In a project, tasks and operations may be linked. For example, in building a house, the roof can only be installed after the walls have been built.
Building walls and installing a roof are tasks that must be linked, and the order of completion of the tasks specified.
There are other types of links between project types such as the requirement that two or several tasks commence at the same time.
Below is a view of 5 operations and relationships between them.
Operation 20 can proceed during operation 10 allowing for an overlap. Operation 20, 30 and 40 have to start at the same time. This is start synchronization.
Operation 50 can only start after operation 30 and 40, but is a strict successor to operation 30.
In PJM the task and operation linking is done in the Predecessor tab of the Task management function.
A task is selected/highlighted in the task structure, and the tasks linked to this particular task then entered in the Predecessor grid.
We describe the fields on the Predecessor grid.
The Linked project – This can be the current project or another project.
Linked task: - a code for the task linked to the selected task is entered here
Link type – There are four link types as illustrated in the previous screen shot.
End to start, such as 30 and 50
Start to start, such as 20, 30 and 40
End to end, the completion of the two tasks must coincide
Start to end – the reverse of end to start
Below is a summary description of the link types
A constraint on the link types must be defined, whether the link is strict or flexible. A strict link type would be such as between operation 30 and operation 50
where operation 50 commences as operation 30 ends. in screen shot 1 above. A flexible constraint is such as between operation 40 and 50, where operation 50 can
commence anytime after operation 40.
The next field is Lag: this is in days and allows for setting the number of days a task can commence before or after another, depending on the link type.
If a project task B is linked to task A, with a link type End-to-Start, with +5 days lag, it means task B can only commence 5 days after the completion of task A.
If the lag is -2 days, then task B can commence 2 days before task A.
The scheduling of the operations of a project and therefore the completion of the tasks are dependent on the "Default working days", the" Unavailable" calendar
of the site,
the weekly structure and Capacity variation of the task assignee, which is defined in the X3 users (GESAUS), Project Management tab
Suppose a site in the month of September is closed from Friday to Sunday. There are then only 4 days available for project tasks in September.
For example, If task B must commence on the 17th of September, then task A must be completed by the 8th of September.
The ability to define relationships between tasks in a project provides for greater flexibility in planning, scheduling and control of a project.