3. BOOLEAN INFORMATION RETRIEVAL (BIR)
The Boolean Information Retrieval model is based on classical Set theory. Documents are represented as a set of terms it contains (not all words have to be used), while queries are represented as logical expressions. The keywords in the query can be linked together with Boolean operators AND, OR and NOT [8]. Each term can have one of two logic states – it can be either present (logical 1) or absent (logical 0) [8].
The relevance of a document to the query of a user is calculated by evaluating the logical value of the query as either 1 or 0. A value of 1 is given to every term in the query that exists in the set representing document, and 0 for every term that does not exist in the representation of the document.