Lessons Learnt from Experiments on the Ad Hoc Multilingual Test Collections at CLEF

This chapter describes the lessons learnt from the ad hoc track at CLEF in the years 2000 to 2009. This contribution focuses on Information Retrieval (IR) for languages other than English (monolingual IR), as well as bilingual IR (also termed “cross-lingual”; the request is written in one language and the searched collection in another), and multilingual IR (the information items are written in many different languages). During these years the ad hoc track has used mainly newspaper test collections, covering more than 15 languages. The authors themselves have designed, implemented and evaluated IR tools for all these languages during those CLEF campaigns. Based on our own experience and the lessons reported by other participants in these years, we are able to describe the most important challenges when designing a IR system for a new language. When dealing with bilingual IR, our experiments indicate that the critical point is the translation process. However, currently online translating systems tend to offer rather effective translation from one language to another, especially when one of these languages is English. In order to solve the multilingual IR question, different IR architectures are possible. For the simplest approach based on query translation of individual language pairs, the crucial component is the merging of the intermediate bilingual results. When considering both document and query translation, the complexity of the whole system represents clearly a main issue.