From Frames to Inference
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From Frames to Inference Nancy Chang, Srini Narayanan, and Miriam R.L. Petruck International Computer Science Institute 1947 Center St., Suite 600, Berkeley, CA 94704 nchang,miriamp,snarayan ¡ @icsi.berkeley.edu Abstract money ($1000) to another (Jerry) in exchange for some goods (a car) – but differ in the perspective This paper describes a computational they impose on the scene. formalism that captures structural rela- The shared inferential structure of verbs like buy tionships among participants in a dy- and sell is captured in FrameNet by the COMMERCE namic scenario. This representation is frame, which is associated with a set of situational used to describe the internal structure of roles, or frame elements (FEs), corresponding to FrameNet frames in terms of parameters event participants and props. These FEs are used for active event simulations. We apply our as annotation tags for sentences like those in (1), formalism to the commerce domain and yielding, for example: show how it provides a flexible means of handling linguistic perspective and other Buyer Goods challenges of semantic representation. (2) a. [Chuck] bought [a car] [from Jerry]Seller [for $1000]Payment. 1 Introduction b. [Jerry]Seller sold [a car]Goods [to Chuck]Buyer [for $1000]Payment. The development of lexical semantic resources is widely recognized as a prerequisite to progress in FE tags act as a shorthand that allows diverse verbs scalable natural language understanding. One of the to tap into a common subset of encyclopedic knowl- most semantically sophisticated efforts in this direc- edge. Moreover, regularities in the set of FEs real- tion is FrameNet (Baker et al., 1998; Fillmore et al., ized with specific lexical items can be taken as cor- 2001), an online lexical resource1 designed accord- related with their favored perspective. ing to the principles of frame semantics (Fillmore, 1985; Petruck, 1996). FrameNet takes as founda- A significant gap remains, however, between the tional the assumptions that (1) lexical items draw unstructured and intuitively chosen tag sets used in on rich conceptual structures, or frames, for their FrameNet and a formal characterization of the inter- meaning and function; and (2) conceptually related related actions and relations holding among them. lexical items may foreground different aspects of The explicit representation of such frame semantic the same background frame. Verbs involved with information is needed for FrameNet’s potential use commercial events serve as canonical examples: in text understanding and inference (Fillmore and Baker, 2001) to be fully realized. In this paper we (1) a. Chuck bought a car from Jerry for $1000. attempt to bridge the gap by defining a formalism b. Jerry sold a car to Chuck for $1000. that unpacks the shorthand of frames into structured c. Chuck paid Jerry $1000 for a car. event representations. These dynamic representa- d. Jerry charged Chuck $1000 for a car. tions allow annotated FrameNet data to parameter- e. Chuck spent $1000 on a car. ize event simulations (Narayanan, 1999b) that pro- duce fine-grained, context-sensitive inferences. We The sentences in (1) might describe the same inter- illustrate our formalism for the COMMERCE frame action – in which one individual (Chuck) transfers and show how it can account for some of the wide- 1http://www.icsi.berkeley.edu/framenet/ ranging consequences of perspective-taking. 1 Figure 1: Results of a query on the FrameNet COMMERCE frame, showing annotated data for the verb buy. 2 The FrameNet COMMERCE frame (e.g., many but not all appear in the ditransitive con- struction), and not all of them license the expression The FrameNet project has thus far produced two of all FEs (e.g., spend rarely appears with the Seller). databases: a collection of approximately 80 frames Also, some FEs are realized in different ways for with frame descriptions, chosen to cover a broad different verbs: the pattern of appearance with from- range of semantic domains; and a hand-annotated or to- headed PPs differs for buy and sell, and for- dataset of about 50,000 sentences from the British headed PPs may mark either the Payment (for buy National Corpus (Baker et al., 1998). The databases and sell) or the Goods (for pay). document both syntactic and semantic behavior of a Much of this diversity has been attributed to dif- wide variety of lexical items (or lemmas) and thus ferences in perspective, but the complex connec- have the potential to allow corpus-based techniques tions among perspective, argument structure and FE to be applied to semantically oriented tasks.2 realization have been difficult to explicate. One ap- The current release of the FrameNet databases3 proach is to distinguish the COMMERCE frame from defines a COMMERCE frame with frame elements other perspectivized frames exhibiting more con- including the familiar Buyer, Seller, Payment and sistent behavior; proposals along these lines differ Goods, along with several other FEs needed to cover in their criteria for making these divisions and the the data. The frame includes 10 verbs relevant to relationships among the resulting frames.4 commercial transactions, for a total of 575 anno- Our proposal likewise imposes additional struc- tated sentences. Figure 1 shows a sampling of data ture on the COMMERCE frame to reflect both annotated with respect to the COMMERCE frame. perspective-neutral and perspectivized situations. The COMMERCE frame verbs exhibit relatively But for current purposes, we concentrate on cap- greater variety in argument structure possibilities turing perspectival effects on inference in discourse 2See (Gildea and Jurafsky, 2000) for some promising ini- tial work in applying statistical techniques to the FrameNet 4FrameNet II is currently considering a reorganization database to automatically label frame elements. scheme along these lines. Gawron (ms.) and Hudson (in press) 3Throughout the paper we refer to data from FrameNet I; an address these and related issues, both arguing against handling interim release of FrameNet II data is expected soon. perspective solely with multiple inheritance. 2 interpretation. Our structures are thus designed a predicate on accessible structures.6 The keyword to support dynamic inferences about interrelated self refers to the structure being defined, which we events and actions, and not specifically to reflect FE can consider a special kind of role. We use ‘//’ to realization patterns. introduce italicized comments. We take the original COMMERCE frame as ¤ schema £ name our starting point and define the interrelationships ¥ ¤ subcase of £ schema present among its FEs; the resulting event represen- ¦ evokes § ¤ £ ¤©¨ tation can license inferences for sentences like those £ schema as local-name in the annotated FrameNet data. We assume that roles ¤ £ local-role any frame reorganization scheme (as well as any £ ¤ £ ¤ local-role : restriction ¤£ ¤ method for labeling roles in novel text) will define £ local-role role ¤£ ¤ £ ¤ a mapping to the original FEs and thus could be in- £ local-role role : restriction tegrated with our dynamic representations within a constraints ¤£ ¤ larger language understanding enterprise. £ role role ¤ £ ¤ £ phase :: condition 3 Structured event representations Figure 2: Schema definition formalism. In this section, we present a formal specification The first line names the schema being defined. used for mapping the flat set of FEs in COMMERCE onto explicitly structured event representations that The next few lines (subcase of and evokes) indi- characterize commercial transactions. Our repre- cate how this schema relates to other schemas. The sentation is based on the Embodied Construction subcase relation defines a lattice of schemas, with Grammar (ECG) formalism (Bergen and Chang, the local schema inheriting all roles and constraints. 2002). As in that work, we assume that understand- The evokes relation also makes the specified struc- ing an utterance involves the evocation of a com- tures and constraints of the evoked schema (re- plex network of conceptual schemas and the mental ferred to within the current definition using a £ local- simulation of these schemas in context to produce name ¤ ) locally accessible, but it implies neither full a rich set of inferences.5 inheritance of the evoked schema’s roles nor con- Among the features of the ECG schema formal- tainment in either direction. ism that we exploit to represent commercial transac- The indented block labeled roles lists and con- tions are (1) the ability to flexibly evoke and relate strains the schema’s local roles, which are equiv- multiple schemas; and (2) the ability to assert dy- alent to frame FEs. Roles are declared with a lo- ¤ namic conditions that apply to specific event stages. cal name ( £ local-role ) and may be accompanied by We rely heavily on the fact that schemas can be in- type restrictions (indicated with ‘:’) and/or identi- terdefined in our eventual representation of differ- fication (or binding) constraints (‘ ! ’). The lat- ences in perspective. ter (which may also appear in the constraints block) We briefly describe the schema definition lan- causes roles and constraints to be shared between its guage shown in Figure 2, deferring additional de- arguments, similar to unification or coindexation in tails for the examples. Keywords are shown in other frameworks (Pollard and Sag, 1994). bold; a left square bracket ([) marks optional blocks; The final constraint type allowed is a simulation constraint, which uses the ‘::’ notation to assert and curly