Message-based Integration is one of the common categories of patterns for connectivity solutions.
An Enterprise Service Bus can extend an existing messaging infrastructure by providing an environment for building and deploying message-based applications at the infrastructure level. Examples of these applications include routing and transformation services, and logging services. This environment can extend a single underlying messaging infrastructure or provide a bridge between different products and technologies. Adapters can be used to provide access to applications or services that do not have an in-built messaging capability.
The following diagram illustrates an example of a Message-based Integration scenario: