1. Syntactic Requirements
Uniform syntactic interpretation
Everyone looking at a SysML diagram should describe it the same way (using SysML terminology) , including whether it is “legal” SysML (well-formed).
Includes SysML:
Specification writers
Teachers and consultants
Model builders
Modeling tool builders (terminology = metamodel, translation = instantiating metmodel)

2. Semantic Requirements
Uniform semantic interpretation
Everyone looking at a SysML model should get the same idea of how the system is built according to how the model will behave.
Includes SysML:
Specification writers
Teachers and consultants
Model builders
Analysis tool builders (might overlap modeling tool builders).

3. Specific Requirements
RFP can specify language architecture, eg:
Use UML without changing:
Anything:
Profile + equivalent MOF model + mapping.
Replace XMI (MOF interchange) with OWL or RDF (maybe via MOF2RDF).
Metamodel: eg, add model theoretic semantics to UML as it is.
Concrete classes: Specialize UML (metamodel) from formal language, eg, OWL (eg, “onto behavior”).
Some: “Branch” off UML, reusing some, not all of UML.
The non-MOF subset: Replace MOF subset of UML with OWL.