Schedule Constraint is a specific limitation placed upon a project schedule to regulate the start or finish dates of a task or activity. Schedule constraints are used to impose limits upon work items to prevent certain activities from being started too early (an activity should be started no earlier than a specified date) or finished too late (restriction on delay). This happens because some of activities in certain cases may not be allowed for a planning process which could place these items to different dates, but they rather should be tied up to fixed dates. The project managers when planning a new project must take into account existing schedule constraints, so they can build Project Critical Paths.
You can meet the schedule constraints of the following types:
- As soon as possible: no fixed date to start, but this work should be started right along with the stage it belongs to, so it can be finished as soon as possible as well;
- Start no earlier than: a task has a fixed start time which strongly restricts it from being started any time earlier than it is dictated by circumstances;
- Finish no later than: a very widespread constraint which imposes limitations upon the end date of a task and strongly prevents it from any delay. When it is combined with Start limitation, then you can say that this task is fixed in time, so it lies on the Project Critical Paths;