The term model has gained such popularity that it threatens to become an all purpose word for relationship among concepts. Many writers have attempted to define the term more narrowly but with little success to date. Eg one writer defines a mode as anything used to represent something else a map used represent a section of countryside is a model and so is a chart used to represent concurrent changes in fuel oil sales and temperature. Another view is since the purpose of the model is the representation of relationship between or among concepts the prerequisite for any model is a conceptual scheme. Models are not substitutes for conceptual schemes principles hypothesis or theories but rather are devices to depict their concepts and the relationship which are involved.