Monday, 3 February 2014

FOREST: a higher-level RESTful interaction model

I was having a good chat with my buddy Jim Barritt today, and the subject came up of how one could describe the difference between my FOREST approach to REST and the widely-used, traditional AtomPub style.


Quick summary of the AtomPub style: you have a client and a server where the server is a lot like a database of articles and HTTP is used by the client to edit those articles.

So the editor client says "POST" and a new article is created. It says "PUT" and the article is updated. "DELETE" is pretty obvious. The client, and indeed the world, can "GET" to read an article.

The client basically runs things and the server more-or-less does what it's told, modulo whatever it needs to do to ensure security and integrity. There are other bits like Media Types and Link Relations, but that's basically the model.

Almost Database Integration

When people want to "do REST", if they think they want to do it "properly", chances are they'll use this approach as their paradigm. I was slightly involved in the creation of the AtomPub spec, so I'm not knocking it, at least for this use case - editing articles.

Trouble is, it only makes sense if your application is a lot like a database, where you have some data that you want to create, update, delete or read. So, in order to do what they believe to be "proper REST", people end up forcing their inter-server interaction protocols into this simple, low-level, data read-write model.

And that feels uncomfortably close to a database integration style!


In contrast, in the FOREST style, two application servers talk to each other at a higher level, as peers - they can be both client and server to one another.  A peer can GET the data of another - pull or poll - and can POST its own data to another - push.

It's a simple, symmetric model of interaction where the application protocol is like a two-way conversation. Being RESTful, all such data can be found at their URLs - this isn't just a substitute for messaging. PUT and DELETE aren't used at all, because the interaction model isn't about just low-level editing of data.

I'll be illustrating FOREST with an example on this blog, to show how such a conversation between peers can proceed. You'll see how it enables interactions that are at a higher, domain level.

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