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Section 11.3 Features structures in the Grammar ─ Jin Wang

Section 11.3 Features structures in the Grammar ─ Jin Wang. How to specify a way to integrate feature structures and unification operations into the specification of a grammar?.

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Section 11.3 Features structures in the Grammar ─ Jin Wang

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  1. Section 11.3 Features structures in the Grammar ─ Jin Wang

  2. How to specify a way to integrate feature structures and unification operations into the specification of a grammar? Augmenting the rules of ordinary context-free grammars with attachments that specify feature structures for the constituents of the rules, along with appropriate unification operations that express constraints on those constituents.

  3. β0─> β1 . . . Βn(PATR-Ⅱ system, Shieber 1986) {set of constraints} The specified constraints have one of the following forms: ﹤βifeature path＞= Atomic value ﹤βi feature path＞= ﹤βj feature path＞

  4. How to use these constraints??? At the beginning of this chapter: S ─> NP VP Only if the number of the NP is equal to the number of the VP Using the new notation: S ─> NP VP ﹤NP NUMBER﹥= ﹤VP NUMBER﹥ So, the simple generative nature of context-free rules has been fundamentally changed by this augmentation.

  5. Agreement subject-verb agreement S ─> NP VP ﹤NP AGREEMENT＞= ﹤VP AGREEMENT ＞ - This flight serves breakfast. Unification constraints can be applied to four interesting linguistic phenomena: Agreement Grammatical heads Subcategorization Long-distance dependencies. S ─> Aux NP VP ﹤Aux AGREEMENT＞= ﹤NP AGREEMENT＞ - Does this flight serve breakfast? - Do these flight serve breakfast? • Does this flight serve breakfast? • Do these flight serve breakfast?

  6. Agreement Determiner-nominal agreement NP ─> Det Nominal ﹤Det AGREEMENT ＞= ﹤Nominal AGREEMENT ＞ ﹤NP AGREEMENT ＞= ﹤Nominal AGREEMENT ＞

  7. Non-lexical grammatical constituents can acquire values for at least some of their features from their component constituents. VP ─> Verb NP <VP AGREEMENT> = <Verb AGREEMENT> Verb ─> serves <Verb AGREEMENT NUMBER> = SG <Verb AGREEMENT PERSON> = 3 The same technique works for the remaining NP and Nominal categories.

  8. VP ─> Verb NP <VP AGREEMENT>=<Verb AGREEMENT> NP ─> Det Nominal <Det AGREEMENT>=<Nominal AGREEMENT> <NP AGREEMENT>=<Nominal AGREEMENT> Nominal─> Noun <Nominal AGREEMENT>=<Noun AGREEMENT> VP ─> Verb NP <VP HEAD>=<Verb HEAD> NP ─> Det Nominal <NP HEAD>=<Nominal HEAD> <Det HEAD AGREEMENT>=<Nominal HEAD AGREEMENT> Nominal─> Noun <Nominal HEAD>=<Noun HEAD> Head Features The features for most grammatical categories are copied from one of the children to the parent. Head of the phrase: The child that prvides the features. Head features: The features that are copied.

  9. Subcategorization Verbs can be picky about the pattern of arguments they will allow themselves to appear with. SUBCAT:An atomic feature. A proper way to introduce feature structures to distinguish among the various members of the verb category. Verb ─> serves <Verb HEAD AGREEMENT NUMBER> = SG <Verb HEAD SUBCAT> = TRANS

  10. This constraint is enforced by adding corresponding constraints to all the verb phrase rules in the grammar: VP ─> Verb <VP HEAD> = <Verb HEAD> <VP HEAD SUBCAT> = INTRANS VP ─> Verb NP <VP HEAD> = <Verb HEAD> <VP HEAD SUBCAT> = TRANS VP ─> Verb NP NP <VP HEAD> = <Verb HEAD> <VP HEAD SUBCAT> = DITRANS However, this approach is somewhat opaque since these unanalyzable SUBCAT symbols do not directly encode either the number or type of the arguments that the verb expects to take.

  11. A somewhat more elegant solution: - One argument (Serves dinner ) Verb ─> serves <Verb HEAD AGREEMENT NUMBER> = SG <Verb HEAD SUBCAT FIRST CAT> = NP <Verb HEAD SUBCAT SECOND> = END - Two arguments (leaves Boston in the morning ) Verb ─> serves <Verb HEAD AGREEMENT NUMBER> = SG <Verb HEAD SUBCAT FIRST CAT> = NP <Verb HEAD SUBCAT SECOND CAT> = PP <Verb HEAD SUBCAT THIRD> = END

  12. Those examples just show rather simple subcategorization structures for verbs. In fact, verbs can subcategorize for quite complex subcategorization frames. Also, the notion of subcategorization can be used in other parts of speech, such as the prepositions.

  13. Long-Distance Dependencies Sometimes, a constituent subcategorized for by the verb is not locally instantiated, but is in a long-distance relationship with the predicate. What cities does Continental service ? Which flight do you want me to have the travel agent book ?

  14. Many solutions to representing long-distance dependencies in unification grammars involve keeping a gap list, implemented as a feature GAP, which is passed up from phrase to phrase in the parse tree.

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