SE 477
Software and Systems Project Management
Dennis Mumaugh, Instructor
dmumaugh@cdm.depaul.edu
Office: CDM, Room 429
Office Hours: Monday, 4:00 – 5:30
April 28, 2014
SE 477: Lecture 5
1 of 133
Administrivia
 Comments and feedback
 Midterm Examination this coming week [April 30 – May 5]





Will use Desire2Learn
See important information about Taking Quizzes On-line
On-line tutorial:
http://www.itd.depaul.edu/website/documentation/d2l/mp
4based/quizzes/quizzes.html
On-line guide:
http://www.itd.depaul.edu/website/documentation/d2l/Qui
zzes.pdf
Midterm study guide [note solution to some problems on
last page].
April 28, 2014
SE 477: Lecture 5
2 of 133
Team Project
Start working on
 Project Time Management
 Perform activity definition, sequencing, and duration
estimation;
 Perform activity resource estimation;
 Develop schedule based on estimates
April 28, 2014
SE 477: Lecture 5
3 of 133
Assignment 3
 Effort conversion factors




8 working hours per day, 5 days per week
person-months = person-days times 19
person-months = person-hours times 152
Holidays – include them in the scheduling
 Memorial Day, Independence Day, Labor Day
 Thanksgiving and the day after, Christmas Eve,
Christmas, New Year’s
Start each major phase on a new day.
Unit Testing vs. Code Inspection [order can be reversed
depending on team’s process]
Preparation and reviews; choice of participants
April 28, 2014
SE 477: Lecture 5
4 of 133
SE 477 – Class 5
Topics:
 Size and complexity Estimation
 Activity Resource Estimating
 Activity Duration Estimating
 Project Planning – Schedule
Development
 Scheduling
 Schedule network analysis
 Calculating float
 Schedule compression
 Resource leveling
April 28, 2014
 Schedule development output
 Mythical Man Month
 Project Planning – Schedule
Development Workflow and
Example
 Reading:
 PMP Study Guide: Chapters
5 and 7
 Appendix
 PERT Estimation
 Critical Path Method (CPM)
 Forward and backward pass
analysis
SE 477: Lecture 5
5 of 133
Thought for the day
“The single most important task of a project: setting
realistic expectations. Unrealistic expectations
based on inaccurate estimates are the single largest
cause of software failure.”
– Futrell,
April 28, 2014
Shafer, Shafer, “Quality Software Project Management”
SE 477: Lecture 5
6 of 133
Last time
 Charter
 Project Planning


WBS details
Activity:
» Activity Definition
» Activity Sequencing
April 28, 2014
SE 477: Lecture 5
7 of 133
Project Planning
Project Time Management I
Size and Complexity Estimation
Activity Resource Estimating
Activity Duration Estimating
April 28, 2014
SE 477: Lecture 5
8 of 133
Estimating Project Size And
Complexity
April 28, 2014
SE 477: Lecture 5
9 of 133
Estimations


Very difficult to do, but needed often
Created, used or refined during
 Strategic planning
 Feasibility study and/or SOW
 Proposals
 Vendor and sub-contractor evaluation
 Project planning (iteratively)
 Basic process
1) Estimate the size of the product
2) Estimate the effort (person-months)
3) Estimate the schedule
 NOTE: Not all of these steps are always explicitly
performed
April 28, 2014
SE 477: Lecture 5
10 of 133
Estimations
 Remember, an “exact estimate” is an oxymoron
 Estimate how long will it take you to get home from
class tonight
 On what basis did you do that?
 Experience right?
 Likely as an “average” probability
 For most software projects there is no such
‘average’
 Most software estimations are off by 25-100%
April 28, 2014
SE 477: Lecture 5
11 of 133
Estimation
 Target vs. Committed Dates
Target: Proposed by business or marketing
» Do not commit to this too soon!
 Committed: Team agrees to this
» After you’ve developed a schedule
 Size:
 Small projects (10-99 FPs), variance of 7% from postrequirements estimates
 Medium (100-999 FPs), 22% variance
 Large (1000-9999 FPs) 38% variance
 Very large (> 10K FPs) 51% variance

April 28, 2014
SE 477: Lecture 5
12 of 133
Estimation Methodologies






Top-down
Bottom-up
Analogy
Expert Judgment
Priced to Win
Parametric or Algorithmic Method
 Using formulas and equations
Let’s look at each of these …
April 28, 2014
SE 477: Lecture 5
13 of 133
Top-down Estimation
 Based on overall characteristics of project
Some of the others can be “types” of top-down (Analogy,
Expert Judgment, and Algorithmic methods)
 Advantages
 Easy to calculate
 Effective early on (like initial cost estimates)
 Disadvantages
 Some models are questionable or may not fit
 Less accurate because it doesn’t look at details

April 28, 2014
SE 477: Lecture 5
14 of 133
Bottom-up Estimation
 Create WBS
 Add from the bottom-up
 Advantages
Works well if activities well understood
 Disadvantages
 Specific activities not always known
 More time consuming

April 28, 2014
SE 477: Lecture 5
15 of 133
Expert Judgment
 Use somebody who has recent experience on a similar




project
You get a “guesstimate”
Accuracy depends on their ‘real’ expertise
Comparable application(s) must be accurately chosen
 Systematic
Can use a weighted-average of opinions
April 28, 2014
SE 477: Lecture 5
16 of 133
Estimation by Analogy
 Use past project
Must be sufficiently similar (technology, type,
organization)
 Find comparable attributes (ex: # of inputs/outputs)
 Can create a function
 Advantages
 Based on actual historical data
 Disadvantages
 Difficulty ‘matching’ project types
 Prior data may have been mis-measured
 How to measure differences – no two exactly same

April 28, 2014
SE 477: Lecture 5
17 of 133
Priced to Win





Just follow other estimates
Save on doing full estimate
Needs information on other estimates (or prices)
Purchaser must closely watch trade-offs
Priced to lose?
April 28, 2014
SE 477: Lecture 5
18 of 133
Algorithmic Measures
 Lines of Code (LOC)
 Function points
Feature points or object points
 Other possible
 Number of bubbles on a DFD
 Number of ERD entities
 Number of processes on a structure chart
 LOC and function points most common (of the algorithmic
approaches)
 Majority of projects use none of the above

April 28, 2014
SE 477: Lecture 5
19 of 133
Code-based Estimates
 LOC Advantages
Commonly understood metric
 Permits specific comparison
 Actually it is easily measured
 LOC Disadvantages
 Difficult to estimate early in cycle
 Counts vary by language
 Many costs not considered (ex: requirements)
 Programmers may be rewarded based on this
» Can use: # defects/# LOC
 Code generators produce excess code

April 28, 2014
SE 477: Lecture 5
20 of 133
LOC Estimate Issues





How do you know how many in advance?
What about different languages?
What about programmer style?
Stat: avg. programmer productivity: 3,000 LOC/yr
Most algorithmic approaches are more effective after
requirements (or have to be after)
April 28, 2014
SE 477: Lecture 5
21 of 133
Function Points
 Software size should be measured by number & complexity
of functions it performs
 More methodical than LOC counts
 House analogy
 House’s Square Feet ~= Software LOC
 # Bedrooms & Baths ~= Function points
 Former is size only, latter is size & function
 Four basic steps
April 28, 2014
SE 477: Lecture 5
22 of 133
Function Point Process
1. Count # of business functions per category

Categories: outputs, inputs, db inquiries, files or data structures, and
interfaces
2. Establish Complexity Factor for each and apply



Simple, Average, Complex
Set a weighting multiplier for each (0 –>15)
This results in the “unadjusted function-point total”
3. Compute an “influence multiplier” and apply

It ranges from 0.65 to 1.35; is based on 14 factors
4. Results in “function point total”

This can be used in comparative estimates
[This is covered in detail in SE 468. See the SE 468 reading
list for more information].
April 28, 2014
SE 477: Lecture 5
23 of 133
Wideband Delphi






Group consensus approach
Rand corp. used orig. Delphi approach to predict future technologies
Present experts with a problem and response form
Conduct group discussion, collect anonymous opinions, then feedback
Conduct another discussion & iterate until consensus
Advantages
 Easy, inexpensive, utilizes expertise of several people
 Does not require historical data
 Disadvantages
 Difficult to repeat
 May fail to reach consensus, reach wrong one, or all may have same
bias
April 28, 2014
SE 477: Lecture 5
24 of 133
Effort Estimation
 Now that you know the “size”, determine the “effort” needed
to build it
 Various models: empirical, mathematical, subjective
 Expressed in units of duration
 person-months (or ‘staff-months’ now)
 Efficiency/productivity of people
 Motivation
 Ability of team
 Application experience
 Range of personnel
April 28, 2014
SE 477: Lecture 5
25 of 133
Duration
 What is the duration?
The duration of a project is the elapsed time in business
working days, not including weekends, holidays, or other
nonworking days.
 Duration is different from work effort.
 Work effort is labor required to complete an activity. That
labor can be consecutive or nonconsecutive hours.
 Duration is work effort divided by number of people doing
the work:
 Or, work effort is the duration multiplied by the number of
people doing the work
 E.g. five people reviewing a document; the duration may
be 10 hours but the work effort is 50 staff-hours
April 28, 2014
SE 477: Lecture 5
26 of 133
Duration
 When we talk about estimates and duration, there are two
types of time that are not the same:
 Labor Time
 Clock time
 For example, if we estimate that a task would require 40
hours of labor to complete, then in a normal business setting
we need at least 50 business hours, Why?
April 28, 2014
SE 477: Lecture 5
27 of 133
Duration
 Your average business day may include few of the following
activities or perhaps a number of each:
 Meetings – non-project related
 Phone calls
 E-mails
 Coffee breaks
 Lunches
 Friendly chat with your teammates
 The duration of the activity is the clock time or “Elapsed”
time” that we want to estimate.
 Productivity is usually 50-75% of a business day
April 28, 2014
SE 477: Lecture 5
28 of 133
Variation in Activity Duration
 Since we cannot know what factors will be effective when
work is underway on an activity, we cannot know exactly
how long it will take.
 One of the goals in estimating the activity duration is to
define the activity to a level of granularity that estimates
have a narrow variance; the estimate is as good as you can
get it at the planning stages of the project.
 There are several causes of variation in the actual activity
duration:




Varying skill levels – see Journal Exercise
Unexpected events
Efficiency of work time
Mistakes and Misunderstandings
 Let’s look at these in a bit more detail …
April 28, 2014
SE 477: Lecture 5
29 of 133
Causes of Variation
Causes of Variation in the Actual Activity Duration
 Varying skill levels. Our estimate of the activity duration is based on
average skilled engineer. We may get a higher or lower skilled engineer
assigned to the activity, causing the actual duration to vary from the
planned duration.
 Unexpected events. Random acts of nature, vendor delays, traffic
jams, power failures, etc.
 Efficiency of work time. Every time a worker is interrupted it takes
more time to get up to the level of productivity prior to the time of the
interruption. These interruptions may have little or substantial impact on
the worker’s productivity
 Mistakes and Misunderstandings. In organizations that have a
documented process, rework may have its toll on the actual activity
duration.
April 28, 2014
SE 477: Lecture 5
30 of 133
Estimation Issues
 Quality estimations needed early but information is limited
 Precise estimation data available at end but not needed
Or is it? What about the next project?
 Should have determined just how accurate your original
estimate was.
 Best estimates are based on past experience
 Politics of estimation:
 You may anticipate a “cut” by upper management
 For many software projects there is little or no data for
estimation
 Technologies change
 Historical data unavailable
 Wide variance in project experiences/types
 Subjective nature of software estimation

April 28, 2014
SE 477: Lecture 5
31 of 133
Over and Under Estimation
 Over estimation issues
The project will not be funded
» Conservative estimates guaranteeing 100% success
may mean funding probability of zero.
 Parkinson’s Law: Work expands to take the time allowed
 Danger of feature and scope creep
 Be aware of “double-padding”: team member + manager
 Under estimation issues
 Quality issues (short changing key phases like testing)
 Inability to meet deadlines
 Morale and other team motivation issues

April 28, 2014
SE 477: Lecture 5
32 of 133
Estimation Guidelines
 Estimate iteratively!





Process of gradual refinement
Make your best estimates at each planning stage
Refine estimates and adjust plans iteratively
Plans and decisions can be refined in response
Balance: too many revisions vs. too few
April 28, 2014
SE 477: Lecture 5
33 of 133
Know Your Deadlines
 Are they ‘Real Deadlines’?
Tied to an external event
 Have to be met for project to be a success
 Ex: end of financial year, contractual deadline, Y2K
 Or ‘Artificial Deadlines’?
 Set by arbitrary authority
 May have some flexibility (if pushed)

April 28, 2014
SE 477: Lecture 5
34 of 133
Estimation “Presentation”
 How you present the estimation can have huge impact
 Techniques






Plus-or-minus qualifiers [6 months ±1 month]
Ranges [6-8 months]
Risk Quantification
» ± with added information
• +1 month if new tools not working as expected
• -2 weeks for less delay in hiring new developers
Cases [Best / Planned / Current / Worst cases]
Coarse Dates [Q4 13]
Confidence Factors [April 1 – 10% probability, July 1 –
50%, etc.]
April 28, 2014
SE 477: Lecture 5
35 of 133
Other Estimation Factors
 Account for resource experience or skill
Up to a point
 Often needed more on the “low” end, such as for a new
or junior person
 Allow for “non-project” time & common tasks
 Meetings, phone calls, web surfing, sick days
 There are commercial ‘estimation tools’ available
 They typically require configuration based on past data

April 28, 2014
SE 477: Lecture 5
36 of 133
Other Estimation Notes
 Remember: “manage expectations”
 Parkinson’s Law
“Work expands to fill the time available”
 The Student Syndrome
 Procrastination until the last minute (cram) and term
projects

April 28, 2014
SE 477: Lecture 5
37 of 133
Activity Resource Estimating
Resource Management
 Assessing Competencies and Skills
 Resource allocation
Estimating tools
Personal Software Process (PSP)
Activity resource estimating output
April 28, 2014
SE 477: Lecture 5
38 of 133
Introduction
 Resource estimating is concerned with who/what, how
much, and when
 Who/what
 Resource requirements of people or equipment
 Matching the right resources to activities
 May be generic (n Java programmers) or resourcespecific (Richard Parker as senior architect)
 How much. Amount of resource(s) needed for activity
 When. When the resource will be needed for activities
April 28, 2014
SE 477: Lecture 5
39 of 133
Introduction
 Controlling factors in resource estimating



Enterprise environment. May be defined by constraints
and assumptions identified in Project Scope Statement
Organization policy. How the organization allocates and
manages resources from within and from without
» Note: Enterprise environment and organization policy
may be closely-coupled
Resource availability. When the resource will be
available for activities and whether dedicated or part-time
April 28, 2014
SE 477: Lecture 5
40 of 133
Estimating tools
 Expert judgment. One of the most effective tools for
estimating. May be used in conjunction with other tools
 Alternative analysis. Examines different approaches to
applying resources, such as in-house development vs.
contracting vs. COTS
 Published estimating data. May be available in-house in
form of historical project data or may be available from
outside sources (e.g. unclassified U.S. Government-funded
projects)
April 28, 2014
SE 477: Lecture 5
41 of 133
Estimating tools
 Project management software. PM software can provide
automated assistance in defining resources, calendars,
rates, etc.
 Bottom-up estimating
 Use if activity is a natural work package but still complex
 Decompose activity into more manageable (estimable)
pieces
 Adhere to 100% rule: sum of activities should exactly
equal work package (mind the scope!)
 Example: Architectural quality and cost/benefit analysis
(ATAM and CBAM)
April 28, 2014
SE 477: Lecture 5
42 of 133
Sidebar: Personal Software Process (PSP)
 All the estimating tools in the world won’t help if you don’t have good





estimates
Historical data has its limits – sometimes you need to estimate
completely new activities
PSP is a highly-disciplined approach to software engineering (in this
context, any software development)
PSP includes techniques in:
 Time management and tracking through use of a design notebook
and logs
 Product planning, size measurement and estimation
 Basic project scheduling and planning
 Managing defects and product quality
Goal is to have developers who can provide accurate and meaningful
estimation data
See SEI at CMU: http://www.sei.cmu.edu/tsp/tools/bok/
April 28, 2014
SE 477: Lecture 5
43 of 133
Activity Resource Estimating Output
 Activity resource requirements
Identify what and how much of resource(s) are needed
for each activity in a work package
 Activity resource requirements are summed to provide
estimate for entire work package
 Resource calendar
 Documents working and non-working days
 Resource-specific holidays may be identified
 Requested changes
 Activity resource estimating process may generate
requests for changes to activity list
 Processed within the Integrated Change Control process

April 28, 2014
SE 477: Lecture 5
44 of 133
Activity Duration Estimating
Estimating tools
PERT estimation technique
April 28, 2014
SE 477: Lecture 5
45 of 133
Introduction
 Focuses on estimating the number of work periods needed
to complete individual schedule activities
 Estimates originate from person or groups most familiar with
the type of work needed in the activity
 Estimate is progressively elaborated: duration estimates are
improved as project progresses
 Activity duration output
 Quantitative activity duration estimates, including range
of possible values
April 28, 2014
SE 477: Lecture 5
46 of 133
Introduction
 Controlling factors in duration estimating

Historical data. If available, enterprise- or industryspecific historical data can be used as starting point for
estimates

Activity resource requirements. The type and number
of resources applied to an activity must account for
» Resource qualifications
» Quantity-quality productivity trade-offs: putting more
people on a task may reduce productivity

Resource calendars. Must account for full/part time
commitments
April 28, 2014
SE 477: Lecture 5
47 of 133
Sidebar: A useful rule of thumb
 Keep all times in the same units
 Don't mix increments

Example: Schedule everything in hours, then convert to
days and fractions as a last step

Note: Most PM software tools enforce this rule by using a
uniform time unit and increment
April 28, 2014
SE 477: Lecture 5
48 of 133
Estimating tools
 Expert judgment. As in resource estimating, one of the
most effective tools for estimating. May be used in
conjunction with other tools
 Analogous estimating. Estimation based on similar
activities performed in a previous project
 Most useful if both activity and project are more similar
than different
 Document similarities and differences
 Example: Developing the database schema for a project
in the same domain and of similar scope
April 28, 2014
SE 477: Lecture 5
49 of 133
Estimating tools
 Reserve analysis. Contingency or time reserves can be
added to schedule to allow for schedule risks
 Contingency reserves may be used or adjusted as more
precise project information becomes available
 Aka buffer time. Do not confuse with slack time.
 Three-point estimating techniques use a mathematical
combination of three different estimates: Most likely,
Optimistic, and Pessimistic
 There are variations in defining each of these estimates
among different techniques
April 28, 2014
SE 477: Lecture 5
50 of 133
Three Point Estimating
 Used whenever there is a potential variance in an estimate.
Assumes a Gaussian distribution of estimates.
 Duration
 Effort
 Size
 Three-point estimating techniques use a mathematical
combination of three different estimates:
 Get estimates from experts: Most likely, Optimistic, and
Pessimistic
 Compute an average:
(Optimistic + 4(Likely)+ Pessimistic)/6
☛ See Appendix: PERT Estimation Technique for more details
and a worked example.
April 28, 2014
SE 477: Lecture 5
51 of 133
Example: Estimation of LOC
CAD program to represent mechanical parts

Estimated LOC = (Optimistic + 4(Likely)+ Pessimistic)/6
Optimistic
1,500
Most
Likely
2,300
Pessimistic
3,100
Estimated
LOC
2,300
2DGA
3,800
5,200
7,200
5,300
3DGA
4,600
6,900
8,600
6,800
DBM
CGDF
1,600
3,700
3,500
5,000
4,500
6,000
3,350
4,950
1,400
7,200
23,800
2,200
8,300
33,400
2,400
10,000
41,800
2,100
8,400
33,200
Major Software Functions
ID
User interface and control
facilities
Two-dimensional geometric
analysis
Three-dimensional geometric
analysis
Database management
Computer graphics display
features
Peripheral control
Design analysis modules
Estimated lines of code
UICF
April 28, 2014
PC
DAM
SE 477: Lecture 5
52 of 133
Schedule Development
April 28, 2014
SE 477: Lecture 5
53 of 133
Definition
 Schedule development is the culmination of the other
Project Time Management processes we have discussed:
 Activity definition
 Activity sequencing
 Activity resource estimating
 Activity duration estimating
 It is an iterative process to determine planned start and
finish dates for activities
 It is a continuous process throughout project, addressing
approved changes and risks
April 28, 2014
SE 477: Lecture 5
54 of 133
Controlling factors in schedule development
 Project scope statement




Scope statement is the source of assumptions and
constraints on the project
(PMI) “Assumptions are those documented, schedulerelated factors that, for schedule development purposes,
are considered to be true, real, or certain.”
(PMI) “Constraints are factors that will limit the project
management team’s options when performing schedule
network analysis.”
Date constraints (contract dates, market windows,
external deliveries) and milestones (deliverable dates)
are of greatest importance in schedule development
April 28, 2014
SE 477: Lecture 5
55 of 133
Controlling factors in schedule development
 Project management plan



Almost any of the many sub-plans and other elements in
the Project Management Plan may exert an influence on
schedule development
One of the most critical elements for schedule
development in the PM Plan is the risk register and riskassociated plans
We will discuss risk and risk-related planning in an
upcoming lecture
April 28, 2014
SE 477: Lecture 5
56 of 133
Network Analysis
The First Steps
April 28, 2014
SE 477: Lecture 5
57 of 133
Network Analysis
 Network analysis is the technique that generates the
project schedule
 Network analysis may use several different analysis
methods to calculate the early and late start dates for
project activities. These methods may be combined and
include:





April 28, 2014
Gantt Charts
Critical Path Method (CPM)
Critical Chain Method (CCM)
What-if analysis
Resource leveling
SE 477: Lecture 5
58 of 133
Network Analysis
 There are a number of network analysis techniques
available – we will concentrate on the Critical Path Method
(CPM)
 We have already seen a significant component of another
network analysis technique, the PERT estimates for activity
duration
 The Precedence Diagram Method (PDM) is a graphical
network technique that establishes activity sequencing
 Network analysis may also make use of mandatory or
discretionary parallelism in project activities to allow
schedule compression
April 28, 2014
SE 477: Lecture 5
59 of 133
Network Analysis Terminology
 Activity. An activity always consumes time and may also consume
resources. I use task and activity equivalently
 Critical. A critical activity or event is one that must be achieved by a
certain time, having no latitude (slack or float)
 Critical path. The critical path is the longest path through a project
network. Because it has no slack, all activities on the critical path must
be completed as scheduled, or the end date will slip
 Events. Beginning and ending points of activities are known as events.
An event is a specific point in time
 Milestone. An event representing a point in a project of special
significance. Usually the completion of a major phase of the work.
Project reviews are often conducted at milestones
April 28, 2014
SE 477: Lecture 5
60 of 133
Creating a precedence table
 A Precedence table documents task durations and
interdependencies
 Estimating duration of each task
 Duration estimated from historical information:
» Ideally, based on organization’s historical experience,
if available
» More likely: ‘expert’ knowledge
 Estimation done by task leaders or functional managers
 Any potentially risky task (technology, skills,
dependencies) should include contingency factor
 Include contingencies to mitigate potential resource
shortages
April 28, 2014
SE 477: Lecture 5
61 of 133
Creating a precedence table
 Determining task interdependencies

Goal is to determine predecessor/successor relations

Understanding interdependencies allows proper ordering
in scheduling tasks

Understanding interdependencies also helps in finding
possible parallel tasks, which can shorten schedule

Parallel tasks should be truly independent to minimize
risk of backtracking

Determining task interdependencies must be a team
effort to avoid unpleasant surprises
April 28, 2014
SE 477: Lecture 5
62 of 133
Sample evolutionary precedence table
April 28, 2014
SE 477: Lecture 5
63 of 133
Planning
Project Time Management II
PERT Chart
CPM
April 28, 2014
SE 477: Lecture 5
64 of 133
What is a PERT?
Program Evaluation & Review Technique or PERT
 Identify the tasks (or activities) required to complete the
given project
 Use the WBS
 List the activities in a structured fashion, along with their
interdependencies
 Use a Gantt Chart
 Precedence table
 A "network" of the activities and their dependencies is drawn
up. In MS Project, PERT is called Network Diagram
 Each event may be represented by a node
 Before any activity can begin, all its predecessor activities
must have been completed
April 28, 2014
SE 477: Lecture 5
65 of 133
• Program Evaluation and Review
Technique.
• Help understand relationship between
tasks and project activity flow.
Slack Time
 Slack time, also known as float, is the amount of delay expressed in
units of time that could be tolerated in the starting time or completion
time of an activity without causing a delay in the completion of the
project.
 Slack time is the difference between the late finish and the early
finish (LF-EF). If the result is greater than zero, then the activity has
a range of time in which it can start and finish without delaying the
project completion date, as shown in the figure below:
A
Duration
Slack
E
S
April 28, 2014
E
F
SE 477: Lecture 5
LF
67 of 133
Slack Time
 If an activity has zero slack, it determines the project
completion date. In other words, all the activities on the
critical path must be done on their earliest schedule or the
project completion date will suffer.
 If an activity with total slack greater than zero were to be
delayed beyond its late finish date, it would become a
critical path activity and cause the completion date to be
delayed.
 The sequence of activities that has zero slack is defined as
the critical path
 In general, the critical path is the path that has minimum
slack.
April 28, 2014
SE 477: Lecture 5
68 of 133
Critical path method
 The critical path method (CPM) focuses on calculating
theoretical start and finish dates for every activity in the
project. In the context of the CPM, the following definitions
are essential:


Critical. A critical activity or event is one that must be achieved by
a certain time; a critical activity has no latitude (slack or float)
Critical path. The critical path is the longest path through a project
network. Because it has no slack, all activities on the critical path
must be completed as scheduled, or the end date will slip
 CPM performs these calculation without regard for
resource limitations, which can lead to resource overallocation or inefficient multitasking
April 28, 2014
SE 477: Lecture 5
69 of 133
Critical path method
 A forward pass analysis performs schedule calculations that identify the




☛
early start and finish dates of activities and the project
A backward pass analysis performs schedule calculations that identify
the late start and finish dates of activities and the project, as well as total
and free float
Total float (TF) is the amount of time an activity can be delayed without
delaying the project as a whole
Free float (FF) is the amount of time an activity can be delayed without
delaying its successor (dependent) activities
Note that total float is global to the project, while free float is local to the
neighborhood of the activity
See Appendix: CPM Details and Example for more details and a worked
example of CPM calculations
April 28, 2014
SE 477: Lecture 5
70 of 133
Simple critical path example
Critical Path
April 28, 2014
SE 477: Lecture 5
71 of 133
Carrying out the example critical path
analysis above shows us:
April 28, 2014
•
That if all goes well the project can
be completed in 10 weeks
•
That if we want to complete the task
as rapidly as possible, we need:
•
1 analyst for the first 5 weeks
•
1 programmer for 6 weeks starting
week 4
•
1 programmer for 3 weeks starting
week 6
•
Quality assurance for weeks 7 and
9
•
Hardware to be installed by the end
of week 7
•
That the critical path is the path for
development and installation of
supporting modules
•
That hardware installation is a low
priority task as long as it is
completed by the end of week 7
SE 477: Lecture 5
72 of 133
Project Planning Tools
Gantt Chart
April 28, 2014
SE 477: Lecture 5
73 of 133
What is a Gantt chart?
A Gantt Chart (named for Henry Laurence Gantt) consists of
a table of project task information and a bar chart that
graphically displays project schedule, depicting progress in
relation to time and often used in planning and tracking a
project.
 Horizontal bar chart format, with bars representing the
phases and activities of the WBS
 Time extends along the horizontal axis
 Able to show planned and actual progress on tasks as well
as task dependencies
 Effective communication tool but with limitations
 Very low information density: lots of wasted space
 Not very useful for large projects
April 28, 2014
SE 477: Lecture 5
74 of 133
GANTT Schedule
• View Project in Context of
time.
• Critical for monitoring a
schedule.
• Granularity 1 –2 weeks.
• 2 week window approach
Sample evolutionary Gantt chart
April 28, 2014
SE 477: Lecture 5
76 of 133
Gantt Example:
Suppose a project comprises five activities: A,B,C,D, and E. A and B have
no preceding activities, but activity C requires that activity B must be
completed before it can begin. Activity D cannot start until both activities
A and B are complete. Activity E requires activities A and C to be
completed before it can start. If the activity times are A: 9 days; B: 3
days; C: 9 days; D: 5 days; and E: 4 days, determine the shortest time
necessary to complete this project.
Identify those activities which are critical in terms of completing the project
in the shortest possible time. [Critical path ]
1
2
3
4
5
6
7
8
9
1
0
1
1
1
2
1
3
1
4
1
5
A
B
C
1
6
1
7
1
8
Time is 16 days
Critical path is
B, C, E
D
E
April 28, 2014
SE 477: Lecture 5
77 of 133
Critical chain method
 The critical chain method (CCM) focuses on the resources
required for project activities, attempting to keep them
leveled throughout the project
 CPM scheduling is rigid and brittle: most activities have little
or no float, while the critical path, by definition, has no float
whatsoever— any delay in a critical path activity leads to a
project delay
 CCM, by contrast, assumes that all activities have a
statistically-probable range of durations and uses this
assumption to create a more flexible and resilient schedule
April 28, 2014
SE 477: Lecture 5
78 of 133
Critical chain method
 Each activity is assigned two durations: a ‘most likely’ or
‘best guess’ duration and a ‘pessimistic’ or ‘safe’ duration
 The most likely duration represents the time it would take
to complete the activity 50% of the time;

half of the time it would take less time, half of the time it would
take more time
 The pessimistic duration represents the time it would take
to complete the activity 90% of the time;

90% of the time it would take less time, only 10% of the time it
would take more time
 Resources are assigned to the activities using the most
likely durations
 The longest sequence of activities in the project is called
the critical chain
April 28, 2014
SE 477: Lecture 5
79 of 133
Critical chain method
 The pessimistic time ‘surpluses’ of all activity durations in the critical
chain are summed together to create a buffer that is placed at the end
of the project, the project buffer
 The pessimistic time surplus of an activity is the difference
between the 50% (most likely) duration of the activity and the 90%
(pessimistic) duration
 Example: For an activity with a 50% duration of 5 days and a 90%
duration of 9 days, the pessimistic time surplus is 4 days
 All sequences of activities that feed into the critical chain have buffers
(feeding buffers) placed at the points that they join the critical chain
 During execution, project resources focus on completing the current
activity within the 50% duration and avoiding multitasking
 CCM project management focuses on monitoring and controlling
buffer usage rather than on monitoring and controlling individual
activity completion dates
April 28, 2014
SE 477: Lecture 5
80 of 133
Critical chain method
April 28, 2014
SE 477: Lecture 5
81 of 133
What-if analysis
 Scenario-based analysis of schedule to determine effects of various
scenarios on different aspects of the project
 Example: Delay delivery of a critical component by various amounts
to determine effect on schedule
 Example: COTS supplier is unable to provide a critical component at
all
 What-if scenario analysis effectively tests the robustness of the project
schedule in response to adverse circumstances
 Most common technique uses Monte Carlo analysis to generate a
population of possible project schedule outcomes
 Think of executing the same project 10,000 times with the same
resources, different boundary conditions, and no memory between
executions
 Very useful in preparing contingency and response plans for project
risks (to be discussed in upcoming lecture)
April 28, 2014
SE 477: Lecture 5
82 of 133
Resource leveling
 Resource leveling is applied to a schedule analyzed by
CPM
 Addresses situation where resource availability is
constrained by time or amount of the resource available
 May also be used to keep resource usage at a constant
level during certain time periods in the project
 Resource leveling is needed when resources have been
over-allocated or assigned to two or more activities in the
same time period
 May change the critical path in the schedule model
☛ Beware of automated resource leveling—the project
schedule network may be nearly unrecognizable after
leveling
April 28, 2014
SE 477: Lecture 5
83 of 133
Resource leveling
 Uses a number of different approaches, including:




Assign under-allocated resources to multiple tasks to
keep them busy
Move key resources off of non-critical tasks
Delay start of task until required resources are available,
possibly using lags
Split tasks into two or more subtasks so the subtasks can
be assigned to different resources
April 28, 2014
SE 477: Lecture 5
84 of 133
Keeping a sense of
perspective
Project management is not just scheduling.
(Though sometimes it seems that way.)
April 28, 2014
SE 477: Lecture 5
85 of 133
Applying leads and lags
 Applying leads and lags allows refinement of a schedule
once the major schedule network analysis effort has been
completed
 Use of leads and lags may be used to meet imposed
constraints, help in resource leveling, or incorporate
contingency reserves into a schedule
April 28, 2014
SE 477: Lecture 5
86 of 133
Calendars
 Identify days and dates when work can be performed
 Affect all project-related activities
 General project calendars govern overall limitations on
when project work may be performed
 Example: Work is performed at a client site, and the
client shuts down for three weeks during the summer
 Resource calendars govern limitations on when particular
resources (or resource groups) may perform project work
 Example: Individual project team member vacation
schedules
 Example: Development team training schedules
April 28, 2014
SE 477: Lecture 5
87 of 133
Schedule development output
 Project schedule network diagrams
Show both project network logic (sequencing) as well as
critical path schedule activities
 Usually displayed as an activity-on-node diagram
 Gantt charts
 Specialized bar charts format to show activity start and
end dates, along with durations
 Easy to read but limited by low information density
 Milestone charts
 ‘Stripped-down’ version of Gantt chart, showing only
milestones

April 28, 2014
SE 477: Lecture 5
88 of 133
Reducing Project Duration
 How can you shorten the schedule?
 Via




Reducing scope (or quality)
Adding resources
Concurrency (perform tasks in parallel)
Substitution of activities
April 28, 2014
SE 477: Lecture 5
89 of 133
Schedule compression
 Shortens the project schedule without changing the project
scope, to meet schedule constraints, imposed dates, or
other schedule objectives
 There are two types of schedule compression, crashing and
fast-tracking
 Crashing. Analyzes cost and schedule trade-offs to get the
greatest amount of compression with the least cost
 Examples: Use of additional resources, being more
efficient, changing approach used to perform work, work
overtime
 Schedule crashing only works for activities where
additional resources may shorten the duration of the
activity
April 28, 2014
SE 477: Lecture 5
90 of 133
Schedule compression
 Fast-tracking. Activities that would normally be done
sequentially are done in parallel.
 Fast-tracking can lead to rework and increased risks due
to unforeseen dependencies
 Fast-tracking only works when activities can be
overlapped to shorten the total duration
April 28, 2014
SE 477: Lecture 5
91 of 133
Compression Techniques
Shorten the overall duration of the project
 Crashing
» Looks at cost and schedule tradeoffs
» Gain greatest compression with least cost
» Add resources to critical path tasks
» Limit or reduce requirements (scope)
» Changing the sequence of tasks
 Fast Tracking
» Overlapping of phases, activities or tasks that would
otherwise be sequential
» Involves some risk
» May cause rework
 Barry Boehm says you cannot compress more than 25%
April 28, 2014
SE 477: Lecture 5
92 of 133
Task









Name
ID
Description of work
Duration (days)
 Start Date (Earliest, Latest)
 Finish Date (Earliest, Latest)
Resources (People and equipment)
 Effort (In staff-days)
Predecessors (other tasks)
Inputs (documents, decisions, information)
Successors (other tasks)
Outputs (documents, decisions, information)
April 28, 2014
SE 477: Lecture 5
93 of 133
Mythical Man-Month
 Book: “The Mythical Man-Month”
Author: Fred Brooks
 “The classic book on the human elements of software engineering”
 First two chapters are full of terrific insight (and quotes)
Sample Quotes
 “Cost varies as product of men and months, progress does
not.”
 “Hence the man-month as a unit for measuring the size of
job is a dangerous and deceptive myth”

April 28, 2014
SE 477: Lecture 5
94 of 133
Mythical Man-Month
 Why is software project disaster so common?
1. Estimation techniques are poor & assume things will go
well (an ‘unvoiced’ assumption)
2. Estimation techniques fallaciously confuse effort with
progress, hiding the assumption that men and months
are interchangeable
3. Because of estimation uncertainty, manager lack
courteous stubbornness
4. Schedule progress is poorly monitored
5. When schedule slippage is recognized, the natural
response is to add manpower. Which, is like dousing a
fire with gasoline.
April 28, 2014
SE 477: Lecture 5
95 of 133
Mythical Man-Month
 Optimism
“All programmers are optimists”
 1st false assumption: “all will go well” or “each task takes
only as long as it ‘ought’ to take”
 The Fix: Consider the larger probabilities
 Cost (overhead) of communication (and training)
» His formula: n(n-1)/2
 How long does a 12 month project take?
• 1 person: 12 months
• 2 persons = 7 months (2 man-months extra)
• 3 persons = 5 months (3 man-months extra)
 Fix: don’t assume adding people will solve the problem

April 28, 2014
SE 477: Lecture 5
96 of 133
Mythical Man-Month
 Sequential nature of the process
“The bearing of a child takes nine months, no matter how
many women are assigned”
 What is the most mis-scheduled part of process?
 Testing (the most linear process)
 Why is this particularly bad?
 Occurs late in process and w/o warning
 Higher costs: primary and secondary
 Fix: Allocate more test time
 Understand task dependencies

April 28, 2014
SE 477: Lecture 5
97 of 133
Mythical Man-Month
 Reliance on hunches and guesses
What is ‘gutless estimating’?
The myth of additional manpower
 Brooks Law:
“Adding manpower to a late project makes it later”
Q: “How does a project get to be a year late”?
 A: “One day at a time”
Studies
 Each task: twice as long as estimated
 Only 50% of work week was programming
Fixes
 No “fuzzy” milestones (get the “true” status)
 Reduce the role of conflict
 Identify the “true status”





April 28, 2014
SE 477: Lecture 5
98 of 133
Schedule Development
Workflow and Example
April 28, 2014
SE 477: Lecture 5
99 of 133
Scheduling workflow
 Define activities
Use of WBS template helps guide definition process and
organize activities
Perform activity sequencing
 Develop schedule framework according to what is
logically possible – perform resource allocation later
Estimate effort – the total number of labor units (e.g. staffdays) for each activity
Identify resources for each activity
Apply calendars to schedule framework





April 28, 2014
SE 477: Lecture 5
100 of 133
Scheduling workflow
 Estimate activity duration based on resources for activity
 Perform forward pass or backward pass critical path
analysis to generate schedule model
 Perform ‘what-if’ scenario analysis to identify contingency
and risk response needs
 Apply resource leveling to schedule model
 Apply schedule compression, if needed
April 28, 2014
SE 477: Lecture 5
101 of 133
WBS template
Component groups with a ‘+’ in
front of them are ‘rolled up’ –
subcomponents are hidden to
reduce clutter
April 28, 2014
SE 477: Lecture 5
102 of 133
Activity
definition
Added System architecture
definition WBS component
Note expansion and
detailing of WBS template
Architecture design
modeling entry; renamed
Software architecture
description to Document
software architecture
Note expansion and
detailing of WBS template
Design demonstration
planning and conduct entry
Note rework of WBS
template Elaboration phase
assessment entry
Note expansion and
detailing of WBS template
Critical component coding
demo integration entry
April 28, 2014
SE 477: Lecture 5
103 of 133
Activity
sequencing
Note dual predecessors.
Default relationship is
Finish-to-Start. Here, we
have defined a Start-to-Start
relationship with an added
lag of 5 days
Here, we have defined a Finishto-Finish relationship: this is
common for
implementation/integration task
pairs
Effort
Estimation
Effort (called work in
MS Project) is the
total number of
labor units needed
to complete a task
Measured in staff
units (-hours, days, -weeks, etc.)
Effort allocated
among resources
provides duration
estimates
April 28, 2014
SE 477: Lecture 5
105 of 133
Activity resource estimating
 Walk through activities
and identify classes of
resources needed
 If possible, do not specify
individuals at this point,
only their role/title
 Identify specific
individuals as resources
only if necessary
April 28, 2014
SE 477: Lecture 5
106 of 133
Duration estimation
 The effort
estimated in the
effort estimation
step is the total
labor units needed
to complete a task
 Duration
estimation results
from taking the
effort and
distributing it
among the
resources for task
April 28, 2014
SE 477: Lecture 5
107 of 133
Duration
estimation
The resource allocation for
this task is detailed on the
preceding slide. Note the 20
day work (effort) estimate
vs. the 8 day duration
Long durations for these
summary components are
due to incomplete data entry
for all subcomponents
April 28, 2014
SE 477: Lecture 5
108 of 133
Critical path: early/late start and finish with float (slack)
Schedule compression
Use Finish-to-Start dependency with 5
day negative lag (-5) for successor to
get reasonable relationship between
two tasks. Equivalent to a 5 day lead
for successor
Alternatively:
Use Start-to-Start
dependency with 5 day
lag for successor to get
reasonable relationship
between two tasks
Note schedule compression
of 5 days
April 28, 2014
SE 477: Lecture 5
110 of 133
Determining resource utilization
 Resource graphs
show the utilization
of individual
resources as a
function of time
 Resource graphs
can be used to
identify over- and
under-utilized
resources
 Resource leveling
can be used to
balance utilization
and/or to shift tasks
to lower-cost
resources
April 28, 2014
SE 477: Lecture 5
111 of 133
Next Class
 Topic:
Risk Management: Planning, risk identification,
quantification and prioritization; Risk analysis, response
planning, avoidance, mitigation, monitoring.
Reading:


PMP Study Guide: Chapter 6

Kerzner: Chapter 17

Taylor: Chapter 7

Taylor (Survival Guide): Chapter 13
 Assignment 3 – due May 5
April 28, 2014
SE 477: Lecture 5
112 of 133
Journal Exercises
 Read the paper: Programmer Productivity: The "Tenfinity
Factor”
<http://www.devtopics.com/programmer-productivity-thetenfinity-factor/>
 Comment.
 Given the above, what about the impact on estimating?
 Also, think about programmer style and lines of code
measurements.
April 28, 2014
SE 477: Lecture 5
113 of 133
Midterm Examination
“Nobody expects the Spanish Inquisition!”
– Monty Python
April 28, 2014
SE 477: Lecture 5
114 of 133
Mid-term Examination
 Midterm Examination will be on the Desire2Learn system starting
Wednesday, April 30, through Monday, May 5
 See important information about Taking Quizzes On-line
 Login to the Desire2Learn System (https://d2l.depaul.edu/)
 On-line tutorial:
http://www.itd.depaul.edu/website/documentation/d2l/mp4based/quiz
zes/quizzes.html
 On-line guide:
http://www.itd.depaul.edu/website/documentation/d2l/Quizzes.pdf
 Take the Mid-term examination.
 It will be made available Wednesday, April 30, 2014.
 You must take the exam by COB Monday, May 5, 2014.
 Allow 3 hours (should take about one hour if you are prepared); note:
books or notes should not be used.
 Midterm study guide [note solution to some problems on last page].
April 28, 2014
SE 477: Lecture 5
115 of 133
SE 477 – Class 5: Appendices
This is material that is relevant but not used often enough to present in the
main part of the class.
Topics:
 Scheduling
 PERT Estimation technique
 Critical Path Method (CPM)
 Forward and backward pass analysis
 Calculating float
April 28, 2014
SE 477: Lecture 5
116 of 133
Appendix: PERT Estimation
Technique
April 28, 2014
SE 477: Lecture 5
117 of 133
PERT estimation technique
 Most widely used three-point estimate is PERT (Program Evaluation
and Review Technique)
 Defines three estimate points as:
 Most likely: estimate that occurs with greatest frequency
 Optimistic: shortest duration, taken as 10th percentile value
 Pessimistic: longest duration, taken as 90th percentile value
 PERT activity duration estimate TE and its standard deviation (sE or
σ) are calculated according to:
TE  ( Eoptimistic  4 Emost _ likely  E pessimistic ) / 6
sE  ( E pessimistic  Eoptimistic) / 6
April 28, 2014
SE 477: Lecture 5
118 of 133
Duration estimates distribution
Most Likely Estimate is peak of
distribution. For symmetric
distributions, Most Likely Estimate
and mean coincide. However, for
skewed distributions the peak will
be shifted off-center and differ from
the mean.
Optimistic Estimate
For this activity,
only 10% of the time activity
will take less time than this.
Conversely, 90% of the time
activity will take more time
than this.
Pessimistic Estimate
For this activity,
90% of the time activity will
take less time than this.
Conversely, only 10% of the
time activity will take more
time than this.
Note that this is a symmetric, continuous distribution.
Actual data will be discrete, will likely be skewed,
and will best be displayed in a histogram.
10th
Percentile
~ μ -2.24σ
μ
90th
Percentile
~ μ +2.24σ
Duration
April 28, 2014
SE 477: Lecture 5
119 of 133
How to calculate PERT estimates
 This is for statistics majors and rarely used except when analyzing data.
 Calculate the sample mean:
1
x
N
N
x
i
i 1
 Calculate the sample standard deviation:
s
1 N
2
(
x
i

x
)

N  1 i 1
 Use Chebyshev’s rule to approximate optimistic and pessimistic
estimates:
 At least (1 − 1/k2) · 100% of the values are within k standard
deviations from the mean
 So, solving for k when this equation equals 80% (for the 20% outside the
10 and 90 percentiles), we get approximately:
Optimistic  x  2.24s
April 28, 2014
Pessimistic  x  2.24s
SE 477: Lecture 5
120 of 133
PERT calculation example
You have the following estimates for an activity, in staff-hours:
24, 24, 24, 40, 48, 48
Calculate the sample mean:
1
x  (24  24  24  40  48  48)
6
1
x  (208)  34.7
6
Calculate the sample standard deviation (s or σ):
1 6
s
(xi  34.7 ) 2

6 1 i1
s
1
((24  34.7) 2  (24  34.7) 2  (24  34.7) 2  (40  34.7) 2  (48  34.7) 2  (48  34.7) 2 )
5
s  (0.2)(114.5  114.5  114.5  28.1 176.9  176.9)
s  0.2  725.4
s  145.1
s  12
April 28, 2014
SE 477: Lecture 5
121 of 133
PERT calculation example
Now, calculate the PERT estimates :
Optimistic  x  2.24s  34.7  (2.24 12)
Optimistic  34.7  26.9  7.8
Most _ Likely  24
Pessimistic  x  2.24s
Pessimistic  34.7  (2.24 12)  34.7  26.9  61.6
Finally, the PERT estimated activity duration is:
TE  ( Eoptimistic  4 Emost _ likely  E pessimistic ) / 6
TE  (7.8  (4  24)  61.6) / 6  165.4 / 6
TE  27.6
sE  ( E pessimistic  Eoptimistic) / 6  (61.6  7.8) / 6
sE  8.97  9
April 28, 2014
SE 477: Lecture 5
122 of 133
PERT calculation
Beta Distribution
 See Journal exercise
April 28, 2014
SE 477: Lecture 5
123 of 133
Journal Exercises
 Think about the problems with getting a good estimate.
 The PERT and three point estimations all rely on the assumption that
the distribution of estimates are Gaussian in nature. What if they are
not? What if there is a large tail for pessimistic?
Hint: lookup Beta Distributions:
 Hint: Better Project Management Through Beta Distribution
http://www.isixsigma.com/methodology/project-management/betterproject-management-through-beta-distribution/
April 28, 2014
SE 477: Lecture 5
124 of 133
Appendix: CPM Details and
Example
April 28, 2014
SE 477: Lecture 5
125 of 133
Critical path method
 A forward pass performs schedule calculations that identify
the early start and finish dates of tasks and the project
 A backward pass performs schedule calculations that
identify the late start and finish dates of tasks and the
project, as well as total and free float
April 28, 2014
SE 477: Lecture 5
126 of 133
Critical path method
 A forward pass analysis performs schedule calculations
that identify the early start and finish dates of activities
and the project


April 28, 2014
Early Start Date (ES). ES represents the theoretically earliest date
a activity can start
‣ ES = Maximum EF of predecessor activity(-ies)
Early Finish Date (EF). EF represents the theoretically earliest
date a activity can finish
‣ EF = ES + duration of activity
SE 477: Lecture 5
127 of 133
Critical path method
 A backward pass analysis performs schedule calculations
that identify the late start and finish dates of activities and
the project, as well as total and free float


April 28, 2014
Late Start Date (LS). LS represents the theoretically latest date a
activity can start without delaying the project
‣ LS = LF – duration of activity
Late Finish Date (LF). LF represents the theoretically latest date a
activity can finish without delaying the project
‣ LF = Minimum LS of successor activity(-ies)
SE 477: Lecture 5
128 of 133
Critical path method
 Total float (TF) is the amount of time a activity can be
delayed without delaying the project as a whole



TF = LF - EF
If LF < EF then TF < 0
If a project has a fixed finish date constraint then TF might be less
than zero, meaning it must complete before LF to satisfy the finish
date constraint
 Free float (FF) is the amount of time a activity can be
delayed without delaying its successor (dependent)
activities

FF = Minimum ES (successor activities) – EF
 Note that total float is global to the project, while free float
is local to the neighborhood of the activity
April 28, 2014
SE 477: Lecture 5
129 of 133
Critical Path Method




List all activities in plan.
Plot tasks onto chart. (Tasks = arrows. End Tasks = dots)
Show dependencies.
Schedule activities
 Sequential activities on critical path.
 Parallel activities.
 Slack time for hold-ups.
 Find longest path through chart.
 This is the critical path
 What is the difference between critical path and critical
chain?
 Critical chain also manages buffer activity durations and
resources
April 28, 2014
SE 477: Lecture 5
130 of 133
Performing forward pass CP analysis
10
TF
ES = Maximum EF of predecessor task(s)
EF = ES + duration of task
5 days
2
A
5/11
5/7
30
1
4 days
C
5/16
1
TF
20
TF
4
5/19
10 days
B
5/7
5/16
2
Key
3
ID
TF DUR
Name
EF
ES
LS
LF
April 28, 2014
SE 477: Lecture 5
131 of 133
Performing backward pass CP analysis
10
TF
LF = Minimum LS of successor task(s)
LS = LF – duration of task
5 days
3
A
5/11
5/7
30
5/12
4 days
5/16
C
4
4
TF
20
TF
10 days
5/16
5/19
5/16
5/19
1
B
5/7
5/7
April 28, 2014
Key
5/16
5/16
3
2
SE 477: Lecture 5
ID
TF DUR
Name
EF
ES
LS
LF
132 of 133
Calculating float
FF = 6
10
6 days
TF = LF - EF
FF = Minimum ES (successor task) – EF
5 days
A
5/11
5/7
30
5/12
0 days
4 days
Critical path
5/16
C
20
0 days
10 days
5/16
5/19
5/16
5/19
B
Key
5/16
5/7
ID
5/7
TF DUR
Name
EF
ES
LS
LF
5/16
FF = 0
April 28, 2014
SE 477: Lecture 5
133 of 133