A criticism that may, with some justification, be levelled at many visual programming languages is that they are simply not scalable to real world problems. In creating a visual language capable of handling multiple concurrent threads of control in addition to a graphical depiction of data, we were acutely confronted with such difficulties. The language we devised, based on the Petri net model, incorporates an object oriented view of data which, together with a number of innovations designed to alleviate screen contention and complexity, has helped to address the scalability issue.
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