Designing a Database:
Designing a database in a business environment can be a complex project involving many people. In some companies, the database administrator is in charge of designing, implementing, and maintaining the database and all related activities. The database administrator, along with the users and other specialists, analyzes the requirements of the proposed database. Of course, the main factor to be considered is the user’s needs.
After determining the database requirements, a schema and subschemas are developed. The schema is the conceptual, or logical design showing the relationships among data elements in a database. The schema and subschemas comprise the database’s logical design, which is the user’s view of how the data appears to be arranged on the secondary storage media.
To help maintain database security, many users will be denied access to some of the information stored in a database; therefore the logical design must take this into consideration. With the overall schema developed, various subsets of the schema, or subschemas can be designed to limit access of individual users. Users are then limited to accessing only the data in the subschemas that they are authorized to use as shown in the figure.
To complete the design of the database, the physical design- how the data are actually stored on a secondary storage media and how data are accessed- has to be determined. Users of prepackaged DBMSs are not concerned with these issues because the physical design is already determined and implemented by the program. With prepackaged DBMSs, the users need only to make sure that the software’s physical design fits that company’s needs.
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