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"
}
