Abstract

The current study examines the development of diagrams by groups of people. Diagrams are graphical representations of a design, concept or object. Entity Relationship diagrams are created during a usability study of CoDiagram, a system supporting multiple people working simultaneously on the diagram. Computer support for diagramming allows groups of people to work on the diagram at the same time, improving productivity. However, multiple users working together can interfere with each other's work. During the usability study, it was confirmed that people work with shapes in the diagram that were created by other people, demonstrating the potential for interference. While it was found that interference is relatively rare, the people rated the impact of the interference as significant. At a minimum, the interference results in lost time as they resolve the conflict. If undetected, the interference can cause inconsistencies or errors that can make the diagram practically worthless. The conclusion from this initial phase of research is that a concurrency control mechanism is needed to maintain integrity for collaborative diagrams.

Concurrency control in computer supported cooperative work (CSCW) has been left to social protocols, implemented as single user floor control or developed using database techniques. Since interference was observed when using only social protocols with CoDiagram, it is concluded that social protocols alone are not sufficient. CSCW systems with database style locking have had a problem with long transactions blocking user actions. A new concurrency control method, Concurrency Control for Collaborative Diagramming (CCCD) uses constraints from the diagram domain to identify user transactions. These user transactions are non-traditional transactions that supplement the traditional database transactions that maintain internal data. This improvement in user transaction identification reduces resource blocking by releasing locks without explicit user actions. It was found that CCCD would have prevented a significant amount of the interference that occurred with only social protocols.