DMN12 — Confusing semantics of ItemDefinitons

According to the ItemDefinition specification, an ItemDefinition can be defined in two ways:

• reference to a built-in or imported typeRef
• composition of ItemDefinition via itemComponents

According to the metamodel in Figure 7.6 and Table 23 typeRef is optional and itemComponent has [0..*] cardinality.

That means an ItemDefinition can be defined as

<itemDefinition id="1234" name="name"/>

What is the actual semantics of this type? Is it some sort of a root type in a type system?

To make the semantics more readable and fix some some typos or missing info, I suggest the following:
1. Add missing cardinality for ItemDefintion.itemComponent in Figure 7.6. (missing info)
2. In Table 23 change cardinality of typeRef to be [0..1] to match the metamodel (typo).
3. Add an extra constraint in Table 23 itemComponent row:
When typeRef is missing, itemComponent has at least one ItemDefinition.

Improve type checking semantics

see attached word doc v8