xcit'ed

Statistical association measures have been widely applied in information retrieval research, usually employing a clustering of documents or terms on the basis of their relationships. Applications of the association measures for term clustering include automatic thesaurus construction and query expansion. This research evaluates the similarity of six association measures by comparing the relationship and behavior they demonstrate in various analyses of a test corpus. Analysis techniques include comparisons of highly ranked termpairs and term clusters, analyses of the correlation among the association measures using Pearson’s correlation coefficient and MDS mapping, and an analysis of the impact of a term frequency on the association values by means of z-score. The major findings of the study are as follows: First, the most similar association measures are mutual information and Yule’s coefficient of colligation Y, whereas cosine and Jaccard coefficients, as well as x2 statistic and likelihood ratio, demonstrate quite similar behavior for terms with high frequency. Second, among all the measures, the x2 statistic is the least affected by the frequency of terms. Third, although cosine and Jaccard coefficients tend to emphasize high frequency terms, mutual information and Yule’s Y seem to overestimate rare terms.

well constructed thesaurus has long been recognized as a valuable tool in the effective operation of an information retrieval system. This paper reports the results of experiments designed to determine the validity of an approach to the automatic construction of global thesauri (described originally by Crouch in [1] and [2]) based on a clustering of the document collection. The authors validate the approach by showing that the use of thesauri generated by this method results in substantial improvements in retrieval effectiveness in four test collections. The term discrimination value theory, used in the thesaurus generation algorithm to determine a term’s membership in a particular thesaurus class, is found not to be useful in distinguishing between thesaurus classes (i.e., in differentiating a “good” from an “indifferent” or “poor” thesaurus class). In conclusion, the authors suggest an alternate approach to automatic thesaurus construction which greatly simplifies the work of producing viable thesaurus classes. Experimental results show that the alternate approach described herein in some cases produces thesauri which are comparable in retrieval effectiveness to those produced by the first method at much lower cost.

The term word association is used in a very particular sense in the p!ycholinguistic literature. (Generally speaking, subjects respond quicker than normal to the word "nurse" if it follows a highly associated word such as "doctor.") We will extend the term to provide the basis for a statistical description of a variety of interesting linguistic phenomena, ranging from semantic rehtions of the doctor/nurse type (content word/content word) to lexico-syntactlc co-occurrence constraints between

Statistical models for parsing natural language have recently shown considerable success in broad-coverage domains. Ambiguity often leads to an input sentence having many possible parse trees; statistical approaches assign a probability to each tree, thereby ranking competing trees in order of plausibility. The probability for each candidate tree is calculated as a product of terms, each term corresponding to some sub-structure within the tree. The choice of parameterization is the choice of how to break down the tree. There are two critical questions regarding the parameterization of the problem:

Abstract: Context is used in many NLP systems as an indicator of a term's syntactic and semantic function. The accuracy of the system is dependent on the quality and quantity of contextual information available to describe each term. However, the quantity variable is no longer fixed by limited corpus resources. Given fixed training time and computational resources, it makes sense for systems to invest time in extracting high quality contextual information from a fixed corpus. However, with an effectively limitless quantity of text available, extraction rate and representation size need to be considered. We use thesaurus extraction with a range of context extracting tools to demonstrate the interaction between context quantity, time and size on a corpus of 300 million words.

This paper describes a method to construct related terms thesauri automatically based on Web information. We utilize Web search engine to obtain word co-occurrence information and propose a new efficient similarity metrics applying \chi^2 value to solve problems of the existing methods. We also introduce a new method to identify related terms using word-clustering. We do word-clustering on that associative network to identify related terms using latest clustering methods, "Newman method". We make evaluations and show the effectiveness of our approach using sets of related terms extracted from a corpus and a current thesaurus.

Abstract: A method of determining the similarity of nouns on the basis of a metric derived from the distribution of subject, verb and object in a large text corpus is described. The resulting quasi-semantic classification of nouns demonstrates the plausibility of the distributional hypothesis, and has potential application to a variety of tasks, including automatic indexing, resolving nominal compounds, and determining the scope of modification.

Abstract. Is it possible to discover semantic term relations useful for thesauri without any semantic information? Yes, it is. A recent approach for automatic thesaurus construction is based on explicit linguistic knowledge, i.e. a domain independent parser without any semantic component and implicit linguistic knowledge contained in large amounts of real world texts. Such texts include implicitly the linguistic, especially semantic knowledge that the authors needed for formulating their texts. This article explains how implicit semantic knowledge can be transformed to an explicit one. Evaluations of quality and performance of the approach are very encouraging.

Abstract: We describe and evaluate experimentally a method for clustering words according to their distribution in particular syntactic contexts. Words are represented by the relative frequency distributions of contexts in which they appear, and relative entropy between those distributions is used as the similarity measure for clustering. Clusters are represented by average context distributions derived from the given words according to their probabilities of cluster membership. In many cases, the clusters can be thought of as encoding coarse sense distinctions. Deterministic annealing is used to find lowest distortion sets of clusters: as the annealing parameter increases, existing clusters become unstable and subdivide, yielding a hierarchical "soft" clustering of the data. Clusters are used as the basis for class models of word coocurrence, and the models evaluated with respect to held-out test data.