Friday, April 6, 2012

A brief history of scheduling

Patrick Weaver gave a talk at Primavera06 about the history of scheduling. His talk is captured in an interesting paper: "A brief history of scheduling: back to the future"

Patrick is somewhat of a historian and prognosticator on matter such as these. He also has written:
So, what is the history of scheduling? I certainly remember the days of yester-year before MSProject and its adult cousin Primavera; I remember when the only scheduling tool I had was graph paper, and I remember when the mainframe scheduling tools began to replace hand-drawn bar chart schedules and simple networks.

Weaver writes:
Modern schedule control tools can trace their origins to 1765. The originator of the ‘bar chart’ appears to be Joseph Priestley (England, 1733-1804); his ‘Chart of Biography’ plotted some 2000 famous lifetimes on a time scaled chart “…a longer or a shorter space of time may be most commodiously and advantageously represented by a longer or a shorter line.”

Priestley’s ideas were picked up by William Playfair (1759-1823) in his ‘Commercial and Political Atlas’ of 1786. Playfair is credited with developing a range of statistical charts including the line, bar (histogram), and pie charts

We learn these additional nuggets:
  • The science of ‘scheduling’ as defined by Critical Path Analysis (CPA) celebrated its 50th Anniversary in 2007.
  • In 1956/57 Kelly and Walker started developing the algorithms that became the ‘Activity-on-Arrow’ or ADM scheduling methodology for DuPont.
  • The PERT system was developed at around the same time for the US Navy's Polaris missile program 
  • PERT lagged CPM (Critical Path Analysis) by 6 to 12 months (although the term ‘critical path’ was invented by the PERT team).
  • Later the Precedence (PDM) methodology was developed by Dr. John Fondahl; his seminal paper was published in 1961 describing PDM as a ‘non-computer’ alternative to CPM.

Of course, one of the most profound developments was the arrival and market penetration of the low cost PC-based personal scheduling tools like MSProject. In Weaver's view that made schedulers out of everyone, but everyone is not a scheduler, or can even spell the word.

In my personal opinion, the integration of Monte Carlo tools with low cost scheduling applications like MSProject was equally profound. The MC simulation "fixes" some of the most egregious problems with PERT and the simulation idea has largely run PERT into obsolescence. The main thing that PERT does not handle well is schedule joins or merge, and the statistical merge bias that goes with it.

On the dark side, MSProject has profoundly muddled the whole idea of the WBS. The fact that one of the fields in MSP is called "WBS" is most unfortunate. There are a whole generation of project analysts who believe they created a WBS by the simple act of making that field visible. Not so: schedule is the "verbs" of the project; WBS is the "nouns". Together, WBS + schedule = project narrative.

Now, in Weaver's view, we return to the future:
The changing role of the scheduler has been almost as interesting:
• The mainframe era saw scheduling as:
  • o A skilled profession
  • o Central to the success of projects
• Then came the PCs…… everyone and no-one was a ‘scheduler’ in the 1980s and 90s
• However, in the 21st century, the new ‘enterprise’ era sees scheduling as:
  • o A skilled profession
  • o Central to the success of projects