need pointers to get started with API's

Question

Most of the applications these days provide an API...be it twitter,gmail,fb and millions others.

I understand API Design can not be explained in just an answer but I would like some suggestions on how to get started with API design. Maybe some tutorial/book that makes an application and has some chapters on how to go about providing API's for it. I'm mostly a java developer (learning Groovy) but am open to other languages also, if it is easier to get started with API design in that language.

As a side note, before I was curious about the difference between an API and a webservice. But now as I understand it, webservice is just a form of an API

Answer 1

I don't have any great resources however, I want to stress how correct that API is Application Programing Interface, and is simply a mechanism for how you expose your application to be consumed by others. Be it from script, web service (soap or rest), Win32 API Style Calls....

About 10 years ago when we talked API it seemed like everyone felt like all APIs were like Win32, and that was it. One of the more interesting I've worked on was an API with a PICK based Management System. In this case we wrote an XML processor in PICK and were screen scrapping XML back and forth over a telnet session.

The first thing you need to decide, is how do you want to expose your data. Are you going to expose over the web? Or is your application a desktop application? How I would structure an API for cross machine communication tends to be different then if the API is running in a single process or even on a single machine.

I would also start by writting a test client, You have to understand how your API will be used first and try to make it as simple as possible. If you dive right in with the implementation you might loose perspective and make assumptions that a client developer might not.