---

University of California, Davis

Application Development Methodology

---

Development Technique Concepts

Domain

The collection of values from which each of the values of one or more attributes or fields must be taken.

Domains to Group Attributes

An attribute describes only one entity type and has only one meaning; Employee Start Date is not the same attribute as Seminar Presentation Start Date and Employee Start Date is distinct from Employee Birth Date. These are, however, all dates. They share the same formats, and take their values from the set of all valid dates.

Sharing a domain has a further implication for attributes that can be compared or that may participate in the same computations. For example, it is permissible to add money values together, but not to add money to weight values.

Domains are useful for classifying similar attributes so that modules developed by separate teams can share data easily. The time spent in considering them will usually pay off in an increased understanding of attributes and a reduction in the complexity of the business description and significantly foster system integration..

Hierarchy of Domains

It may be useful to develop a hierarchy of domains so that conversion of values is evenly applied among all applications. For instance a domain of volume may include "cubic centimeter" and "gallon" and the algorithm used to convert from one to the other. A second example, important to international business is the domain "money" which contains Dollars, Francs and other currency.