PROJECT REPORT ON DATABASE MANAGEMENT SYSTEM


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Abstract

A distributed database can be defined as consisting of a collection of data with different parts under the control of separate DBMSs running on independent computer systems. All the computers are interconnected and each system has autonomous processing capability serving local applications. Each system participates, as well, in the execution of one or more global applications. Such applications require data from more than one site. The distributed nature of the database is hidden from users and this transparency manifests itself in a number of ways.

Fragmentation Independence (Transparency)

• A distributed system supports data fragmentation if a given relation can be divided up into pieces or "fragments" for physical storage purposes
• A system that supports data fragmentation should also support fragmentation
independence (also known as fragmentation transparency)

Operating System Independence

It is obviously desirable, not only to be able to run the same DBMS on different hardware systems, but also to be able to run it on different operating systems - even different operating systems on the same hardware
• From a commercial point of view, the most important operating system environments, and hence the ones that (at a minimum) the DBMS should
• support, are probably MVS/XA, MVS/ESA, VM/CMS, VAX/VMS, UNIX (various flavours), OS/2, MS/DOS, Windows

Why distributed databases?

1) Organizational and economic reasons Many organizations are decentralized, and a distributed database approach fits more naturally the structure of the organization. With the recent developments in computer technology, the economy-of-scale motivation for having large, centralized computer centers is becoming questionable. However, the organizational and economic motivations are probably the most important reason for developing distributed databases.
2) Interconnection of existing databases distributed databases are the natural solution when several databases already exist in an organization and the necessity of performing global applications arises. In this case, the distributed database is created bottom-up from the preexisting local databases.
3) Incremental growth if an organization grows by adding new, relatively autonomous organizational units (new branches, new warehouses, etc), then the distributed database approach supports a smooth incremental growth with a minimum degree of impact on the already existing units.
4) Reduced communication overhead In a geographically distributed database like the database of Example 1.1, the fact that many applications are local clearly reduces the communication overhead with respect to a centralized database.
5) Performance considerations The existence of several autonomous processors results in the increase of performance through a high degree of parallelism. This consideration can be applied to any multiprocessor system, and not only to distributed databases.
6) Reliability and availability the distributed database approach, especially with redundant data, can be used also in order to obtain higher reliability and availability.