Nur Izura Udzir

A Framework for Localizing Integrity Constraints Checking in Distributed Database

The validity, accuracy, and semantic of data are significant requirements in modern database applications. Semantic data in database is normally represented under the form of integrity constraints. Integrity constraints are properties, typically depending on the nature of the application domain, which must always be satisfied for the data to be considered consistent. Maintaining obedience of data with respect to integrity constraints is an essential requirement, since, if some data lacks integrity, then answers to queries cannot be trusted. Databases usually contain massive collections of data that rapidly evolve over time; this makes perfect checking at each update too time consuming a task to be feasible. In this regard, DBMS needs to be extended with the ability to automatically verify that database updates do not introduce any violation of integrity (Martinenghi, 2005; Christiansen & Martinenghi, 2006). The way we pursue here is the so-called simplification of integrity constraints. Simplification means to generate a set of integrity tests from the initial constraints whose satisfaction implies the satisfaction of the original constraints in the updated state. The main interest of the simplification process is to obtain a set of integrity tests (simplified forms) that are as easy to evaluate as possible. In this sense, simplification technique is feasible in terms of the cost of evaluating the constraints. Integrity constraint checking is the process of ensuring that the integrity constraints are satisfied by the database after it has been updated. Checking the consistency of a database state will generally involve the execution of integrity tests on the database which verify whether the database is satisfying its constraints or not. The problem of checking integrity constraints in database system has been addressed by many researchers, and has been proved to be extremely difficult to implement, particularly in distributed database. This chapter presents a framework for checking integrity constraints in a distributed database by utilizing as much as possible the information at a local site. This is achieved by considering several types of integrity tests and not focusing only on certain type of test as suggested by previous researchers. In addition, an approach for ranking and selecting suitable integrity tests that reduces the amount of data transferred across the network, the amount of data accessed, and the number of sites involved is also presented. The remainder of this chapter is organized as follows. In Section 2, the previous works related to this research are reported.