Three easy pieces on schema mappings for tree-structured data

Schema mappings specify how data organized under a source schema should be reorganized under a target schema. For tree-structured data, the interplay between these specifications and the complex structural conditions imposed by the schemas, makes schema mappings a very rich formalism. Classical data management tasks, well-understood in the relational model, once again become challenging theoretical problems. Recent results on non-mixing integrity constraints help to push the decid-ability frontier further for three such problems: consistency of mappings, membership in the composition of mappings, and query answering.