A network breaks project work into activities and defines the dependencies between them. Where the WBS is a container for cost, the network is a container for schedule and execution.
Activity categories
| Category | Content | Cost |
|---|---|---|
| Internal processing | Work by own staff and equipment | Activity rate times duration |
| External processing | Subcontracted work | Generates a purchase requisition |
| Service | Procured services | Service lines and entry sheets |
| Cost activity | Cost only | Direct cost posting |
External processing activities generate purchase requisitions automatically, which is what ties scheduling to procurement.
Relationships
| Kind | Meaning | Example |
|---|---|---|
| FS (finish–start) | Start after the predecessor finishes | Erect steel after foundations are complete |
| SS (start–start) | Start when the predecessor starts | Begin inspection alongside construction |
| FF (finish–finish) | Finish when the predecessor finishes | Align completion of work and inspection |
| SF (start–finish) | Finish when the predecessor starts | Rare; used at handovers |
Scheduling and the critical path
| Date | Meaning |
|---|---|
| Earliest start | The soonest the activity can begin |
| Earliest finish | Earliest start plus duration |
| Latest start | The latest it can begin without delaying the project |
| Latest finish | The latest it can end without delaying the project |
| Float | Latest start minus earliest start |
The chain of activities with zero float is the critical path: a day lost there is a day lost on the project.
Milestones
| Use | Content |
|---|---|
| Progress tracking | Making key achievements visible |
| Milestone billing | Billing the customer on achievement, via SD |
| Triggering | Releasing other activities automatically |
| Progress analysis | A basis for percentage of completion |
Milestone billing is common on large contracts — thirty per cent on design completion, forty on manufacture, thirty on handover — expressed through milestones and an SD billing plan, with the billing block released as each is achieved.