Hans-Jörg Kreowski Sabine Kuske Grzegorz Rozenberg Graph Transformation Units - An Overview. 57-75 2008 Concurrency, Graphs and Models http://dx.doi.org/10.1007/978-3-540-68679-8_5 conf/birthday/2008montanari db/conf/birthday/montanari2008.html#KreowskiKR08