Thông tư Quản lí chapter5

Chapter 5 - Getting Tasks Done in the Right Order,
at the Right Time
Introduction
The Power of Linking
Determine the Best Sequence for Your Tasks
Which Task Link Should You Use?
Create a Task Link
Change or Remove a Task Link
Overlap or Delay Tasks

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Introduction
When you’re creating a project plan, it’s easy to accomplish the first step: simply enter a list of tasks in the order
you expect them to be done. But if you don’t go on to the next step, Microsoft Project does not actually schedule
one task after the other, as you might expect. In fact, if you stop here, all your tasks will have the same start
date.

The Power of Linking
To enable Microsoft Project to start each task at its proper time, you need to link the tasks to each other, based
on their start and finish dependencies.

For example, a clockwork exhibit crew will hang the clocks only after painting the walls. The task of hanging
clocks is linked to the task of painting walls, because the start date for hanging clocks can occur only after the
finish date for painting walls.

Once these tasks are linked, Microsoft Project will always schedule the start date for hanging clocks relative to
the finish date for painting walls, no matter when these tasks occur. Thus, they avoid being tied (perhaps
unrealistically) to a specific date. For example, if the original finish date for painting the walls is February 3, then

the start date for hanging the clocks is February 3 or later. If painting the walls gets delayed 5 days later than
originally planned, then Microsoft Project automatically gives hanging the clocks a new start date of February 8
or later.

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The power of linking tasks is twofold:
• You can let Microsoft Project calculate all dates for you: task start and finish dates, as well as the project
finish date. You won’t worry about clocks being hung before walls are painted, because linking maintains
the proper order of tasks as scheduling changes occur.
• You can see instantly how changes in the start, finish, and duration of a task affect related tasks and the
schedule as a whole.
When necessary, you can exercise even finer control by specifying overlaps and time gaps between tasks. The
amount of overlap between two tasks is called lead time. The time gap, or delay, between tasks is called lag
time. With Microsoft Project, you can add lead or lag time between any two linked tasks.

Determine the Best Sequence for Your Tasks
Before you link tasks, you need to determine the sequence of tasks. In particular, you need to decide how the
start or finish of one task depends on the start or finish of another task. To figure out the task sequence, answer
these questions for each task:
• Does the start or finish date of this task depend on the start or finish date of another task? Not every
task depends on another task. For example, the gallery windows can be cleaned any time before the
clock exhibit opens to the public(without waiting for any other task to begin or end. If a task doesn’t
depend on another task, don’t link it. Just specify a start or finish date.
For more information about specifying an exact start or finish date for a task, see Chapter 6, "Tying Tasks
to Specific Dates."
• Which tasks does this task depend on? One of the most common dependencies between tasks is that
one task must finish before another task can begin. For example, the task of painting the gallery walls

depends on when the walls will be built.
• Which tasks depend on this task? Which other tasks must wait for this task to be started or finished
before they can begin? The start time for hanging the clocks depends on when the walls are finished
being painted.
A task that must start or finish before another task can begin is called a predecessor task. Painting the walls is
the predecessor task for hanging the clocks. Building the walls would not be a predecessor task for hanging the
clocks, but would be a predecessor task for painting the walls. A task that depends on the start or finish of a
preceding task is called a successor task. Hanging the clocks is the successor task to painting the walls.

Which Task Link Should You Use?

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Your project tasks can depend on each other in a variety of ways. You’ll probably find that in most instances, one
task must finish before another task begins. But this is only one type of task dependency. In another type of task
dependency, two tasks can start together. For example, if the museum crew already knows where each clock is
going to hang on the walls, they can begin attaching descriptive labels below each clock’s space while they are
hanging clocks.
After you decide task sequence — you’ve identified the predecessor and successor tasks for each task — you
need to decide which type of link to use to connect one task to another. Microsoft Project provides four different
types of task links, which are described in the following table. By default, Microsoft Project applies a finish-tostart (FS) link to tasks, but you can choose the type of link that most accurately reflects the dependency
between the tasks.

To indicate

Use this task link

A task starts after its predecessor finishes

Finish-to-start (FS)

A task starts when its predecessor starts

Start-to-start (SS)

A task finishes when its predecessor finishes

Finish-to-finish (FF)

A task finishes after its predecessor starts

Start-to-finish (SF)

Finish-to-start (FS) is the task
link most frequently used. Startto-finish (SF) is seldom used.

The types of links you choose will affect your project length. Applying FS links between all tasks would probably
drag out your project longer than necessary, because most projects involve some tasks that can overlap. One
way to shorten your schedule is to look for where you can replace FS links with either SS or FF links.

Create a Task Link
Once you’ve decided which type of link best reflects the dependency between two tasks, you’re ready to link
those tasks.
The most commonly used task link in a typical project schedule is FS. Because you’ll be applying this link often,
Microsoft Project enables you to link tasks in an FS dependency quickly. However, FS links don’t always mirror
the dependencies that exist between tasks.
To link tasks in an FS dependency
1.

2.

On the View Bar, click Gantt Chart
.
In the Task Name field, select two or more tasks you want to link.

3.

Click Link Tasks
.
A link line appears on the Gantt Chart, connecting the two tasks.

You can also create an FS link
between summary tasks: the
start of one group of tasks
depends on the end of another.

Select nonadjacent tasks by
holding down CTRL while you
select the task.
Avoid Entering Start and Finish Dates - Link Your Tasks
When you enter start and finish dates for tasks, you force those tasks to begin and end no earlier than the dates
you have entered. Changes elsewhere in the schedule might not affect the start and finish dates of these tasks.
As a result, your schedule can’t accurately reflect the real-life fluidity of your project and its tasks.
Linking tasks saves you time because Microsoft Project will calculate start and finish dates for tasks, as well as
the project finish date, so you don’t have to. Task linking also lets you see exactly how a slip in the project
schedule changes the start and finish dates of individual tasks and the project’s finish date. If one element of the
schedule shifts, the overall task time frame remains flexible. Microsoft Project automatically moves tasks forward
or backward in time in a logical way, while maintaining the links between tasks.
Your best strategy is to enter just the duration for each task and leave start and finish date calculations to

Microsoft Project. (Specify a start or finish date only for a task that doesn’t depend on another task and therefore
shouldn’t be linked.)

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Change or Remove a Task Link
If the link between tasks doesn’t accurately reflect the dependency between those tasks, you can easily change
the type of link that connects them. If you later decide that you don’t want a link between particular tasks, you
can remove that link.
To change a task link
1.
2.
3.

On the View Bar, click Gantt Chart
.
Double-click the link line of the tasks you want to change.
In the Type box, click the task link you want.

To remove a task link
1.
2.

On the View Bar, click Gantt Chart
.
In the Task Name field, select the tasks you want to unlink.

3.

Click Unlink Tasks
.
The task will be rescheduled based on any other dependencies.

Overlap or Delay Tasks
Sometimes task links alone might not show accurately when tasks will actually start. For example, in the
clockwork project, painting the walls precedes hanging the clocks, and those tasks have a finish-to-start link. The
schedule shows that the clocks will be hung immediately after the painter finishes painting, but that’s before the
paint has had a chance to dry.
You can fine-tune task links — and make sure you don’t gum up the clockwork — by using lag time and lead
time. By using lag time, you can specify a waiting period, or delay, between the finish of a predecessor task and
the start of a successor task. To avoid making the museum crew crowbar the clocks out of hardened paint, the
exhibit planner should probably add lag time between painting the walls and hanging the clocks.

With lead time, you can overlap two tasks so that a successor task starts before the predecessor task finishes.
The exhibit planner could assign one person to begin hanging labels soon after the first clock is hung.

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After you enter tasks and assign dependencies to them, analyze your schedule and look for instances where you
can apply lead or lag time. By using lead and lag time, you can make your schedule more accurate, and you may
be able to shorten it as well.
You can express lead or lag time as units of time or as a percentage of the predecessor task’s duration. For
example, the paint on the walls must dry for 1 day before clocks can be hung, so the exhibit manager can
specify a 1-day lag between painting the walls and hanging the clocks. Or, if the electrician can begin wiring
display cases after half the cases are installed, the "Install and position case lights" task can start when the
"Install wood and glass cases" task is 50 percent complete, regardless of the duration of the predecessor task.

To add lead or lag time
1.
2.
3.
4.

To add lead or lag time to a
successor task quickly, doubleOn the View Bar, click Gantt Chart
.
In the Task Name field, select the successor task you want, and then click the link line on the Gantt
Chart and type the lead or lag
click Task Information
.
time in the Lag box of the Task
Select the Predecessors tab.
Dependency dialog box.
In the Lag field, type the lead time or lag time you want, as a
duration or as a percentage of the predecessor task’s duration.
Type lead time as a negative number or as a negative completion percentage. Type lag time as a positive
number or as a positive completion percentage.
Use minute, hour, day, or week for the lead or lag time units. To specify elapsed duration, precede the
time unit with the letter "e" (for example, edays for elapsed days). Elapsed days include weekends and
other nonworking days.

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