Project Network Analysis

Origin. PERT/CPM developed in the US (1950s); adopted and extended in Soviet planning as "setevoe planirovanie" (network planning).

Mechanism. Represent a project as a network: nodes are milestones, edges are tasks with durations and dependencies. The critical path is the longest path through the network and determines the minimum project duration. Tasks on the critical path have zero slack; any delay extends the project. Tasks off the critical path have slack that can absorb delays or allow resource reallocation.

Procedure. Decompose the project into tasks. Identify dependencies: which tasks must complete before others can start. Estimate durations (deterministic for CPM, probabilistic for PERT). Construct the network. Compute earliest start and finish times (forward pass). Compute latest start and finish times (backward pass). The critical path connects tasks where earliest = latest. Monitor critical path tasks closely; they control the schedule.

Applies to. Project management, construction, software development, any complex undertaking with interdependent tasks.

Limitations. Duration estimates are uncertain; treating them as point estimates biases the schedule optimistically (merge bias: paths converge at milestones, and all must complete). Dependencies are often incomplete or change during execution. The critical path can shift as tasks complete; yesterday's slack path is today's critical path. Focus on the network obscures resource constraints; CPM/PERT does not ensure resource feasibility.