SE503 Advanced Project Management Dr. Ahmed Sameh, Ph.D. Professor, CS & IS Critical 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 B B B 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

Gantt Chart with Buffers

Gantt Chart with Buffers Late start all tasks

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 Dependencies Tasks E and H use the same resource

Chart with Resource Dependencies Late start all tasks

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?