Model management is an approach to simplify the programming
of metadata-intensive applications. It offers developers powerful
operators, such as Compose, Diff, and Merge, that are applied to
models, such as database schemas or interface specifications, and
to mappings between models. Prior model management solutions
focused on a simple class of mappings that do not have executable
semantics. Yet many metadata applications require that mappings
be executable, expressed in SQL, XSLT, or other data transformation
languages.
In this paper, we develop a semantics for model-management
operators that allows applying the operators to executable mappings.
Our semantics captures previously-proposed desiderata and
is language-independent: the effect of the operators is expressed
in terms of what they do to the instances of models and mappings.
We describe an implemented prototype in which mappings are represented
as dependencies between relational schemas, and discuss
algebraic optimization of model-management scripts.