CLEF 2006: Ad Hoc Track Overview

We describe the objectives and organization of the CLEF 2006 ad hoc track and discuss the main characteristics of the tasks offered to test monolingual, bilingual, and multilingual textual document retrieval systems. The track was divided into two streams. The main stream offered mono- and bilingual tasks using the same collections as CLEF 2005: Bulgarian, English, French, Hungarian and Portuguese. The second stream, designed for more experienced participants, offered the so-called \u201drobust task\u201d which used test collections from previous years in six languages (Dutch, English, French, German, Italian and Spanish) with the objective of privileging experiments which achieve good stable performance over all queries rather than high average performance. The performance achieved for each task is presented and the results are commented. The document collections used were taken from the CLEF multilingual comparable corpus of news documents