4D Scheduling & 5D Cost Model in OpenConstructionERP

Concepts

• 4D = schedule + BIM: every task can reference BIM elements so the sequence is visual.
• 5D = schedule + cost: cost roll-ups per task/phase from linked BOQ lines.
• Both live on the same task graph — one source of truth for time and money.

Workflow

1. Build the task graph — tasks, durations, dependencies (FS/SS/FF), milestones, critical path.
2. Link BIM elements to tasks (from oce-bim-takeoff) — visual sequencing and progress colouring.
3. Link BOQ lines to tasks (from oce-estimate-boq) — each task carries its direct cost.
4. Roll up — phase/project totals, cash-flow curves (cost over time), SPI/CPI views.
5. Track — daily diary entries and punch items update actuals; variance reports compare plan vs actual.

Key endpoints

• tasks: create/update, dependencies, assignees, status board
• scheduling: timeline data for the Gantt, milestone markers
• cost model: GET-side roll-ups per task/phase; export to XLSX/PDF reports

Integration rules

• One region/currency per project — the cost model never blends currencies.
• Quantity changes from BIM re-link update BOQ line quantities, which update the cost model in turn.
• Re-validate the BOQ after bulk changes; schedule conflicts surface in the timeline.

Best practices

1. Keep dependencies explicit — the critical path is only as good as the logic.
2. Use milestones for payments/tender gates, not for activity progress.
3. Compare plan vs actual weekly; adjust the forecast, not history.
4. For multi-project portfolios, roll up by project and by currency group (never blended).