Conditionality and Multiplicity
The answer to the quiz question from yesterday is, “yes”. The model allows for a stray dog (a dog without an owner, poor thing).
The way that the model shows this is by the ‘conditionality’ of the association. On the dog owner end of the relationship ‘0..1’ is shown. This means that a ‘dog is owned by 0 to 1 dog owner’. A dog with zero owners is a stray dog. The relationship is said to be ‘conditional’ on this end.
Also encoded into the ‘0..1’ and ‘1..*’ are the ‘multiplicities’ of this association. We can understand from the multiplicity that a dog owner can own more than one dog. A dog owner must own at least 1 dog. We can also tell that a dog cannot be owned by more than one dog owner.