Appendix A - Network Analysis/Scheduling

Network Analysis/Scheduling

Safran Planner uses the Critical Path Method to calculate activity dates. This method is based on estimated activity durations and logical relationships between the activities. Project logic may not reflect all conditions; sometimes, you must impose constraints on specific dates. You can constrain certain activities, affecting how Safran Planner calculates activity dates and links.

Logic

One of the key elements of modeling project work is the ability to link activities using different types of relationships or constraints logically. The constraint type specifies the relationship between the preceding and succeeding activity. There are four types of constraints:

Finish to Start Link (FS)

The start of an activity depends on the finish of the preceding one.

Activity B may not start until Activity A has finished.

Start to Start Link (SS)

The activity may not start until the preceding activity has started.

Activity B may not start until Activity A has started.

Finish to Finish Link (FF)

The activity may not finish until the preceding activity has finished.

Activity B may not finish until Activity A has been completed.

Start to Finish Link (SF)

The activity may not finish until the activity preceding it has started.

Activity B may not finish until Activity A has started. The SF constraint discussed above is rarely needed in practice.

All link types above may be modified using positive or negative lags. It is therefore possible to specify whether a succeeding activity is to start immediately, if there is to be an overlap, or whether there should be a delay.

Lags may be specified as a number of days/hours/minutes (depending on Calendar type) or as a percentage. The percentage will be relative to the duration of the preceding activity. If multiple predecessors exist, the percentage will be relative to the driving activity.

The image below illustrates the effects of using percentages for lags.

Date Constraints

In many projects, it may be necessary to impose dates on specific activities that need to have a higher priority than the project logic itself. Examples of such may be specific dates that must be met to achieve the project's desired or contractual goals. Date constraints may lock the start or finish of a single activity, a phase of work, a particular work package, a sub-project, or the entire project. Date constraints have higher priority than logical constraints and will affect the schedule analysis calculations, further influencing float values.

Date constraints may be assigned to both activities and logic constraints. The latter is called a Split Target. The following Date Constraints are available in Safran Planner:

Start No Earlier Than

Start No Earlier Than is used to prevent from beginning before a specified date. If a value for the field is entered, it means that the activity must not commence before this date. It may, however, start later than this date.

Start No Later Than

A Start No Later Than date may be specified to determine that the activity's early start must not be later than a particular date. This will allow the activity to start earlier than the selected date but not after that.

Finish No Earlier Than

Finish No Earlier Than specifies that the activity must not be completed earlier. The activity's early finish date may not be before the Finish No Earlier Than date.

Finish No Later Than

Finish No Later Than is used to specify that the activity must not finish later than this date. The activity's early finish date may not be after the Finish No Later Than date.

Must Start On

A Must Start On date is when an activity must start. If a Must Start On date is present, it takes precedence over all other targets. A Must Start On date sets early and late start dates to the imposed date.

Must Finish On

A Must Finish On date is when an activity must finish. If a Must Finish On date is present, it takes precedence over all other targets. A Must Finish On date sets early and late start dates to the imposed date.

As Late As Possible

An As Late As Possible constraint delays the activity as much as possible without delaying any succeeding activities. The As Late As Possible restriction uses the activity-free float to delay the start and finish dates.

Must Start on Day

Must Start on Date may be used to ensure that an activity starts on a specific day of the week. If entered, the date will have a slightly higher priority than a Start no Earlier/Must Start on Date in that the activity will start on the first chosen weekday after the Start no Earlier/Must Start on date.

It is used in both the forward and backward passes for scheduling. However, for resource leveling, it will only be used on the forward pass.

Must Start on Time

Users can define a given time of day for the activity to start. The value may be set to the hour in hour-based plans and the minute in minute-based plans. Setting a start time will move the activity to the next available time that meets the criteria.

It is used in both the forward and backward passes for scheduling. However, for resource leveling, it will only be used for the forward pass.

Suspend/Resume Date

A planned temporary pause may be inserted for an activity by entering these dates. The date constraints may be used for both progressed and non-progressed activities.

Suspend and Resume dates may be added as columns in the Barchart Editor. They are also available in the Status tab in "Activity Information View."

The rules for Suspend and Resume dates are as follows:

• You cannot enter a Resume date unless there is a Suspend date.
• Resume dates must be later than Suspend dates.
• Removing a Suspend date will automatically remove the Resume date.
• Suspend dates don't impact time analysis.
• Resume dates take precedence over any other date constraints.
• Logic can move a suspended activity beyond the resume date.
• Timenow and cutoff dates control activities with a resume date before Timenow or Cutoff.
• Actual Start date must be earlier than Suspend date.
• Suspend and Resume dates may only be used on activities of activity type 'Activity.'

The Assign Fields function does not support the update of Suspend or Resume dates. However, a fill-down is possible if it follows the rules above.

Minimum Continuous Start Duration

By entering a duration here, Safran ensures that the activity can proceed for the number of days chosen before any non-working period. If you enter three days for an activity with a five-day work-week (Mon-Fri), it would typically start on a Monday, Tuesday, or Wednesday to honor the constraint.

Split Targets

Split Targets are used where a natural break occurs in the network. Suppose a Split Target value is entered into a logic constraint. In that case, it is a barrier between the preceding and succeeding activities, making the two sets independent. The preceding activity may not be completed later than the split target date, and the succeeding activity cannot commence before the split target date.

The Split Target date may distribute available float in the network. Float is an asset common for all activities on the project path. Therefore, a split target date may be used to distribute float between project phases, sub-projects, or areas of responsibility. Using split targets prevents any single part of a project from acquiring all available float.

Scheduled Dates Explained

During the Network Analysis Process (also known as Scheduling), Safran Planner takes into consideration the Project's Timenow, an activity's duration, which Calendar it follows, Network Logic, and any relevant Date Constraints present to arrive at a set of Scheduled Dates for each activity.

The first part of this process is called the Forward Pass, in which Safran Planner calculates from the start of the project through all logical paths of the Network to find the earliest possible finish date for the final activity. This results in a set of early dates for each activity. Early dates (Start/Finish) are the earliest possible time for an activity to start and finish.

The second part of the process is called the Late Pass, in which Safran Planner calculates from the Early Finish date of the latest activity and backward through all the logical paths towards the start activity. This results in a set of late dates for each activity. Late dates (Start/Finish) are the latest possible times an activity can start and finish without delaying the project's completion date determined in the Forward Pass.

The final part of the process calculates the Float (Free/Total) for each activity. Two types of float are calculated: Free and Total Float. Free Float is the amount of time an activity may slip before it affects the start date of any first succeeding activity. Total Float is the time an activity may slip before it affects the project finish date.

Please remember that Safran Planner calculates all Scheduled Dates so they are therefore non-editable.

Additional Scheduled Dates

In addition to the Scheduled Dates discussed above, Safran Planner also stores several date sets during various other processes that the user may initiate during the lifetime of a project. The most common are the Reschedule and Set Comparison dates Processes, which are often carried out for a project during execution.

As mentioned briefly, the Implied Start date is most relevant for activities in progress to show/present a start date. An activity in progress will have an early start set to be the start of the remaining portion of the activity. So, to have a start date for the activity or starting point for a bar symbol, the Implied Start becomes a valuable option.

Start and Finish date fields

In addition to the Scheduled dates available in the Scheduled panel of the Activity information area, you’ll also find the fields Start and Finish available as fields in the Barchart editor.

These date fields are derived from earlier versions of Safran Planner in order to achieve functional similarity to MS Project. These fields are no longer active, however they are kept in order to support backward compatibility for layouts and report configurations from earlier versions of Safran Planner and Safran Project.