6.9.4 FS Selection Union Constraint

The selection union constraint is the latest arrival in this family of constraints. It is exported on feature union of module Select. All its variables are sets and we write it abstractly as follows:


and concretely thus:

S={Select.union [S1 ... Sn] SI}

Its declarative semantics is simply:


Again the information about S can be improved as follows. If D_i\subseteq S_i\subseteq D_i' and D\subseteq \textit{SI}\subseteq D', then:

\bigcup\limits_{i\in D} D_i\subseteq S\subseteq
\bigcup\limits_{i\in D'} D_i'

Denys Duchier
Version 1.2.0 (20010221)