Francesco Scarcello Georg Gottlob Gianluigi Greco Uniform Constraint Satisfaction Problems and Database Theory. 156-195 2008 Complexity of Constraints http://dx.doi.org/10.1007/978-3-540-92800-3_7 conf/dagstuhl/2008coc db/conf/dagstuhl/coc2008.html#ScarcelloGG08