Domain
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Cows, sheep and deer are all mammals.
Cows and sheep are domesticated, deer are not.
No reptiles are domesticated but they are animals like mammals.
Snakes are examples of reptiles.
Reptiles lay eggs like birds, mammals do not.
Birds are animals too but are not reptiles.

[Note that, for simplicity, the domain knowledge above is not accurate with respect to the real world, but that is irrelevant for the exercise.]

Exercise
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Define suitable classes and arrange them in an is-a hierarchy that accurately reflects the knowledge above.


Possible solution
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Classes: Animal, Egg-laying, Domesticated, Mammal, Reptile,
         Cow, Sheep, Deer, Snake

Inheritance structure: (< means subclass)

Cow < Mammal
Sheep < Mammal
Deer < Mammal

Cow < Domesticated
Sheep < Domesticated

Snake < Reptile

Mammal < Animal
Reptile < Animal

Reptile < Egg-laying