This work was funded in part by the Companions project sponsored by the European Commission as part of the Information Society Technologies (IST) programme under EC grant number IST-FP6-034434 and by Ministry of Education of the Czech Republic projects No. LM2010013 (Lindat-Clarin - Centre for Language Research Infrastructure in the Czech Republic) and MSM0021620838 (Modern Methods, Structures and Systems of Computer Science).