If you completed Lecture 2 of the “Developing iOS7 Apps for iPhone and iPad (Fall 2013) by Stanford University” you will see that in total 4 model classes were created:
If you are new object oriented programming it might be a little difficult to wrap your head around all the classes and how they relate to each other, what methods they inherit, override, etc. So here is a class diagram overview that shows the 4 classes and their relations. I have mentioned all the public and private properties and methods.
You might find this diagram handy for referencing back and forth as you continue developing the Matchismo game in the forthcoming lectures.
Remember, PlayingCard is just a subclass of Card. Deck is a collection of Cards. PlayingCardDeck is a collection of PlayingCards 🙂