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Establishing Relationships
Create relationships between activities to indicate whether an activity can begin only after other activities start or finish. Once you assign relationships, schedule the project to calculate early and late dates for each activity.
Establish relationships between activities in the same project, or link projects by creating relationships between activities in different projects within the EPS. You can define relationships to activities in any other project (not including what-if/inactive projects), even if the project is not opened in the current display.
There are several methods for assigning relationships. Use the Activity Network to visualize the flow of logic as you link activities, or use the Gantt Chart to view relationships according to time. You can also use the Relationships tab in Activity Details to assign relationships to activities in the same project or in other projects in the EPS.
Relationship types and lag You can define the following four types of relationships. Typically, you define relationships from the predecessor to the successor activity.
Finish to start. The successor activity can begin only when the predecessor activity completes.
Finish to finish. The finish of the successor activity depends on the finish of the predecessor activity.
Start to start. The start of the successor activity depends on the start of the predecessor activity.
Start to finish. The successor activity cannot finish until the predecessor activity starts.
When a successor activity cannot start or finish as soon as its predecessor starts or finishes, you can define a lag time for the relationship. Lag is the number of time units from the start or finish of an activity to the start or finish of its successor. Lag can be a positive or negative value. For example, a start to start relationship with a three-day lag indicates that the successor activity can start three days after the start of its predecessor.
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For more information on advanced scheduling options, see “Updating, Scheduling, and Leveling” on page 283.
You can select a calendar to calculate the lag between predecessors and successors for all activities. If you do not select a calendar, the Successor Activity Calendar is used to calculate lag. You can calculate lag based on the Predecessor Activity Calendar; the 24 Hour Calendar, which uses continuous, 7 days/week, 24 hours/day workperiods; or the Project Default Calendar, which is the calendar selected as Default for New Activities on the Defaults tab of Project Details. To select the calendar for scheduling relationship lag, choose Tools, Schedule. Click Options. In the General tab, select a calendar in the Calendar for Scheduling Relationship Lag field.
View relationships in the Gantt Chart To assign relationships in the Gantt Chart, make sure relationships are displayed onscreen. Click the Layout Options bar, then choose Bars. Click Options in the Bars dialog box. Click the General tab in the Bar Chart Options dialog box and mark the Show Relationships checkbox, then click OK.
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While you are dragging the relationship line between two activities, a hint window displays that indicates the type of relationship that will be created when you release the mouse button.
Create relationships in the Gantt Chart or Activity Network
Drag the mouse between any two activities that you want to connect. Point to the left or right of the predecessor activity and drag the mouse to the left or right of the successor activity. The mouse pointer changes to a 
as you define relationships.
Drag the mouse from the end of activity A114380 to the start of A1143820 to define a finish to start relationship.
To modify or delete a relationship, double-click the relationship line.
Dissolving Activities
To maintain relationships when deleting activities, choose Edit, Dissolve, in the Activities window. Dissolving deletes an activity and joins its predecessor and successor activities with a finish to start relationship. The selected activity to be dissolved must have a predecessor and successor.
This sequence of activities above can be completed with just two activities. Dissolve activity A114400. Activity A114390 and A114410 automatically join with a finish to start relationship.
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To assign a relationship between projects, click the Display Options bar in the Assign Predecessors/ Assign Successors dialog box, then choose Select Project. Select activities to define relationships the same way as you would from the same project.
Click the arrows to move from one activity to the next activity in the display.
Assign relationships using Activity Details In the Activities window, select the activity to which you want to add a predecessor or successor relationship. Display Activity Details by clicking the Layout Options bar and choosing Show on Bottom, Activity Details, then click the Relationships tab. Click Assign in either the Predecessors or Successors section. Select the predecessor or successor activity you want to assign, click the Assign button, then click the Close button. Double-click the Relationship Type field, then select a relationship type. Double-click the Lag field, then type the relationship’s lag time value.
To expand either the Predecessors or Successors area, drag the split bar separating the right and left panes.
You can also use the Predecessors or Successors tabs in Activity Details to assign relationships. The Relationships tab combines the predecessor and successor information in a single tab. The data stored in the Relationships tab is synchronized with the information in the Predecessors and Successors tabs.
Trace Logic The Trace Logic layout enables you to examine a path while still viewing the entire project. Click the Layout Options bar and choose Show on Bottom, Trace Logic. In the Gantt Chart or Activity Network upper layout, select the activity from which you want to begin tracing logic.
To move through the chain of activities, click a predecessor or successor of the selected activity. To modify the number of predecessor/successor levels, click the Layout Options bar and choose Bottom Layout Options.
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This Trace Logic layout shows three levels for both predecessors and successors.
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