DMN12 — Unclear meaning of unique name constraint for ItemDefinitions and DRGElements

The following sentence on page 65 / 69 in paragraph 7.3.2 has been interpreted differently:

"The name of an ItemDefinition element SHALL be unique within the containing instance of Definitions and its associated namespace"

Also, may be common to use same name for input data and an item definition that describes its shape, e.g. PurchaseOrder.

Need to account for namespaces (uniqueness always within Definitions element)

At least, all the 'variables' should have unique names, that is, Decisions, InputData, BKMs, and DecisionServices must have unique names within the containing Definitions. Further, all ItemDefinitions must have unqiue names (but could duplicate an input data, e.g.).

Imported elements are qualified by the name of the import. e.g. short.my-decision + 1

re-phrase unique name constraint for ItemDefinitions

improve description of unique name constraint for ItemDefinitions to make clear that it refers to ItemDefinition only