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SOA Implementation: Should top down meet bottom up?

When implementing a service-oriented architecture, one application development service provider says a balance between top-down and bottom-up models is needed.

When implementing a service-oriented architecture, should business users or IT teams drive the development process? Increasingly, those two alternatives may be the prime choices. One application development service provider says either model will get you into trouble.

Application development service house Exigen Services says it has developed a middle road. Ilja Vinogradov, Vice President of engineering at Exigen, said both models are flawed.

The ''top-down'' approach starts with the enterprise looking at business processes and then considers the underlying technical services that must be provided by its systems.

"The trouble with top-down is the analysis phase is quite lengthy," said Vinogradov. You could end up with architecture that is obsolete before it is implemented."

Due to the complexity of all the pieces involved in business processes, Vinogradov said it is not uncommon to spend six months on the top-down analysis alone.

In addition, business users are less familiar with the interdependencies of existing services than development teams. This greatly increases the time it takes to develop new services.

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"The 'bottom-up' approach looks at what services they provide, and then builds those services into a business process," said Vinogradov. "The issue with a pure bottom up approach is that it usually starts small, on a few systems."

Because of this, a team of developers would have trouble covering all the complexities of an entire business process. Vinogradov said this often ends up resulting in several SOA implementations that duplicate each other and are tough to integrate.

Middle-road approach to SOA implementation

Exigen has been working with its clients on an approach that brings business users and developers together much more closely than in the more typical implementation models.

The company helps works with clients in a range of industries including software, financial services and telecomm.

"When you talk about SOA you can look at it from a pure systems integration angle or business process integration angle," said Vinogradov. "But those are connected."

The middle-road approach involves a more generalized top-down analysis and design married to a bottom-up implementation style.

The first phase involves a high-level analysis of a BPM and identifies key services and processes. The goal here is to define the scope and concepts.

"We're not overly concerned at that stage with implementation definitions," said Vinogradov, "so it's flexible enough to be able to complete that top-down phase in a short amount of time."

This commonly occurs over a period of four to eight weeks, Vinogradov says. And at that point, he said it is easier to give clients a better idea of just how much time and money they will have to spend on SOA implementation.

Under this approach, the development of the services themselves can often begin in parallel with the initial analysis. Typically, Exigen aims for three-month release cycles.

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