The basic architecture of most DBMSs is relatively similar. The three-schema architecture is the basis of DBMS and consists of an external schema, logic schema and internal schema.
- The external schema defines one view of the data as it is seen by specific applications or end-users.
- The conceptual or logic schema defines data as it is viewed from the perspective of the system designer.
- Finally, the internal schema of the DBMS, defines data as it is arranged and stored inside the application itself and is totally dependent on particular implementation.
As a user enters commands regarding retrieval or manipulation of data, it is entered into the DBMS on the external end of the three schema architecture and further through the process it is translated into machine language on the internal end, where it can then be pulled from the stored data.
The process of normalization is used to organize the data within a DBMS so that it is more easily maintained and manipulated.
Examples
Oracle- A large enterprise DBMS. Relatively expensive, but worth the expense due to it's reliability. It includes many features which are important to large companies. It is able to run queries very quickly and using less disks.
MySQL-Opensource DBMS. Free to users and the public to improve the software and make adjustments.
AccPac- Accounting based DBMS
References
Three schemes architecture. (2009) Accessed April 6, 2009 from: http://www.gitta.info/DBSysConcept/en/html/DBMSArchitec_learningObject1.html
Oracle web-site: http://www.oracle.com/index.html
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