This article outlines everything you need to know to work with primary constraints for activities and milestones in ALICE:

• Primary Constraint Types
  • Soft Restrictions
  • Mandatory Restrictions
• How to Assign Constraints to Tasks/Milestones on the Plan Page
• How to Modify Constraints to Tasks/Milestones on the Explore Page

Primary Constraint Types

Primary constraints are powerful tools that control the scheduling of activities and milestones within a project. These constraints help users model the project schedule accurately, considering various project constraints and requirements. Each constraint has its use case, depending on the project's specific needs and constraints. There are two types of constraint categories in ALICE: Mandatory Restrictions and Soft Restrictions.

Constraint types and constraint dates can be assigned to both activities and milestones. Similarly, both activities and milestones do not have to have constraint types or constraint dates assigned to them.

Soft Restrictions

As Late As Possible

• Task/milestone ideally starts on the last day of the project, given other constraints. A task that has an ALAP constraint is started as late as possible, given that it does not cause delays to any other task.

Start On

• Task/milestone ideally starts on a given date. It cannot start before this date, but it can start later. If it starts later, it starts generating penalties to push it back to its correct finish date.

Start On or After

• Task/milestone does not have an ideal start. It cannot start before this date. It can start anywhere from the starting date to infinity. In this case, all tasks/milestones connected to this task/milestone are also pushed to the future.

Start On or Before

• Task/milestone has an ideal latest start date. If it starts later than that, it starts generating penalties, which motivates the ALICE solver to avoid starting it later.

Finish On

• Task/milestone ideally finishes on a given date. It can finish after this date, but it cannot finish earlier. If it finishes later, it starts generating penalties to push it back to its correct finish date.

Finish On or After

• Task/milestone does not have an ideal finish date. It cannot finish before this date, but it can finish anywhere from the finish date to infinity.

Finish On or Before

• Task/milestone has an ideal latest finish time. If it finishes after this date, it starts generating penalties, which motivates the ALICE solver to avoid finishing it later.

Mandatory Restrictions

Mandatory Start

• Task/milestone must start on a given day. If this is not possible, the critical path and longest path are affected, breaking the logic. This means infeasibility will occur.

Mandatory Finish

• Task/milestone must finish on a given day. If this is not possible, the critical path and longest path are affected, breaking the logic. This means infeasibility will occur.

How to Assign Constraints to Tasks/Milestones on the Plan Page

Constraint types and constraint dates can be assigned on the Plan page for both tasks and milestones. It is not required for tasks and milestones to have a constraint type or date assignment.

In this section, you will learn how to assign a constraint type and date on the Plan page:

For a more hands-on experience, navigate through the player for an interactive walk-through, or if you prefer a more detailed approach, scroll down for a step-by-step guide:

Constraint Assignment for Task or Milestone:

1. In the Gantt chart, "right-click" and select "Edit Columns."
2. Select "Constraint Type" and "Constraint Date" and click "Done" to add the column to the Gantt chart. 
3. Double-click on the Constraint Type cell to open the assignment window.
4. Select the required constraint type (nine possible types):
   • As late as possible 
   • Start On
   • Start On or After
   • Start On or Before
   • Mandatory Start
   • Finish On
   • Finish On or After
   • Finish On or Before
   • Mandatory Finish
5. Click Save to complete the process.
6. Double-click on the Constraint Date cell to open the assignment window.
7. Select the required date for this specific activity or milestone.
8. Click outside of the calendar window or click ENTER to complete the assignment process.

How to Modify Constraints to Tasks/Milestones on the Explore Page

In the Explore page, scenarios can be rapidly created to iterate different constraint type and constraint date options. Here are the conditions where primary constraints can be edited in the Milestones tab under the Create New Scenario menu:

1. All milestones (with or without primary constraints assigned on the Plan page)
2. Only tasks with primary constraints assigned on the Plan page

In the image below, the example project has 1 milestone and 1 activity that can be edited in the Explore page when running a new scenario.

Modify Constraint Type and Date for Task and Milestone in Explore Page:

1. In the Explore page, select +Create New Scenario
2. Select Milestones tab
3. Use the Search by name or ID field, Filter by type field, or scroll through to find the desired task or milestone that you are looking for
4. Change the Constraint type using the dropdown
5. Change the Date
6. Select Run Scenario