Jost, Beate; Ketterl, Markus; Budde, Reinhard; Leimbach, Thorsten (2014). "Graphical Programming Environments for Educational Robots: Open Roberta - Yet Another One?". 2014 IEEE International Symposium on Multimedia. pp. 381–386. doi:10.1109/ISM.2014.24. ISBN978-1-4799-4311-1. S2CID8272806.
Rekers, J.; Schürr, A. (1997). "Defining and parsing visual languages with layered graph grammars". Journal of Visual Languages & Computing. 8 (1): 27–55. doi:10.1006/jvlc.1996.0027. S2CID40088910.
Jost, Beate; Ketterl, Markus; Budde, Reinhard; Leimbach, Thorsten (2014). "Graphical Programming Environments for Educational Robots: Open Roberta - Yet Another One?". 2014 IEEE International Symposium on Multimedia. pp. 381–386. doi:10.1109/ISM.2014.24. ISBN978-1-4799-4311-1. S2CID8272806.
Rekers, J.; Schürr, A. (1997). "Defining and parsing visual languages with layered graph grammars". Journal of Visual Languages & Computing. 8 (1): 27–55. doi:10.1006/jvlc.1996.0027. S2CID40088910.