For instance, if we make the simplifying assumption that the possible argument realizations are limited to those given in Figure 8, the Subject, Object, ByObject, and IndirectObject classes would be defined as follows.
23 we define the Subject class as an abstraction for talking about the set of tree fragments that represent the possible realizations of a subject argument-namely, in Similarly, tree families for non-verbal predicates (adjectives, nouns) can be defined using the abstraction over grammatical functions defined for verbs.