Over the course of the past decade, we have all been witnesses to an explosion of information, in terms of both the amounts of knowledge that exists within the world and the availability of such information, with the proliferation of the World Wide Web being a prime example. Although these advancements of knowledge have undoubtedly been beneficial, they have also created new challenges in information retrieval, in information
processing, and in the extraction of relevant information. This is in part due to a diversity of file formats as well as the proliferation of loosely structured formats, such as HTML.

The solution to such information retrieval and extraction problems has been to develop specialized parsers to conduct these tasks. This book will address these tasks, starting with the most basic principles of data parsing.

The book will begin with an introduction to parsing basics using Perl’s regular expression engine. Once these regex basic are mastered, the book will introduce the concept of generative grammars and the Chomsky hierarchy of grammars. Such grammars form the base set of rules that parsers will use to try to successfully parse content of interest, such as
text or XML files. Once grammars are covered, the book proceeds to explain the two basic types of parsers—those that use a top-down approach and those that use a bottom-up approach to parsing. Coverage of these parser types is designed to facilitate the understanding of more powerful parsing modules such as Yapp (bottom-up) and RecDescent (top-down).

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