[qvtd-dev] [Dev]QVTi unbound variables

[Horacio Hoyos Rodriguez <hhr502@xxxxxxxxxx>]

Hello,

 

On the small description of QVTi in the QVTd wiki (http://wiki.eclipse.org/M2M/QVT_Declarative_Languages) it says that at each node (mapping) a new unbound variable is introduced by one of the input (domain) or middle guard patterns. What is the rationale behind this restriction? I understand limiting the number of unbound variables to 1 enforces the loop semantics of nested mappings, but I don’t understand why they should be introduced in guard patterns.

 

From a semantics view, I would think of guards as IF..THEN conditions. So variables and predicates in guard patterns should only be used to condition the evaluation of domains and middle bottom patterns. Additionally, if we consider the base structure of a QVTi transformation:

 

map container in transformation {

                map {                    -- L to M

                                check L() {

                                }

                …

}

map {                    -- M To R

…

}

}

 

Does having a guard in the first domains (the check L() in the example) makes sense? If it doesn’t and these initial domains are an exception then the proposed ocl invariant should reflect this.

 

Personally I think that the unbound variable should be introduced in check domains (L to M) or in MiddleBottomPatterns (M to R).

 

Regards,

 

Horacio Hoyos Rodríguez

EngD Student

University of York