Delft University of Technology
Faculty Mechanical, Maritime and Materials Engineering Transport Technology / Logistic Engineering
D.W. Beekhuis An assignment method for workflow systems.
Masters thesis, Report 98.3.LT.4992, Transport Technology, Logistic Engineering.
Workflow is the automation of a business process during which documents, information or tasks are passed from one participant to another for action, according to a set of procedural rules. A business process is a sequence of activities in a specific order necessary to achieve a business goal. The workflow engine has as task to control the different processes, executed by the system. This is possible as the process steps are defined in the engine. The engine controls the sequence of the process and it provides the applications with the activities. The Resource Manager, a component of the workflow engine, takes care of the distribution of the activities to the resources. Each activity has its own requirements concerning the needed resource. lt is the task of the Resource Manager to make sure that the resource, which is going to perform the activity, fits the right requirements.
Document Access has designed a Resource Manager for the workflow engine. This Resource Manager uses a filter method to select suitable resources. For each activity is defined what filters are to be used.
The structure of this Resource Manager is principally based on the idea that the activities are directly assigned to the resources. The workflow engine pushes the activities to the resources. The pushing of labour to employees is not socially accepted under all circumstances. So some of the customers of Document Access want a combination of push and pull. In case of a combined environment the activities are being pushed to a worklist and the resources, working on this worklist, pull an activity from the worklist. The combination of push and pull demands other rules for the assignment of the activities. The Resource Manager is not looking for a suitable available resource, but has to select one of the worklists of the system. It is expected that the Resource Manager designed by Document Access is not ideal for controlling the distribution of the workload of the different worklists, because it is especially designed for a push environment. The subject of the research is to design an alternative method for the allocation of activities to worklists. In the literature is searched for algorithms to control the workflow. After a selection the Classical Assigrunent Problem has been selected as algorithm for an alternative method for assignment. The Classical Assignment Problem is a special type of linear programming problem where assignees are being assigned to perform tasks. The number of assignees and the number of tasks are the same, each assignee is to be assigned to exactly one task and each task is to be performed by exactly one assignee. A cost cij is associated with assignee i (i = 1, 2, .... n) performing task j (i = 1, 2, .... n). The objective is to determine how all n assignments should be made in order to minimise the total cost.
By dynamic building of the cost matrix the Classical Assignment Problem can be part of an assignment method for the Resource Manager. The requirements of the activities, like authorisation and priority, and data concerning the situation in the worklists, like workload waiting to be executed, are processed in the matrix. So each possibie assignment has its own specific value. The n assigmnents are now searched by a Classical Assignment Algorithm, which minimises the total cost.
Both methods are tested in a simulation. A simulation model is created in Arena, a simulation tool. The simulation model is a simplification of the total system. The processes are cut into pieces; the activities are being simulated.
In most circumstances, the Classical Assignment method produces better throughput times than the Filter method. The Classical Assignment method distributes the workload better over the different worklists. This has as effect that the queue times in most worklists are low. The Classical Assignment method performs better in a dynamic environment where it is not clear how many and what kinds of tasks are going to arrive. However the Filter method is more appropriate for environments where a good estimation is possible of the dynamics.
Reports on Logistic Engineering (in Dutch)
