There are two types of constraints:
- Project Constraints which includes the Project Start Date and Project Finish Date, and
- Activity Constraints; the two most common are Start On or After (Early Start) and Finish On or Before (Late Finish).
External dependencies are applied to a schedule using Constraints and these may model the impact of events outside the logical sequence of activities. A constraint would be imposed to specific dates such as the availability of a facility to start work or the required completion date of a project.
Constraints on projects in Sydney should be cross-referenced to the supporting documentation, such as Milestone Dates from contract documentation, using the Notebook Topics function.
A Project Start Date called Project Planned Start in P6 is the earliest date that any activity may be scheduled to start. An activity will start on the Project Start Date unless one of the following stop the activity starting on the Project Start Date::
- There is a Calendar Non Work time, or
- A constraint, or
- A relationship.
A Project Finish Date is optional, but once set this controls Total Float (often referred to as Float in P6).
When a Project Finish Date constraint is assigned in Sydney then Total Float is calculated to this date.
- The picture shows a project with a Project Finish date on Friday 26 September developing 5 days Total Float.
- The picture shows a schedule with a Project Finish date of Friday 12,
- This is earlier than the calculated finish date, thus calculating 5 days Negative Float:
Typical examples of activity constraints would be:
- Start on or After for the availability of a site to commence work, and
- Finish on or Before for the date that a total project must be completed or handed over.
Activity Early Start Constraint
- An activity will no longer start on the Data Date when a Start On or After constraint is assigned
- This is more commonly known as an Early Start constraint.
NOTES: In P6 the time must always be displayed as P6 will often set constraints at 00:00hrs which is midnight and is not very often an appropriate time to set constraints.