1. Green, T.R.G., Petre, M.: When Visual Programs are Harder to Read than Textual Programs. In: Human-Computer Interaction: Tasks and Organisation, Proceedings ECCE-6 (6th European Conference Cognitive Ergonomics) (1992)
2. Petre, M.: Why looking isn’t always seeing: readership skills and graphical programming. Commun. ACM 38(6) (1995)
3. Moher, T.G., Mak, D.C., Blumenthal, B., Leventhal, L.M.: Comparing the Comprehensibility of Textual and Graphical Programs: The Case of Petri Nets. In: Empirical Studies of Programmers - Fifth Workshop (1993)
4. ITU-T: ITU-T Recommendation Z.100: Specification and Description Language (SDL). International Telecommunication Union (2002)
5. Lecture Notes in Computer Science;H. Krahn,2007