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Last
month we had a look at entering the basic task data into Project: that is
Tasks and their Durations. This month we will have a look at logic linking.
My introductory guide to network analysis at: http://www.mvps.org/project/networkanalysis.htm
indicated in Step 1, when listing what has to be done, the importance of not
considering who is going to do what, but to concentrate on WHAT. Step
2 was deciding the ORDER in which it is to be done. Do not type in Start
or Finish dates—let Project do that work for you using the precedence links,
so that Project can tell you what is possible. In this step always assume you
have infinite resources so that who does what does not cloud the issue—concentrate
only on the LOGIC.
Entering Dependencies
A dependency link can be entered in several ways. When the link is created,
Project will calculate the new start of the successor task, and move the bar
to its new date.
Click And Drag
On the Gantt chart, position the mouse pointer on the centre of the predecessor
task bar until the mouse cursor turns into a 4-way arrow. Hold down the
left mouse button and drag up or down until it changes to a link
image.
A Finish-to-Start Link box will show to help you link to the correct task.
Drag the pointer over the successor task to be linked and release the
mouse button. A link line will join the bars in the default finish-to-start
relationship. Although click and drag works, it is not very convenient particularly
when the successor task requires you to scroll to a remote task, as you cannot
control the speed of scrolling. Beware of momentarily releasing the left button
as this could cause the link to be mis-directed. If you hover the mouse over
a link line, a link box will appear giving details of the selected link (not
in Project 98), and double clicking will show a Task Dependency form from which
you can delete the link (see later).
Link Tasks Tool
Click on the Task Name of the predecessor task to highlight it.
Hold down the Ctrl key and click on the successor task. Select
Edit/Link Tasks or Ctrl/F2 or click on the Link Tasks
tool button to create a finish-to-start relationship. Several tasks
can be linked at the same time by sequentially selecting them
and clicking the Link Tasks tool button.
Task Form
Click on the Task Name of the successor task or its bar to highlight
it. If selecting the bar, a tip will appear giving details of the selected task.
Select Window/Split or right-click in a free area of the Gantt
chart and select Split. A combination view (an extremely useful technique
bye the way) will be seen with the Gantt chart in the upper pane and the Task
Form in the lower pane.
Enter the ID numbers or the Predecessor Name of the linkages
required in the predecessor part of the form (bottom pane right-hand side).
If the predecessor is off the screen, you can scroll up or down to find precisely
the task you want without losing the focus of the cursor, so having found it,
just type its ID and it will automatically enter the ID in the correct place.
You could also click in the predecessor area and select the task from the pick
list, though you have to be careful if there is more than one task of the same
name. Select Previous or Next buttons on the form or press Enter
to go to the next task.
Using the Task form is the most positive method of entry and is less
likely to cause errors and is thus the recommended technique. Lag times
(or Lead times as negative Lag) or other task relationships can also be entered
(see later).
Unlinking Tasks
To unlink a task from its predecessor, select the unwanted ID in the
Task Form and press the delete key. Alternatively, double-click
on a link line in the Gantt chart (a bit fiddly) to bring up the Task
Dependency dialog box and select Delete (you can also use this box
to change the dependency Type or Lag—see later).
Or select the linked tasks then Edit/Unlink Tasks, or click the Unlink
Tasks button on the Standard toolbar.
Logical Task Relationships
There are four Types of task relationships in Project:
The illustration above shows the following diagram display:
- Finished-toStart (FS)—Task (B) cannot start until another task (A)
finishes.
- Start-to-start (SS)—Task (B) cannot start until another task (A) starts.
- Finish-to-finish (FF)—Task (B) cannot finish until another task (A)
finishes.
- Start-to-finish (SF)—Task (B) cannot finishe until another task (A)
starts.
Lag or Lead
Lag or Lead (which is entered as negative lag) can be entered in the Task
Dependency Form or in the Task Form to enhance the scheduling
of the requirement. For example, you want to lay a cable across a field; you
might estimate the job in 3 parts: dig trench (3 days), lay cable (1 day) and
fill trench (3 days). If these were scheduled as a chain of tasks it would take
7 days. However, you don't necessarily have to wait for the trench to be completely
dug before you can start to lay the cable. Thus, you could have a Start-to-Start
relationship with a lag of 1 day: i.e., the cable laying can start after the
first day of digging the trench. A bit of thought would lead to the conclusion
that filling the trench also doesn't have to await completion of the laying
of the cable. Thus, by using lag the whole project can be finished earlier,
as the cable laying part can be done within the total time and the trench filling
will have only 1 day left after the cable is laid: i.e., totalling 5 days. This
type of project scheduling is known as a progressive feed. (Actually, by also
splitting the lay cable task into three, the total Duration can be reduced to
4.33 days.)
Gantt Layout
Selecting Format/Layout or right-clicking in a blank area
of the Gantt chart and selecting Layout will allow the layout of the
Gantt chart to be changed. Here a different link style can be chosen or turned
off altogether.
Next Month
Next month we'll have a look at manipulating data and appearance. Enjoy!
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