DMN12 — While BKMs enable re-use, the options for re-use are restricted to single pieces of decision logic

It should be possible to re-use a decision subgraph by extracting it to another diagram and replacing it with a reference and an invocation to the extracted decision in the original diagram.

Given the current MM, I see two ways of making that possible:

• introducing a sub-type of BKM that allows referencing a decision in another diagram
• introducing a sub-type of Invocation that allows referencing a decision in another diagram

The attachment illustrates the missing and proposed re-use possibilities of the "affordability calculation" (from the example section). The attached example uses the second option of the two.

Allow Decision Service to be invoked from decision logic in a decision model

Revised text is attached as Invocable (Issue 10) - OMG Proposal (version 14).
XML Schema changes described by: https://github.com/omg-dmn-taskforce/omg-dmn-spec/commit/82d171eafa8be4e5659b6e47b46a76a025f15d0d
All figures will be separately attached in the final report as .svg files

Argument for Backward Compatibility
The newly added class (complexType) Invocable is abstract and thus not in the serialization. Concrete attributes are unchanged (except made optional).
Note that before this change, there was no standard way to serialize a decision model containing a decision service; hence, w.r.t. decision services, there is no compatibility to maintain.