what in general does the SCC API do?

I can't seem to find general documentation on the Microsoft SCC API. I don't want to wade through detailed documentation on the specific interfaces/methods/etc, I just would like to know what in general it allows and what concepts it uses. (edit: without having to download the whole SDK 开发者_StackOverflow中文版or applying for a license requiring an NDA.)

edit: what's the abstraction layer that it sees in common between different systems? e.g. there's files and changesets? or just files? and each file has a name?

As I understood it, you had at one time to be a Microsoft Partner to get at the SCC API SDK which would've included the documentation however, I later found that they had relaxed that requirement. AFAIK this API describes the interface between Visual Studio and an SCC provider. So it would allow you to write a provider to allow Visual Studio to interact with a version control system. Microsoft examples would be the SourceSafe provider and probably the Team System provider. A non-Microsoft example would be the Visual SVN plugin for Subversion.