June 5, 2023

External Early Start Date Constraints


This is the second blog post in a four-part series about external early start date and external late finish date constraints. This post discusses external early start date constraints.

External early start dates are date constraints that the Primavera P6 software program adds during the import process of an *.XER data file into a Primavera P6 database. External early start dates represent the earliest finish date of lost predecessor relationships due to missing schedule-to-schedule links. For example, when importing the EPC Project JKL work schedule below into a Primavera P6 database, the driving predecessor link from the Site Development work activity A1020 to the EPC work activity B3020 is missing. Figure 1 shows EPC work activity B3020 without its driving predecessor link to the Site Development work activity A1020.

Figure 1: EPC Activity B3020 Without Its Driving Predecessor Link to Site Development Activity A1020

Although the driving predecessor link from Project ABC is missing, the Primavera P6 program applied an external early start date constraint to the start of EPC activity B3020. The external early start date constraint simulated the finish of the Site Development work activity A1020 on 24 November 2022 so that the forecasted start of EPC work activity B3020 would begin on 25 November 2022. Within Primavera P6, external early start date constraints are located and displayed using the tabular column display option. After expanding the date information, a user selects the external early start column, which is then added to the Primavera P6 bar chart summary.1 Figure 2 summarizes the process of adding external early start date information to a Primavera P6 bar chart.

Figure 2: Process of Adding External Early Start Date Information to a Primavera P6 Bar Chart

As shown above, if a work activity has an assigned external early start date, then the work activity has a missing external predecessor link to a potentially unidentified work schedule. If the source of the external link is unknown, research is needed to determine the origin of and rationale for the external early start date dependency.

1    The same process is used to find and select external late finish dates.


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