Believe it or not, the concept of whether a class "Is a [something]" or "Has a [something]" comes up quite a bit in object oriented design. For instance, consider the questions "Is a transmission a car?" and "Does a car have a transmission?"
Clearly, the second question is the only of the two that one would answer in the affirmative. A transmission is not a car, but a car does have a transmission. This is a classic "Is-A/Has-A" example. And sometimes the answer to the questions are not so clear cut, particularly if the relationship is more obscure, like the relationship between a wall and sheetrock. For example, sheetrock, if hanged, could perform the duties of a wall, and a wall can contain sheetrock. The implementation of the solution to that question could probably be solved with either implementing a "Is-A" paradigm, or a "Has-A" paradigm.
So, I haven't described how "Is-A" and "Has-A" are implemented in object oriented design. Well the answer to that is really quite simple:
"Is-A" is implemented via I