Methods for cross-language information retrieval

This article reviews technical methods for enhancing effectiveness of cross-language information retrieval (CLIR), in which target documents are written in different languages from that used for representing a search request. As the Internet has spread since the 1990s, the importance of CLIR has grown, and the research community of information retrieval has been tackling various CLIR problems. The purpose of this article is to overview exhaustively CLIR techniques developed in the research efforts. The following research issues on CLIR are covered: (1) strategies for matching the query and documents written in different languages, e.g., automatic translation or transliteration techniques, (2) techniques for solving the problem of translation ambiguity, (3) formal retrieval models for CLIR such as application of the language modeling, (4) methods for searching a multilingual document collection in which two or more languages are used for writing documents, etc.