Driver duty: A pattern for public transport systems

The pattern language of transport systems (PLOTS) consists of a set of TOPS (transport object patterns) that work together to solve transport problems. Space constraints allow us to only cover one or two closely related TOPS in any one article. We therefore intend to present PLOTS in a series of articles so that these individual patterns can be pieced together to form a greater whole. In this article, we present a TOP - Driver Duty - that provides a framework within which driver duty components can be assembled. The intent of the Driver Duty pattern is to support a tree structure for explicitly ordering and layering the driver duty components; to provide clients with a consistent interface to all the duty components and their compositions; and to cope with many variations in defining driver duties uniformly. This pattern and others such as Driver Duty Builder, which creates the driver duty components, have been developed for understanding and describing offline scheduling processes, but we have noted that some aspects may be reused for realtime scheduling as well.