Subclause 7.3 uses the GFM (Figure 3) to identify and describe the concepts used to define features and how these concepts are related. The GFM is a model of the concepts required to classify a geographic view of the real world. UML has its own model of concepts (metamodel). As both the GFM and the UML metamodel deal with classification, the concepts are very similar. There is one big difference: the concepts in the GFM establish a basis for the classification of features, whereas the UML metamodel provides a basis for classification of any kind. The things we want to classify we call features; the relations between feature types are feature association types and inheritance. Feature types have properties that are feature attributes, feature operations and feature association roles. The GFM is a metamodel of feature types.