Hey Ben,
That's a good question. Here's my take on it. The Richardson Maturity model describes various levels of maturity to RESTful APIs. More mature levels are typically considered "more REStful". While the Valence Learning Framework APIs are built on a RESTful approach, their maturity level according to the Richardson model really only varies between Level 1 (Resources) and Level 2 (HTTP verbs) leaning more towards the Level 2 end of that spectrum than the Level 1 end.
Typically when people describe an API as RESTful, there may be an implication that the API is quite mature, approaching or attaining the full-on Hypermedia characteristics of Level 3.
The Valence Learning Framework API is not yet there, and in its current incarnation it's unlikely to approach that, where we think internal consistency and coverage are likely more important goals than being fully RESTful. We do have a goal to reach towards a more fully RESTful approach, but it's likely that this will arrive in a future major version or revision of the platform as a whole and be some time in arriving.
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Viktor Haag