An API in a way for a software creator to allow other programmers to interface and work with their application. In short, if you want to integrate the functionality of an application into the matrix of an application you are writing you will need an API in order to do that. This is sort of a win-win for all parties in that you get the functions and benefits of the application woven into your application and the application that your integrating with gets more access to public use.
There are several well known examples of API interfaces including Google, Twitter, Facebook, and Amazon . By providing the API to interface with their application platforms they are enhancing their brand recognition, public use, and client base. Programmers can write software that is more dynamic and multi-functional in that they can connect with other platforms. Additionally, it cuts down on redundant code .
The question is should an API be copyright protected, thereby limiting its free and unhindered use. Should there be an expectation by the software creator that their API is protected by license? This really becomes a debacle when the software the API is allowing communication with is open source and so the software creator is not benefiting from the interface.
Once you let the cat out of the bag by releasing your software as open source you have fairly much rendered any API you release a gift to the masses. It would be difficult at best to argue that your software is open source if you license the API another way. With software that is not open source the matter becomes mute insomuch that allowing and providing a means for other programs to interface with your software is a positive and often a profitable natural step. It is also a reasonable expectation that software should be able to communicate in order to maintain a certain acceptable level of functionality on the Internet.
If an API becomes a way for developers to strengthen their bank account the result will be a weaker Internet and a strong stumbling block to the future of software development.
by Jim Atkins 'thedosmann"