An Implementation

But behind an offer to provide a service must be an implementation that satisfies the contract defined by the interface. So this level of abstraction is again looking at the server side, but this time from the ``inside'', and not the ``outside''. The concern here is with the high level approach that is being used to provide the designated service.

For example, a stack data type can be implemented using a linked list, an array, or a number of other techniques.

[audio] [real] Text to accompany slide10, in Chapter 2 of An Introduction to Object-Oriented Programming