Evolution, architecture, and metamorphosis

dominant force driving software development in the 90's is the need to confront rapid change. Software that cannot adapt as requirements change will perish. This paper presents three patterns that address these forces. SOFTWARE TECTONICS shows how continuous evolution can prevent cataclysmic upheaval. FLEXIBLE FOUNDATIONS catalogs the need to construct systems out of stuff that can evolve along with them. METAMORPHOSIS shows how equipping systems with mechanisms that allow them to dynamically manipulate their environments can help them better integrate into these environments. Abstract 2 | FOOTE This paper presents a trio of patterns that had their genesis in an unusual collaboration between the authors. The second author is involved in a project to investigate new approaches to software development for Caterpillar, one of the worlds largest manufacturers of heavy construction equipment, and, not incidentally, a major consumer and developer of software. The first author is involved in research on object-oriented reflection and metalevel architectures, an area that has earned for itself a not altogether undeserved reputation for abstruseness. This collaboration was suggested by Ralph Johnson, who noticed an unusual and interesting connection between what the Caterpillar group was doing to try to get beyond traditional approaches to software design and development, and some of the little-known findings coming out of the reflection community. This paper represents an effort to cast these commonalties as patterns. The ultimate focus of the paper will be on two patterns that attempt to show how the forces that drive contemporary software development lead to more reflective systems. However, it is difficult to properly comprehend the forces that give rise to these patterns without setting them in the broader contexts of software reuse and evolution. As a result, this paper begins, in the Alexandrian tradition, with a high-level pattern, SOFTWARE TECTONICS, that pertains to evolution and reuse. It casts the need to cope with unrelenting change as one of the principal forces driving the software development process, and shows how this force can be dealt with. The second pattern, FLEXIBLE FOUNDATIONS, attempts to resolve some of the forces unleashed by the first by showing how to construct systems that can cope with change. The third pattern, METAMORPHOSIS, shows how the need for flexibility is omnipresent, and often can only be resolved dynamically. Our hope is that these patterns, taken together, will help the reader to perceive how objects, with their continuous, highly iterative lifecycles, encourage …