Service-Oriented Architecture or SOA is a growth concept that stretches over the entire breadth of the organization. Application integration is an integration framework composed of a collection of technologies and services which form a middleware to enable integration of systems and applications across an enterprise. It is the process of making independently designed application systems work together.
Integration is generally difficult because, in every case, developers must reconcile disparate information architectures involving different data, process and object models. In addition, in most cases, developers must also make the overall solution operate across multiple operating systems, databases and middleware technologies.
Here are the four different levels of the application integration process: