Information retrieval is the process of searching within a document collection for information most relevant to a user's query. However, the type of document collection significantly affects the methods and algorithms used to process queries. In this chapter we distinguish between two types of document collections: traditional and Web collections. Traditional information retrieval is search within small, controlled, nonlinked collections (e.g., a collection of medical or legal documents),

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... s Web information retrieval is search within the world's largest and linked document collection. In spite of the proliferation of the Web, more traditional nonlinked collections still exist, and there is still a place for the older methods of information retrieval.