A locking model adopting a multi-granularity approach is proposed for concurrency control in object-oriented database systems.The model is motivated by a desire to provide high concurrency and low locking overhead in accessing objects. Locking in schemas and locking in instances are developed separately and then are integrated. Schema changes and composite objects are also taken into account. A dual queue scheme for efficient scheduling of lock requests is developed. The model consists of a

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... set of lock modes, a compatibility matrix, and a locking protocol. Characteristic query examples on single class, class lattice, and composite objects are used to illustrate the comparison between the ORION model and the proposed model. It is shown that our locking model has indeed made some improvements and is suitable for concurrency control in object-oriented databases. Although there is some common consensus [I], 121, 1221, 1231, [24], [25], 1261, [27] on what object-oriention means and what an object-oriented database is, each object-oriented database system has its own data model. We will first introduce a basic object-oriented data model. Then, some specific features relevant to our proposed locking model are reviewed.