What You Need to Know About Trace Logic: Solid Versus Dotted Relationship Lines

Written on . By CPM Solutions

Many of you already know what Trace Logic is without needing to be told. It is the process of working through (“tracing”) predecessor and successor relationships through the project schedule. Primavera P6 makes this process fast by using the Trace Logic feature. Similar to the Activity Network diagram, Trace Logic displays activities in boxes and links relationships using lines. The difference is that Trace Logic works with the Activity Table, Gantt Chart, Activity Usage Spreadsheet, or Activity Network to identify activity details in the predecessor / successor relationships.

How to View Trace Logic

To open the Trace Logic layout:
1) Click on the View menu.
2) Click on Show on Bottom, Trace Logic.


How Trace Logic Works

Once you open Trace Logic, you can click on activities in the Activity Table and the same activity will be highlighted in the Trace Logic network and vice versa. The activity that is selected will be outlined in blue to indicate. Relationship lines will connect to predecessor and successor activities to help you evaluate the logic. Relationship lines in Trace Logic are especially important because Primavera P6 can identify which relationships are critical, driving and non-driving relationships. This will allow you to manipulate the schedule to fit within a specific time frame or change the progression of activities.

There are three types of relationship lines in Trace Logic:

1) Critical
2) Driving
3) Non-Driving

Critical Relationships

Activities are critical and have critical relationships if they are on the critical path (ie, the shortest duration path from the start to finish of the project). Activities that are critical will have a red outline and critical relationships will have a solid red line because they are also driving.

Driving Relationships

An activity will have a driving relationship if the relationships are used to calculate the start and finish dates of predecessor or successor activities, but are not on the critical path. Driving relationships are displayed as a solid black line.

Non-Driving Relationship

An activity will have a non-driving relationship if the relationships are not used to calculate the start and finish dates of predecessor or successor activities and are not on the critical path. Non-driving relationships are displayed as a dotted black line.

Here is an example that displays the three relationship types:

Screen 1 - Dotted_Lined Relationships

Printing Trace Logic

If you want to print Trace Logic, follow these quick steps:

1) Click on the File menu, Print Setup.


2) In the Page Setup dialog box, select Options.


3) Click on the checkbox next to Trace Logic. Click OK.

Note: The Trace Logic checkbox will not be available unless you have already opened the Trace Logic tool in the bottom layout in P6.



You’ll see solid and dotted relationship lines in other tools in P6, like the Gantt Chart and Activity Network. You can use driving and non-driving relationships to understand why activities are scheduled on certain dates in your project schedule. Use this information to adjust the project schedule without affecting the critical path or extending the project finish date.