@TechReport{	  it:2008-018,
  author	= {Pierre Flener and Xavier Lorca},
  title		= {A Complete Characterisation of the Classification Tree
		  Problem},
  institution	= {Department of Information Technology, Uppsala University},
  department	= {Computing Science Division},
  year		= {2008},
  number	= {2008-018},
  month		= jun,
  abstract	= {Finding a classification tree over a given set of elements
		  that is compatible with a given family of classification
		  trees over subsets of that set is a common problem in many
		  application areas, such as the historical analysis of
		  languages, the theory of relational databases, and
		  phylogenetic supertree construction. We present a
		  constraint programming approach to this problem. First, we
		  introduce a natural and compact graph representation of a
		  family of classification trees. Second, we provide a
		  complete filtering algorithm for the classification tree
		  problem, based on this normal form.}
}