Section 3.1. Heterogeneity of Communication Mechanisms

3.1. Heterogeneity of Communication Mechanisms

Techniques for the distribution of enterprise software components are manifold. As will be seen in the remainder of this book, this heterogeneity is inevitable due to the various communication requirements of enterprises.

The situation is comparable to communication in real lifemany forms of communication exist (verbal, non-verbal, written, etc.), and every form has its own purpose. It is not possible to replace one form with another without reducing expressiveness.

Figure 3-1 depicts three possible levels of heterogeneity of distribution techniques:

• Communication mode

• Products

• Additional runtime features

Figure 3-1. Distribution techniques for enterprise applications are characterized by manifold requirements and consequently by various dimensions of heterogeneity.

Communication modes are basically distinguished between synchronous and asynchronous mechanisms. Evidently both are required in real-world projects. However, in practice, there are usually numerous variants of these basic modes of communication. Obviously, one can encounter numerous products that provide distribution mechanisms. In addition, a concept that is supposed to cover all the distribution issues of an enterprise must also provide a set of additional runtime features such as security support, fault tolerance, load balancing, transaction handling, logging, usage metering, and auditing.

It should be noted that our classification scheme is arbitrary. It is possible to define other classifications or to find additional levels of heterogeneity. However, independent of the classification scheme, it is true that enterprise distribution techniques tend to create heterogeneity at different levels.

From a technical point of view, this scenario leads to three different layers, as shown in Figure 3-2. The first layer contains the core assets of the enterprise application landscape, including all business logic. The second layer provides technology-dependent adapters that connect the core assets to various software busses. Finally, the third layer represents the sum of the enterprise's communication facilities.

Figure 3-2. Technology-dependent adapters connect participants of an enterprise application landscape with its communication infrastructure.

The remainder of this chapter focuses on the second layer. Chapters 4 to 7 provide an in-depth discussion of the first layer, while Chapter 9 discusses the third layer.