Most of today's synchronous communication within enterprise systems is realized via HTTP. Enterprise applications expose HTTP endpoints that are accessed by the clients. These endpoints are typically in the form of web services or web frontends as HTML over HTTP.

Web services can be designed and specified in various ways. In the simplest form, we just want to call a function of another system over the wire. That function needs to be specified with input and output values. These functions or remote procedure calls (RPC) are in this case realized over HTTP, typically using an XML format that specifies the parameter arguments. In the age of J2EE, these types of web services were pretty common. The most prominent example for this was the SOAP protocol which is implemented with the JAX-WS standard. However, the SOAP protocol and its XML format was quite cumbersome to use and not well supported by other languages other than Java and .NET.

In today's system, the REST architectural style with its concept and constraints is used far more often.