MY BOOK REVIEW

OBJECT ORIENTED ANALYSIS and DESIGN

Book

Edward Yourdon and Carl Argila

Author

QA 76.64 Y68 1996

Reference no.

CHAPTER 7

            Grasp the subject, the word will follow.

                                                                                                                                   - Cato               

One of the characteristics of the structured analysis/ design methodology you may have practice in the past was that of hierarchical decomposition. This technique allowed complex function, data structures, etc. to be decomposed into managed chunks. The “7 + 2 rule” has been widely used as a guideline for hierarchical decomposition. Unlike structure models, however, most OOA models are relatively flat, unless the application domain lends itself to substantial used of Gen-Spec or Whole-Part structures. The complexity of large model may, instead, be dealt with by establishing a number of subjects. Each subject may be view as a sub-model, or perhaps a sup-system. In this chapter we discuss Subject layer of the OOA model for both the ESC and SBSS.

Note that the case studies in this book are sufficiently simple that each could reasonably be considered a single subject. The subject layer developed in this chapter is thus more  for pedagogical benefits than technical necessity.

The concept of a subject tends to be in the eye of the beholder, some analysts may distinguish subject on the basis of sub-domain, sub-systems, even organizational (i,e., political) or geographical subjects. Any of this criteria will work for it applied consistently. You may find to think it useful of a any subject as a Whole-Part relationship on the application domain. Ask yourself the question: ”if a decide that x should be an application domain, sub-system or whatever,

Gen-Spec structures often strongly suggest a subject. However, it is possible that the components of a Gen-Spec structure may be split between two different subjects.      

For small OOA models, a subject layer may not be necessary. A model can be partitioned into subject in a variety ways, the subjects must simply be meaningful to the user. Very large OOA models may best be approached by first establishment subjects, then component objects.