Critical Chain A Novel by Eliyahu Goldratt Copyright 1997.
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Transcript of Critical Chain A Novel by Eliyahu Goldratt Copyright 1997.
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?