You can see in the above image, there is ‘Global schema’ at the top label. Global schema defines all the data Which are contained in the distributed database as if the database were not distributed at all.
The Global schema consists of the definition of a set of global relations.
Each global relation can be split into 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.
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 site(s) a fragment is located.
The Local mapping schema maps fragments in the allocation schema onto external objects in the local database.
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Can anyone please explain what is local mapping in the above architecture?
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