Transactional Middleware and Application Integration

In this section, we will examine those situations in which transactional middleware is a good match for application integration, and we will discuss how to develop application integration around transactional middleware. The first half of the section will be devoted to basic transactional middleware features. The remainder will be devoted to the integration of those features with "traditional" transactional middleware TP monitors. We will conclude by exploring the new breed of transactional middleware application servers.

Transactional middleware, including TP monitors and application servers, provides scalability, fault tolerance, and an architecture that centralizes application processing benefits to distributed computing and application integration that cannot be found in traditional development tools, or even in other types of middleware. Transactional middleware also provides virtual systems and single log-on capabilities. Its strengths often reduce the overall cost of a system.

Transactional middleware can be a good match for application integration because it provides a centralized server capable of processing information from many different resources, such as databases and applications. It ensures delivery of information from one application to the next and supports a distributed architecture (see Figure 7.1). Offsetting transactional middleware's many advantages is the cost of implementation, as well as its intrusiveness, which may preclude its use in many application integration problem domains. For transactional middleware to be most effective, applications must be altered to use it, an option that is generally forbidden within trading communities.

Figure 7.1. Transactional middleware solves the application integration problem by coordinating the connection of many different resources.

Despite its invasiveness, transactional middleware is still worth discussing because application servers are a good match for many types of application integration problem domains. Indeed, many application vendors have added application integration features to their products. For example, Portal-Oriented Application Integration, which we discussed in Chapter 5, typically leverages application servers as a mechanism to externalize many applications and data sources through the Web.

Transactional middleware has clear limitations within most application integration problem domains. Although transactional middleware excels at Service-Oriented Application Integration, or at least the sharing of common business logic to promote application integration, none of the current crop of TP monitors or application servers support "out-of-the-box" content transformation or message transformation services at least not without a lot of programming. Nor do they generally support event-driven information processing. As a result, transactional middleware does not fit well into IOAI. And if method-oriented integration proves to be transactional middleware's only benefit, then much better options may be available to the application integration architect or developer.

Message brokers or traditional message-oriented middleware are better tools for the simple sharing of information between applications. This is not to suggest that transactional middleware is not worthwhile for some application integration projects. However, its greatest benefit is at the application services level. As in all aspects of application integration, architects and developers need to understand the relative advantages and disadvantages of their options so they can make the best choices.