jurafsky&martin_3rdEd_17 (1).pdf

We call this shallow semantic representation level

Info icon This preview shows pages 377–379. Sign up to view the full content.

View Full Document Right Arrow Icon
We call this shallow semantic representation level semantic roles . Semantic roles are representations that express the abstract role that arguments of a predicate can take in the event; these can be very specific, like the BUYER , abstract like the AGENT , or super-abstract (the PROTO - AGENT ). These roles can both represent gen- eral semantic properties of the arguments and also express their likely relationship to the syntactic role of the argument in the sentence. A GENTS tend to be the subject of an active sentence, THEMES the direct object, and so on. These relations are codified in databases like PropBank and FrameNet. We’ll introduce semantic role labeling , the task of assigning roles to the constituents or phrases in sentences. We’ll also discuss selectional restrictions , the semantic sortal restrictions or preferences that each individual predicate can express about its potential arguments, such as the fact that the theme of the verb eat is generally something edible. Along the way, we’ll describe the various ways these representations can help in language understanding tasks like question answering and machine translation. 22.1 Semantic Roles Consider how in Chapter 19 we represented the meaning of arguments for sentences like these:
Image of page 377

Info icon This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
378 C HAPTER 22 S EMANTIC R OLE L ABELING Thematic Role Definition AGENT The volitional causer of an event EXPERIENCER The experiencer of an event FORCE The non-volitional causer of the event THEME The participant most directly affected by an event RESULT The end product of an event CONTENT The proposition or content of a propositional event INSTRUMENT An instrument used in an event BENEFICIARY The beneficiary of an event SOURCE The origin of the object of a transfer event GOAL The destination of an object of a transfer event Figure 22.1 Some commonly used thematic roles with their definitions. (22.1) Sasha broke the window. (22.2) Pat opened the door. A neo-Davidsonian event representation of these two sentences would be 9 e , x , y Breaking ( e ) ^ Breaker ( e , Sasha ) ^ BrokenThing ( e , y ) ^ Window ( y ) 9 e , x , y Opening ( e ) ^ Opener ( e , Pat ) ^ OpenedThing ( e , y ) ^ Door ( y ) In this representation, the roles of the subjects of the verbs break and open are Breaker and Opener respectively. These deep roles are specific to each event; Break- deep roles ing events have Breakers , Opening events have Openers , and so on. If we are going to be able to answer questions, perform inferences, or do any further kinds of natural language understanding of these events, we’ll need to know a little more about the semantics of these arguments. Breakers and Openers have something in common. They are both volitional actors, often animate, and they have direct causal responsibility for their events. Thematic roles are a way to capture this semantic commonality between Break- Thematic roles ers and Eaters .
Image of page 378
Image of page 379
This is the end of the preview. Sign up to access the rest of the document.

{[ snackBarMessage ]}

What students are saying

  • Left Quote Icon

    As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

    Student Picture

    Kiran Temple University Fox School of Business ‘17, Course Hero Intern

  • Left Quote Icon

    I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

    Student Picture

    Dana University of Pennsylvania ‘17, Course Hero Intern

  • Left Quote Icon

    The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

    Student Picture

    Jill Tulane University ‘16, Course Hero Intern