An association specifies a semantic relationship that can occur between typed instances. It has at least two ends represented by properties, each of which is connected to the type of the end. More than one end of the association may have the same type. When a property is owned by an association it represents a non-navigable end of the association. In this case the property does not appear in the namespace of any of the associated classifiers. When a property at an end of an association is owned by one of the associated classifiers it represents a navigable end of the association. In this case the property is also an attribute of the associated classifier. Only binary associations may have navigable ends.