It's fun to think of a software product as a giant ADT (Abstract Data Type), as it specifies operations that may be carried out (via a GUI, or command line, or

It's fun to think of a software product as a giant ADT (Abstract Data Type), as it specifies operations that may be carried out (via a GUI, or command line, or webpage, or webservice, etc), while the detail of the implementation of those operations is hidden. Each instance (running copy) of a software product contains its own data.