"Focusing on one vendor provides the benefit of reducing finger-pointing between vendors when things go wrong," Heffner says, but that doesn't mean having to choose a single provider for your SOA infrastructure. Instead, companies that don't want to manage lots of vendors for their SOA infrastructure can use an integrator to handle the various providers or choose a primary vendor that then manages the other providers. "Forrester's rule of thumb is to focus on a primary vendor without ruling out 'best of breed' substitutions," he says.

IT's challenge is to figure out the right way to deploy its architecture, which is where the SOA infrastructure choices come up. At a practical level, most companies already have some SOA infrastructure in place, such as EAI (enterprise application integration) middleware, Web services and related Web platforms, and messaging middleware. That established infrastructure often determines who will provide the rest of the SOA infrastructure, says Tim Hall, director of Hewlett-Packard's SOA Center.

For example, a company that has standardized on Oracle for these systems will likely go to Oracle for the rest of the SOA platform. But a company with heterogeneous systems in place is likely to continue buying "best of breed" components from a variety of vendors.

"You talk to major customers, and they have some flavor of middleware from all these companies. The question is it's not so much the issue of what you select but how do you use what you have [effectively]," Hall says. Almost every customer has middleware from different vendors, agrees Sandy Carter, IBM's vice president of SOA and WebSphere.

That heterogeneous reality means that many customers pick and choose their SOA infrastructure components as well, says Miko Matsumura, product marketing manager at Software AG: "Not all of our customers have every single component [that Software AG provides]."

A tour of SOA infrastructure providers
Vendors tend to promote themselves as offering pretty much everything a customer requires, says Forrester's Heffner. "All of them would say, 'We can do all or most all of what you need,'" directly or through partnerships.

Here's what the major providers actually offer themselves:

Hewlett-Packard: HP offers SOA governance tools and a services registry through its acquisition of Mercury Software, as well as quality management tools through its purchase of Talking Blocks.

IBM: Big Blue's SOA wares include an ESB, a process server, a portal, a mashup engine, an application server, and capabilities for business services. IBM's Tivoli unit provides services management software, and IBM's acquisition of AppSoft adds event processing.

Itko: The company provides SOA test and validation tools.

Microsoft: The software giant doesn't offer SOA products per se, but it positions products such as BizTalk Server and Windows Communication Foundation as an ESB without actually having an ESB in its product catalog.

Oracle: Its SOA arsenal includes an ESB, a BPEL process manager, business activity monitoring, and Web services management. Oracle also acquired a repository in its BEA buy.

Progress Software: The company is putting together a wide roster of SOA tools through aggressive acquisition, most recently of Iona for SOA services management. It has also bought ESB provider Sonic Systems, application infrastructure company Mindreef, Web services management vendor Actional, integration provider Pantero, and complex event processing firm Apama.

Software AG: The company offers a wide palette of SOA products for governance, design, runtime, business process management, and business activity monitoring, as well as a composite application framework. An ESB is on the roster, thanks to the company's acquisition of WebMethods.

Tibco: The vendor's offerings include a runtime platform, an ESB, and a registry.

WSO2: Taking the open source approach to SOA, WSO2 bills itself as a full-service provider, offering an ESB, a registry, identity management, a Web services application server, and a mashup server.

Paul Krill is editor at large at InfoWorld.