Neural Network: API and library

I was asked to design a Java software for creating (basic) aritifical neural networks from a specified XML file.

I also need to design an API and a library, which implements this API. The XML parser should use the API to create a neural network.

However, the problem is that I have implemented most of the functionality but I do not really know how the relationship between the XML parser, the API and the library should be.

Could you please tell me (just in general, no code needed) what functionality the API and the library should provide and how the XML parser, API and library interact?

Any help would be much appreciated!