Task Dependencies

Dependencies define relationships between tasks, controlling when tasks can start or finish based on other tasks.

Understanding Dependencies

Dependencies provide:

• Sequence Control - Define task order
• Schedule Calculation - Automatic date updates
• Critical Path - Identify important sequences
• Realistic Planning - Model real constraints

Dependency Types

Finish-to-Start (FS)

The most common type. Successor starts after predecessor finishes.

Task A ────────┐
              └─→ Task B

Example: "Excavation must finish before Foundation can start"

Start-to-Start (SS)

Successor can start when predecessor starts.

Task A ────────
  └─→ Task B ────────

Example: "Inspection can start when Construction starts"

Finish-to-Finish (FF)

Successor finishes when predecessor finishes.

Task A ────────
Task B ──────┘

Example: "Documentation finishes when Development finishes"

Start-to-Finish (SF)

Successor finishes when predecessor starts. (Rare)

      Task A ────────
Task B ──────┘

Example: "Old system shutdown finishes when new system starts"

Dependency Summary

Creating Dependencies

From Task Details

1. Open task detail view
2. Find dependencies section
3. Click Add Dependency
4. Select predecessor task
5. Choose dependency type
6. Set lag (optional)
7. Save

From Gantt View

1. Open timeline view
2. Hover over task bar
3. Drag from connection point
4. Drop on successor task
5. Dependency created (FS default)

From Task List

1. Select task
2. Open dependencies panel
3. Add predecessor(s)
4. Configure type and lag

Editing Dependencies

Change Dependency Type

1. Find dependency in task details
2. Click type dropdown
3. Select new type
4. Save changes

Change Lag Time

1. Find dependency
2. Edit lag value
3. Positive = delay after
4. Negative = overlap allowed

Remove Dependency

1. Find dependency
2. Click delete/remove
3. Confirm removal

Lag and Lead Time

Positive Lag (Delay)

Wait time between linked tasks.

Task A ────────┐
              ╌╌╌ (2 day lag)
                 └─→ Task B

Example: "Concrete pour + 7 day lag (cure time) + Framing"

Negative Lag (Lead/Overlap)

Start successor before predecessor finishes.

Task A ────────┐
          └─→ Task B ────
         (2 day lead)

Example: "Rough plumbing can start 2 days before framing completes"

Viewing Dependencies

In Gantt Chart

• Lines connect related tasks
• Arrow shows direction
• Line style may indicate type
• Critical dependencies highlighted

In Task Details

• List of predecessors
• List of successors
• Type and lag for each

In Task List

• Dependency column (if shown)
• Predecessor/successor counts

Dependency Chains

Simple Chain

A → B → C → D

Sequential tasks in order.

Parallel Chains

A → B → C
A → D → E
    B → E

Multiple paths through project.

Critical Path

Longest chain determines project duration. See Critical Path.

Dependency Validation

Circular Dependencies

Not allowed - tasks cannot depend on themselves (directly or indirectly).

A → B → C → A  (INVALID)

YAPL prevents circular dependencies.

Constraint Conflicts

Dependencies may conflict with constraints:

• "Must Start On" date conflicts with predecessor
• System warns or prevents invalid configurations

Impact of Dependencies

Date Calculation

When dependencies exist:

• Successor dates calculate from predecessor
• Changes to predecessor affect successor
• Chain reaction through network

Schedule Changes

Best Practices

Only Necessary Dependencies

• Don't over-constrain schedule
• Only add real dependencies
• Avoid "just in case" links

Prefer FS Dependencies

• Most intuitive
• Easiest to maintain
• Use other types only when needed

Document Why

• Note reason for unusual dependencies
• Explain business logic
• Help future editors understand

Review Regularly

• Check dependencies still valid
• Remove outdated links
• Update lag times as needed

Bulk Dependency Management

Adding Multiple

1. Select multiple tasks (if supported)
2. Add common predecessors
3. Apply to all selected

Dependency Matrix

Some views show dependency matrix:

• All tasks in rows and columns
• Marks show relationships
• Quick overview of network

Troubleshooting

Cannot Add Dependency

"Circular dependency detected"

• Task already depends on successor
• Review dependency chain
• Remove conflicting link

"Invalid dependency"

• Check task exists
• Verify same plan

Dates Not Updating

• Check scheduling mode
• Verify dependency saved
• Review constraint conflicts

Dependencies Not Showing

• Check view settings
• Verify Gantt lines enabled
• Refresh the view

Unexpected Schedule Impact

• Trace dependency chain
• Check lag values
• Review critical path

Related Topics

• Task Properties - Task configuration
• Critical Path - Schedule analysis
• Gantt Charts - Timeline visualization