Maintaining Dataflow Constraints in Real-Time Collaborative Graphic Editing Systems
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The attributes of graphic objects are often inherently related to each other. For example, the width and height of a square are the same; the y coordinates of the two end-points of a horizontal line are identical. The ability to describe the relationships between graphic attributes and to automatically maintain these relationships opens many possibilities for making graphic objects behave in complex and sophisticated ways. Nowadays, many single-user commercial graphic editing systems are able to automatically maintain the relationships between graphic objects by means of constraints. As a result, to leverage these constraint-based single-user applications for multi-user collaboration, constraints must be maintained in collaborative environments. A constraint is a relationship or condition that should be maintained in a system. Constraint-based applications are able to simplify users’ jobs by allowing users to concentrate on saying what should be true, thereby leaving the constraint systems to worry about when and how to make these things true. However, maintaining constraints in collaborative systems is difficult. Users may concurrently define conflicting constraints in a collaborative system; the satisfaction methods of different constraints may interfere with each other; maintaining both constraints and consistency in replicated collaborative systems is a challenge. Accordingly, most of the existing collaborative graphic editing systems are unable to maintain constraints. This thesis concentrates on maintaining a type of frequently used constraint, dataflow constraint, in real-time collaborative graphic editing systems. Dataflow constraints have been applied in a wide variety of single-user applications, including spreadsheet, user interface, simulation, and graphic editing systems. Dataflow constraints are especially useful in maintaining the relationships between graphic attributes in graphic editing systems. A dataflow constraint is an equation. Any relationship that can be expressed by an equation can be represented as a dataflow constraint. A dataflow constraint can be characterized as one-way or multi-way according to how many constraint satisfaction methods are associated with it. One-way dataflow constraints are widely adopted by single-user commercial systems because of their simplicity, efficiency and manageability. In contrast, multi-way dataflow constraints, which are more flexible and powerful, are adopted by some sophisticated graphic editing systems, such as CAD systems.
Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
School of Information and Communication Technology
Item Access Status
Graphic editing systems