This example shows companies and persons working
for them.

The example corresponds to the example
model in the section `Validating Pre- and Postconditions
with USE

Employee.use:
Corresponds to examples/monitoring/Employee.use,
but the invariant context Person inv: age >= 18
is missing here

two classes Person and Company with at least
one operation with side effects
one association WorksFor
no invariants, but one constraint for every operation

Employee.cmd:
creates one Company and one Person
the operation hire is executed to create a link
between both objects
after that, the raiseSalary operation with return value
is executed
finally the new link is destroyed by executing the
operation fire

Employee.dgm:
