What is Information retrieval?
{{Rquote|right|But do you know that, although I have kept the diary [on a [[Phonograph record|phonograph]]] for months past, it never once struck me how I was going to find any particular part of it in case I wanted to look it up?|Dr Seward [[Bram Stoker]]'s ''[[Dracula]]'', 1897}} '''Information retrieval''' is a field of [[Computer science]] that looks at how non-trivial [[data]] can be obtained from a collection of information resources. Commonly, either a full-text search is done, or the metadata which describes the resources is searched. Depending on the content, there may also be other indices. Information retrieval is about finding existing information; it is different from [[knowledge discovery in databases]] which is about finding new relationships between different datasets, which were unknown. Techniques from information retrieval are commonly used in internet [[search engine|search engines]], but also when looking for information on a subject in a [[library]], or when searching complex content such as [[image|images]] in a [[database]]. This kind of content is usually described using [[metadata]]. == Problem description == When looking for information, the following problems are commonly encountered: # The database contains an insufficient amount of information about the content of the documents it contains. A search may yield an incorrect answer, or no answer at all. # The search is done with terms and keywords that are vague, so that the results returned do not exactly match the needs of the request. A system for information retrieval will attach a score to each document returned. This score reflects how well the document matches the query of the user. The documents with the best scores are shown to the user, who has the possibility to refine the query. == Different models == There are different kinds of models that are used in information retrieval === First dimension: the mathematical model === * Set-theoretic models represent documents as a [[set]] of words or features. * Algebraic m