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Architecture of Distributed Database - DDBMS


Architecture of Distributed Database

The architecture of distributed database is basically composed of:

 1)    Global Schema: At the top level of figure 2.7 is the global schema defines all the data which are contained in the distributed database the database were not distributed at all. The global schema consists 0; the definition of a set of global relations.

2) Fragmentation Schema: Each global relation can be split in to several non-overlapping portions which are called fragments. The mapping between global relations and fragments is defined in the fragmentation schema. This mapping is one to many, i.e., several fragments correspond to one global relation, but only one global relation corresponds to one fragment.

3) Allocation Schema: Fragments are logical portions of global relations which are physically located at one or several sites of the network. The allocation schema defines at which sites (s) a fragment is located.