In past decades, the ability of a system to index thousands of documents and conduct key word searches was deemed good enough. Today, systems must be able to quickly scale to tens of millions of documents and search not only keywords and expressions but also the meaning of those keywords. This book explains the theories behind fundamental informational retrieval technologies. It looks at available technologies and solutions, and discusses in clear and practical terms how to evaluate, apply, and implement these technologies. The author, a leading IT analyst addresses semantics, concept mining, concept searching, and information extraction.