Critical ChainCritical Chain

A Novel by Eliyahu Goldratt

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, HDTV, 3D-HDTV, tablets, etc.

Frequently projects go awryFrequently projects go awry

Budget overruns Time (schedule) overruns Compromising functionality or content

QuestionsQuestions

What is student syndrome? Procrastination

What is multitasking? Doing multiple tasks concurrently

What is safety? Adding extra time to estimates, beyond what

would make the estimate 50% probable

More QuestionsMore Questions

What about measurements? What about early start vs. late start? Of how much value is a project status

report? What about project planning tools like MS

project? Let’s look at Goldratt’s recommendations

Task Duration Probability -- a Beta Task Duration Probability -- a Beta distributiondistribution

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 anybody 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

Conclusion>>>Conclusion>>>

Most of the time we have built into our projects is …..

SafetySafety

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

What about IT TypesWhat about IT Types IT Types tend to underestimate the time it takes

them to do tasks, because They have never done the task before They tend to be intuitive/thinkers—MEANING THEY

ARE OPTIMISTS They have not been told to take their estimates and

double them Especially when the task is NEW to them

IT developer productivities vary by as much as 10 to 1

Probabilistic task durationsProbabilistic task durations

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

Early durations do not show up Recall Parkinson’s Law and all the reasons for

it This explains why safety disappears

More MeasurementsMore Measurements

E

D

C

B

A

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 (late finishes) get passed on; advances (early finishes) don’t

Problems other than safetyProblems other than safety

Early start vs. late start Goldratt does not like BCWP, BCWS,

ACWP, CV, SV, CPI, SPI, BAC, EAC, etc. Existing measurements are not very useful

because they are based on a cost world mentality

Goldratt believes managers should ‘live’ in a throughput world mentality.

MultitaskingMultitasking

A finishes

A finishes

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?

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, Goldratt suggests

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 and placing the safety time that was removed in a PROJECT BUFFER at the end

SolutionSolution

More solutionsMore solutions At the point where each feeding path intersects with

the critical path, place another time buffer, called a feeding buffer. This feeding buffer protects the critical path from delays occurring in the corresponding non-critical paths that would make them critical. The feeding buffer duration should be half of the largest slack on that non-critical path.

You can now use a late start on all non-critical tasks, which Goldratt favors

Duration of Critical Path: 44 Duration of Critical Path: 44 weeksweeks

A/8

B/16

C/8

D/6

E/6

F/14

G/6

Goldratt: Put Safety in a Goldratt: Put Safety in a Project Buffer at the endProject Buffer at the end

A/4

B/8

C/4

D/3

E/3

F/7

G/3 Project Buffer/22

Insert Feeding Buffers and set Insert Feeding Buffers and set their durationstheir durations

A/4

B/8

C/4

D/3

E/3

F/7

G/3 PB/22

FB/2

FB/2

FB/2.5

A/4

B/8

C/4

D/3

E/3

F/7

G/3 PB/22

FB/2

FB/2

FB/2.5

A/4

B/8

C/4

D/3

E/1

F/6

G/2 PB/22

FB/3

FB/2

FB/2.5

A Different Network

More solutions More solutions When resources are needed on the critical

path, these resources are advised ahead of time (3 days??) exactly when they must make themselves available, through use of RESOURCE FLAGS. When that time comes, they must drop everything else and do the required critical tasks—no multitasking or student syndrome—150% focus

This is …..This is …..

The project manager must stay focusedThe project manager must stay 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

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%,” in many cases

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

Figure 6-11. Example of Critical Chain Figure 6-11. Example of Critical Chain SchedulingScheduling

31

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

MeasurementsMeasurements

Goldratt likes UNUSED BUFFER DAYS as a measure

Goldratt does not like: Lines of code created per hour BCWP, BCWS, ACWP, CV, SV, CI, SI EAC (Estimated cost at completion)

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 that managers should manage in the throughput world, a totally different paradigm must find the constraint--the weakest link concentrate on that By the way, what is the ultimate constraint???

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 Go back to step 1, and find another

constraint

Which is not one of the five Which is not one of the five steps in the TOC?steps in the TOC?

IDENTIFY the project constraint--the critical path

Decide how to EXPLOIT that constraint SUBORDINATE that decision to

everything else ELEVATE the systems’ constraint 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

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.

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 a project leader measure progress on a non critical path 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

More SuggestionsMore Suggestions

Put your “BEST” people on the critical path Watch out for critical chains

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 the Borland founder what the implications of

getting a product late to the marketplace are

What about Procurement??What about Procurement??

Most firms enter into LOSE/LOSE Strategies A fixed-price lowest bidder contract is LOSE/LOSE

Strategy This forces Contractors to under bid their costs,

hoping to make it back on the changes to the requirements that the customer will have to pay for

Instead, Contractors should be induced to deliver product on time, with as much functionality as possible

How would you do this?

Shrinking task time—upon Shrinking task time—upon further review???further review???

Not recommended for creative activity Some studies show that the added duress

causes more frustration More mistakes, more rework, more fixes Source: “Deadline,” by Tom Demarco

Time Batching--Another Time Time Batching--Another Time WasterWaster

Analysis paralysis Approval cycles Formal document release Regularly scheduled meetings Planning cycles Work queues

Fast Tracking and Reduced Time Fast Tracking and Reduced Time BatchingBatching

Fast Tracking and Reduced Time Fast Tracking and Reduced Time BatchingBatching

That’s all, FolksThat’s all, Folks