Nothing in enterprise IT should exist in isolation. That's the big idea underlying SOA -- leverage existing data and application assets by provisioning them as shareable services, and when you build new functionality, create it as a service so that current and future apps can draw on its power.

That architectural vision can result in a harmonious, scalable ecosystem or an unholy mess of point-to-point spaghetti; it all depends on how you plan, build, deploy, and manage. One great advantage of SOA compared with other models is that you can start small and grow organically. But the idealized endgame of SOA, which few organizations will ever reach but all should bear in mind, is an entire enterprise infrastructure that functions as one giant, service-based meta-application that can meet any business requirement.

Just as applications have lifecycles, so should an SOA. Yet whereas application lifecycle management organizes requirements, assets, testing, and change control for finite IT projects, an SOA is a broad initiative without completion date and needs a unique master plan.

To develop this lifecycle, we tapped an extended family of practitioners to examine each node in the SOA lifecycle. The advice here applies to the broadest array of SOA implementations -- from small-scale deployments that serve a limited set of requirements to projects that encompass an entire organization. Because the focus is squarely on the lifecycle, we have not addressed infrastructure issues, such as the messaging technologies that enable services to communicate. SOA security also falls outside the lifecycle, but Linthicum provides his security viewpoint at the end of this article nonetheless.

As enterprises get into the SOA game, they'll probably traverse the lifecycle more than once as initiatives grow more and more ambitious. Initial Web services efforts driven by IT may give way -- and become modified beyond recognition -- to bigger plans driven by top-down business process analysis. You may not reach, nor may there exist, an SOA end state. But at least the path to SOA success is getting clearer.

Written by Eric Knorr