Cloud theory is a new theory handling uncertainty based on the uncertain transition between quality and quantity. The theory includes cloud model, virtual cloud, cloud operation, cloud transform and uncertainty reasoning. It provides new solutions for many basic problems in data mining and knowledge discovery, such as concept and knowledge representation, transition between quality and quantity, concept synthesization and resolution, concept and concept hierarchy generation from data, etc. Clod model is a model of the uncertain transition between a linguistic term of a qualitative concept and its numerical representation. Cloud model represents a qualitative concept with three digital characteristics, expected...