Advanced Temporal Constraints for Business Processes Modelling and Execution

Introduction

In several fields workflow applications require co-ordination and synchronisation among activities. Several control and data dependencies arise that must be specified, validated as conflict free, and maintained during workflow execution. These kinds of dependencies can be viewed as constraints that impose temporal restrictions on the relative order of execution of the activities. In this context the concept of time is dominant in workflow execution, because time constraints impose the activity synchronisation requirements, while their fulfilment or the extent of their fulfilment, judges the execution correctness. As a result, temporal synchronisation can be no longer be limited to a consequence of value dependencies among activities.

One of the limitations of workflow systems is that they lack the expressiveness for specifying temporal relationships across activities. Therefore, they fail to provide adequate timing control during the execution. The importance of time-related issues and their corresponding semantics have been identified in the literature (Liu et al., 2011).

We motivate and present the applicability of our approach with a health care example based on the scenario presented in Haimowitz et al. (1996) regarding the emergency room procedure. When a patent enters the emergency room he has to be evaluated by nurses in “triage”. The nurse takes patient history, treats pressing problems and takes a few preliminary tests such as temperature, blood pressure, etc. At this point there are several alternatives: the patient might be re-examined and sent home, might be sent for further tests like x-rays, blood test, etc., or he might be sent for surgery. After that the patient is discharged.

In the diagrammatic notation (see Figure 1), tasks are represented as rectangles while constraints as directed arcs labelled by expressions in italic that denote the name of the constraint. The OR constructs are represented as circles, denoting OR-split and OR-join. We can see that activities a₆ and a₇ have to start and complete at the same time (are constrained by “equals”). Therefore, traditional synchronisation techniques that allow only precedence/parallel execution cannot support advanced temporal requirements.

Figure 1.

Emergency room example

In this article, we develop a model for temporal workflow, a mechanism for consistency checking, and algorithms for consistent execution of activities with respect to temporally constrained workflow applications. Specifically, we addressed the following problems: