Chapter 1
Introduction

The definition of information retrieval (IR), in its broadest sense, is finding relevant information in response to queries issued by users [237, 296]. It is a highly dynamic discipline with a relatively short but rich history in which many techniques and methods have been proposed towards improving effectiveness, i.e., finding more relevant information given a query. In essence, IR subsumes two highly related activities: indexing (which deals with how information is represented) and searching (which deals with matching an expression of an information need—the query—with indexed information). A schematic overview of an IR system is provided in Figure 1.1.