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Logical resources are defined as shared passive entities that can be concurrently accessed by multiple processes. Concurrency restrictions depend upon the mode or manner in which a process may manipulate a resource. Models incorporating these single unit resources can be used to analyze information locking for consistency and integrity purposes. Mode compatibility is defined and used to derive dead-lock detection and avoidance methods. These methods generalize well-known deadlock results for single unit resources by permitting greater concurrency while still guaranteeing data consistency. This model is applicable to the standard shared (read-only) and exclusive (read-write) access modes as well as a useful subset of those proposed in the CODASYL DBMS report.
Date of Publication: Sept. 1979