Defining Types

As you know, one of the primary characteristics of an attribute is its logical data type. When completing the logical modeling phase in preparation for the physical model, one must ensure that every attribute is assigned an appropriate data type.

Advanced data models borrow from OO principles by supporting the concept of a user-defined type. This can be either a simple or a complex type created by the user which is based upon the standard system-defined types, but extends these in some important way. User-defined types allow the model to represent a greater degree of abstraction, accuracy and flexibility. We will discuss the following forms of user-defined types:

• Distinct types
• Structure types
• Collection types

Using our selected modeling tool, one can work with advanced types by using this sequence: