Physical and Logical Database Design

After all business requirements have been gathered for a proposed network, they must be modeled. Models are created to visually represent the proposed network so that business requirements can easily be associated with network objects to ensure that all requirements have been completely and accurately gathered. Basically data modeling can fall into two types of categories: Physical modeling and Logical modeling.

Logical modeling deals with gathering business requirements and converting those requirements into a model. The logical model revolves around the needs of the business, not the network, although the needs of the business are used to establish the needs of the network. Logical modeling involves gathering information about business processes, categories of data, and organizational units. After this information is gathered, diagrams and reports are produced including entity relationship diagrams, business process diagrams, and eventually process flow diagrams. The diagrams produced should show the processes and data that exist, as well as the relationships between business processes and data. Logical modeling should accurately render a visual representation of the activities and data relevant to a particular business.

The diagrams and documentation generated during logical modeling is used to determine whether the requirements of the business have been completely gathered. Management, developers, and end users alike review these diagrams and documentation to determine if more work is required before physical modeling commences.

Typical deliverables for a logical model include entity relationship diagrams, business process diagrams and some type of user feedback report. Entity relationship diagrams consist of providing the development team with a picture of the different categories of data for the business, as well as how these categories of data are related to one another. The business process diagram illustrates all the parent and child processes that are performed by individuals within a company. The process model gives the development team an idea of how data moves within the organization. The logical model is probably the most important model that you are going to have to do. Even if budget money is tight, this is not a step that you want to take shortcuts on. The logical model is the building block for deigning the rest of your network.

Here is an example of an entity relationship diagram that you might use. I used an example from the movie industry, which I am used to dealing with.

Physical modeling involves the actual design of a database according to the requirements that were established during logical