@InProceedings{Kuh09edgefinding,
    author =       {Sebastian Kuhnert},
    title =        {Efficient edge-finding on unary resources with optional
                    activities},
    editor =       {Dietmar Seipel and Michael Hanus and Armin Wolf},
    booktitle =    {Applications of Declarative Programming and Knowledge
                    Management (Proceedings of INAP/WLP 2007)},
    year =         2009,
    series =       {LNCS},
    number =       5437,
    publisher =    {Springer},
    address =      {Berlin},
    isbn =         {978-3-642-00674-6},
    doi =          {10.1007/978-3-642-00675-3_3},
    pages =        {38-53},
}

Efficient edge-finding on unary resources with optional activities.
Applications of Declarative Programming and Knowledge Management (Proceedings of INAP/WLP 2007). Springer, 2009. Pp. 38-53.

Abstract. Unary resources play a central role in modelling scheduling problems. Edge-finding is one of the most popular techniques to deal with unary resources in constraint programming environments. Often it depends on external factors if an activity will be included in the final schedule, making the activity optional. Currently known edge-finding algorithms cannot take optional activities into account. This paper introduces an edge-finding algorithm that finds restrictions for enabled and optional activities. The performance of this new algorithm is studied for modified job-shop and random-placement problems.

Keywords: constraint-based scheduling, global constraints, optional tasks and activities, unary resources