• Resources and their URIs
• Applications and Hypermedia
• Representations and Media Types
• Methods
• Conditional GET

Regarding the “Applications and Hypermedia” area, I feel Roy Fielding’s pain that many efforts labeled as being RESTful seem to completely ignore the hypermedia constraint. I believe many developers tend to miss this constraint because they’re so used to using libraries and frameworks that offer lots of entry points, and having knowledge of those entry points in the client normally isn’t that bad since the client and library/framework are tightly coupled into the same address space anyway. In a distributed system, though, this definitely does not hold true; when the client knows a bunch of entry points into the service, it ties the client to that service and inhibits their independent evolution.

Anyway, please read the column and let me know what you think, and thanks again to Stefan Tilkov for his helpful review of the draft.

Coincidentally I also feel Roy’s pain when it comes to writing about REST. He states:

I don’t try to tell them exactly what to do because, quite frankly, I don’t have anywhere near enough knowledge of their specific context to make such a decision.
…
So, when you find it hard to understand what I have written, please don’t think of it as talking above your head or just too philosophical to be worth your time. I am writing this way because I think the subject deserves a particular form of precision. Instead, take the time to look up the terms. Think of it as an opportunity to learn something new, not because I said so, but because it will do you some personal good to better understand the depth of our field.

Exactly.

Obviously, Roy is the ultimate REST authority, given that he defined it, so I’m not at all claiming to be anywhere near as authoritative about it as he is, yet I’ve also experienced what he says above. For example, consider this informal review of my columns I received a few months ago in a comment on someone else’s blog:

The articles of yours that I’ve read are…amorphous to me. They speak in generalities. I haven’t read an article where you sit down and write the same service using both REST and RPC and compare the two. When you speak in generalities, we can’t objectively evaluate any of the specific trade-offs between approaches… Arguments that happen at too abstract a level can’t go anywhere, because our positions aren’t specific enough for anyone to evaluate anybody else’s claims.

In other words, “since your columns don’t do my thinking and experimentation for me, they’re useless to me.” Hmm. Maybe I’m just old school, but I’d much rather understand mathematics than require someone to hold my hand while I blindly punch buttons on a calculator. In other words, as the old proverb goes, I’d much rather try to teach you to fish so you can feed yourself. As I state in this new column:

Whether developers of RESTful HTTP-based services write their code in IDEs or with simple text editors, and regardless of which programming languages they use, they must understand REST and HTTP fundamentals to succeed.

The problem with that assertion is that it assumes coupling is a fixed constant — if you eliminate it from one point, whatever you’ve gotten rid of just has to pop up somewhere elsewhere, like some sort of strange “Conservation of Coupling” law. Of course, that’s not true. In my latest column, Demystifying RESTful Data Coupling (PDF), I turn my attention to this claim and explain how RESTful data works, and why it too, like RESTful interfaces, reduces coupling when compared to WS-* and other similar approaches.

Constructive feedback welcomed, as always.