Coordination for multi-person visual program development

Typically, visual programming has been limited to only one person developing one program at a time. This article describes a technique for helping multiple people coordinate working together on the same diagram at the same time. This approach identifies transactions based on domain syntax. These transactions are used to notify people when someone else changes the diagram in a way that is likely to impact other people's work. In particular, the system assigns ownership of each syntactically incorrect element to the person who last acted upon that element. This ownership can be transferred between people. The potential problem of incomplete transactions when work extends beyond a single session is resolved by restarting transactions when work resumes. This syntax-based approach is particularly appropriate for visual languages. Various domain constraints are described as alternatives or supplements to the syntactic criteria. The technique was validated with data from 20 groups of three people using CoDiagram, a proof of concept system.