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Database modeling is generally focused on logical and physical database models. A logical database model is composed of entities and attributes, and it includes relationships between the different entities, which can be mandatory or not. The logical model consists of a normalized model that is generally set to third normal form. It includes many elements that make up a database, but it is not specific to any software or database implementation. Performance factors are not a major consideration at this point nor are the applications that will be using the database. The main concern is building a model of what the database would look like when capturing the data needed by the users.
The denormalization process begins with the physical database model. The database team takes the work performed in the logical model and starts to optimize it for queries, specific database implementations, and applications that may talk to the database. More specific items, like views, are added to make working with the database easier for users. The physical database model also needs to be mapped back to the logical database model; they can be very different, and each has its own purpose. As changes occur, the team must update one model from the other and maintain that mapping between them.
While database modeling focuses mostly on depicting the database, database design encompasses the entire process from the creation of requirements, business processes, logical analysis, and physical database constructs to the deployment of the database. For example, in database design, physical data modeling includes the modeling of not only tables and columns but also tablespaces, partitions, hardware, and the entire makeup of the database system. Database design includes uncovering and modeling requirements, the business processes (as they are today and where they are going in the future), the activities of the business, the logical models, and the physical database models, as well as ad dressing issues of what information is needed, how the different parts relate, how applications communicate with the data, and how the entire system is implemented.
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