I heard it said that REST is "document-centric". Unclear what this meant, I began poking around and found the term document-oriented being used of databases, particularly NoSQL databases, and in contrast to a barebones key-value store. Thus it seems that documented-orientation of databases has to do with their internal representations being JSON or XML; I saw on the Wikipedia page that many document-oriented databases claim to support a RESTful API, but not having experience with any NoSQL databases and also being new to REST, I'm unsure what that means (the database itself is directly accessible through a service?); and anyway, as far as I know, REST does not constrain the underlying data model of an application, but only its service contract.
So what does it mean to say that REST is document-centric/oriented? Does it mean that REST constrains a service to use JSON or XML in its contract? Does it mean that REST is more friendly towards NoSQL databases than conventional relational databases?