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The (standard) Boolean model of information retrieval (BIR) [1] is a classical information retrieval (IR) model and, at the same time, the first and most-adopted one. [2] The BIR is based on Boolean logic and classical set theory in that both the documents to be searched and the user's query are conceived as sets of terms (a bag-of-words model ).
Search engine queries also employ Boolean logic. For this application, each web page on the Internet may be considered to be an "element" of a "set." The following examples use a syntax supported by Google. [NB 1] Doublequotes are used to combine whitespace-separated words into a single search term. [NB 2]
Ranking of query is one of the fundamental problems in information retrieval (IR), [1] the scientific/engineering discipline behind search engines. [2] Given a query q and a collection D of documents that match the query, the problem is to rank, that is, sort, the documents in D according to some criterion so that the "best" results appear early in the result list displayed to the user.
The search engine supports limited boolean logic in searches. Logical NOT (negation) can be indicated by a "-" (minus sign) or a "!" (exclamation point) character prefixed to a search term, or by the NOT keyword. Parentheses (…) are ignored by the search engine and have no effect. Search terms are implicitly joined by logical AND (conjunction).
Only tokens are defined in the CFG. Web search engines often use this approach. Boolean. A query language that also supports the use of the Boolean operators AND, OR, NOT. Structured. A language that supports searching within (a combination of) fields when a document is structured and has been indexed using its document structure. Natural language.
With search engines that support Boolean operators and parentheses, a technique traditionally used by librarians can be applied. A user who is looking for documents that cover several topics or facets may want to describe each of them by a disjunction of characteristic words, such as vehicles OR cars OR automobiles .
Phrase search is one of many search operators that are standard in search engine technology, along with Boolean operators (AND, OR, and NOT), truncation and wildcard operators (commonly represented by the asterisk symbol), field code operators (which look for specific words in defined fields, such as the Author field in a periodical database ...
Searching for textual content in databases or structured data formats (such as XML and CSV) presents special challenges and opportunities which specialized search engines resolve. Databases allow logical queries such as the use of multi-field Boolean logic, while full-text searches do not. "Crawling" (a human by-eye search) is not necessary to ...