Summary: Principles of building Re-usable Models in GRAIL

Here then are two key principles for producing re-usable models in GRAIL:

• Keep the asserted hierarchy of elementary categories simple and clean. Always make sure there is just one principle involved in the asserted hierarchy - e.g. whether vehicles are road or rail vehicles. Don’t mix different principles in the same hierarchy;
• Make as much of the information as possible explicit by using necessary statements and definitions. Check the categories when you are finished to make sure that all of the information which applications may need is explicitly represented in the criteria.

A common problem in many representations which violates these principles, is that modellers confuse the part-of and kind-of relations. Often this is inevitable, because many systems do not provide adequate support for part-of relations. This is one of GRAIL’s important features which will be explained in the next chapter.