Online edition (c) 2009 Cambridge UPDRAFT!©April 1, 2009 Cambridge University Press. Feedback welcome.11Boolean retrievalThe meaning of the terminformation retrievalcan be very broad. Just gettinga credit card out of your wallet so that you can type in the cardnumberis a form of information retrieval. However, as an academic field of study,information retrievalmight be defined thus:I NF O RMAT IONRET RI EVALInformation retrieval (IR) is finding material (usually documents) ofan unstructured nature (usually text) that satisfies an information needfrom within large collections (usually stored on computers).As defined in this way, information retrieval used to be an activity that onlya few people engaged in: reference librarians, paralegals,and similar pro-fessional searchers. Now the world has changed, and hundreds of millionsof people engage in information retrieval every day when they use a websearch engine or search their email.1Information retrieval is fast becomingthe dominant form of information access, overtaking traditional database-style searching (the sort that is going on when a clerk says toyou: “I’m sorry,I can only look up your order if you can give me your Order ID”).