Using constraints

Sometimes you might need to show that a task cannot start before a certain date or must be completed by a particular date. For example, you might not be able to start work on a task until certain permissions have been granted, or you might need to complete a task no later than a specific date in order to meet an interim deadline. You can show these external influences on the bar chart by using start flags and finish flags. These flags let you constrain a task to start or finish on, before, or after specific dates.

When using constraints, notice that:

On or After and Holding Pin flags may result in tasks moving forward.
On or Before flags may result in tasks moving backward.
On flags fix tasks to a specific date.

You can also constrain tasks to be worked on between two specific dates. This is useful if you know that a task must be completed between two particular dates.

A start or finish constraint overrides any link logic that conflicts with the constraint. For example, using a Start On or After flag prevents a task from starting earlier than the start flag date, even though link logic might allow it to start sooner:

In the illustration above, the second task could start immediately after the first one has finished, but the Start On or After flag prevents it from starting any earlier than its start flag date.

Rescheduling positions tasks so that they conform to their constraint, even if this means that tasks overlap and links go backwards.

You can also constrain tasks so that they start on a new day, or so that they must be completed within a single time period, shift or work pattern. Constraining tasks in this way often reflects more accurately the way in which tasks are worked on in real life:

Depending on the type of task, it may be very unlikely that someone would start work on a task midway through an afternoon; it may be much more likely that they would start work on the task at the beginning of the next day.
Some tasks, once started, must be completed without a break. For example, a task that involves pouring concrete might need to be completed without a break.