A generalization relationship between two associations.
See also association, generalization.
Generalization among associations is permitted, although it is somewhat uncommon. As with any generalization relationship, the child element must add to the intent (defining rules) of the parent and must subset the extent (set of instances) of the parent. Adding to the intent means adding additional constraints. A child association is more constrained than its parent. For example, in Figure 14-33, if the parent association connects classes Subject and Symbol, then the child association may connect classes Order and OrderSymbol, where Order is a child of Subject and OrderSymbol is a child of Symbol. Subsetting the ...