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In data exchange, data are materialised from a source schema to a targetschema, according to suitable source-to-target constraints. Constraints arealso expressed on the target schema to represent the domain of interest. Aschema mapping is the union of the source-to-target and of the targetconstraints.  In this paper, we address the problem of containment of schema mappings fordata exchange, which has been recently proposed in this framework as a steptowards the optimization of data exchange settings. We refer to a naturalnotion of containment that relies on the behaviour of schema mappings withrespect to conjunctive query answering, in the presence of so-called LAV TGDsas target constraints. Our contribution is a practical technique for testingthe containment based on the existence of a homomorphism between special"dummy" instances, which can be easily built from schema mappings.  We argue that containment of schema mappings is decidable for most practicalcases, and we set the basis for further investigations in the topic. This paperextends our preliminary results.

Containment of Schema Mappings for Data Exchange (Preliminary Report)