Further Work

While the majority of this project was spent working with directed edge constraints, page boundary constraints were explored and implemented into Dunnart as a minor investigation into the interactive placement and modelling of containment constraints. Further work with containment constraints could involve incorporating functionality into Dunnart that allows the grouping of nodes into a containment area, and following the work of page boundary constraints, generate constraints that keep those nodes inside the containment area boundaries.

The work presented here only investigated subsets of the greater constraint family. Other constraints in the family are alignment constraints, and non-overlap constraints. Further work in this area could investigate how to develop and incorporate functionality into an interactive diagramming editor to support the interactive placement of these other type of constraints. Combined with the work done here, this added functionality can result in even better layouts.

One issue that arises with the IPSep-CoLa layout algorithm is the issue of how to handle unsatisfiable constraints. An example shown in Fig.  shows a directed edge between two shapes that also happen to have an alignment constraint. The directed edge constraint states that the source node must be above the destination node in the vertical dimension, whereas the alignment constraint states that the two nodes must be in the same place in the vertical dimension. These are conflicting unsatisfiable constraints that must be addressed in order for the layout algorithm to satisfy the constraints and layout the graph. Further work on this problem may include an algorithm that has the tool automatically resolve the conflict, or a user interface that allows the user to specify how to resolve the conflict.

Figure: A graph with two conflicting constraints being the directed edge constraint, and the alignment constraint symbolised with the dotted blue edge.