SYSML12 — Merge UML DataType into SysML ValueType

Even though SysML ValueType includes all the capabilities of UML DataType, plus its own optional extensions, SysML currently both of these separately in its diagram elements and abstract syntax. This adds unnecessarily to the complexity of the specification (where both DataType and ValueType must be mentioned in multiple places) and to the language that the SysML user must learn. It's inconsistent with other renaming of UML elements by SysML, in which the neutral SysML term (e.g. Block) replaces the UML term (e.g. Class). Just as SysML Block replaces the UML term Class, there's no reason the SysML term ValueType can't replace the UML term DataType. Statement of OCL constraints and metamodel and diagram syntax specifications can be simplified as a result.

Because ValueType includes all capabilities UML DataType, plus its own optional
extensions, no user need for keeping them both was identified during discussions
within the RTF. In SysML user models, there’s no reason that the SysML term
ValueType can’t replace the UML term DataType, in the same way that the
SysML term Block replaces the UML term Class. In both cases, the substitute
terms were chosen to be less software-specific than possibly appropriate for use
by system modelers. Regardless of this rationale, consolidating to just ValueType
simplifies the language including the specification of diagram elements and
constraints.