Mariska Netjes, Wil M.P. van der Aalst, Hajo A. Reijers - Analysis of resource-constrained processes with Colored Petri Nets CPN Workshop 2005 Analysis

Mariska Netjes, Wil M.P. van der Aalst, Hajo A. Reijers - Analysis of resource-constrained processes with Colored Petri Nets

CPN Workshop 2005

Analysis of resource-constrained processeswith Colored Petri Nets

Mariska Netjes

Wil M.P. van der Aalst

Hajo A. Reijers


CPN Workshop 2005

Outline

• Introduction

• Developed CPN model

• Application of the CPN model

• Conclusions

• Reflection


CPN Workshop 2005

Introduction (1)

• Business Process Redesign:

improving performance with process oriented redesign

• From literature best practices for business process improvement are collected by H.A. Reijers & S. Limam Mansar, 20051

• It should be noted that many of the best practices lack adequate (quantitative) support

1. H.A. Reijers, S. Limam Mansar. Best practices in business process redesign. Omega (33.4), 2005


CPN Workshop 2005

Introduction (2)

• We investigate two of these best practices

• Both best practices aim at the improvement of resource-constrained processes

• We built a CPN model to:– provide an easy way to model a resource-constrained

process and

– change it to evaluate best practices under different circumstances

– with simulation


CPN Workshop 2005

Outline

• Introduction



• Conclusions

• Reflection


CPN Workshop 2005

CPN model – overview


CPN Workshop 2005

CPN model – task building block


CPN Workshop 2005

CPN model – resource module


CPN Workshop 2005

CPN model – resource allocation methods

• Random allocation

from all the available resources with a suitable role one is randomly selected

• Priority based allocation

the available resource with the highest priority role is selected


CPN Workshop 2005

Outline

• Introduction



• Conclusions

• Reflection


CPN Workshop 2005

Example process: opening a bank account


CPN Workshop 2005

The use of monitors


CPN Workshop 2005


CPN Workshop 2005

Specialist - generalist trade-off (1)

• Two mechanisms– specialist performs the work faster– generalist can perform more tasks

• Performance indicator = average throughput time• Allocation method = random assignment• Optimal ratio of specialists and generalists

– too many alternatives to evaluate and compare– find a distinctive ratio– global search and further investigation


CPN Workshop 2005


Alternatives Throughput time Utilization rate

0 [ 16.134 ; 18.604 ] 0.84

1 [ 14.541 ; 16.451 ] 0.89

2 [ 16.438 ; 19.086 ] 0.89

3 [ 29.694 ; 34.838 ] 0.92

4 [ 36.390 ; 43.550 ] 0.93

5 [ 51.831 ; 58.895 ] 0.94


CPN Workshop 2005


Alternatives Throughput time Utilization rate

0 [ 16.134 ; 18.604 ] 0.84

1a [ 13.529 ; 14.867 ] 0.86

1b [ 13.852 ; 15.538 ] 0.86

1 [ 14.541 ; 16.451 ] 0.89

2 [ 16.438 ; 19.086 ] 0.89

3 [ 29.694 ; 34.838 ] 0.92

4 [ 36.390 ; 43.550 ] 0.93

5 [ 51.831 ; 58.895 ] 0.94


CPN Workshop 2005


Conclusions• A ratio with mainly specialists and one or a few

generalists will provide the best trade-off between the shorter service times of the specialist and the flexibility offered by the generalist.

• Preconditions for finding a distinctive ratio:– high resource utilization– proportional distribution of specialized resources– service times should not differ too much


CPN Workshop 2005

Flexible assignment policy (1)


CPN Workshop 2005


Flexible assignment random assignment

Our expectations:

• initial process performs the same

• more specialists than generalists: almost equal selection, minor differences

• more generalists than specialists: more specialists allocated, lower queueing and service times for the process


CPN Workshop 2005


Flexible assignment Random assignment

Alt. Throughput time Ut. rate Throughput time Ut. rate

0 [ 16.703 ; 19.731 ] 0.84 [ 16.134 ; 18.604 ] 0.84

1a [ 14.066 ; 16.158 ] 0.87 [ 13.529 ; 14.867 ] 0.86

1b [ 14.149 ; 15.687 ] 0.87 [ 13.852 ; 15.538 ] 0.86

1 [ 14.569 ; 16.613 ] 0.88 [ 14.541 ; 16.451 ] 0.89

2 [ 15.817 ; 17.410 ] 0.90 [ 16.438 ; 19.086 ] 0.89

3 [ 29.131 ; 34.279 ] 0.93 [ 29.694 ; 34.838 ] 0.92

4 [ 38.070 ; 44.872 ] 0.92 [ 36.390 ; 43.550 ] 0.93

5 [ 47.594 ; 54.428 ] 0.94 [ 51.831 ; 58.895 ] 0.94


CPN Workshop 2005

Flexible assignment policy (4)New simulations for alternatives 3 and 4 with less cases arriving to lower the utilization rate.

Arrival rate Alt. Allocation method

Throughput time Ut. rate

120 cases per hour

3 Random

Flexible

[ 12.075 ; 12.249 ]

[ 11.312 ; 11.478 ]

0.64

0.60

4 Random

Flexible

[ 12.489 ; 12.647 ]

[ 11.707 ; 11.993 ]

0.67

0.62

150 cases per hour

3 Random

Flexible

[ 12.276 ; 12.614 ]

[ 11.814 ; 12.186 ]

0.78

0.76

4 Random

Flexible

[ 13.076 ; 13.664 ]

[ 12.563 ; 13.019 ]

0.81

0.79


CPN Workshop 2005


Conclusions

• Flexible assignment can improve a process with both specialized and generic resources

• Preconditions to benefit from flexible assignment:– the process is not loaded too heavily

– extra benefit when the specialists work faster than the generalists


CPN Workshop 2005

Outline

• Introduction



• Conclusions

• Reflection


CPN Workshop 2005

Conclusions

• The developed CPN model was useful and easy to change

• Specialist-generalist trade-off:the best ratio is one with mainly specialists and one or a few generalists

• Flexible assignment:improvement, especially when more generalists than specialists are availabe

• Same mechanisms, but opposite working


CPN Workshop 2005

Outline

• Introduction



• Conclusions

• Reflection


CPN Workshop 2005

Reflection on project

• Characteristics of project:• ideas and modelling the first ideas: more people• further development and application: mainly 1 person• first time using CPN Tools (version 1.2.0)• 3 weeks of modelling (development)• 1 week of analysis (application)

• Difficulties:• Many internal errors in the beginning• Lack of programming skills


CPN Workshop 2005

The End

Documents

Mariska Netjes, Wil M.P. van der Aalst, Hajo A. Reijers - Analysis of resource-constrained processes with Colored Petri Nets CPN Workshop 2005 Analysis