Sheffield University: CLEF 2000 Submission (Bilingual Track - German to English)

We investigated dictionary based cross language information retrieval using lexical triangulation. Lexical triangulation combines the results of different transitive translations. Transitive translation uses a pivot language to translate between two languages when no direct translation resource is available. We took German queries and translated then via Spanish, or Dutch into English. We compared the results of retrieval experiments using these queries, with other versions created by combining the transitive translations or created by direct translation. Direct dictionary translation of a query introduces considerable ambiguity that damages retrieval, an average precision 79% below monolingual in this research. Transitive translation introduces more ambiguity, giving results worse than 88% below direct translation. We have shown that lexical triangulation between two transitive translations can eliminate much of the additional ambiguity introduced by transitive translation. Introduction and Background Cross Language Information Retrieval (CLIR) addresses the situation where the query that a user presents to an IR system, is not in the same language as the corpus of documents they wish to search. This situation presents a number of challenges (Grefenstette (1998)) but primary amongst these is the problem of crossing the language barrier (Schauble & Sheridan (1997)). Almost all the approaches to this problem require access to some form of rich translation resource to map terms in the query language (the source) to terms in the corpus (the target). “Transitive” CLIR aims to address the situation where there are limited direct translation resources available (Ballesteros (2000)). A transitive CLIR system translates the source language terms by first translating the terms into an intermediate or "pivot" language and then translating the resulting terms into the target language. Thus, a transitive system could translate a query from German to English via either Dutch, or Spanish. The main aim of this work is to combine translations from two different transitive routes to discover if this can reduce the ambiguity introduced by transitive translation. Ballesteros suggested the possibility of using this approach in the summary to her recent chapter (Ballesteros (2000)). We have chosen to call this approach “lexical triangulation”, see figure 1. We have chosen to simulate a Machine-Readable Dictionary (MRD) approach to CLIR. This follows on from the work of Ballesteros & Croft (1996, 1997, 1998), and Ballesteros (2000). The Experimental Environment The underlying IR system used in the Sheffield submission was the GLASS system (Sanderson (2000)). The translation resources were derived from the German, Spanish, Dutch, and English components of EuroWordNet (Vossen (1999)). The data used to lemmatise the German queries was derived from the CELEX German databases.