Constraints (constraint: A restriction set on the start or finish date of a task. You can specify that a task must start on or finish no later than a particular date. Constraints can be flexible [not tied to a specific date] or inflexible [tied to a specific date].) impose restrictions on the way Microsoft Office Project 2003 calculates the start (start date: The date when a task is scheduled to begin. This date is based on the duration, calendars, and constraints of predecessor and successor tasks. A task's start date is also based on its own calendars and constraints.) and finish dates (finish date: The date that a task is scheduled to be completed. This date is based on the task's start date, duration, calendars, predecessor dates, task dependencies, and constraints.) of tasks. By default, Project applies flexible constraints (flexible constraint: A constraint that is flexible and does not tie a task to a single date. Flexible constraints are As Soon As Possible, As Late As Possible, Finish No Earlier Than, Finish No Later Than, Start No Earlier Than, and Start No Later Than.), such as As Soon As Possible (ASAP), to tasks.
For optimal scheduling flexibility, it's recommended that you allow Project to use flexible constraints to calculate the start and finish dates for tasks based on the durations (duration: The total span of active working time that is required to complete a task. This is generally the amount of working time from the start to finish of a task, as defined by the project and resource calendar.) and task dependencies (task dependencies: A relationship between two linked tasks; linked by a dependency between their finish and start dates. There are four kinds of task dependencies: Finish-to-start [FS], Start-to-start [SS], Finish-to-finish [FF], and Start-to-finish [SF].) you enter. Only if you have unavoidable constraints, such as an event date that cannot be moved, should you consider setting a constraint for a task manually.
Setting of constraints
When you enter a new task in the Task Name field, Project assigns the As Soon As Possible (ASAP) constraint when you schedule your project from the start date. When scheduling from the finish date, Project assigns the As Late As Possible (ALAP) constraint.
If you drag the mouse in the chart portion of the Gantt Chart to create a new task, however, Project automatically assigns the Start No Earlier Than (SNET) constraint when you schedule your project from the start date. When scheduling from the finish date, Project automatically assigns the Start No Later Than (SNLT) constraint.
When you manually enter a start or finish date for task, you automatically apply a constraint to it.
When you schedule your project from the start date and you type a start or finish date for a task, Project constrains the task to begin or complete no earlier than that date. If you schedule your project from the finish date, however, Project constrains the task to begin or complete no later than the date you type.
Constraints and task dependencies