Schedule dependencies

Dependencies define temporal relationships between tasks that are logically related to each other. You define dependencies by using precedence and succession relationships. Use dependencies to create a succession of linked tasks in your project plan schedule.

This feature is available only if you are using the Formal Project Management process template.

Dependencies are implemented by using Schedule Predecessor and Schedule Successor links between work items. If you are using the Formal Project Management process template, the schedule dependencies are used to calculate the schedule of work items in a plan. In a Scrum process template, schedule dependencies do not affect the plan schedule.

Finish-to-start dependencies

You can create finish-to-start dependencies between work items. In these dependencies, the start of the successor work item, depends on the completion of another work item, the predecessor. The successor work item can start only after the predecessor work item is completed. For example, you create a finish-to-start dependency between the “Create test plan” task, which is the predecessor, and the “Verify test plan” task, which is the successor. The “Verify test plan” task can start only after the “Create test plan” task is completed.

Dependencies and constraints

Constraints that impose start or finish dates on a work item can affect the schedules of work items when dependencies are created. When a constraint restricts the start or finish date of the work item, the constraint date always takes precedence over the dates that the dependency determines.

In the following examples, Task A and Task B have an estimated duration of two days each.

Dependencies without date constraints

When date constraints are not specified, work items have the default, As soon as possible constraint. The calculated or scheduled start dates for the work items, Task A and Task B, are the same as the plan start date of June 1. After you create the dependency, Task B is scheduled to start as soon as Task A is completed. If Task A finishes before its scheduled finish date, Task B can start earlier than scheduled.

Plan without and with a dependency that does not have date constraints

Figure 1: Plan without and with a dependency that does not have date constraints

Dependencies with start date constraints

For Task B, the date of the Start no earlier than constraint is June 4. After you create the dependency, Task B cannot start before June 4. This rule applies even though Task A is scheduled to finish on June 2. In this case, the dependency relationship is applied with a scheduling slack of one day. However, this slack does not provide scheduling flexibility. During calculation of the critical path, the slack is not considered, and Task B is on the critical path.

Plan without and with a dependency that has a start date constraint

Figure 2: Plan without and with a dependency that has a start date constraint

Dependencies with finish date constraints

For Task B, the date of the Finish no later than constraint is June 3. When you create the dependency, Task B is scheduled to finish on June 4. Because this schedule violates the constraint, an error is displayed in the plan.

Plan without and with a dependency that has a finish date constraint

Figure 3: Plan without and with a dependency that has a finish date constraint

To resolve the error, do any of the following tasks:
  • Modify the finish constraint date of Task B to be on or later than the scheduled finish date of June 4.
  • Remove the dependency
  • Remove the constraint

video icon Video

Jazz.net channel
Software Education channel

learn icon Courses

IoT Academy
Skills Gateway

ask icon Community

Jazz.net
Jazz.net forums
Jazz.net library

support icon Support

IBM Support Community
Deployment wiki