Applying UML and Patterns: An Introduction to Object-Oriented Analysis and Design and the Unified Process, Second Edition

Introduction

Object design is sometimes described as some variation of the following:

After identifying your requirements and creating a domain model, then add methods to the software classes, and define the messaging between the objects to fulfill the requirements.

Such terse advice is not especially helpful, because there are deep principles and issues involved in these steps. Deciding what methods belong where, and how the objects should interact, is terribly important and anything but trivial. It takes careful explanation, applicable while diagramming and programming.

And this is a critical step—this is at the heart of what it means to develop an object-oriented system, not drawing domain model diagrams, package diagrams, and so forth.