DMN15 — Incorrect typeRef for variables associated to BKMs

The typeRef attribute in the variable attribute of Business Knowledge Models in file 'Chapter 11 Example.dmn' from the examples archive is incorrect. The values references the output type (e.g. an item definition) and not a function item (introduced in DMN 1.3).

According to DMN 1.3 (Table 14, page 57), the semantic of variable attribute is:

This attribute defines a variable that is bound to the
function defined by the FunctionDefinition, allowing
decision logic to invoke the function by name.

Hence, the typeRef attribute has to reference a FunctionItem, Any or no type at all.

The issue was reported initially by Daniel Thanner in the TCK group (https://github.com/dmn-tck/tck/issues/376) and lead to the introduction of FunctionItems.

Proposal:

There are 3 ways to address this:
1. Remove typeRef from variables in BKMs
2. Change value to Any
3. Create FunctionItems for every BKM in the dmn file and reference them

Remove typeRef from variable of BKMs

Remove typeRef from BKM variables but keep it on their encapsulatedLogic in 9 places