The aim of this thesis is to answer whether a group of databases dedicated to selling books or a group of databases dedicated to lending books is more efficient. The measurements used to determine the efficiency of the two kinds of databases are Cumulated Gain and precision in modified versions. The inquiry has been conducted thus that the same 18 queries have been put forth to six databases and these results have consequently been judged according to relevance on a 4-graded scale by five respondents. The rankinglevels have then been merged to one average value per respondent and ranking. These values have then been used to determine CG/iCG/nCG and P@n per query, rank 1-10, per database and per group (the groups being STORE (BUTIK) and LIBRARY (BIBLIOTEK). To measure precision the relevance rankings were merged into binary values representing not relevant and relevant. These ones and zeros have then been used to judge precision per rank 1-10, per database and per group. The precision values regarding individual databases have been calculated for comparison against the average values of the entire groups BUTIK & BIBLIOTEK.No significant differences in efficiency between STORE and LIBRARY were observed at DCV=10 although differences were obvious at positions 1-10 and between individual databases. The method is unsuccessful in answering whether the purpose of a database is a factor in how well it performs in regards to efficiency / Program: Bibliotekarie