This page describes the WSO2 ESB architecture in the following sections:
...
4. Both message transformation and routing can be seen as a single unit. As the diagram specifies, there is no clear separation between message transformation components and routing components. WSO2 ESB call this the mediation framework. Some transformations happens before routing decision has taken. Some transformations happens after the the routing decision has taken. This part is the Synapse implementation.
...
Proxy services are virtual services that receive messages and optionally process them before forwarding them to a service at a given endpoint. This approach allows you to perform necessary transformations and introduce additional functionality without changing your existing service. Any available transport can be used to receive and send messages from the proxy services. A proxy service is externally visible and can be accessed using a URL similar to a normal web service address.
See Working with Proxy Services.
...