Together with dependencies, constraints determine how multiple tasks within a project must be sequenced and scheduled.

Assigning constraints to tasks is an important part of making sure that multiple tasks within a project are appropriately sequenced and scheduled. Most constraints serve one of two functions: minimize the time between successive tasks, or schedule tasks in such a way that subsequent tasks or the project at large are not delayed overall.

Moreover, constraints help ensure that project teams have completed the necessary predecessor tasks to be able to embark on subsequent tasks when they arrive in the project schedule.

Consider a simplified product development cycle with three stages: ideation, iterative prototyping, and user testing. We know that the three stages need to happen in this order, but constraints help us plan for when each stage can begin and end. 

Once we’ve completed the ideation stage, we want to begin our iterative prototyping as soon as possible. But once our team starts building prototypes, we want to get them in the hands of users for testing as our team is still refining the product. User testing needs to begin no earlier than the start of iterative prototyping, but doesn’t need to begin after the completion of the entire stage.

In Spreadsheet.com, these constraints are expressed with the Constraint type and Constraint date data types.

Understanding Constraints and Float

Together with dependencies, constraints determine how multiple tasks within a project should be sequenced and scheduled. Constraints dictate when successor tasks will begin in relation to their predecessors, or in relation to specified constraint dates.

Constraints are important to understand and properly manage a project’s float. Float refers to the amount of time that a task can be delayed without causing other delays in the project. There are two types of float in project management: total float and free float:

• Total float refers to the amount of time that a task can be delayed without affecting the overall completion date of the project
• Free float refers to the amount if time that a task can be delayed without affecting other tasks, most commonly its successor task

Project managers aiming to complete their projects on time should always be aware of total float, but keep in mind that issues with free float can quickly cause a ripple effect and delay the project overall.

Read on to learn more about the different types of constraints supported by Spreadsheet.com, or skip ahead to learn how to create and manage task constraints in a Gantt view.

Types of Constraints

Spreadsheet.com supports eight different types of constraints to reflect the different relationships between your tasks:

Flexible constraints don’t tie tasks to specific start or end dates, but instead schedule them in relation to their predecessor or successor tasks. Semi-flexible constraints work with specified start or end dates, but still allow for some variation in when a task can be scheduled depending on its predecessors. Inflexible constraints tie tasks to specific start or end dates.

Flexible constraints have one component: a constraint type. Semi-flexible and inflexible constraints have two components: a constraint type and a constraint date. In Spreadsheet.com, constraint types and constraint dates are specified with their own column data types.

Read on to learn more about the different types of constraints, or learn more about creating and managing task constraints in Spreadsheet.com.

Let’s take a closer look at each constraint:

As Soon as Possible (ASAP)

When a task has an As Soon as Possible (ASAP) constraint, it will begin at the earliest possible start date depending on the scheduling of its predecessor task. With an ASAP constraint, a task will be scheduled to begin at the beginning of its free float period.

ASAP constraints are flexible in that tasks need not start or finish on a specific date or within a certain period, but are scheduled relative to their predecessor tasks.

ASAP constraints minimize the time between successive tasks and help schedule projects to be completed as quickly as possible. New dependencies created in Spreadsheet.com adopt the ASAP constraint type by default.

As Late as Possible (ALAP)

When a task has an As Late as Possible (ALAP) constraint, it will begin at the latest possible date so as to not delay its successor task. With an ALAP constraint, a task will be scheduled to finish at the end of its free float period.

ALAP constraints are flexible in that tasks need not start or finish on a specific date or within a certain period, but are scheduled relative to their successor tasks.

ALAP constraints maximize the time between successive tasks, and as such are not as commonly used as ASAP constraints.

Finish No Earlier Than (FNET)

When a task has a Finish No Earlier Than (FNET) constraint, it is scheduled to be completed on or after a specified constraint date. FNET constraints are semi-flexible in that tasks need not finish on a specific date, but must finish within a certain period of time.

In Spreadsheet.com, FNET constraint dates are represented with a vertical dotted line on the Gantt chart.

Start No Earlier Than (SNET)

When a task has a Start No Earlier Than (SNET) constraint, it is scheduled to begin on or after a specified constraint date. SNET constraints are semi-flexible in that tasks need not start on a specific date, but must start within a certain period of time.

In Spreadsheet.com, SNET constraint dates are represented with a vertical dotted line on the Gantt chart.

Finish No Later Than (FNLT)

When a task has a Finish No Later Than (FNLT) constraint, it is scheduled to be completed on or before a specified constraint date. FNLT constraints are semi-flexible in that tasks need not finish on a specific date, but must finish within a certain period of time.

In Spreadsheet.com FNLT constraint dates are represented with a vertical dotted line on the Gantt chart.

Start No Later Than (SNLT)

When a task has a Start No Later Than (SNLT) constraint, it is scheduled to begin on or before a specified constraint date. FNLT constraints are semi-flexible in that tasks need not start on a specific date, but must start within a certain period of time.

In Spreadsheet.com, SNLT constraint dates are represented with a vertical dotted line on the Gantt chart.

Must Finish On (MFO)

When a task has a Must Finish On (MFO) constraint, it must be completed on a specified constraint date. MFO constraints are inflexible in that tasks can only be completed on the specified date.

In Spreadsheet.com, MFO constraint dates are represented with a vertical solid line on the Gantt chart.

Must Start On (MSO)

When a task has a Must Start On (MSO) constraint, it must begin on a specified constraint date. MSO constraints are inflexible in that tasks can only begin on the specified date.

In Spreadsheet.com, MSO constraint dates are represented with a vertical solid line on the Gantt chart.