5. The Fractal Nature of SOA Federations: A Real World Example

Fractal concepts are often said to be recursively self-similar across multiple levels of abstraction. In this paper, we describe our experience with the fractal nature of SOA designs for sustainment management tools as these tools evolve into even more dynamic, federated systems that are orchestrated over the web. This chapter summarizes insights gained from more than twenty years of software development, maintenance, and evolution of a major pavement engineering tool named PAVER™. We consider both theoretical and experiential aspects of SOA federations at three levels of abstraction: (1) a loosely coupled federation of enterprise systems with PAVER™ as one member, (2) a tightly coupled federation of two pavement management tools (PAVER™ and PCASE) where each has a separate domain identity and development team, and (3) an emerging federation of plugin tools, which provide additional pavement engineering functionality and can come from competing civil engineering firms. These plugin tools exist at different levels of abstraction within the level of the main system and are, again, fractal. We organize the presentation of our experiences in this domain by describing how SOA elements including Ontologies, Discovery, Composition, and Orchestration are fractal whether we are looking at algorithms or persistent state. We also define and describe a third orthogonal fractal dimension: Evolution. Although the details of the implementation solutions at the differing levels of abstraction can be substantially different, we will show that the underlying principles are strikingly similar in what problems they need to solve and how they generally go about solving them.