FAQ 4.07 What is the key to planning for change?

Understanding the problem domain.

Almost every OO analysis and design method promotes understanding the problem domain through some form of domain analysis. This is the process of becoming familiar with the problem domain by (among other things) interviewing domain experts, analyzing existing business processes, working with customers, and validating and refining these findings. This process produces a model of the problem domain including domain objects, services provided by these objects, and the interaction patterns of these objects.

The domain model is the extensible, flexible, reusable basis on which the software architecture should be based. The beauty of OO technology and C++ is that public inheritance (see FAQ 2.24, 7.01) can be used to reflect the fundamental, immutable properties of the problem domain and the domain model. In this way, the public inheritance relationships model the problem domain rather than depending on the fickle requirements of the even more fickle customer. Thus the architecture can and should be made to reflect the problem domain rather than the particular problem at hand.

These issues will be discussed at great length later in the book.

The key is to recognize that OO technology provides flexibility when the domain analysis is solid and the software faithfully reflects the domain analysis. Under these circumstances, changing the details of the problem creates incidental disturbances rather than fundamental disruptions.