistency conditions if it is to constitute a component of a transaction program specification.