# Information retrieval
## Introduction

Information retrieval (IR) in computing and information science is the task of identifying and retrieving information system resources that are relevant to an information need. The information need can be specified in the form of a search query. In the case of document retrieval, queries can be based on full-text or other content-based indexing. Information retrieval is the science of searching for information in a document, searching for documents themselves, and also searching for the metadata that describes data, and for databases of texts, images or sounds.
Automated information retrieval systems are used to reduce what has been called information overload. An IR system is a software system that provides access to books, journals and other documents; it also stores and manages those documents. Web search engines are the most visible IR applications.

## Learning Tasks

* (Information Systems) Explore the learning resource about Information Systems and identify the links between different information systems and information retrieval.
* (Mathematical Foundations) Explain, how mathematics can be used to handle
** search requests,
** how to represent knowledge
* (Web Crawler) What is web crawler and why is it necessary to rely on web crawlers to create e.g. an web index to handle search requests of users.

## Learning Modules

* Information Systems
* Mathematical Foundations
* History

## Overview

An information retrieval process begins when a user enters a query into the system. Queries are formal statements of information needs, for example search strings in web search engines. In information retrieval, a query does not uniquely identify a single object in the collection. Instead, several objects may match the query, perhaps with different degrees of relevance.
An object is an entity that is represented by information in a content collection or database. User queries are matched against the database information. However, as opposed to classical SQL queries of a database, in information retrieval the results returned may or may not match the query, so results are typically ranked. This ranking of results is a key difference of information retrieval searching compared to database searching.
Depending on the application the data objects may be, for example, text documents, images, audio, mind maps or videos. Often the documents themselves are not kept or stored directly in the IR system, but are instead represented in the system by document surrogates or metadata.
Most IR systems compute a numeric score on how well each object in the database matches the query, and rank the objects according to this value. The top ranking objects are then shown to the user. The process may then be iterated if the user wishes to refine the query.

## Applications

Areas where information retrieval techniques are employed include (the entries are in alphabetical order within each category):

### General applications

* Digital libraries
* Information filtering
** Recommender systems
* Media search
** Blog search
** Image retrieval
** 3D retrieval
** Music retrieval
** News search
** Speech retrieval
** Video retrieval
* Search engines
** Site search
** Desktop search
** Enterprise search
** Federated search
** Mobile search
** Social search
** Web search

### Domain-specific applications

* Expert search finding
* Genomic information retrieval
* Geographic information retrieval
* Information retrieval for chemical structures
* Information retrieval in software engineering
* Legal information retrieval
* Vertical search

### Other retrieval methods

Methods/Techniques in which information retrieval techniques are employed include:
* Adversarial information retrieval
* Automatic summarization
** Multi-document summarization
* Compound term processing
* Cross-lingual retrieval
* Document classification
* Spam filtering
* Question answering

## Major conferences

* SIGIR: Conference on Research and Development in Information Retrieval
* ECIR: European Conference on Information Retrieval
* CIKM: Conference on Information and Knowledge Management
* WWW: International World Wide Web Conference
* WSDM: Conference on Web Search and Data Mining
* ICTIR: International Conference on Theory of Information Retrieval

## Awards in the field

* Tony Kent Strix award
* Gerard Salton Award
* Karen Spärck Jones Award