consistency constraints
how they arise
- when an association is represented by multiple instance vars
- the instance vars of different objects are related
example
- the owns association
- person has possessions, thing has owner
how they are maintained
- cannot be maintained all the time!
- when one object changes, it calls methods on the related objects
abstract constraints
- not all constraints arise from implementation
- example:
destination assocation connects Transporter to Place
might want to say that the destination cannot be a transporter
or that there are no “transporter loops”