DMN15 — Underspecified when ranges may include a qualified name for the endpoint, which resolves to null

It is underspecified when the ranges may include a qualified name for the endpoint, which resolves to null.

This was identified by Greg McCreath and Octavian Patrascoiu during TCK contributions.

Ranges' Endpoints can be either a literal or a qualified name. If the qualified name resolves to null, and the endpoint inclusivity flag is false, it is semantically equivalent to the case of single-endpoint-range. This leads to ambiguity in Table 55: Semantics of decision table syntax

This also requires the typo fix in https://issues.omg.org/browse/INBOX-1337

Example

With reference to examples in Table 42: Examples of range properties values

Instead of (1..10]
do consider (x..10]
if x resolves to null
then this is semantically equivalent to <=10.

However, Table 55, row 9, cites:

e1 in (e2..e3] is equivalent to e1 > e2 and e1<=e3

// exercise by hand..
e1 in (x..10] is equivalent to e1 > x and e1<=10
// if x resolves to null..
e1 in (null..10] is equivalent to e1 > null and e1<=10
e1 > null and e1<=10

which is NOT equivalent to e1<=10, hence the ambiguity.

Clarify edge cases and range options

Clarify that ranges are defined based on a combination of comparison and conjunction operators and therefore the result of an comparison with a range containing a null endpoint will be either false or null but never true.

Add text to the description of the range that mentions the possibility of using expressions.