DMN11 — Need to clarify which DMNElements must and must not have names

In the MM, Fig 15, all classes inherit the optional name attribute. Thus, any DMNElement may or may not have a name. What is closer to the truth, is that some DMNElements MUST have a name, and others MUST NOT. Attached is proposed MM that splits the elements into the named and unnamed. There will be numerous text changes, especially to explain that decision tables, being expressions, do not have names. The apparent 'names' of expressions like DTs are really the name of the Information Item that has said expression as its valueExpression. It is dangerous (misleading) to supply a name for an expression, because it may appear that one could refer to the named expression's value by that name. But you cannot. You can only refer to an Information Item by name in an expression.

define NamedElement subclass of DMNElement

Revised text, MM figures, and XSD (github links)