Dücker, M., Christian Geiger, Georg Lehrenfeld, Wolfgang Müller, and C. Tahedl. “A Visual Programming Language for Qualitative Data.”https://doi.org/10.1109/VL.1997.626593__In Proceedings of the 1997 IEEE Symposium on Visual Languages. Capri, Italy, 1997.https://doi.org/10.1109/VL.1997.626593 .