Relation Variables in Qualitative Spatial Reasoning
  We study an alternative to the prevailing approach to modelling qualitative
spatial reasoning (QSR) problems as constraint satisfaction problems. In the
standard approach, a relation between objects is a constraint whereas in the
alternative approach it is a variable. The relation-variable approach greatly
simplifies integration and implementation of QSR. To substantiate this point,
we discuss several QSR algorithms from the literature which in the
relation-variable approach reduce to the customary constraint propagation
algorithm enforcing generalised arc-consistency.
