Partial information based on integrity constraint checking

Integrity constraints are useful for specifying consistent states of a database, especially in distributed database systems where data may be under the control of multiple database managers. Constraints need to be checked when the underlying database is updated. Integrity constraint checking in a distributed environment may involve a distributed transaction and the expenses associated with it: two phase commit protocols, distributed concurrency control, network communication costs, and multiple interface layers if the databases are heterogeneous. The information used for constraint checking may include the contents of base relations, constraint specifications, updates to the databases, schema restrictions, stored aggregates etc. We propose using only a subset of the information potentially available for constraint checking. Thus, only data that is local to a site may be used for constraint checking thus avoiding distributed transactions. The approach is useful also in centralized systems because relatively inexpensively accessible subsets may be used for constraint checking. We discuss constraint checking for the following three subsets of the aforementioned information. (1) Constraint Subsumption. How to check one constraint C using a set of other constraint specifications C and no data, and the knowledge that the constraints in set C hold in the database? (2) Irrelevant Updates. How to check a constraint C using the database update, a set of other constraints C, and the knowledge that the constraints $\{C\}\cup{\rm\bf C}$ all hold before the update? (3) Local Checking. How to check a constraint C using the database update, the contents of the updated relation, a set of other constraints C, and the knowledge that the constraints $\{C\}\cup {\rm\bf C}$ all hold before the update? Local checking is the main focus and the main contribution of this thesis.