ABSTRACT
One of the primary goals of a data management system (DBMS) is to retrieve the records under its control upon user requests. In the SQL language, such retrievals are typically formed as queries. Answering these queries efficiently is a key design objective of a data management system. To achieve this goal, one needs to consider many issues including data organization, available methods for accessing the data, user interface, effective query execution planning, and the overall system design. In this chapter, we primarily focus on the aspects that have the most direct influence on the efficiency of query processing, which primarily include three of them: the data organization, access methods, and query execution planning.25,39,47,67,79,99
Usually a query can be answered in different ways, for example, the tables and columns involved may be retrieved in different orders or through different access methods.23,44,81 However, these choices are built on top of a set of good access methods and data organizations. Therefore, we choose to concentrate more on the issues of data organizations and access methods. Furthermore, many common types of queries on scientific data do not require complex execution plans, as we explain in the next section. Thus, optimizing the execution plan is less important than the other two issues. Furthermore, much of the scientific data is not under the control of a DBMS system, but is under the control of some stand-alone systems or emerging scientific DBMSs. A discussion on the core data access methods and data organizations may influence the design and implementation of such systems.
