DMN16 — No way to show dependencies of a grey-box decision service

When a decision service is fully defined, its dependencies are shown as the information requirements of its encapsulated decisions on external decisions or input data. If the encapsulated decisions of a decision service are not fully defined (e.g. temporarily during analysis, or because it is modelling a 3rd-party service with partial obfuscation), this may not be possible. It would be convenient in such cases to be able to draw information dependencies attaching to the boundary of the decision service. Such a service would not be executable.

This issue is a continuation of https://issues.omg.org/browse/DMN15-36 which was deferred to 1.6.