الفهرس | Only 14 pages are availabe for public view |
Abstract The designer of a database system faces many difficult probl ems. Examples of these problems are : Designing a physical data structure that facilitates rapid search time and convenient update Saving data integrity. Maintaining data security and privacy; and Achieving data independence. This thesis studies the objectives of a database system. It surveyes the main physical structures and addressing techn iques for single—key and multikeyed files. It focuses on the problem of coordinating concurrent accesses and updates to a database in a multiuser environment while preserving the data integrity. It surveys practical solutions to the concurrency control problem. A multiuser multikeyed access method is desig ned and implemented. It is proposed for PDP-11 computers running under the Resource Sharing Time Sharing /Extended (RSTS/E) operat ing system. The proposed access method provides a multikeyed file structure that Basic-Plus users can access and update in a, sequ ential or random order using any of t,.,ro keys. The proposed access method supports multiple concurrent accesses and updates to multikeyed files while preserving the database integrity. This is achieved through the provision of a concurrency control mecha nism that enforces transactions to follow deadlock-free locking |