Stephen Boyd Didar Zowghi Vincenzo Gervasi Optimal-Constraint Lexicons for Requirements Specifications. 203-217 2007 conf/refsq/2007 REFSQ http://dx.doi.org/10.1007/978-3-540-73031-6_15 db/conf/refsq/refsq2007.html#BoydZG07