![]() The inability to identify partial matches can lead to poor performance ( Baeza-Yates & Ribeiro-Neto, 1999). Thus, a document is judged as relevant or irrelevant - there is no concept of a "partial match" between documents and queries. The Boolean information retrieval model considers which keywords are present or absent in a document or title. Any number of logical statements can be combined using the three Boolean operators. For example, the Boolean AND of two logical statements x and y means that both x AND y must be satisfied, while the Boolean OR of these same two statements means that at least one of these statements must be satisfied. The adjective "Boolean" refers to the use of Boolean algebra, whereby words are logically combined with the Boolean operators AND, OR, and NOT. More refined descendents of this model are still used by most libraries. The Boolean model of information retrieval, one of the earliest and simplest retrieval methods, uses exact matching to match documents to a user "query" or information request by finding documents that are "relevant" in terms of matching the words in the query. Specifics of some of these techniques can easily become very complicated and are, in general, hard to come by, since many vendors refuse to share in this competitive environment. ![]() I outline here just a few of the most basic information retrieval techniques, in order to provide a context for the techniques we will study in more detail.
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