jurafsky&martin_3rdEd_17 (1).pdf

The following diagram illustrates a dependency style

Info icon This preview shows pages 245–247. Sign up to view the full content.

View Full Document Right Arrow Icon
The following diagram illustrates a dependency-style analysis using the standard graphical method favored in the dependency-parsing community. (14.1) I prefer the morning flight through Denver nsubj dobj det nmod nmod case root Relations among the words are illustrated above the sentence with directed, la- beled arcs from heads to dependents. We call this a typed dependency structure Typed dependency because the labels are drawn from a fixed inventory of grammatical relations. It also includes a root node that explicitly marks the root of the tree, the head of the entire structure. Figure 14.1 shows the same dependency analysis as a tree alongside its corre- sponding phrase-structure analysis of the kind given in Chapter 11. Note the ab- sence of nodes corresponding to phrasal constituents or lexical categories in the dependency parse; the internal structure of the dependency parse consists solely of directed relations between lexical items in the sentence. These relationships di- rectly encode important information that is often buried in the more complex phrase- structure parses. For example, the arguments to the verb prefer are directly linked to it in the dependency structure, while their connection to the main verb is more dis- tant in the phrase-structure tree. Similarly, morning and Denver , modifiers of flight , are linked to it directly in the dependency structure. A major advantage of dependency grammars is their ability to deal with lan- guages that are morphologically rich and have a relatively free word order . For Free word order example, word order in Czech can be much more flexible than in English; a gram- matical object might occur before or after a location adverbial . A phrase-structure grammar would need a separate rule for each possible place in the parse tree where such an adverbial phrase could occur. A dependency-based approach would just have one link type representing this particular adverbial relation. Thus, a depen- dency grammar approach abstracts away from word-order information, representing only the information that is necessary for the parse. An additional practical motivation for a dependency-based approach is that the head-dependent relations provide an approximation to the semantic relationship be-
Image of page 245

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

View Full Document Right Arrow Icon
246 C HAPTER 14 D EPENDENCY P ARSING prefer flight Denver through morning the I S VP NP Nom PP NP Pro Denver P through Nom Noun flight Nom Noun morning Det the Verb prefer NP Pro I Figure 14.1 A dependency-style parse alongside the corresponding constituent-based analysis for I prefer the morning flight through Denver. tween predicates and their arguments that makes them directly useful for many ap- plications such as coreference resolution, question answering and information ex- traction. Constituent-based approaches to parsing provide similar information, but it often has to be distilled from the trees via techniques such as the head finding rules discussed in Chapter 11.
Image of page 246
Image of page 247
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