In this chapter our aim is to extend the use of metamodels in maintaining method knowledge in evolving ISD situations. Accordingly, we shall develop incremental method engineering principles and thus focus on our second research question (cf. Section 1.5.3):

 

 

The question deals with extending the dominant a priori ME principles through an a posteriori approach. We collect situational experiences of method use for refining methods. Whilst current ME approaches focus solely on the construction phase and expect information about methods and their use situations to be known completely beforehand, we assume that constructed methods are not necessarily applicable in the first place, situations in which they are applied change, and method users learn through their use. A posteriori refinement of methods is based on collecting and analyzing differences between intended and actual use of modeling techniques, on studying how techniques have supported modeling, and on understanding how they support problem solving. In contrast to learning about object systems under development (via IS models), our aim is to learn about methods and especially about modeling techniques (via metamodels). The proposed principles complement, but do not substitute, the ME frameworks and (meta)methods.

This chapter is organized as follows. First, in Section 5.1 we describe the motivation for incremental ME in general, and experience-based evaluation and refinement in particular. Second, in analyzing the principles of incremental ME it is useful to place this work in relation to other similar work reported in the literature. Therefore, in Section 5.2 we describe approaches proposed for method evaluation as well as point out some problems and difficulties in such evaluations. This leads us in Section 5.3 to propose mechanisms which, through the use of metamodels, can help to gather, analyze and communicate experiences about the use of modeling techniques. The ME process is explained in more detail from the view of a posteriori evaluation and refinement. Finally, Section 5.4 summarizes the chapter.