ULoad: Choosing the Right Storage for Your XML Application.

A key factor for the outstanding success of database management systems is physical data independence: queries, and application programs, are able to refer to the data at the logical level, ignoring the details on how the data is physically stored and accessed by the system. The corner stone of implementing physical data independence is an access path selection algorithm: whenever a disk-resident data item can be accessed in several ways, the access path selection algorithm, which is part of the query optimizer, will identify the possible alternatives, and choose the one likely to provide the best performance for a given query [13].