The importance of text mining applications is growing proportionally with the exponential growth of electronic text. Along with the growth of internet many other sources of electronic text have become really popular. With increasing penetration of internet, many forms of communication and interaction such as email, chat, newsgroups, blogs, discussion groups, scraps etc. have become increasingly popular. These generate huge amount of noisy text data everyday. Apart from these the other big contributors in the pool of electronic text documents are call centres and customer relationship management organizations in the form of call logs, call transcriptions, problem tickets, complaint emails etc., electronic text generated by Optical Character Recognition (OCR) process from hand written and printed documents and mobile text such as Short Message Service (SMS). Though the nature of each of these documents is different but there is a common thread between all of these—presence of noise. An example of information extraction is the extraction of instances of corporate mergers, more formally MergerBetween(company1,company2,date), from an online news sentence such as: “Yesterday, New-York based Foo Inc. announced their acquisition of Bar Corp.” Opinion(product1,good), from a blog post such as: “I absolutely liked the texture of SheetK quilts.” At superficial level, there are two ways for information extraction from noisy text. The first one is cleaning text by removing noise and then applying existing state of the art techniques for information extraction. There in lies the importance of techniques for automatically correcting noisy text. In this chapter, first we will review some work in the area of noisy text correction. The second approach is to devise extraction techniques which are robust with respect to noise. Later in this chapter, we will see how the task of information extraction is affected by noise.
Noisy Text Correction
Before moving on to techniques for processing noisy text we will briefly introduce methods for correcting noisy text. One of the most common forms of noise in text is wrong spelling. Kukich provides a comprehensive survey of techniques pertaining to detecting and correcting spelling errors (Kukich, 1992). According to this survey, three types of nonword misspellings are typically found viz. typographic such as teh, speel, cognitive such as recieve, conspeeracy and phonetic such as abiss, nacherly. A distinction must be made between automatically detecting such errors and automatically correcting those errors. The latter is a much harder problem. Most of the recent work in this area is about correcting spelling mistakes automatically. Golding and Roth (Golding & Roth, 1999) proposed a combination of a variant of Winnow, a multiplicative weight-update algorithm and weighted majority voting for context sensitive spelling correction. Mangu and Brill (Mangu & Brill, 1997) have shown that a small set of human understandable rules is more meaningful than a large set of opaque features and weights. Hybrid methods capturing the context using trigrams of the parts-of-speech tags and a feature based method have also been proposed to handle context sensitive spelling correction (Golding & Schabes, 1996). There is a lot of work related to automatic correction of spelling errors (Agirre et. al., 1998), (Zamora et. al., 1983), (Golding, 1995). A complete bibliography of all the work related to spelling error detection and correction can be found in (Beebe, 2005). On a related note, automatic spelling error correction techniques have been applied for other applications such as semantic role labelling (Sang et. al., 2005).
There is also recent work on correcting the output of SMS text (Aw et. al., 2006) (Choudhury et. al., 2007), OCR errors (Nartker et. al., 2003) and ASR errors (Sarma & Palmer, 2004).
Key Terms in this Chapter
Text Analytics: The process of extracting useful and structured knowledge from unstructured documents to find useful associations and insights.
Information Extraction: Automatic extraction of structured knowledge from unstructured documents.
Automatic Speech Recognition: Machine recognition and conversion of spoken words into text.
Rule Induction: Process of learning, from cases or instances, if-then rule relationships that consist of an antecedent (if-part, defining the preconditions or coverage of the rule) and a consequent (then-part, stating a classification, prediction, or other expression of a property that holds for cases defined in the antecedent).
Knowledge Extraction: Explicitation of the internal knowledge of a system or set of data in a way that is easily interpretable by the user.
Noisy Text: Text with any kind of difference in the surface form, from the intended, correct or original text.
Data Mining: The application of analytical methods and tools to data for the purpose of identifying patterns, relationships or obtaining systems that perform useful tasks such as classification, prediction, estimation, or affinity grouping.
Optical Character Recognition: Translation of images of handwritten or typewritten text (usually captured by a scanner) into machine-editable text.