Tutorials SOA DevelopmentPerhaps the most common of the categories, the Enterprise Service Bus, or ESB, is considered by many to be "the technology" associated with SOA adoption. In reality, an ESB is just one way of providing the capabilities associated with consumers and providers.
There is no standard architecture for an ESB. Some vendors use a gateway-based approach exclusively, others are exclusively agent-based architecture, and others provide both. The one common thing in all of them is that the ESB represents the policy enforcement point. Enterprises that have adopted ESB technologies typically require that all requests go through it, and take measures to ensure that requests which are not sent through the ESB are not allowed.
The biggest risk that an organization may face with an ESB is that many of these products are targeted at developers. As a result, the separation of policies, or even the notion of a policy itself, may not be as clear as with other solutions. This will certainly vary by vendor; therefore, an analysis of the conceptual model of the product should be part of your evaluation process.
A s econd category of products that can provide this policy-driven infrastructure is XML appliances. These products primarily started in the XML acceleration space, expanded into perimeter security for XML over HTTP transactions, and now provide broader capabilities for additional policy domains associated with service connectivity. Some vendors are now marketing their appliances as ESBs.
Being appliances, these products typically adhere to a gateway-based model, although some of the vendors in this space create appliances by placing software on a commodity hardware platform. Those that have taken this approach may have the ability to repackage the software for installation as an agent.
The XML appliances are less likely to have a developer-centric operating model. They are more likely to present an operational model that is targeted towards an operations team rather than a development team, although just as with ESBs, there is significant variability from vendor to vendor.
