This is a follow up on a question asking for an [explanation of REST](https://stackoverflow.com/questions/551933/can-you-explain-the-web-concept-of-restful/).

As you can see from the comments to my answer, we've had a small argument with [Darrel Miller](https://stackoverflow.com/users/6819/darrel-miller) on the best media representation of the resources. We've had a further email discussion that resulted in this question.

The main difference between Darrel's and mine understanding of REST is whether the semantic of the data is part of the REST API.

Darrel believes (my interpretation of his words :-)) that the semantic of the data is an essential part of the REST API and as such, the media representation choosen should reflect it. Thus, a proper REST API should choose either:

* a well-known media like ATOM to represent the data, so that as many clients could understand the semantic of the resource natively;
* an app-specific media type like application/vdn.mycomany.mymedia and expect the client to understand this media type to be able to consume the resources data.
Application/xml is not a good resource representation, as it does not represent the semantic in the media type, yet requires the client to know more about the semantic.

I, on the other hand, believe that the REST API is a separate layer from the actual data representation. The media type exposed by the API is just a container to transfer the resource data. The actual semantic of the data is treated separately. Thus, a client that does not understand the data, can still consume the REST API. Application/xml is a really good data representation, as it allows tight coupling for clients that understand the schema, yet still allows client that don't understand the schema to do some basic processing of the resources.

**Thus, the question**: is the data semantic part of the REST API? Should we choose only media types for resources representation that actually represent the semantic of the data as well?

I would appreaciate if people post in their answers some citations, preferably from the Roy man himself. :-)