Josh Nankivel has a post on his PMStudent site about the Critical Path. This presentation is one of those "let me re-examine the obvious." This worth the time to watch, but it brings out several issues in the domain of project and program management.
Some of the questions asked by the author include:
- Where does the CP begin and end?
- CP start and end on date constraints?
- Fixed completion of intermediate milestone impact the CP?
But first you must watch the presentation to connect with the comments below.
But first a pre-apology. This topic is wickedly obtuse for all the right reasons. So this very narrow bandwidth blog channel is replaced in practice with a 3 day workshop, and continuous hands on mentoring, coaching, and keyboarding for the programs we work using Monte Carlo Simulation.
If you'll go to the Lijit search box on the right panel of this blog and enter "monte carlo" you'll see the tip of the ice berg of this topic.
This discussion starts with a primary problem
When you put hard constraints in the middle of the schedule, you have essentially "broken" the schedule. In Murry Wolf's presentation, complexity is created by this approach.
In our defense domain, hard constraints such as Must Finish On (MFO), Finish Now Later Than (FNLT) are strong discourages in principle and in practice ruin the use of Monte Carlo Simulation, since the probabilistic finish date are now anchored in the schedule and cannot move.
Here's the Real Problem
In our domain, the notion of the Critical Path as an "entity" that exists in the schedule, is replaced by a probabilistic assessment of the confidence of completing on or before a planned date. This is the role of the Monte Carlo Simulation of the schedule.
This approach removes all the hand waving, re-definition of terms, and arguing what is meant by Critical and Path.
The identification of the paths the impact the confidence of a deliverable is called the cruliality of the schedule. Using Wolf's classification are useful however:
- Acute Path - this is a path through the schedule that has negative slack that will substantially impact a deliverable
- Watch Path - this is a path through the schedule that needs to be corrected so the deliverable can be made as promised
- Free Paths - are paths that have positive float
This is an interesting view from Construction
At one time I was a member of the College of Scheduling. But the construction paradigm did not sit well with me for a few reasons:
- The litigation support issues dominate the style of scheduling. In the defense world, the Integrated Master Plan is "on contract." The Integrated Master Schedule (IMS) is subject to change of course - through a change control process - but the contributes to the IMS - the Integrated Product Teams (IPT) have similarly "promised" to deliver on time, on schedule.
- Litigation is rare and usually takes place after some complete disaster occurs.
- The use of constraints is common and remove the ability of Monte Carlo Simulation.
It's the Monte Carlo Simulation that got me hooked on the method of doing the IMP/IMS. The IMS in the defense world MUST have minimum constraints. The DCMA 14-Point Assessment sets the upper limit of constraints.
To answer Mr. Wolf's pressing question - "which paths should we be looking at," means answering the cruciality question with a Monte Carlo model.
Cruciality is the combination of criticality and sensitivity of the drivers of the deliverables. That is what activities drive the "lateness" of the deliverable, how sensitive is this lateness and how critical are they?
That's how you answer all confusion created by constraints, multiple critical paths - which are always there in any real schedule, since the durations are random numbers - and the identification where to look for the next "emerging" problem with staying on schedule.
