It's also important to note that you don't need Web services to create an SOA. This is true for all levels.

While services are a part of Level 1 SOAs, it's really all about information and not about application behavior. For instance, while you do indeed invoke a service to push a message on queue and retrieve a message off a queue, it really leverages services as a well-defined interface and not accessing application functionality. Sometimes SOA architects may attempt to abstract application behavior using an ESB; if that's the case, you're moving up to level 4 (discussed below). However, doing this is typically much more trouble than it's worth because you're dealing with information- oriented integration technology that is merely attempting to deal with services/behavior? an unnatural act.

At this level we have the ability to broker services between systems, allowing systems to both discover and leverage application behavior as if the functionality was local. This is the real goal of Web services, and the ability to share services not having to worry about platform-specific issues nor where the services are actually running.

What's important here is that we understand that the value is in the behavior, as well as the information bound to that behavior. This level of SOA is able to provide capabilities for discovery, access, and management. Most SOAs are built with level 4 capabilities in mind, but may work up from the lower levels. If you do that, make sure you are leveraging the right technology and standards that support all levels.

Indeed, orchestration is really another complete layer on the stack, over and above more traditional application integration approaches we deal with at the lower levels. Thus, orchestration is the science and mechanism of managing the movement of information and the invocation of services in the correct and proper order to support the management and execution of common processes that exist in and between organizations and internal applications. Orchestration provides another layer of easily defined and centrally managed processes that exist on top of existing processes, application services, and data within any set of applications.

The goal of this type of SOA is to define a mechanism to bind relevant processes that exist between internal and external systems in order to support the flow of information and logic between them, thus maximizing their mutual value. Moreover, we're looking to define a common, agreed-upon process that exists between many organizations and has visibility into any number of integrated systems, as well as being visible to any system that needs to leverage the common process model.

Summary
As services, and architectures that support them, become more of an asset within the enterprise, we need to begin to learn how to categorize the patterns of the architectures, thus the SOA levels discussion in this column. This both provides a better understanding of what is a true SOA, and allows us to pick the right level to meet the needs of our business.