Constructing a network diagram

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1. BUSINESS DECISION BUSINESS DECISION
ANALYSISANALYSIS
Constructing a Network Diagram
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this lecture as a Slide Show

2. Are there any
pre-requisites
for this topic?
NO.
You may have
come across
terms like
“critical path”
but no
knowledge is
pre-supposed.

3. Project management is also referred to as:
network analysis
critical path analysis
PERT - program evaluation
& review technique

4. OK, so what’s
a project?
Well any
managerial
activity can be
represented as
a project.
For example:
• developing a new product or service
• marketing a new product or service
• breaking into a new market
• building a new plant
• installing a new computer system
• planning a training programme
• re-locating head office.

5. What do your
example
projects have
in common?
Each can be
decomposed into its
constituent parts,
called ACTIVITIES.
We can then define a
project as a collection
of related activities.
Three things are important:
• each activity takes time
• each activity uses up resources
• activities are structured.

6. What gives
activities
structure?
Precedence:
some activities have to be
completed before others
can be started.
But that’s too vague. A roof cannot be erected
unless the foundations have been dug. Obviously
true! So digging foundations must precede
erecting the roof! But what about the walls?
So we refer to the immediately preceding activities.

7. The first step for any project is to:
• list the constituent activities
•arrange them into a Precedence Table.
Activity Description Preceding Time
Activity(weeks)
A Survey site - 6
B
Develop initial
proposal
- 8
C
Obtain approval of
governors
A,B 12
D Choose architect C 4
E Work out budget C 6
F Finalise design D,E 15
G Agree financing E 12
H Hire contractor F,G 8
The project is to
build an extension
to the Recreation
Centre. The table
lists the activities
and their
immediate
predecessors – up to
the point of starting
construction.

8. And here’s another project …………. “purchase of a new car”.
Activity Description
Preceding
Activity
Duration
(days)
A Decide feasibility of purchase - 3
B Find buyer for existing car A 14
C Decide on possible models A 1
D Investigate models decided upon C 3
E Discuss with knowledgeable friendsC 1
F Get information from dealers C 2
G Put all information together D,E,F 1
H Narrow down to three options G 1
I Test drive all three H 3
J Get warranty & finance informationH 2
K Choose one car 1,J 2
L Compare dealers & choose one K 2
M Decide upon colour etc L 4
N Test drive chosen model L 1
O Buy new car B,M,N 3

9. Is activity B a pre-condition for starting activity I?
NO
Activity Description
Preceding
Activity
Duration
(days)
A Decide feasibility of purchase - 3
B Find buyer for existing car A 14
C Decide on possible models A 1
D Investigate models decided upon C 3
E Discuss with knowledgeable friendsC 1
F Get information from dealers C 2
G Put all information together D,E,F 1
H Narrow down to three options G 1
I Test drive all three H 3
J Get warranty & finance informationH 2
K Choose one car 1,J 2
L Compare dealers & choose one K 2
M Decide upon colour etc L 4
N Test drive chosen model L 1
O Buy new car B,M,N 3

10. Is activity A a pre-condition for starting activity K?
YES
Activity Description
Preceding
Activity
Duration
(days)
A Decide feasibility of purchase - 3
B Find buyer for existing car A 14
C Decide on possible models A 1
D Investigate models decided upon C 3
E Discuss with knowledgeable friendsC 1
F Get information from dealers C 2
G Put all information together D,E,F 1
H Narrow down to three options G 1
I Test drive all three H 3
J Get warranty & finance informationH 2
K Choose one car 1,J 2
L Compare dealers & choose one K 2
M Decide upon colour etc L 4
N Test drive chosen model L 1
O Buy new car B,M,N 3

11. Can activities E and F take place at the same time?
YES
Activity Description
Preceding
Activity
Duration
(days)
A Decide feasibility of purchase - 3
B Find buyer for existing car A 14
C Decide on possible models A 1
D Investigate models decided upon C 3
E Discuss with knowledgeable friendsC 1
F Get information from dealers C 2
G Put all information together D,E,F 1
H Narrow down to three options G 1
I Test drive all three H 3
J Get warranty & finance informationH 2
K Choose one car 1,J 2
L Compare dealers & choose one K 2
M Decide upon colour etc L 4
N Test drive chosen model L 1
O Buy new car B,M,N 3

12. Precedence tables aren’t
that easy to use. Is there
some other way of
representing a project?
Y
E
S
A useful visual representation
of a project is obtained by
drawing a network diagram.

13. This is how we represent an activity.

activityevent of starting
an activity
event of ending
an activity
get out of bed

So somewhere in
the project “Get
to University
Monday
Morning” will be:

14. Err .. but we’ll need to
link activities together,
won’t we.
That’s correct.
Sometimes we might want to show:
Activity
Preceding
Activity
A -
B A
C B
A B C

15. Err .. but we’ll need to
link activities together,
won’t we.
That’s correct.
Sometimes we might want to show:
Activity
Preceding
Activity
M K,L

M
K
L

16. Activity
Preceding
Activity
B A
C A
Err .. but we’ll need to
link activities together,
won’t we.
That’s correct.
Sometimes we might want to show:

A
B
C

17. Are there any rules to
follow when drawing
network diagrams?YES
1.Must be drawn from left to right.
2. Must have a single starting point.
3. Also a single ending point.
4. One arrow (only) per activity.
5. Must correctly reflect the precedence table.

18. There is one complication that we need to allow for.
OK, tell me
the worst!!
Sometimes we have to
use Dummy activities.
We use a dashed
arrow to record these.
A dummy activity may be needed:
•to prevent 2 or more activities sharing the same starting and
ending events.
•to maintain network logic – i.e. to ensure that the network
abides by the precedence table.

19. DETAILS
OK. Let’s
have a go
at drawing
a network.
We’ll draw the one
for the extension to
the recreation centre.

20. DETAILS
Where
do I
start?
Well, a network must have
a single starting point – a
circle or node.
Once the project has started which
activities can be begun?
A Survey site
B Develop initial proposal

21. DETAILS
A
B
So we draw arrows for
activities A & B running
from the starting event. Make sure that you label
the activities as you include
them in the network.
What
comes
next?
Activity Preceding Activity
C A,B

22. DETAILS
Well is this correct. Does it
abide by the rules for
drawing network diagrams?
That’s no
problem.
Just do
this.
Activity Preceding Activity
C A,B
A
B
C
RULES
NO
Two or more
activities may not
share the same
starting and ending
event.

23. DETAILS
Use a dummy activity. Here’s one way in which it can be done. It
prevents A & B from sharing the same starting and ending event.
So how do
I remedy
this
error?
RULES
A
B
C

24. DETAILSRULES
A
B
C
Activities D &
E can start
when C is
finished.
E
D
So we’ll add these to
the network.

25. DETAILSRULES
The table says
that F can start
when D & E are
completed.
So can we do this?
A
B
C
E
D
F

26. DETAILSRULES
No. We’ve
broken the
rules again.
A
B
C
E
D
F
So another
dummy activity
is needed.

27. DETAILSRULES
This
will
work.
A
B
C
E
D
F

28. RULES
Now we
can add
activity G.
A
B
C
E
D
F
DETAILS
G
G can be started
once E is
completed.

29. RULES
That
leaves
activity H.
A
B
C
E
D
F
DETAILS
G
The start of H
requires the
completion of F
and G.

30. RULES DETAILS
A
B
C
E
D
F
G
H
So we bring the arrows for F & G into
the starting event for activity H.
And this is
the finished
network.

31. RULES DETAILS
A
B
C
E
D
F
G
H
Always check the
network against the
precedence table
before continuing.

32. RULES DETAILS
Right, now we’ll draw the
network for the project of
buying a new car.
For this project
there’s only one
starting activity,
namely A

33. RULES DETAILS
A
Activities B & C
can be started
once A is
completed.
B
C

34. RULES DETAILS
A
And D, E & F
can be started
when C is
completed.
B
C
D
E
F

35. RULES DETAILS
Activity G
requires
completion of
D, E & F.
So two dummy activities
are needed to prevent D,
E & F having the same
starting and ending
events.
A B
C
D
E
F
G

36. RULES DETAILS
Activity H
can now be
added to the
network.
A B
C
D
E
F
G
H

37. RULES DETAILS
I & J
can now
start.
A B
C
D
E
F
G
H
I
J

38. RULES DETAILS
Since the start of K
needs completion
of I & J we need
another dummy
activity.
A B
C
D
E
F
G
H
I
J
K

39. RULES DETAILS
Now we
add
activity L
A B
C
D
E
F
G
H
I
J
K
L

40. RULES DETAILS
A B
C
D
E
F
G
H
I
J
K
L
M
N
Activities M &
N can now be
started.

41. RULES DETAILS
A B
C
D
E
F
G
H
I
J
K
L
M
N
That
leaves
activity O.
It can be
started when
activities B,
M & N are
completed.

42. RULES DETAILS
A B
C
D
E
F
G
H
I
J
K
L
M
N
That
leaves
activity O.
A dummy
activity will
be needed to
separate
activities M
and N.

43. RULES DETAILS
A
C
D
E
F
G
H
I
J
K
L
M
N
The
network is
now
completed.
OB
But
remember to
check it
against the
precedence
table.

44. What should I now
be able to do?
Given the precedence
table for a project, you
should be able to draw
its network diagram.

45. That’s the end of this
lecture. You should now
explore the problems, on
drawing networks, that
are available within
Blackboard.