1. Adjusting Task Relationships
Tere are four types of task
dependencies, or relationships:
-
Finish-to-start (FS): The finish date of the predecessor
task determines the start date of the successor task. -
Start-to-start (SS): The start date of the predecessor task
determines the start date of the successor task. -
Finish-to-finish (FF): The finish date of the predecessor
task determines the finish date of the successor task. -
Start-to-finish (SF): The start date of the predecessor task
determines the finish date of the successor task.
When you enter tasks in Project and link them by clicking the
Link Tasks button on the Task tab, the tasks are given a
finish-to-start relationship. This is fine for many tasks, but you
will most likely change some task relationships as you fine-tune a
project plan. The following are some examples of tasks that require
relationships other than finish-to-start:
-
You can start setting pages as soon as you start
illustration work on a book project (a start-to-start
relationship). This reduces the overall time required to complete
the two tasks, as they are completed in parallel.
-
Planning the editorial work for a book can begin before the
manuscript is complete, but it cannot be finished until the
manuscript is complete. You want the two tasks to finish at the
same time (a finish-to-finish relationship).
Task relationships should reflect the sequence in which work
should be performed. After you have established the correct task
relationships, you can fine-tune your schedule by entering overlap
(called lead time) or delay (called lag time) between the finish or
start dates of predecessor and successor tasks.
Assuming that two tasks have a finish-to-start
relationship:
The following is an illustration of how lead and lag
time affect task relationships. Assume that you initially planned the
following three tasks using finish-to-start relationships.
Before task 2 can begin, you need to allow an extra day for the
copyedited manuscript to be shipped to the author. You do not want to
add a day to the duration of task 5 because no real work will occur on
that day. Instead, you enter a one-day lag between tasks 1 and
2.
However, task 3 can start as soon as task 2 is halfway
completed. To make this happen, enter a 50 percent lead time between
tasks 2 and 3.
You can enter lead and lag time as units of time, such as two
days, or as a percentage of the duration of the predecessor task, such
as 50 percent. Lag time is entered in positive units and lead time in
negative units (for example, –2d or
–50%). You can apply lead or lag time to any type
of task relationship: finish-to-start, start-to-start, and so
on.
Places in which you can enter lead or lag time include the Task
Information dialog box (Task tab), the Predecessors column in the
Entry table, and the Task Dependency dialog box (viewable by
double-clicking a link line between Gantt bars).
Lucerne Publishing is about to begin editorial and
design work on a new children’s book. At this stage, you have an
initial project plan with task names, durations, and relationships,
and resource assignments.
In this exercise, you enter lead and lag time and change task
relationships between predecessor and successor tasks.
Set Up
Start Project 2010 if it’s not already running.
-
On the File tab, click
Save As.
The Save As dialog box appears. -
In the File name box,
type Advanced Tasks A, and then
click Save. -
On the Task tab, in the
Tasks group, click Inspect.
The Task Inspector pane appears. This pane succinctly
reveals the scheduling factors that affect the selected task, such
as predecessor task relationships, resource calendars, and/or task
calendars. You can click any item in the Task Inspector that
appears in blue to get more details. For example, you can click
the assigned resource’s name under Calendar to see the resource
calendar. -
Select the name of task 31, Print and
ship.
In the Task Inspector pane, you can view the scheduling
factors affecting this task.
For task 31, you can see that its predecessor is task 30,
Generate proofs. You can see in the pane that
the two tasks have a finish-to-start relationship with zero lag
time. Next, you’ll adjust the lag value on the task relationship
to account for the transit time of the proofs to the printer.
Because you cannot edit this value directly in the pane, you’ll
display the Task Information dialog box. First, though, you’ll
display this task’s Gantt bar so you can more easily observe the
effect of adjusting the lag. -
On the Task tab,
in the Editing group, click
Scroll to Task.
Next, you’ll adjust the lag value between this task and its
predecessor. -
On the Task tab, in the
Properties group, click
Information.
The Task Information dialog box appears. It contains details
about the currently selected task, 31. -
Click the Predecessors
tab. -
In the Lag field for
predecessor task 30, type 3d,
and then click OK to close the
Task Information dialog
box.
Task 31 is now scheduled to start three working days after
the end of task 30.
Next, you will adjust the lag time between two other
tasks. -
Click the name of task 10, Copyedit
incorp.
You’d like to overlap this task with its predecessor; the
Copyedit incorp task can start before the
author review of copyedit is completed. -
On the Task tab, in the
Properties group, click
Information, and then click the
Predecessors tab. -
In the Lag field
for predecessor task 9, type –25%, and then click OK.
Entering lag time as a negative value produces lead
time.
To see the adjustment you made more directly, you’ll scroll
to the task’s Gantt bar again. -
On the Task tab, in the
Editing group, click Scroll to Task.
Task 10 is now scheduled to start at the 25 percent
remaining point of the duration of task 9. Should the duration of
task 9 change, Project will reschedule the start of task 10 so
that it maintains a 25 percent lead time.
To conclude this exercise, you will change the task
relationship between two tasks. -
Double-click the name of task 14, Interior
illustration design.
The Task Information dialog box appears. The Predecessors
tab should be visible. Note also that the Task Inspector pane in
the background updates to display the scheduling details for task
14, the currently selected task. -
On the Predecessors tab,
click in the Type column for
predecessor task 13. Select Start-to-Start
(SS), and click OK.
Project changes the task relationship between tasks 13 and
14 to start-to-start.
Assigning tasks start-to-start relationships and
entering lead times where appropriate are both excellent
techniques to fine-tune task relationships so that you get the
results you want. However, Project cannot automatically make such
schedule adjustments for you. As project manager, you must analyze
the sequences and relationships of your tasks and make those
adjustments where necessary.
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