Kalervo Järvelin Timo Niemi Airi Salminen The visual query language CQL for transitive and relational computation. 39-51 2000 35 Data Knowl. Eng. 1 db/journals/dke/dke35.html#JarvelinNS00 http://dx.doi.org/10.1016/S0169-023X(00)00021-5