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Paper text:
in order to develop a practical natural language processing ( nlp ) system , it is essential to deal with ill - formed sentences that can not be parsed correctly according to the grammar rules in the system . in this paper ,
an `` ill - formed sentence '' means one that can not be parsed as a unified structure .
a syntactic parser with general grammar rules is often unable to analyze not only sentences with grammatical errors and ellipses , but also long sentences , owing to their complexity .
thus , ill - formed sentences include not only ungrammatical sentences , but also some grammatical sentences that can not be parsed as unified structures owing to the presence of unknown words or to a lack of completeness in the syntactic parser . in texts from a restricted domain , such as computer manuals ,
most sentences are grammatically correct
. however , even a well - established syntactic parser usually fails to generate a unified parsed structure for about 10 to 20 percent of all the sentences in such texts , and the failure to generate a unified parsed structure in syntactic analysis leads to a failure in the output of a nlp system .
thus , it is indispensable to establish a correct analysis for such a sentence .    to handle such sentences ,
most previous approaches apply various heuristic rules @xcite , including    * relaxing constraints in the condition part of a grammatical rule , such as number and gender constraints * joining partial parses by using meta rules .    either way , the output reflects the general plausibility of an analysis that can be obtained from information in the sentence ; however , the interpretation of a sentence depends on its discourse , and inconsistency with recovered parses that contain different analyses of the same phrase in other sentences in the discourse often results in odd outputs of the natural language processing system .
starting from the viewpoint that an interpretation of a sentence must be consistent in its discourse , we worked on completing incomplete parses by using information extracted from complete parses in the discourse .
the results were encouraging .
since most words in a sentence are repeatedly used in other sentences in the discourse , the complete parses of well - formed sentences usually provided some useful information for completing incomplete parses in the same discourse .
thus , rather than trying to enhance a syntactic parser s grammar rules in order to support ill - formed sentences , which seems to be an endless task after the parser has obtained enough coverage to parse general grammatical sentences , we treat the syntactic parser as a black box and complete incomplete parses , in the form of partially parsed chunks that a bottom - up parser outputs for ill - formed sentences , by using information extracted from the discourse .    in the next section , the effectiveness of using information extracted from the discourse to complete syntactic analysis of ill - formed sentences . after that
, we propose an algorithm for completing incomplete parses by using discourse information , and give the results of an experiment on completing incomplete parses in technical documents .
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we have proposed a method for completing partial parses of ill - formed sentences on the basis of information extracted from complete parses of well - formed sentences in the discourse .
our approach to handling ill - formed sentences is fundamentally different from previous ones in that it reanalyzes the part of speech and modifiee - modifier relationships of each word in an ill - formed sentence by using information extracted from analyses of other sentences in the same text , thus , attempting to generate the analysis most appropriate to the discourse .
the results of our experiments show the effectiveness of this method ; moreover , implementation of this method on a machine translation system improved the accuracy of its translation . since this method has a simple framework that does not require any extra knowledge resources or inference mechanisms , it is robust and suitable for a practical natural language processing system . furthermore , in terms of the turn - around time ( tat ) of the whole translation procedure , the improvement in the parses achieved by using this method along with other disambiguation methods involving discourse information , as shown in another paper @xcite , shortened the tat in the late stages of the translation procedure , and compensated for the extra tat required as a result of using the discourse information , provided the size of the discourse was kept to between 100 and 300 sentences .    in this paper ,
the term `` discourse '' is used as a set of words in a text together with the usage of each of those words in that text  namely , a part of speech and modifiee - modifier relationships with other words . the basic idea of our method is to improve the accuracy of sentence analysis simply by maintaining consistency in the usage of morphologically identical words within the same text .
thus , the effectiveness of this method is highly dependent on the source text , since it presupposes that morphologically identical words are likely to be repeated in the same text .
however , the results have been encouraging at least with technical documents such as computer manuals , where words with the same lemma are frequently repeated in a small area of text .
moreover , our method improves the translation accuracy , especially for frequently repeated phrases , which are usually considered to be important , and leads to an improvement in the overall accuracy of the natural language processing system .
i would like to thank michael mcdonald for invaluable help in proofreading this paper .
i would also like to thank taijiro tsutsumi , masayuki morohashi , koichi takeda , hiroshi maruyama , hiroshi nomiyama , hideo watanabe , shiho ogino , naohiko uramoto , and the anonymous reviewers for their comments and suggestions .
in a consistent text , many words and phrases are repeatedly used in more than one sentence . 
 when an identical phrase ( a set of consecutive words ) is repeated in different sentences , the constituent words of those sentences tend to be associated in identical modification patterns with identical parts of speech and identical modifiee - modifier relationships . 
 thus , when a syntactic parser can not parse a sentence as a unified structure , parts of speech and modifiee - modifier relationships among morphologically identical words in complete parses of other sentences within the same text provide useful information for obtaining partial parses of the sentence .    in this paper 
 , we describe a method for completing partial parses by maintaining consistency among morphologically identical words within the same text as regards their part of speech and their modifiee - modifier relationship . 
 the experimental results obtained by using this method with technical documents offer good prospects for improving the accuracy of sentence analysis in a broad - coverage natural language processing system such as a machine translation system .