@TechReport{Kahl-2009b,
  author = 	 {Wolfram Kahl},
  title = {Collagories for Relational Adhesive Rewriting},
  institution =  {Software Quality Research Laboratory,
                  Department of Computing and Software,
                  McMaster University},
  year = 	 {2009},
  type = 	 {SQRL Report},
  number = 	 {56},
  month = 	 JUL,
  note = {In: \url{http://sqrl.mcmaster.ca/sqrl_reports.html}},
  abstract = {We define collagories essentially as
      ``distributive allegories without zero morphisms'',
      and show that they are sufficient for
      accommodating the relation-algebraic approach to graph transformation.
      Collagories closely correspond to the adhesive categories
      important for the categorical DPO approach to graph transformation.
      but thanks to their relation-algebraic flavour
      provide a more accessible and more flexible setting.}
}