Scheduled Start and Finish Dates

Each task has a scheduled start date and a scheduled finish date (usually just called the task's start date and finish date)  The way that they are used and set depends on whether the task is manual or automatic.

In this article, we'll talk about how scheduled start and finish dates are set, how to choose between manual or automatic scheduling (also known as calculated scheduling), and the role of constraints, dependencies, deadlines and milestones.

See the article on Scheduled Date Modes for how scheduled dates may be automatically changed based upon the actual progress of a task.

1. Manual vs. Automatic Scheduling

Use a manual (i.e. manually scheduled) task when you

  • want to explicitly set its scheduled start and finish dates
  • do not want the workplan scheduler to automatically change its scheduled start and finish dates based on changes to other tasks or to dependencies or constraints.

If a manual task has both start and finish dates set, then its duration is the # of project working days between its start and finish dates.  Changing any one of those three attributes will change one of the other two attributes to maintain that relationship among them.  See the article on Manual Tasks for more details.

Use an automatic (i.e. automatically scheduled) task when you

  • want the workplan scheduler to automatically set its start and finish dates, based upon its specified work and duration, its constraints, and its dependencies on other tasks
     
  • do not generally want to set its scheduled start and finish dates explicitly, except as a shorthand way to set constraints that will limit where the workplan scheduler can subsequently place the task.  See the article on Task Constraints for more details.

An automatic task is generally scheduled so that its scheduled duration -- the # of project working days between its scheduled start and finish dates – corresponds to its specified duration.  However

  • The durations will not generally match until the workplan is rescheduled, which (at least currently) must be done explicitly by the user.
  • There are some cases (albeit uncommon) where, even after scheduling, the durations will not match.  So to be safe, think of the specified duration of an automatic task as an expected duration

See the article on Automatic Tasks for more details.

2. Dependencies, Constraints and Deadlines

Each task may have

  • Dependencies – specifies other tasks that must start or finish before it can start or finish, with an optionally specified lag
  • Constraints – requires that a task must start (and/or finish) no earlier than, no later than, or on a specified date.  See the article on Task Constraints for more details.
  • Deadline – a specified date when the task should be done

None of these are enforced at all for manual tasks.  For automatic tasks, only dependencies and constraints are enforced, and only when the workplan is rescheduled (although, once we add support for leveling, deadlines will be enforced to the extent possible)

However, it is always possible to tell whether dependencies, constraints and even deadlines are being violated by a task's scheduled dates, for both automatic and manual tasks.

Workplan Properties > Status Icons and Colors contain a number of task status conditions, including "Task's scheduled dates violate dependencies, constraints or deadline".  It is possible to

  • Set a color, so that when a violation occurs, the color is used as the task's background in the workplan
  • Set an icon, so that when a violation occurs, the icon is included in the Status Icons field for that task in the workplan

Dependencies can potentially be cyclical, but project.net detects cycles in a workplan whenever the user sets or changes a dependency, or changes the parent of a task (by making it a subtask of a different parent), and disallows changes that could cause a cycle.

3. Milestones

Any task can be marked as a milestone, using the Milestone checkbox in the workplan, or in the Work section of New Task or edit Task.  A list of milestone tasks, with associated information, is displayed on the project's dashboard.

Simple milestones are leaf tasks that have no work or duration.  However, even tasks with work and duration, and even summary tasks, can be marked as milestones.

You can use either manual or automatic tasks as milestones.

  • If you use a manual task for a milestone, then its scheduled dates will be fixed.  To use a manual task for a simple milestone, just set its scheduled start or finish date, leaving the other date blank, as well as the duration.
     
  • If you use an automatic task for a milestone, it will be scheduled automatically by the workplan scheduler, and its scheduled dates may change depending on the tasks it depends on.  If you want it to start or finish on or no later than a specific date, set the appropriate constraint for the milestone task. 

Ellis S Cohen
Project.net
Feb 2015