ABSTRACT
Relational database systems provide physical data independence. That is, no matter which index configuration constitutes the physical design of the database, queries always return the same results. Of course, the performance of evaluating queries over different physical designs (i.e., different index configurations) can vary significantly. For that reason, together with the capabilities of the execution engine and query optimizer (discussed in Chapter 2), the physical design of a database determines how efficiently a query is executed.
