DMN11 — would like to annotate Expression with typeRef

when we removed the redundant variable references from Expression, we also removed the redundant InformationItem (now typeRef) reference. The result type of an expression is redundant because you can always compute the result type from the input types, and a good tool will have to perform this computation anyway in order to verify that the redundant value is correct. However, simple tools may benefit from a declaration of the expected type of an expression, and the benefit may outweigh the drawbacks of redundancy, hence the issue.

add typeRef attribute to Expression, and derived association to ItemDefinition

Affects MM, XSD, and spec text