In this chapter, however, as well as in Chapters 11, 12, and 13, we probe below
the higher levels as we describe various methods for implementing the data
models and languages presented in preceding chapters. We start with characteristics
of the underlying storage media, such as disk and tape systems. We then
define various data structures that allow fast access to data. We consider several
alternative structures, each best suited to a different kind of access to data. The
final choice of data structure needs to be made on the basis of the expected use of
the system and of the physical characteristics of the specific machine.