Getting a grip on tasks that coordinate tasks

• Authors: Rinus Plasmeijer;Bas Lijnse;Peter Achten;Steffen Michels
• Venue: Proceedings of the Eleventh Workshop on Language Descriptions, Tools and Applications
• Year: 2011

Workflow management systems (WFMS) are software systems that coordinate the tasks human workers and computers have to perform to achieve a certain goal. The tasks to do and their interdependencies are described in a Workflow Description Language (WDL). Work can be organized in many, many ways and in the literature already more than hundred of useful workflow patterns for WDL's have been identified. The iTask system is not a WFMS, but a combinator library for the functional language Clean to support the construction of WFMS applications. Workflows can be described in a compositional style, using pure functions and combinators as self-contained building blocks. Thanks to the expressive power of the underlying functional language, complex workflows can be defined on top of just a handful of core task combinators. However, it is not sufficient to define the tasks that need to be done. We also need to express the way these tasks are being supervised, managed and visualized. In this paper we report on our current research effort to extend the iTask system such that the coordination of work can be defined as special tasks in the system as well. We take the opportunity to redesign editors which share information and the combinators for defining GUI interfaces for tasks, such as buttons, menu's and windows. Even though the expressiveness of the resulting system increases significantly, the number of core combinators can be reduced. We argue that only two general Swiss-Army-Knife higher order functions are needed to obtain the desired functionality. This simplifies the implementation significantly and increases the maintainability of the system. We discuss the design space and decisions that lead to these two general functions for constructing tasks.