IT Project Scheduling Techniques

1
Project Scheduling Techniques

• Extra Lecture

2003, 2004 Dr. Ernest Cachia
2
Project Scheduling Techniques

• CPM
• WBS
• Gantt Chart
• PERT
• Calendar Method
• Etc.etc.

3
The Problem

• Scheduling requires strict planning and a fair
  amount of prognosis
• There are many factors that determine a schedule
  (explore)
• Getting all the aspects of a schedule rightly
  concerted is a very difficult task even for
  relatively small projects
• Scheduling is of paramount importance in project
  management

Therein lies the problem!
4
A Solution

• Techniques and supporting tools

5
Activity Network Diagrams

• Available in two flavours
• Activity-On-Arrow (AOA)
• Activity-On-Node (AON)
• Diagram type names
• PERT (Program Evaluation Review Technique)
• CPM (Critical Path Method)
• PN (Precedence Network)
• AOA PERT and CPM
• AON Precedence Networks

Not part of the NCC BCIS syllabus
Practically the same
A more modern variation of PERT and CPM
6
AOA Diagrams

• Diagram components (symbols)
• Nodes (drawn as circles)
• Links (drawn as directed arcs)
• Symbol meanings
• Nodes Start/Stop events (points)
• Links Activities

7
AOA Diagrams Construction Rules

• Must contain only one start and one end node
• A link has duration (optionally shown)
• A node has no duration (simply start/stop point)
• Time flows from left to right
• Nodes are numbered sequentially
• Loops are not allowed (by concept)
• Dangles are not allowed (except in the case of
  the one and only end node)

8
AOA Diagram Example (1/2)
E
A
C
F
H
1
2
3
5
6
D
G
B
4
Explanation The above project (or part of)
consists of eight activities (AH). The
duration of each activity is not indicated. The
project starts at node one and ends at node six.
The derived duration of activity A is the time
difference between node two and node one the
derived duration of activity B is the time
difference between node four and node 1 and so
on.
9
AOA Diagram Example (2/2)
Read sources
Type personal notes
1
4
3
. . .
. . .
Start word processor
Write some rev. questions
2
5
Explanation There are four activities in all. A
student reads from various sources and starts a
word-processor to then type in some personal
notes and furthermore, manually writes some
questions on paper to remember to ask the
lecturer. IN PRACTICE reading and writing
questions can proceed separately from starting
the word processor to type in some personal
notes. THEREFORE
10
Separating Activity Paths (from example on
previous slide)
Read sources
Type personal notes
3
1
4
. . .
. . .
Start word processor
Write some rev. questions
2
5
3a
Dummy link
Please note, that a dummy link has zero duration
time and uses absolutely no resources.
11
Lagged Parallel Activities

• To show the delayed start/finish of parallel
  activity sequences.

Get client feedback on first prototype
1
3
3 days
1 day
. . .
. . .
Develop second prototype
2
5
12
Labelling Activities (PERT Style)
One way
ID
Earliest date
Latest date
Slack
A simpler way
Earliest date
Latest date
13
Scheduling Analysis (using PERT)
Project schedule specification table

• Example
• (taken from Hughes)
• Initial activity network

Activity Duration (weeks) Precedents
A H/W selection 6
B S/W design 4
C Install H/W 3 A
D Code/Test S/W 4 B
E Data input 3 B
F User manuals 10
G User training 3 E,F
H Install/Test sys. 2 C,D
C
A
B
D
H
E
G
F
14
Analysis The Forward Pass

• Rule The earliest date for an event is the
  earliest finish date for all activities ending at
  that event. Where common ending activities are
  present, the latest of the earliest finish dates
  is taken.
• Start date for A, B, F 0.
• If duration of A 6 weeks (see project schedule
  specification table), then earliest date for
  event 2 is 6 weeks.
• If duration of B 4, then earliest date for
  event 3 is 4 weeks.
• And so on, simply adding on the weeks from one
  event to the next on every path through the
  network
• This will produce the diagram on the next slide

15
Resulting from the Forward Pass
This is the resulting diagram from a forward
pass
C3
A6
B4
D4
H2
E3
G3
F10
16
The Backward Pass

• Rule The latest date for an event is the latest
  start date for all activities commencing from
  that event. Where common commencement from an
  even is present, the earliest of the latest start
  dates is taken.
• Latest finish date for H, G their earliest
  finish date 13.
• If duration of H 2 weeks, then latest date for
  event 4 is latest date for event 6 duration of
  H (i.e. 13-2) 11. While the latest date for
  event 5 is latest for 6 duration of G (i.e.
  13-3) 10.
• The latest for event 3 is the latest of (11-4)
  and (10-3), both giving the value 7.
• And so on, simply subtracting the duration of an
  activity from the latest date of the event it
  terminates at, for every path through the network
  (hence backward pass)

17
Resulting from the Backward Pass
This is the resulting diagram from a backward
pass
C3
A6
B4
D4
H2
E3
G3
F10
18
Calculating Slack (aka Float)

• Rule Slack is the difference between the
  earliest and the latest start/finish dates of an
  event.
• This is the resulting diagram with slack
  included

C3
A6
B4
D4
H2
E3
G3
F10
19
The Critical Path

• This is the longest time to project termination.
  The path through the PERT chart (activity
  network) that has no slack. Therefore

C3
A6
B4
D4
H2
E3
G3
F10
20
AON Diagrams

• Diagram components (symbols)
• Nodes (drawn as circles or squares)
• Links (drawn as directed arcs)
• Symbol meanings
• Nodes Activities with specific durations
• Links Precedence (sequencing)
• These diagrams are not included in your (BCIS)
  syllabus. Feel free to research them individually
  for better background.

21
Project Planning Diagrams

• You should have already discussed this type of
  chart in earlier courses, so I will be very
  brief.
• Bar charts (aka Gantt charts) can be put to
  multiple uses. However in s/w development they
  are mainly used for
• Staff allocation
• Who does what
• Activity schedule
• When activities begin and end (activity extent)

22
Gantt Chart Example
Based on this PERT chart
Activity
A
B
Critical path
C
D
E
F
G
H
Time (weeks)
1
0
3
5
4
7
6
8
10
9
12
11
13
2
23
Exercise

• Explore scheduling tools