The Enterprise Services Bus (ESB) is an architectural style of integration that simplifies the communication between mutually interacting software applications in a Service Oriented Architecture (SOA).
The figure, Point-to-Point Integration, shows the complex connection of systems. Each system is connected to at least one other system.
The Point-to-Point approach forms a spider web of application systems, which keeps growing exponentially as more systems are introduced into a system landscape. If a detail changes in one connection or one message, this detail must also be changed in all connected systems
In order to reduce the complexity and the associated administration effort, you can choose a Service Oriented Architecture. SOA is a design pattern that provides the functionality of an application as a service
SAP AEX acts as an ESB, and takes care of implementing the communication and interaction between the software components that participate in the exchange of data and interacting.
SAP AEX is at the heart of your SOA implementation strategy. The Advanced Adapter Engine Extended plays the role of a middleman, courier, and translator and facilitates the exchange of calls between different systems. Interface definitions are centrally stored in the Enterprise Service Repository (ESR).