Question 11 :
Specifying a key ensures that no two objects belonging to a class have the same value for the key attribute(s).
Question 12 :
If you know all the possible values that an attribute can have, you can enumerate those values in ODL.
Question 13 :
You may specify an object identifier with only one unique tag name.
Question 14 :
In ODL, you specify an operation using parentheses after its name.
Question 15 :
An ordered collection of elements of the same type are called sets.