How might you use a model of a system that already exists? Explain why it is not always necessary for such a system model to be complete and correct. Would the same be true if you were developing a model of a new system?

What will be an ideal response?

You might create and use a model of a system that already exists for the following
reasons:
1. To understand and document the architecture and operation of the existing
system.
2. To act as the focus of discussion about possible changes to that system.
3. To inform the re-implementation of the system.
You do not need a complete model unless the intention is to completely document
the operation of the existing system. The aim of the model in such cases is usually
to help you work on parts of the system so only these need to be modelled.
Furthermore, if the model is used as a discussion focus, you are unlikely to ne
interested in details and so can ignore parts of the system in the model.
This is true, in general, for models of new systems unless a model-based
approach to development is taking place in which case a complete model is
required. The other circumstances where you may need a complete model is when
there is a contractual requirement for such a model to be produced as part of the
system documentation.