Professional SQL Server™ 2005 Programming

7.4. Logical versus Physical Design

In your database work, you may have already heard about the concepts of logical versus physical models. In this section, you'll be exploring the differences between the two.

The physical model is one that's probably pretty easy to grasp. It is essentially what you have been working with up to this point in the book. You can think of anything that you can perform a CREATE statement on as being part of the physical model. Indeed — if you run any statements in SQL Server on it at all then it must be part of the physical model.

That being said, a logical model is a means to a number of different things — the physical model in particular. This means that, as you work on the logical model, you are working your way toward being able to generate DDL (Data Definition Language — or things like CREATE, ALTER, and DROP statements).

7.4.1. Purpose of a Logical Model

The first thing to understand about logical models is that they have somewhat different goals than physical models do. A logical model does several things for you:

• Allows you to begin to build abstracts of complex, data-related business issues as well as provide a high-level effort at identifying your entities

• Allows you to use these abstracts to effectively communicate business rules and content as relates to data

• Represents the purest form of the data (before you start introducing the realities of what will really work)

• Serves as a major piece of documentation in the data requirements portion ...