Text mining concerns looking for patterns in unstructured text. The related task of Information Extraction (IE) is about locating specific items in natural-language documents. This paper presents a framework for text mining, called DiscoTEX (Discovery from Text EXtraction), using a learned information extraction system to transform text into more structured data which is then mined for interesting relationships. The initial version of DiscoTEX integrates an IE module acquired by an IE learning system, and a standard rule induction module. In addition, rules mined from a database extracted from a corpus of texts are used to predict additional information to extract from future documents, thereby improving the recall of the underlying extraction system. Encouraging results are presented on applying these techniques to a corpus of computer job announcement postings from an Internet newsgroup.
ML ID: 159
Many machine learning tasks require similarity functions that estimate likeness between observations. Similarity computations are particularly important for clustering and record linkage algorithms that depend on accurate estimates of the distance between datapoints. However, standard measures such as string edit distance and Euclidean distance often fail to capture an appropriate notion of similarity for a particular domain or dataset. This problem can be alleviated by employing learnable similarity functions that adapt using training data. In this proposal, we introduce two adaptive string similarity measures: (1) Learnable Edit Distance with Affine Gaps, and (2) Learnable Vector-Space Similarity Based on Pairwise Classification. These similarity functions can be trained using a corpus of labeled pairs of equivalent and non-equivalent strings. We illustrate the accuracy improvements obtained with these measures using MARLIN, our system for record linkage in databases that learns to combine adaptive and static string similarity functions in a two-level learning framework.
Obtaining useful training examples for learnable similarity functions can be problematic due to scarcity of informative similar and dissimilar object pairs. We propose two strategies, Static-Active Selection and Weakly-Labeled Negatives, that facilitate efficient training data collection for record linkage. These strategies significantly outperform random selection on real datasets without the computational cost of traditional active learning methods. Additionally, we describe a method for combining seeding with Euclidean distance learning for semi-supervised k-means clustering. Experimental evaluation demonstrates that our method outperforms unsupervised clustering and semi-supervised clustering that employs seeding or metric learning separately.
In future research, we intend to pursue several directions in developing accurate learnable similarity functions and applying them to record linkage and clustering problems. This work will involve improving the proposed string similarity functions as well as introducing several novel approaches to adaptive string distance computation. We also plan to extend our initial work on learnable similarity functions for clustering, particularly for high-dimensional data. Finally, we will investigate the utility of various active learning strategies for learning similarity functions, as well as extend the preliminary work on static-active selection of training pairs.
ML ID: 133
Ensemble methods like Bagging and Boosting which combine the decisions of multiple hypotheses are some of the strongest existing machine learning methods. The diversity of the members of an ensemble is known to be an important factor in determining its generalization error. We present a new method for generating ensembles, DECORATE (Diverse Ensemble Creation by Oppositional Relabeling of Artificial Training Examples), that directly constructs diverse hypotheses using additional artificially-constructed training examples. The technique is a simple, general meta-learner that can use any strong learner as a base classifier to build diverse committees. Experimental results using decision-tree induction as a base learner demonstrate that this approach consistently achieves higher predictive accuracy than both the base classifier and Bagging. DECORATE also obtains higher accuracy than Boosting early in the learning curve when training data is limited.
We propose to show that DECORATE can also be effectively used for (1) active learning, to reduce the number of training examples required to achieve high accuracy; (2) exploiting unlabeled data to improve accuracy in a semi-supervised learning setting; (3) combining active learning with semi-supervision for improved results; (4) obtaining better class membership probability estimates; (5) reducing the error of regressors; and (6) improving the accuracy of relational learners.
ML ID: 132
Identifying approximately duplicate database records that refer to the same entity is essential for information integration. The authors compare and describe methods for combining and learning textual similarity measures for name matching.
ML ID: 131
Inductive Logic Programming (ILP) is the intersection of Machine Learning and Logic Programming in which the learner's hypothesis space is the set of logic programs. There are two major ILP approaches: top-down and bottom-up. The former searches the hypothesis space from general to specific while the latter the other way round. Integrating both approaches has been demonstrated to be more effective. Integrated ILP systems were previously developed for two tasks: learning semantic parsers (Chillin), and mining relational data (Progol). Two new integrated ILP systems for these tasks that overcome limitations of existing methods will be presented.
Cocktail is a new ILP algorithm for inducing semantic parsers. For this task, two features of a parse state, functional structure and context, provide important information for disambiguation. A bottom-up approach is more suitable for learning the former, while top-down is better for the latter. By allowing both approaches to induce program clauses and choosing the best combination of their results, Cocktail learns more effective parsers. Experimental results on learning natural-language interfaces for two databases demonstrate that it learns more accurate parsers than Chillin, the previous best method for this task.
Beth is a new integrated ILP algorithm for relational data mining. The Inverse Entailment approach to ILP, implemented in the Progol and Aleph systems, starts with the construction of a bottom clause, the most specific hypothesis covering a seed example. When mining relational data with a large number of background facts, the bottom clause becomes intractably large, making learning very inefficient. A top-down approach heuristically guides the construction of clauses without building a bottom clause; however, it wastes time exploring clauses that cover no positive examples. By using a top-down approach to heuristically guide the construction of generalizations of a bottom clause, Beth combines the strength of both approaches. Learning patterns for detecting potential terrorist activity is a current challenge problem for relational data mining. Experimental results on artificial data for this task with over half a million facts show that Beth is significantly more efficient at discovering such patterns than Aleph and m-Foil, two leading ILP systems.
ML ID: 130
A variety of experimental methodologies have been used to evaluate the accuracy of duplicate-detection systems. We advocate presenting precision-recall curves as the most informative evaluation methodology. We also discuss a number of issues that arise when evaluating and assembling training data for adaptive systems that use machine learning to tune themselves to specific applications. We consider several different application scenarios and experimentally examine the effectiveness of alternative methods of collecting training data under each scenario. We propose two new approaches to collecting training data called static-active learning and weakly-labeled non-duplicates, and present experimental results on their effectiveness.
ML ID: 129
Inductive Logic Programming (ILP) has been shown to be a viable approach to many problems in multi-relational data mining (e.g. bioinformatics). Link discovery (LD) is an important task in data mining for counter-terrorism and is the focus of DARPA's program on Evidence Extraction and Link Discovery (EELD). Learning patterns for LD is a novel problem in relational data mining that is characterized by having an unprecedented number of background facts. As a result of the explosion in background facts, the efficiency of existing ILP algorithms becomes a serious limitation. This paper presents a new ILP algorithm that integrates top-down and bottom-up search in order to reduce search when processing large examples. Experimental results on EELD data confirm that it significantly improves efficiency over existing ILP methods.
ML ID: 128
The problem of identifying approximately duplicate records in databases is an essential step for data cleaning and data integration processes. Most existing approaches have relied on generic or manually tuned distance metrics for estimating the similarity of potential duplicates. In this paper, we present a framework for improving duplicate detection using trainable measures of textual similarity. We propose to employ learnable text distance functions for each database field, and show that such measures are capable of adapting to the specific notion of similarity that is appropriate for the field's domain. We present two learnable text similarity measures suitable for this task: an extended variant of learnable string edit distance, and a novel vector-space based measure that employs a Support Vector Machine (SVM) for training. Experimental results on a range of datasets show that our framework can improve duplicate detection accuracy over traditional techniques.
ML ID: 127
We present results from a variety of learned information extraction systems for identifying human protein names in Medline abstracts and subsequently extracting interactions between the proteins. We demonstrate that machine learning approaches using support vector machines and hidden Markov models are able to identify human proteins with higher accuracy than several previous approaches. We also demonstrate that various rule induction methods are able to identify protein interactions with higher precision than manually-developed rules.
ML ID: 126
Semi-supervised clustering employs a small amount of labeled data to aid unsupervised learning. Previous work in the area has employed one of two approaches: 1) Search-based methods that utilize supervised data to guide the search for the best clustering, and 2) Similarity-based methods that use supervised data to adapt the underlying similarity metric used by the clustering algorithm. This paper presents a unified approach based on the K-Means clustering algorithm that incorporates both of these techniques. Experimental results demonstrate that the combined approach generally produces better clusters than either of the individual approaches.
ML ID: 125
Information Extraction is a form of shallow text processing that locates a specified set of relevant items in a natural-language document. Systems for this task require significant domain-specific knowledge and are time-consuming and difficult to build by hand, making them a good application for machine learning. We present a aystem, RAPIER, that uses pairs of sample documents and filled templates to induce pattern-match rules that directly extract fillers for the slots in the template. RAPIER employs a bottom-up learning algorithm which incorporates techniques from several inductive logic programming systems and acquires unbounded patterns that include constraints on the words, part-of-speech tags, and semantic classes present in the filler and the surrounding text. We present encouraging experimental results on two domains.
ML ID: 124
The problem of identifying approximately duplicate records in databases is an essential step for the information integration processes. Most existing approaches have relied on generic or manually tuned distance metrics for estimating the similarity of potential duplicates. In this paper, we present a framework for improving duplicate detection using trainable measures of textual similarity. We propose to employ learnable text distance functions for each data field, and introduce an extended variant of learnable string edit distance based on an Expectation-Maximization(EM) training algorithm. Experimental results on a range of datasets show that this similarity metric is capable of adapting to the specific notions of similarity that are appropriate for different domains. Our overall system, MARLIN utilizes support vector machines to combine multiple similarity metrics, which are shown to perform better than ensembles of decision trees, which were employed for this task previously.
ML ID: 123
Ensemble methods like bagging and boosting that combine the decisions of multiple hypotheses are some of the strongest existing machine learning methods. The diversity of the members of an ensemble is known to be an important factor in determining its generalization error. This paper presents a new method for generating ensembles that directly constructs diverse hypotheses using additional artificially-constructed training examples. The technique is a simple, general meta-learner that can use any strong learner as a base classifier to build diverse committees. Experimental results using decision-tree induction as a base learner demonstrate that this approach consistently achieves higher predictive accuracy than both the base classifier and bagging (whereas boosting can occasionally decrease accuracy), and also obtains higher accuracy than boosting early in the learning curve when training data is limited.
ML ID: 122
This paper focuses on a system, Wolfie (WOrd Learning From Interpreted Examples), that acquires a semantic lexicon from a corpus of sentences paired with semantic representations. The lexicon learned consists of phrases paired with meaning representations. Wolfie is part of an integrated system that learns to parse representations such as logical database queries.
Experimental results are presented demonstrating Wolfie's ability to learn useful lexicons for a database interface in four different natural languages. The usefulness of the lexicons learned by Wolfie are compared to those acquired by a similar system developed by Siskind (1996), with results favorable to Wolfie. A second set of experiments demonstrates Wolfie's ability to scale to larger and more difficult, albeit artificially generated, corpora.
In natural language acquisition, it is difficult to gather the annotated data needed for supervised learning; however, unannotated data is fairly plentiful. Active learning methods (Cohn, Atlas, & Ladner, 1994) attempt to select for annotation and training only the most informative examples, and therefore are potentially very useful in natural language applications. However, most results to date for active learning have only considered standard classification tasks. To reduce annotation effort while maintaining accuracy, we apply active learning to semantic lexicons. We show that active learning can significantly reduce the number of annotated examples required to achieve a given level of performance.
ML ID: 121
We present a novel approach to solving definite descriptions in unrestricted text based on searching the web for a particular type of lexicosyntactic patterns. Using statistics on these patterns, we intend to recover the antecedents for a predefined subset of definite descriptions occurring in two types of anaphoric relations: identity anaphora and associative anaphora. Preliminary results obtained with this method are promising and compare well with other methods.
ML ID: 120
This chapter introduces symbolic machine learning in which decision trees, rules, or case-based classifiers are induced from supervised training examples. It describes the representation of knowledge assumed by each of these approaches and reviews basic algorithms for inducing such representations from annotated training examples and using the acquired knowledge to classify future instances. These techniques can be applied to learn knowledge required for a variety of problems in computational linguistics ranging from part-of-speech tagging and syntactic parsing to word-sense disambiguation and anaphora resolution. Applications to a variety of these problems are reviewed.
ML ID: 119