Framework of Distributed Database Design - DDBMS


Framework of Distributed Database Design

The design of a centralised database amounts to:

1) Designing to "conceptual schema" which describes the integrated database.

2) Designing the ”physical database" i.e., mapping the conceptual schema to storage area and determining appropriate access methods.

In a distributed database these two problems become the design of the global schema and the design of the local physical database at each site, the technique which can be applied to these problems are the same as in centralised database.

The distribution of the database adds to the above problems two new ones:

1) Designing the fragmentation, i.e., determining the global relations are subdivided into horizontal, vertical or mixed fragments.

2) Designing the allocation of fragment, i.e., determining how fragments are mapped to physical image.

These two problems fully characterize the design of data distribution

The distinction between these two problems is conceptually relevant, since the first one deal with the logical criteria which motivates the fragmentation of a global relation, while the second one deals with the "physical" placement of data at the various sites.