Efficiency frontiers of XML cardinality constraints

XML has gained widespread acceptance as a premier format for publishing,sharing and manipulating data through the web. While the semi-structured na-ture of XML provides a high degree of syntactic flexibility there are significantshortcomings when it comes to specifying the semantics of XML data. For theadvancement of XML applications it is therefore a major challenge to discover nat-ural classes of constraints that can be utilized effectively by XML data engineers.This endeavor is ambitious given the multitude of intractability results that havebeen established. We investigate a class of XML cardinality constraints that isprecious in the sense that it keeps the right balance between expressiveness andefficiency of maintenance. In particular, we characterize the associated implica-tion problem axiomatically and develop a low-degree polynomial time algorithmthat can be readily applied for deciding implication. Our class of constraints ischosen near-optimal as already minor extensions of its expressiveness cause poten-tial intractability. Finally, we transfer our findings to establish a precious class