Relational & XML Data Exchange Semantics, Consistency and Query

The key findings can be split into two categories. The first one
addresses the issue of semantics in data exchange. The second one is
about developing the complete toolkit for XML data exchange.
Regarding the first group of results, prior to our work everyone used
a single model of data exchange, while admitting its obvious
shortcomings. We explained that these shortcomings come from
mishandling of incomplete information that naturally occurs in
databases arising in data exchange. We developed a framework for
performing key tasks of data exchange based on the semantics of
incompleteness, and applied it in the scenarios of open world, closed
world, and mixed semantics.
Regrading XML data exchange, we developed, essentially from scratch, a
complete toolkit for doing XML data exchange. It covers specification
of mappings, their static analysis, building target solutions, and
query answering. We provided a complete classification of classes of
schema mappings based on the complexity of their static analyses; we
classified schema mappings based on the behavior of query answering
algorithms, and identified a large and practically relevant class of
XML schema mappings that admits particularly efficient static analysis
and query answering algorithms. We have answered long-standing open
questions on the complexity of building solutions in data exchange, by
providing an algorithm with tractable data complexity for
materializing solutions. In addition, we have developed the basics for
doing data exchange on instances with incomplete information, bringing
the theory much closer to practice (so far, this work was done for
relations, as a necessary first step towards extending it to XML).