http://duncan-cragg.org/blog/post/deriving-forest/

I see links only as creating hyperdata graphs, which is quite a different view from the ‘link-rel-action’ approach that is seeing increasing popularity these days.

A few things:
- controls for machines are definitely different than controls for human beings, but that doesn’t mean they are impossible to build
- yes a machine can’t “know” anything, but that doesn’t mean that output messages to the machine can’t put it in a state where it will ultimately generate an acceptable input message
- this works best (and perhaps is only possible when) the hypermedia format is designed for a specific type of machine user
- the link relation approach assumes that the only attributes necessary to define a control are a type and a URI. I think it’s hard to build interesting or useful controls that way
- Here’s my practical example: One can build and evolve all sorts of call control applications using CCXML. These applications are “used” by a machine — a call control platform. While CCXML has its warts, I believe it qualifies as a hypermedia format for machines.

I will definitely elaborate on this in future posts.

…

Machine clients will always rely on ‘out-of-band’ knowledge because they aren’t actually capable of comprehending any in-bound knowledge – they’re just pre-defined mechanisms, afterall – everything a machine client ‘knows’ is out-of-band, because that is where it is created by its developer(s).

Accepting that, ‘simple link relations’ (and accompanied documentation) provide everything a developer needs to comprehend/discover a particular application and build the machine, and given that; everything the machine itself needs to operate.

As a practical example: If I significantly change my customers’ checkout process in my HTML driven web app, I can use natural language and GUI elements to guide them through the new flow; and it is likely most of them will adapt ‘in-band’.. machine clients just aren’t capable of reacting in the same way right now, and possibly never will – so why bother creating unnecessary hypertext controls and bloating your hypermedia types?