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