Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2010.Cataloged from PDF version of thesis.Includes bibliographical references (p. 31).In order to make the best use of the multitude of diverse, semi-structured sources of data available on the internet, information retrieval systems need to reliably access the data on these different sites in a manner that is robust to changes in format or structure that these sites might undergo. An interface that gives a system uniform, programmatic access to the data on some web site is called a web wrapper, and the process of inferring a wrapper for a given website based on a few examples of its pages is known as wrapper induction. A challenge of using wrappers for online information extraction arises from the dynamic nature of the web-even the slightest of changes to the format of a web page may be enough to invalidate a wrapper. Thus, it is important to be able to detect when a wrapper no longer extracts the correct information, and also for the system to be able to recover from this type of failure. This thesis demonstrates improved error detection as well as methods of recovery and repair for broken wrappers for START, a natural-language question-answering system developed by Infolab at MIT.by Erica L. Cooper.M.Eng
