Some answers, may be wrong but this is how it makes sense to me: 1. Possibly both (the one in the URL being the version of the URL-space and the one in the Hea

Some answers, may be wrong but this is how it makes sense to me: 1. Possibly both (the one in the URL being the version of the URL-space and the one in the Header being the more fine grained Representation Version). 2. It depends. For simplicity it often makes sense to put it in the URL. For more generality headers can be better. 3. No 4. They don't have to. They usually do though and it makes most sense when they do. 5. Fully formed URLs are simpler, so go with those if you can. But sometimes you'll need more. 6. URLs are a subset of URIs. All URLs are URIs. URLs give the location of the resource whereas URIs just have to identify it (but could also give the location of course. 7. It depends. I lean towards different but I'm no authority. 8. Using the Accept-Language header. But I'm guessing this is not always the best way to do things.