Critical ChainCritical Chain

A Novel by Eliyahu Goldratt

Copyright 1997

Product lifetimes are Product lifetimes are diminishing fastdiminishing fast

Projects to create new products must be shortened drastically

Consider Modems, cellular telephones, VCR’s, PC’s,

Frequently projects go awryFrequently projects go awry

Budget overruns Time (schedule) overruns Compromising functionality or content

QuestionsQuestions What is the name of the principle role-

player? Who is this person? What about the MBA degree? What is student syndrome? What is multitasking? What is safety?

More QuestionsMore Questions

What about measurements? What about early start vs. late start? Of how much value is a project status report? Where are the bottlenecks?

Where is the organizational bottleneck? Delays _____ but advances do ___.

accumulate, not

What about project planning tools like MS project? What are some of Goldratt’s recommendations?

Task Duration Probability -- a Task Duration Probability -- a Beta distributionBeta distribution

A ScenarioA Scenario

You have been asked to do two tasks: TASK A ---> TASK B TASK A whose average duration is 10 days, but whose

pessimistic duration is 20 days TASK B whose average duration is 10- days, but whose

pessimistic duration is 20 days Estimate how long it will take you to complete these

two tasks? What is the probability that you will finish in 20 days?

Everybody overestimates the Everybody overestimates the time required to do their tasktime required to do their task

According to Goldratt This is called SAFETY Does any body (in the book) want to talk about

how much safety they put into their estimates? Is this true in software development? It is if you have an expert doing the estimating,

who really knows how long it will take him

What happens after that--a What happens after that--a possible scenariopossible scenario

The team leader adds safety time to the task to cover his responsibilities

The project leader adds more safety time The project manager may add still more

safety time

The project manager must The project manager must stay focusedstay focused

Or the project will not be finished on time, within budget

This means applying the Pareto principle 80% of the benefit comes from 20% of the activities

By the time progress reports indicate something is wrong, its usually too late

What about progress reports?What about progress reports?

Progress reports tell you that 90% of the project is finished in 90% of the required time.

However, another equal period of time is required to complete the remaining 10%

It is hard to stay focused It is hard to stay focused when:when:

There are too many project paths on-going, in parallel

There are many critical or near critical paths There are many projects ongoing

Measurements are a major Measurements are a major problem with projectsproblem with projects

Measurements should induce the parts to do what is good for the system as a whole

Measurements should direct managers to the point that needs their attention

So often it occurs that we measure the wrong thing. The wrong measure leads to wrong behavior

Tell me how you measure me and I will show you how I behave

More MeasurementsMore Measurements

Projects are like chainsProjects are like chains

Each task in sequence is a link in a chain Each link has two things

weight, to which cost is analogous strength, to which throughput is analogous

Cost vs ThroughputCost vs Throughput

Goldratt maintains that management in the cost world is a mirage efficiency becomes paramount local improvements are necessary to get global ones

Goldratt suggests the managers should manage in the throughput world, a totally different paradigm must find the constraint--the weakest link concentrate on that

Remember the five steps of Remember the five steps of TOCTOC

IDENTIFY the project constraint--the critical path Decide how to EXPLOIT that constraint SUBORDINATE everything to that decision ELEVATE the systems’ constraint to every thing

else GO BACK to step 1, and find another constraint

ConflictsConflicts

Based on faulty assumptions Use evaporating cloud to surface the

assumptions Then question every one of them A Bad assumption leads to a breakthrough

solution or injection

SafetySafety

Safety is however much time is added on to a task beyond its mean time of completion

Probabilistic task durationsProbabilistic task durations

Late durations tend to accumulate and may increase the length of the project

Early durations do not show up This explains why safety disappears

More MeasurementsMore Measurements

Other problems with safetyOther problems with safety

Is wasted by the “student syndrome” Basically, this is procrastination

Is wasted by multitasking (a person who works on several tasks at the same time) With each change of task, a set up is required

Is wasted by dependencies between steps These dependencies cause delays to accumulate, but

advances are wasted Delays get passed on; advances don’t

Problems other than safetyProblems other than safety

Early start vs. late start Existing measurements are worthless

because they are based on a cost world mentality

Existing measurements do not take into consideration the critical path

Early Start vs. Late StartEarly Start vs. Late Start

How much Safety is there How much Safety is there likely to be?likely to be?

Will project professionals admit how much safety they are putting into their estimates?

What happens when these professionals are asked to cut their durations by 10%, next time?

These professionals want to be 100% sure of getting finished on time

Therefore, the durations are likely to be twice as long as they should be

So CUT THEM IN HALF

Problems with subcontractorsProblems with subcontractors

How are contractors selected?? Lowest bidder

How should contractors be selected? It should be noted that contractors make their money on

the changes that are requested after the fixed-price contract is signed

Is lead time as important as price??? How should contracts with subs be written?

SolutionsSolutions

Take the safety out of the individual tasks and put it at the end of the critical path in the time buffer, called a project buffer

This means making the tasks roughly 50-60% as long as they would otherwise be.

More solutionsMore solutions

At the point where each feeding path intersects with the critical path, place another time buffer, called a feeding buffer. The feeding buffer protects the critical path from delays occurring in the corresponding non-critical paths.

When resources are needed on the critical path, these resources are advised ahead of time exactly when they must make themselves available. When that time comes, they must drop everything else and do the required critical tasks as quickly as possible.

Measurement solutionsMeasurement solutions

Measure progress only on the critical path; what percent of the critical path we have already completed. This is all we care about!!

Have the project leader or team leaders measure progress on non critical paths in terms of unused buffer days

Shrinking the task time: Shrinking the task time: EffectsEffects

There is less procrastination There is much more focus There is less multitasking

What are the ramifications of What are the ramifications of a delayed software product, a delayed software product, intended for commercial sale?intended for commercial sale?

Less market share Less profit; maybe no profit Lower analyst profit expectations Declining share price Out of business? How many firms has Microsoft driven out of

business? Ask Mitch Kapor (founder of Borland) what the

implications of getting a product late to the marketplace are

Programmers have a tendency Programmers have a tendency to…to…

Add bells and whistles that no one needs

What happened to Professor What happened to Professor Silver?Silver?

What happened to the Silver collection?