Data exchange is the problem of finding an instance of a target schema,
given an instance of a source schema and a specification of the relationship
between the source and the target. Such a target instance should correctly
represent information from the source instance under the constraints imposed
by the target schema, and it should allow one to evaluate queries on the
target instance in a way that is semantically consistent with the source
data. Data exchange is an old problem that re-emerged as an active research
topic recently, due to the increased need for exchange of data in various
formats, often in e-business applications. In this lecture, we give an
overview of the basic concepts of data exchange in both relational and XML
contexts. We give examples of data exchange problems, and we introduce the
main tasks that need to addressed. We then discuss relational data exchange,
concentrating on issues such as relational schema mappings, materializing
target instances (including canonical solutions and cores), query answering,
and query rewriting. After that, we discuss metadata management, i.e.,
handling schema mappings themselves. We pay particular attention to
operations on schema mappings, such as composition and inverse. Finally,
we describe both data exchange and metadata management in the context
of XML.

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