framework vs. library

记得一直对这个问题没有一个很清晰的答案，今天看到Martin Fowler的一段文字，觉得很有道理，记录一下。

Inversion of Control is a key part of what makes a framework different to a library. A library is essentially a set of functions that you can call, these days usually organized into classes. Each call does some work and returns control to the client.

A framework embodies some abstract design, with more behavior built in. In order to use it you need to insert your behavior into various places in the framework either by subclassing or by plugging in your own classes. The framework's code then calls your code at these points.

摘自：http://martinfowler.com/bliki/InversionOfControl.html