| Writing is not only an important means of examining English learners' language competence in CET-4,but also a compulsory testing item in most foreign language examinations.And it has a high weight in the scoring system of the whole test.However,for a long time,discourse coherence has been regarded as a semantic and logical concept in the academia,so it is difficult to find an objective evaluation criterion.As far as most of the automatic scoring systems have been developed,the important factor of discourse coherence has not been taken into account in the design of internal evaluation parameters,which leads to the lack of scientific scoring results of each system.Hence it is particularly significant to introduce textual coherence into the scoring system.However,how to evaluate the coherence of discourse,whether there are corresponding evaluation indicators,and whether these indicators can objectively reflect the coherence of discourse are the problems to be solved in this research.Therefore,the hypothesis of this study is that the evaluation indicator of thematic progression fluency can reflect the degree of discourse coherence,namely,there is a certain relationship between thematic progression fluency and the score of discourse coherence.If the fluency of thematic progression is positively correlated with coherence rating,it indicates that there are indicators for evaluating discourse coherence.Then this indicator can be applied into the automatic composition scoring system so as to improve the accuracy of the system.In addition,on the basis of summarizing predecessors' classification of thematic progression patterns,we put forward novel classification of patterns in order to contribute to the development of thematic progression theory.In order to determine the relationship between the fluency of thematic progression and the scoring of discourse coherence,we will first utilize latent semantic analysis,which is commonly used in information retrieval,to obtain the concrete value of thematic progression fluency.Then the regression function between thematic progression fluency and text coherence score is obtained by regression analysis and the relationship between them will be identified.Finally,an automatic scoring model for text coherence is established.In order to test the scoring effect of the model,we will use nonparametric test commonly used in statistics to compare whether there is a significant difference between manual scoring and machine rating.If there is no significant difference,it indicates that the scoring effect of the model is better,otherwise,it is worse.Finally,by comparing the relationship between thematic progression fluency and coherence rating,we find that there is a positive correlation between them.The results of nonparametric test for two related samples also demonstrate that there is no significant difference between the manual scoring and machine scoring,which indicates that the automatic scoring model of discourse coherence established in this study has a better scoring effect,which also reflects the rationality of utilizing thematic progression theory to judge discourse coherence.Therefore,the evaluation index of thematic progression fluency can objectively reflect the coherence of discourse and hypothesis is accepted.In conclusion,this study demonstrates the objectivity of thematic progression fluency as an indicator of textual coherence.Without considering lexical and grammatical factors,the higher the thematic progression fluency is,the higher the score of coherence will have.Throughout this research,it has certain significance both in theory and in practice.Theoretically,this study proves the rationality of thematic progression theory in judging discourse coherence,and reveals its operability in computer processing.Practically,the automatic scoring model of textual coherence based on the fluency thematic progression established in this research has made a useful exploration for improving the automatic essay scoring system of CET-4. |
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