Here now some initial references; best regards - Walter. @InProceedings{Keirouz:et:al:90,   author = 	"Walid Keirouz and Jahir Pabon and Robert Young",   title = 	"{Integrating parametric geometry, features, and 		 variational modeling for conceptual design}",   booktitle = 	"International Conference on Design Theory and Methodology",   year = 	"1990",   editor = 	"{J.\ R.}\ Rinderle",   pages = 	"1--9",   organization = 	"American Society of Mechanical Engineers (ASME)",   OPTpublisher = 	"",   OPTaddress = 	"",   OPTmonth = 	"",   note = 	"Proceedings" }   @InProceedings{Yamaguchi:Kimura:90,   author = 	"Yasushi Yamaguchi and Fumihiko Kimura",   title = 	"{A constraint modeling system for variational geometry}",   booktitle = 	"{Geometric modeling for product engineering}",   year = 	"1990",   editor = 	"{Michael J.}\ Wozny and {J.\ U.}\ Turner and {K.}\ Preiss",   pages = 	"221--233",   organization = 	"IFIP",   publisher = 	"Elsevier Science Publishers B.V.\ (North-Holland), 		 Amsterdam, The Netherlands",   OPTaddress = 	"",   OPTmonth = 	"",   note = 	"Selected and Expanded Papers form the IFIP WG 5.2/NSF 		 Working Conference on Geometric Modeling, Rensselaerville, NY, U.S.A., 		 18--22 September 1988" }  @InProceedings{Chung:et:al:88,   author = 	"{Jack C.\ H.}\ Chung and {Joseph W.}\ Klahs 		 and {Robert L.}\ Cook and Thijs Sluiter",   title = 	"{Implementation issues in variational geometry and 		 constraint management}",   booktitle = 	"Third International Conference on        CAD/CAM, Robotics and Factories of the Future (CARS and FOF'88)",   year = 	"1988",   OPTeditor = 	"",   OPTpages = 	"",   OPTorganization = 	"",   OPTpublisher = 	"",   address = 	"Detroit, Michigan, USA",   month = 	" August 14--17,",   note = 	"Proceedings, probably: Springer-Verlag, 		 Berlin/Heidelberg, 1989" }  @Article{Kimura:et:al:86,   author = 	"Fumihiko Kimura and Hiromasa Suzuki and Toshio Sata",   title = 	"{Variational Product Design by Constraint Propagation 		 and Satisfaction in Product Modelling}",   journal = 	"Annals of the CIRP",   year = 	"1986",   volume = 	"35",   number = 	"1",   pages = 	"75--78",   OPTmonth = 	"",   note = 	"(probably) International Institution for Production Engineering Research" }  @Article{Kimura:et:al:87,   author = 	"{F.}\ Kimura and {H.}\ Suzuki and {H.}\ Ando and {T.}\ Sato and 		 {A.}\ Kinosada",   title = 	"{Variational Geometry Based on Logical Constraints 		 and its Applications to Product Modelling}",   journal = 	"Annals of the CIRP",   year = 	"1987",   volume = 	"36",   number = 	"1",   pages = 	"65--68",  @InProceedings{Chung:Schussel:89,   author = 	"{Jack C.H.}\ Chung and {Martin D.}\ Schussel",   title = 	"{Comparison of Variational and Parametric Design}",   booktitle = 	"Autofact '89",   year = 	"1989",   OPTeditor = 	"",   pages = 	"5-27 -- 5-44",   OPTorganization = 	"",   OPTpublisher = 	"",   address = 	"Detroit, Michigan, USA",   month = 	"October 30 -- November 2,",   note = 	"Conference Proceedings" }   @Article{Pabon:et:al:92,   author = 	"Jahir Pabon and Robert Young and Walid Keirouz",   title = 	"{Integrating Parametric Geometry, Features, and 		 Variational Modeling for Conceptual Design}",   journal = 	"International Journal of Systems Automation: Research 		 and Applications (SARA)",   year = 	"1992",   volume = 	"2",   OPTnumber = 	"",   pages = 	"17--36",   OPTmonth = 	"",   OPTnote = 	"" }  @Article{Kondo:90,   author = 	"Koichi Kondo",   title = 	"{PIGMOD: parametric and interactive geometric 		 modeller for mechanical design}",   journal = 	"CAD, computer-aided design",   year = 	"1990",   volume = 	"22",   number = 	"10",   pages = 	"633--644",   month = 	"december",   note = 	"Butterworth-Heinemann Ltd" }   @InProceedings{Zalik:et:al:92a,   author = 	"Borut {\v{Z}}alik and Nikola Guid and Aleksander Vesel",   title = 	"{Parametric Design Using Constraint Description Graph}",    booktitle = 	"CAD '92, Neue Konzepte zur Realisierung 		 anwendungsorientierter CAD-Systeme",   year = 	"1992",   editor = 	"{Frank-Lothar} Krause and Detlev Ruland and Helmut Jansen",   pages = 	"329--344",   OPTorganization = 	"",   publisher = 	"Informatik aktuell, Springer-Verlag, Berlin/Heidelberg",   OPTaddress = 	"",   month = 	"14./15.\ Mai",   note = 	"GI-Fachtagung, Berlin" }