A system model is a representation of a system. What considerations should be made while building basic models?

Definition of a system model seems to be a good aim, but what exactly does it entail? What should be considered while creating basic models?

It is advisable to give the use of structured language considerable thought when describing processes that are excluded from a system analysis. Giving the possibility some thought is one way to do this.

It is advisable to give the use of structured language considerable thought when describing processes that are excluded from a system analysis. Giving the possibility some thought is one way to do this.