Solutions: Exercise 2

Find the Object Relations

Remember: The solutions below are only suggested solutions.

Telephone

Here is a diagram showing a possible hierarchical ordering of the set of objects, where the hierarchy expresses "consists-of" relations.

The objective with making hierarchies like this, is to simplify the complexity of a model, because we can capture an entity, like Receiver with all its membranes and magnets etc., with three simple concepts; Receiver, Loud Speaker and Microphone.

This way of organising information is quite natural for us humans, and with object-oriented technology, we can organise our software systems the same way.

An object-oriented system consists of a set of interacting objects, connected through object relations, where the relations often map real-world relations or dependencies.

Note that "consists-of" is just an example of one type of relation. Other types of relations may express:

"ownership" between Car and Person objects,
"employment" between Employee and Company objects,
or just the fact that objects are aware of each other, so they can interact by sending messages.