I’ve been playing around a little bit with the idea of creating a RESTFul MOM/ESB where the client requests a specific format and the server transforms the content if it can. For an ESB, this usecase would normally turn up for various XML-based messages and documents. The client would request an XML document of a certain schema and the ESB would return that format, performing a transformation if applicable.

For a RESTFul ESB, I’d want to use HTTP content negotiation. The problem is, AFAIK, there is no standard MIME type, other than “application/xml”, that allows you to specify an XML format with schema information. Being a REST noob, I emailed my friend Steve, a REST enthusiast, and asked him if it would be ok to embed schema information into the media type. My first thought was the media type would be:


Steve’s response was you can’t just make up a MIME type on your own and expect it to work well on the Internet without registering it. At first I thought, what’s the big freakin deal? But then I realized, what if you want to point your browser to a message in a remote RESTFul queue and just view its content? If you use “application/myschema+xml” your browser ain’t gonna understand it.

So, I decided to do a search on “decentralized mime types” and came across a few blogs from Stefan Tilkov, Dan Diephouse, and James Strachan. Here’s a summary (sorry if I left out anything)

Use AtomPub

One idea was to use AtomPub . I don’t like this idea at all. One, I just want to send a bloody XML document! KISS baby KISS! Second, if I’m going to use an envelope format, why not just use SOAP and WS-*? (no thanks). This, IMO, sort of defeats one of the general principles of REST.

Define a new decentralized MIME type

The idea would be to define a decentralized MIME type like this:


The uri would point to something like an RDDL document that defined the real format. Beyond KISS, what I don’t like about this approach is that again, I have no way of pointing my browser (or some other generic client) at the resource and just viewing it.

Use MIME properties

I saved the best for last. The final idea was to embed format information within MIME properties:

application/xml; schema="http:/..."

application/octet-stream; data-format=java

Use a registered MIME type, but append extra format information as a MIME property. I did a test on this with Firefox and Safari and it doesn’t screw up the viewing. So for me, MIME properties it is! I would be interested in links to other thoughts on this.