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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