I have to create an API for our application that is accessible over HTTP. I envision the API's responses to be simple XML documents. It won't be a REST API (not in the strict sense of REST).

I am fairly new to this space - of course I've had to consume some Web API's in my work, but often they are already wrapped in language native libraries (i.e., TweetSharp).

I'm looking for information to guide the design of an API. Are there any articles, blog posts, etc. that review and expound upon the design choices to be made in a Web API?

Design choices would be things like how to authenticate, URL structure, when users submit should the URL they POST to determine the action being performed or should all requests go to a common URL and some part of the POST'd data is responsible for routing to a command, should all responses have the same document root or should errors have a different root, etc., etc.

Ideally, such articles or blog posts would enumerate through the common variations for any given point of design and expound on the advantages and disadvantages, such that they would inform me to make my own decision (as opposed to articles that simply explain one single way to do something).

Does anyone have any links or wisdom they can share?