Given the differences between the software assets and expertise in enterprises, it is inevitable that companies choose different approaches and implementation strategies for EAI. It is important to develop a well thought-out plan for implementing EAI that considers the costs and resources needed and the benefits that are accrued. A slow, methodical, piecemeal approach is most common, where applications are integrated gradually over time. It makes sense to single out some applications and use them as test cases in pilot programs to evaluate specific approaches, tools, and technologies.
The previous section about the different approaches to EAI implied the use of synchronous communication between existing applications. The image is that somewhere beneath the surface, the EAI components use some form of remote procedure call (RPC) to pass appropriate information from one application to others and participate in transactions when necessary. However, synchronous RPCs are not usually a requirement or even recommended for implementing many EAI strategies. Much of this sharing of information is handled effectively using asynchronous communication and messaging.
This process is illustrated by using personnel address information as an example. An employee needs to change home address information. A user enters this change into the primary application (perhaps this is the human resources system) that updates records in the primary data store for this system. Populating these changes to other applications such as the Payroll system probably does not need to be synchronous. The address in the Payroll system is most likely used twice a month or quarterly when checks are sent or W-2 forms are issued to employees. Some messaging or asynchronous process that guarantees updates to Payroll and other applications would work just as well, hence the popularity of message-oriented-middleware (MOM) and other messaging technologies as a tool for implementing EAI.