  As complex software and systems development projects need models as an
important planning, structuring and development technique, models now face
issues resolved for software earlier: models need to be versioned, differences
captured, syntactic and semantic correctness checked as early as possible,
documented, presented in easily accessible forms, etc. Quality management needs
to be established for models as well as their relationship to other models, to
code and to requirement documents precisely clarified and tracked. Business and
product requirements, product technologies as well as development tools evolve.
This also means we need evolutionary technologies both for models within a
language and if the language evolves also for an upgrade of the models. This
chapter discusses the state of the art in model management and evolution and
sketches what is still necessary for models to become as usable and used as
software.
