Database Design

Database Design



Database Design Process

The first step of database design is requirement collection and analysis. During this step, the database designers interview prospective database users to understand and document their data requirements. The result of this step is a concisely written set of user's requirements.


Once all the requirements have been collected and analyzed the next step is to create a conceptual schema for the database, using high-level conceptual data model. This step is called conceptual design which consists primarily of defining the data elements to be included in the database, the relationships that exist between them, and the value constraints that apply.


The conceptual schema is a concise description of the data requirements of the users and includes detailed descriptions of the entity types, relationships, and constraints. These are expressed using the concepts provided by the high-level data model. Because these concepts do not include implementation details, they are usually easier to understand and used to communicate with nontechnical users. The high-level conceptual schema can also be used as a reference to ensure that all user's data requirements are met and that the requirements do not include conflicts. This approach enables the database designers to concentrate on specifying the data, without being concerned with storage details.


The next step in database design is the actual implementation of the database, using a commercial DBMS. Most current commercial DBMSs use an implementation data model. Such as the relational or object database model. So the conceptual schema is transformed from the high-level data model into the implementation data model. This step is called logical design or data model mapping. ER diagram is converted into set relations/tables in the relational data model. Here the logical structures are defined to represent data. The outcome of logical database design is a set of well-structured relations that has a logical relationship among them.


Finally, the last step is the physical design phase, during which the internal storage structures, access paths, and file organizations for the database files are specified. In parallel with these activities, application programs are designed and implemented as database transactions corresponding to the high-level transaction specifications. Physical database design determines the physical structure of the database and includes such decisions as what access method will be used to retrieve data, and what indexes will be built to improve the performance of the system.


Database design decisions are documented in the data dictionary. The DBA control the contents of data dictionary and records there as metadata the names of data elements, files, screens, reports forms and the life. The manipulation is very carefully controlled by the DBA since the data in the data dictionary are vital to the proper functioning of the database system as a whole.


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