Fabio Fassetti Gianluigi Greco Giorgio Terracina Mining Loosely Structured Motifs from Biological Data. 1472-1489 2008 20 IEEE Trans. Knowl. Data Eng. 11 http://dx.doi.org/10.1109/TKDE.2008.65 db/journals/tkde/tkde20.html#FassettiGT08