Introduction

Designing a logical data model is all about preparing for the physical data design. Whether physical elements end up being a simple database, a complex data warehouse, or some other data store, the ideas behind the logical design remain the same. In this stage of development, try not to gear any design to a specific physical structure. It is important to keep in mind that we are still just planning things out, and the decisions regarding the physical elements have yet to be made.

Even though the physical elements have yet to be determined, there is a definite correlation between what you see in the logical model and what will end up being present when the model takes on a physical form. There is almost a one-to-one mapping between the objects that we discuss in the logical stage of development and similar objects in the physical databases, tables, files, and other physical articles.

Though there are many data storage possibilities, the largest percentage of these will be databasesthe storage mechanism of choice for most systems. Relational databases are databases in which data is organized into related objects. Each of the objects contained in a database is related to the others in some way.

Relational databases, based on the paper written by Dr. E. F. Codd in 1970, store sets of data in relations, called tables. The tables are often related to one another through dependencies, but this is not required. In all the time that has passed since then, the modeling of data structures has remained based on this concept.