Process Flexibility Revisited: Graph Expander and Food-From-The-Heart
by Professor Chung-Piaw, Teo
Abstract: The notion of Process Flexibility has been used in many situations to
achieve higher service levels, shorter response times, etc without
requiring additional capacity investments. In this paper, motivated by a bread delivery problem faced by a charity organization (Food From The
Heart Program) in Singapore, we revisit the issue of process flexibility in a
delivery planning setting. In particular, we study how process flexibility
structure should be designed to allow the system to better cope with
fluctuating supply/demand, and to match supply with demand in a more
We show that the process flexibility problem is intimately connected to
the graph expansion problem, a well-studied subject in computer science and mathematics where there have been significant recent breakthroughs. The well-accepted belief that ``a simple chaining strategy (flexibility
structure with small number of links) can perform nearly as well as a
fully flexible structure,'' is merely a result of the fact that certain sparse
graphs can achieve nearly the same expansion as a complete graph. This
connection allows us to prove a mathematically precise statement
concerning the existence of flexibility structure with small number of links, but with close to the capability of a fully flexibile system. We also generalize the notion of graph expansion to allow us to handle the case where supply/demand are non-identical.
We use the bread delivery problem to motivate a few other issues not
commonly addressed in the process flexibility literature. In particular,
we examine the issue of unequal supply and demand, and dynamic supply-demand assignment decision (in real time, as information is released), for any given process flexibility structure. We propose a simple heuristic to construct flexibility structure in this case. We demonstrate the effectiveness of this approach using a set of real data taken from the
bread delivery operation.
Dr. Chung Piaw, Teo is currently Professor of Decision Sciences in the new SKK Graduate School of Business, Sungkyunkwan University, Seoul. He is on leave from the National University of Singapore, where he was an Associate Professor with the Department of Decision Sciences, NUS Business School, and concurrently a Fellow in the Singapore-MIT Alliance Program in High Performance Computation for Engineered System. He graduated from MIT in 1996 with a PhD in Operations Research, and has taught in NUS since then, until the move to Seoul in 2004.
He is currently associate editor of Management Science, Naval Research
Logistics, and IEEE-Transaction on Automation Sciences. His research
focuses on Discrete Optimization, Social Choice, Logistics and Supply
Chain Management. His research work has appeared in journals such as Management Science, Operations Research and Mathematics of Operations Research. He has also consulted actively for the Port, Gaming and Logistics industry, and was one of the co-Principal Investigators in a strategic research program on Maritime Logistics, supported by A* through TLI-AP (The Logistics Institute-Asia Pacific).
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