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The phrase-level parser
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For a last suffix of ’S, three checks are performed. If the previous morph is a
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NOUN, then the part-of-speech set is (NOUN (POSS TR), NOUN .... (CONTR
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TR)), where “....” are the features that the previous morph had (e.g. (NUM PL)). If
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the next to last morph is a PRN, then the part of speech is PRN with the previous
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morph’s features and the additional property (CONTR TR). If that morph also has
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the property (PRNADJ TR), which includes the pronouns ending in body, one, and
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thing, then the part-of-speech set also includes PRN with the prior morph’s fea-
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tures and the property (CASE POSS), as in anybody’s.
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The last three cases of the dispatch deal with contractions. If the last morph is
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N°T, first the program checks if the previous morph is NEED. The part of speech
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of needn’t is MOD, and the features are (AUX A) and (NOT TR). If the next to
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last morph has the part of speech BE, HAVE, or MOD, the processor just adds the
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property (NOT TR). If the last morph is *VE and the previous morph is a modal,
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then the part of speech is the same as the previous morph with the additional
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property (CONTR TR), as in must’ve. Finally, if the last morph is one of the verb
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contractions *VE, °D, ’LL, and ’RE, the processor checks if the prior morph is the
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plural morph S. (The kids’ve been busy. The boys’ll go.) If so, the word’s part
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of speech is NOUN with the features (NUM PL) and (CONTR TR). Otherwise, if
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the previous morph is a NOUN or PRN, the property (CONTR TR) is added to the
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feature set.
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If the last suffix is none of the above, then the part-of-speech set of the word
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is the part-of-speech set of that morph. If a word still has no part of speech (e.g.
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only’s), then the routine which assigns “default” parts of speech is called, as in the
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case of no decomposition.
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4.6 The parser algorithm
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4.6.1 Parsing strategy
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The parser reads information from DECOMP on the words in a text one sentence
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at a time. It then attempts to find phrases in the sentence. The operation of the
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parsing logic can be thought of as having two levels. The global level reflects the
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parsing strategy, which has been found to give the best phrases. It is based on
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three empirical facts:
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1. There are many more noun groups (and prepositional phrases) than
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verb groups in running text.
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2. The initial portions of noun groups are easier to detect than verb
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groups. Verb groups frequently begin with the verb itself which of-
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ten has both NOUN and VERB in its possible part-of-speech set.
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45
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