Entries from November 2009 ↓

Reductio ad Lucidus

In a recent comment on my Architectural Characteristics posts, Andy astutely observes that I may be “shoe-horning”. By this I assume he means that I’m taking a large and rather lumpy concept and trying to squeeze it into a smaller and more uniformly shaped container while risking some distortion in the process. I’ll admit that in this respect I’m probably guilty as charged.

But I should clarify my purpose in doing this. I’m trying to cut back the various architectural styles under consideration to a simpler form where the essential characteristics can be discerned without confusion from some other non-essential characteristics. So rather than shoehorning, I’m trying to setup a strawman model which can be used as a starting point for discussion. Or maybe like a physicist I’m trying to model a very complex phenomenon using linear approximations which explain the broad outlines of the phenomenon at the risk of falling short on some of the details.

To extend this latter metaphor, I don’t think it is too much of a stretch to say that the architectural styles I’m considering could be likened to “fundamental” architectural styles and that real-world architectures could be viewed as “superpositions” of those fundamental architectures.

If we consider the simplified forms of EAI and SOA that I describe, each style falls short of representing a real world architecture, but the upside is that the EAI and SOA styles as I describe them are distinct and easily differentiated. So we have a model which provides a way of distinguishing between different styles (via the characteristics I’ve discussed) but falls short of exactly matching a “real-world” architecure.

If we look at any real-world architecture in recent years, I think we can see a superposition of EAI and SOA concepts. This probably reflects an evolutionary path between the two styles. EAI as practiced in the early noughties had already developed the idea of a normalised data model and technology independent interfaces. These were not standardized, but some of the characteristics of SOA were apparent in what was then called EAI.

Similarly, EAI was not always about data integration. There was (and is) a distinction between data integration and process integration. EAI techniques could be used to orchestrate processes across multiple systems. This is even closer to the concept of SOA which has at its core the notion of an independent process layer seperate from the service layer.

Even if we don’t superpose EAI and SOA into one solution, there are still legitimate ways in which EAI, SOA and EDA coexist within any particular architecture. We can easily imagine a solution in which a business process is orchestrated via SOA services, reference data is synchronised using EAI and overall process state is monitored using EDA techniques such as Event Processing.

So real-world solution architectures exhibit some overlap between the different architectural styles – EAI, SOA and EDA. Some of this is due to evolutionary legacies, or due to plain-old confusion between the different styles (e.g. JABOWS as really being EAI). Some of it is also due to legitimate mixing of different styles for different aspects of a solution.

I think that real-world architectures can benefit from seperating out the “essence” of each architectural style and being explicit about how those styles are being applied. Reducing architectural styles to simplified forms clarifies the stucture of a real-world architecture. Not very different from Design Patterns, really.