se503 advanced project management dr. ahmed sameh, ph.d. professor, cs & is critical chain...
DESCRIPTION
Project Characteristics Statistical Fluctuations Dependent Events – Direct flow (A to B) – Common destination (A to C, B to C) – Common source (B from A, C from A) A A A B B B C CTRANSCRIPT
SE503Advanced Project
Management
Dr. Ahmed Sameh, Ph.D.Professor, CS & ISCritical Chain Project Management
Background
TOC Applied to PM Constraints
– Critical tasks– Critical resources
Inventory– Time buffers– Resource buffers
Different measurements
Project Characteristics
Statistical Fluctuations Dependent Events
– Direct flow (A to B)– Common destination (A to C, B to C)– Common source (B from A, C from A)
A
A
A
BBB C
C
Critical Chain Principles
Optimize globally, not locally Dynamically identify critical tasks/resources Critical path determines project success
Critical Chain
Delay in CC is a delay in the project Buffers should protect CC Optimize critical tasks and resources
– Increased priority– Flexible management
Buffers
Project Buffer – overall uncertainty Feeder buffers – protect critical path Resource buffers
– Wake-up call– Protect critical resources
Limited resource Multiple tasks
Protecting the Critical Path
Reduce estimates to 50% probable Add a project buffer to the end of the project Add feeder buffers to protect the critical path Late start all tasks
Traditional Gantt Chart
ID
1
2
3
4
5
6
7
8
9
10
11
12
13
Project startTask A
Task BTask C
Task DTask E
Task FTask G
Task HTask I
Task JProject finish
9/21 9/28 10/5 10/12 10/19 10/26 11/2 11/9 11/16 11/23 11/30 12/7 12/14 12/21 12/28 1/4 1/11 1/18 1/25 2/1 2/8 2/15 2/22September October November December January February
Gantt Chart with Buffers
ID
3
4
5
6
7
8
9
10
11
12
13
14
15
Task ATask B
Task CTask D
Task ETask F
Task GTask H
Feed Buffer 1Task I
Feed Buffer 2Task J
P.Buffer
9/28 10/5 10/12 10/19 10/26 11/2 11/9 11/16 11/23 11/30 12/7 12/14 12/21 12/28 1/4 1/11 1/18 1/25September October November December January
Gantt Chart with BuffersLate start all tasks
ID
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
Project startTask A
Task BTask C
Task DTask E
Task FTask G
Task HFeed Buffer 1
Task IFeed Buffer 2
Task JP.BufferProject finish
9/28 10/5 10/12 10/19 10/26 11/2 11/9 11/16 11/23 11/30 12/7 12/14 12/21 12/28 1/4 1/11 1/18 1/25September October November December January
Protecting the Critical Chain
Identify over-allocated resources Adjust task schedules to correct resource
allocation Add resource buffers to protect critical
resources– Limited availability– Used on multiple tasks
Late start all tasks
Resource Conflicts
Resource dependencies complicate matters How do we reschedule tasks with conflicts?
– Priorities– Due dates (EDD)– Resource leveling
Resources are bottlenecks!– Place buffers ahead of critical resource tasks
Chart with Resource DependenciesTasks E and H use the same resource
ID
3
4
5
6
7
8
9
10
11
12
13
14
15
Task ATask B
Task CTask D
Task ETask F
E Res. BufferTask G
Task HTask I
Feed Buffer 2Task J
P.Buffer
9/28 10/5 10/12 10/19 10/26 11/2 11/9 11/16 11/23 11/30 12/7 12/14 12/21 12/28 1/4 1/11 1/18 1/25September October November December January
Chart with Resource DependenciesLate start all tasks
ID
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
Project startTask A
Task BTask C
Task DTask E
Task FE Res. Buffer
Task GTask H
Task IFeed Buffer 2
Task JP.BufferProject finish
9/28 10/5 10/12 10/19 10/26 11/2 11/9 11/16 11/23 11/30 12/7 12/14 12/21 12/28 1/4 1/11 1/18 1/25September October November December January
Buffer Management
Focus on buffer remaining– Less on scheduling– Less on milestones– Accurate estimates of remaining duration
Reschedule if buffers are used up– New critical chain– Dynamic constraints
Resource Management
Identify the constraint Exploit the constraint Subordinate the other resources/tasks Elevate the constraint Repeat as needed
Two Views of a Project
External– Based on original schedule– Fixed milestones– Fixed end date– Communication to management
Internal– Critical chain, buffer management– Late-start schedule with buffers
Two Project Types
Internal– Use internal resources– Standard CC approach
External– Contractor/consultant based– Contracts include time/cost tradeoff– Wake-up call instead of firm start date
Critical Chain Issues:Estimates
Task Estimates– Two-point estimates– Estimating 50% probability of completion
Buffer sizes– How big should they be?– Where should they be put?
Critical Chain Issues:Schedule
No firm schedule– Buffers allow date to float– Difficult to interface with other (fixed) events– Management expects firm dates– Rescheduling when buffers are empty
Late starts– Buffers are supposed to insure safety, but…– It still seems like early start is better in many
cases
Critical Chain Issues:Resources
No firm schedule makes resource allocation difficult
Wake-up calls replace firm start dates Contractors must have incentive to perform
well (Parkinson’s, Student’s syndrome, etc.) Contractors may choose not to bid
Critical Chain Issues:Management
Can buffer management really replace project management?
Is there too much focus on schedule, when many managers focus on cost?
Where do technical measures and quality control come in?