The system is defined as a group of objects that are joined together in some regular interaction or interdependence towards the accomplishment of some purpose.

OR

It is defined as an aggregation of objects that are joined together in some regular fashion for the accomplishment of some purpose.

Example: Production system manufacturing automobiles. In this system machines, component parts and workers operate jointly along an assembly line to produce a high quality vehicle.

A model is defined as a representation of a system for the purpose of studying the system.

OR

A model can be also defined as an abstraction of a system only for the purpose of study.

A model contains only those components that are relevant to the study of system. The model should be complex enough to answer the questions raised and should be simple enough to make the understanding easy.

Example: Model of a building is developed before the construction.