One important aspect of OCL that is worth noting is that it expands lists of lists to just a list. An example in plain English; Thing.allinstances.Details – this will come back as a set of details that are all the details from all the Things. If OCL had not expanded lists automatically one could have expected a set of sets containing the details per thing. But this is not the case. The automatically expansion of lists of lists is sometime referred to as flattening of a collection – referring to the reduction of topology in the result.

Some OCL examples

Examples	Results
Bag{'5','1','2','2','3','4'}->ascommalist	5, 1, 2, 2, 3, 4
Bag{'5','1','2','2','3','4'}- >union(Bag{'1','2','2','3','6'})->ascommalist	5, 1, 2, 2, 3, 4, 6
Bag{'5','1','2','2','3','4'}- >union(Bag{'1','2','2','3','6'})->asset- >ascommalist	5, 1, 2, 3, 4, 6
Bag{'5','1','2','2','3','4'}- >union(Bag{'1','2','2','3','6'})->asset- >orderby(a|a)->ascommalist	1, 2, 3, 4, 5, 6
Bag{'5','1','2','2','3','4'}- >intersection(Bag{'1','2','2','3','6'})- >orderby(a|a)->ascommalist	1, 2, 2, 3
Bag{'5','1','2','2','3','4'}- >Difference(Bag{'1','2','2','3','6'})->orderby(a|a)- >ascommalist	4, 5
Bag{'5','1','2','2','3','4'}- >SymmetricDifference(Bag{'1','2','2','3','6'})- >orderby(a|a)->ascommalist	4, 5, 6

If you are in the context of a simple type like string, double, int, datetime or Boolean MDriven will expose the simple operations that are available in the .net Framework. Testing this in the OCL-Editor: