19.4.4 The Proposition Bank

The Proposition Bank, generally referred to as PropBank, is a resource of sentences annotated with semantic roles. The English PropBank labels all the sentences in the Penn TreeBank; there is also a Chinese PropBank which labels sentences in the Penn Chinese TreeBank. Because of the difficulty of defining a universal set of thematic roles, the semantic roles in PropBank are defined with respect to an individual verb sense. Each sense of each verb thus has a specific set of roles, which are given only numbers rather than names: Arg0, Arg1 Arg2, and so on. In general, Arg0 is used to represent the PROTO-AGENT, and Arg1 the PROTO-PATIENT; the semantics of the other roles are specific to each verb sense. Thus the Arg2 of one verb is likely to have nothing in common with the Arg2 of another verb.

Here are some slightly simplified PropBank entries for one sense each of the verbs agree and fall; the definitions for each role ("Other entity agreeing", "amount fallen")

are informal glosses intended to be read by humans, rather than formal definitions of the role.

(19.33) Frameset agree.01

Arg0: Agreer

Arg1: Proposition

Arg2: Other entity agreeing

Ex1: [Arg0 The group] agreed [Arg1 it wouldn't make an offer unless it had Georgia Gulf's consent].

Ex2: [ArgM-Tmp Usually] [Arg0 John] agrees [Arg2 with Mary] [Arg1 on everything].

(19.34) fall.01 “move downward”

Arg1: Logical subject, patient, thing falling

Arg2: Extent, amount fallen

Arg3: start point

Arg4: end point, end state of arg1

ArgM-LOC: medium

Ex1: [Arg1 Sales] fell [Arg4 to $251.2 million] [Arg3 from $278.7 million].

Ex1: [Arg1 The average junk bond] fell [Arg2 by 4.2%] [ArgM-TMP in October].

Note that there is no Arg0 role for fall, because the normal subject of fall is a PROTO-PATIENT.

The PropBank semantic roles can be useful in recovering shallow semantic information about verbal arguments. Consider the verb increase:

(19.35) increase.01 “go up incrementally”

Arg0: Causer of Increase

Arg1: thing increasing

Arg2: amount increased by, EXT, or MNR

Arg3: start point

Arg4: end point

A PropBank semantic role labeling would allow us to infer the commonality in the event structures of the following three examples, showing that in each case Big Fruit Co. is the AGENT, and the price of bananas is the THEME, despite the differing surface forms.

[Arg0 Big Fruit Co. ] increased [Arg1 the price of bananas].

[Arg1 The price of bananas] was increased again [Arg0 by Big Fruit Co.]

[Arg1 The price of bananas] increased [Arg2 5%].