Critical
Chain
A Novel by
Eliyahu Goldratt
Copyright 1997
Product
lifetimes are diminishing fast
- Projects
to create new products must be shortened drastically
- Consider
Modems, cellular telephones, VCR’s, PC’s,
Frequently
projects go awry
- Budget
overruns
- Time
(schedule) overruns
- Compromising
functionality or content
Questions
- 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 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 ___.
- What
about project planning tools like MS project?
- What
are some of Goldratt’s recommendations?
Task Duration
Probability -- a Beta distribution
A 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 time 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 possible 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 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
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 when:
- There
are too many project paths on-going, in parallel
- There
are many critical or near critical paths
Measurements
are a major problem 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 Measurements
-5
-5
-5
+15
Projects
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
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 TOC
- 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
Conflicts
- 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
Safety
- Safety
is however much time is added on to a task beyond its mean time of completion
Probabilistic
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 Measurements
-5
-5
-5
+15
Other 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 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 Start
A
5
B
5
C
10
D
10
E
10
How much
Safety is there 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 subcontractors
- How
are contractors selected??
- 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?
Solutions
- 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 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
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
project leader or team leaders measure progress on non critical paths
in terms of unused buffer days
Shrinking
the task time: Effects
- There
is less procrastination
- There
is much more focus
- There
is less multitasking
What are
the ramifications of a delayed software product, 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 to…
- Add
bells and whistles that no one needs
What happened
to Professor Silver?
- What
happened to the Silver collection?