Design Patterns Explained

Chapter 1 The Object-Oriented Paradigm 13
The people are responsible for themselves, instead of the control
program being responsible for them. (Note that to accomplish
this, a person must also be aware of what type of student
he or she is.)
The control program can talk to different types of people (graduate
students and regular students) as if they were exactly the
same.
The control program does not need to know about any special
steps that students might need to take when moving from class
to class.
To fully understand the implications of this, it’s important to establish
some terminology. In UML Distilled, Martin Fowler describes
three different perspectives in the software development process. 3
These are described in Table 1-1.
Table 1-1 Perspectives in the Software Development Process
Perspective Description
Conceptual This perspective “represents the concepts in the
domain under study. . . . a conceptual model
should be drawn with little or no regard for the
software that might implement it . . .”
Specification “Now we are looking at software, but we are
looking at the interfaces of the software, not the
implementation.”
Implementation At this point we are at the code itself. “This is
probably the most often-used perspective, but in
many ways the specification perspective is often
a better one to take.”
3. Fowler, M., Scott, K., UML Distilled: A Brief Guide to the Standard Object Modeling
Language, 2nd Edition, Reading, Mass.: Addison-Wesley, 1999, pp. 51–52.
Different perspectives