copyright © 1995-2003, dennis j. frailey, all rights reserved day 3, part 1, page 1 4/19/2003 day...

Copyright © 1995-2003, Dennis J. Frailey, All Rights Reserved Day 3, Part 1, 4/19/2003

Day 3, Part 1

Planning the Schedule


Outline• Basic Concepts in Schedule Planning• PERT Charts and Critical Path

Analysis• GANTT Charts • Network Charts• Critical Chain Analysis & Slack

Management• Summary


The Overall Planning Cycle

AnalyzeJob

Manage Risks

Execute

GenerateDetailed Plans

GenerateInitial Plans

Measure, Manage Productivity and Quality


EstimateSize

EstimateEffort and

Cost

EstimateScheduleEvaluate

Source InformationStatement of Work

RequirementsConstraintsStandardsProcesses

Historyetc.

WBS Size

Effort &Cost

Schedule

OKCompleteDetailedPlanning

Revise &Negotiate

Not OK

Detailed Planning - Processes


Architecture of SpreadsheetSize / Reuse Effort Schedules

Cocomo BasedEffort Estimate

Other EffortEstimates ...

Analogy basedSize Estimate

SoftwareReuse

Analysis

Final EffortEstimate

ProductivityBased Effort

Estimate

Generic Schedule

Effort Schedule

Other SizeEstimates ...

Final SizeEstimate

Expert BasedSize Estimate

0

5

10

15

20

25

M1 M2 M3 M4 M5 M6

TotalBuild 1Build 2


Basic Concepts inSchedule Planning


A Hypothetical(?) Scenario

I needA detailed schedule!Tell me how long it Will take and whenEach task will be

Complete.What do Ido now?Yes, sir!

Right away,Sir.


Three Levels of Schedule Detail

• Top Level Schedule– Generally produced during initial

planning, based on integrated master schedule for the project, project constraints, deadlines, etc.

– Focuses on how software tasks relate to the rest of the project


Three Levels of Schedule Detail (continued)

• Generic Schedule (top level software schedule)– Generally produced during effort

estimation, based on the process and the information gained from estimating models

– The focus is on the major (high level) software tasks and when they occur in time

Copyright © 1995-2003, Dennis J. Frailey, All Rights ReservedDay 3, Part 1, 4/19/2003

Three Levels of Schedule Detail (continued)

• Detailed Schedule– Generally produced when you are

about to execute the project or a phase of the project

– The focus is on how and when you will do the detailed work tasks


Schedules Tend to beSomewhat Flexible

• You can vary the actual schedule to fit your conditions– You have flexibility in matching the

schedule to other project constraints– Cycle time improvement techniques

can also improve your schedule– But you can drive up cost as you

deviate too far from what is reasonable


The Optimal Schedule...... depends on people, process, nature

of task, environment, etc. …• Different models make different

assumptions about these factors, reflecting the experience of those who developed the models

• Until we have a better theoretical foundation, experience remains the best way of predicting your optimal schedule


• Many models use a formula• Example: Cocomo formula for optimal

schedule:

e = .35 for most projects; .38 for easy (organic); .32 for hard (embedded)

• Effort is measured in staff months• Schedule is measured in calendar

months

Schedule = 2.5 * Efforte

Total Time to Do the Job


The Cocomo Model ofTime vs Effort

staff-days

required to do

the work

Calendar Time Allocated for the Work

Optimal Schedul

e


Other Models VaryGrady and Caswell compare five different

sources (p34, 35) (see references)• Differences stem from:

– Type of software being developed– Schedule compression– Organizational differences– Process and methods

• Hewlett-Packard recommendations:– Measure actual data & keep for the future– Count everything (overtime, etc.)


For Small Projects ...• Formulas fit large projects better than

small ones• And you may not have a good data

base of historical schedule information

So it may be better to estimate the time in a more detailed manner, as will be shown in the next section and in the

course exercises


Techniques for Developing & Documenting a Detailed

SchedulePERT Charts

– Show dependencies– Can expand to show resources, timing,

and critical pathGANTT Charts

– Show timing and parallelismNetwork Charts

– Combine the benefits of PERT and GANTT– But you need a tool to manage them


Steps of Detailed Scheduling1) Task Dependency and Flow

– Shows dependencies, but not timing2) Task Duration

– Shows minimum schedule length– Identifies the critical path

3) Critical Path Analysis– Determines what must change if the

schedule is to be reduced


Steps of Detailed Scheduling4) Resource Requirements

– Shows manpower loading, cash flow, etc.

5) GANTT Chart – Shows relative timing– But not the dependencies

6) Network Chart – Combines GANTT and PERT


PERT Charts &

Critical Path Analysis


PERT“PERT” stands for

“Program Evaluation and Review Technique”

or“Performance Estimating & Reporting

Tool” (depending on which author you

read)


PERT Origins• PERT was developed in the 1940’s

as a management tool for complex projects

• In its fullest form, PERT involves complex statistical analysis of project schedules and plans


PERT Charts• The basic tool of the PERT

technique is the PERT Chart, which represents the schedule and resource needs of a project

• The PERT chart uses the Precedence Diagramming Method (PDM), which is similar to a flow chart, to represent the dependencies among activities


A Minimal PERT Chart ...• Lists activities to be performed

(from WBS)• Indicates dependencies

– Activity X must precede activity Y, etc.

– This information comes in part from initial planning (life cycle analysis, organizational planning, process definition, etc.)


Sample PERT Chart from Organizational Planning

(in Initial Planning)Prototype Final Design BuildDesignKeyboar

dCodeDesignKeyboar

dSoftware

Test

BuildKeyboardEmulation

DeliverySubcontracted SW for Numeric Key Pad

Contract

This can be produced by

hand or with a project

management or scheduling tool.


Prototype Final Design BuildDesignKeyboard

CodeDesignKeyboardSoftware

Test

BuildKeyboardEmulation DeliverySubcontracted SW for Numeric Key Pad

Contract

An Alternative PERT Notation• Touching boxes implies dependency• Used to reduce space • Used later in this course


• List each task on a “post-it note” or index card

• Lay out the tasks on a board• Indicate task dependencies with

lines (arcs)

Developing a PERT ChartStep 1 - Task Dependencies

Task 1 Task 3 Task 6 Task 7

Task 8Task 2 Task 5

Task 4

Task 9


Design Test Code

Design Spec

Integrate

Develop Hardware

Code VerifyTest

Evaluating Dependencies


“Test” Task

depends on “Code” and “Test

Code”Design Test Code

Design Spec

Integrate

Develop Hardware

Code VerifyTest

Identifying Dependencies• What depends on what?


Design Test Code

Design Spec

Integrate

Develop Hardware

Code VerifyTest

Who needs this? (no successor)

Identifying Dependencies• What dependencies are unknown?


Design Test Code

Design Spec

Integrate

Develop Hardware

Code VerifyTest

External task that

we depend

on

Identifying Dependencies• What external tasks do we depend

on?


Types of PERT Dependencies

Finish to Start First task must finish before the second starts

Start to Start Second task must start x months after first starts

Finish to Finish Second task must finish y months after first finishes

x

y

Task 5Task 23

7

6Task 1 Task 3 Task 6 Task 7

Task 8

Task 4

Task 9


With most PERTtools, you can

specify a priority amongparallel tasks

Task 1 Task 3 Task 5Task 2 Task 4

Task 5Task 1 Task 3

Task 2

Task 4

Verifying Dependencies• Do not overconstrain -- use only the

the essential dependencies• The second PERT chart represents a

much more flexible plan


What to Learn from a Basic PERT Chart

• Identify dependencies you did not know existed

• Identify missing dependencies where you do not know the successor or the predecessor

• Identify critical dependencies, such as a hardware activity that will hold you up if it is late


NOTEPERT Charts are a good method for developing a detailed process description as well as developing a project schedule

Prototype Final Design BuildDesignKeyboard

CodeDesignKeyboardSoftware

Test

BuildKeyboardEmulation

DeliverySubcontracted SW for Numeric Key Pad

Contract


Steps of PERT Scheduling1) Basic PERT -- task dependency and flow

– shows dependencies, but not timing2) More Complete PERT -- task duration

– shows minimum schedule length3) Critical path

– shows what tasks contribute to minimum schedule length (what tasks need to be shortened to shorten the overall schedule)

4) Full PERT - resource requirements– shows manpower loading, resource needs,

etc.


Developing a PERT ChartStep 2 - Task Duration

• Lay out a time line at the bottom of the board

• For each task, estimate its duration and write that information on the post-it note. – Can be minimum feasible duration or

expected duration based on availability of resources

• Place each task in its appropriate position relative to the time line


Developing a PERT Chart Step 2 - Task Duration (continued)

• Proper placement shows earliest start date for each task [or latest start date]

20 weeks8 weeks

Minimum total time for whole activity is 26 weeksJ F M A M J J A S O N D

6weeks

8weeks

12weeks

26 weeks


What to Learn After Durations are Added

• The first task to focus on is the very last task – Will it complete by the project

deadline?• If not, how can you make the whole

schedule shorter?• The answer starts with determining

the Critical Path


The Critical Path is ...… the longest calendar path through

the schedule from the first to the last activity

Task A

Task CTask B

Task D

Task E

The Critical Path in the above example is A,C,D


The Critical Path is ...… the path that must be shortened in

order to shorten the whole schedule… the path that drives schedule slips

– If a critical path task slips, the whole schedule slips

… the riskiest part of the schedule

Be especially wary when the critical path involves dependency on external tasks that you do not

control!


• If the schedule is small, “eyeball” and determine which path is the longest.

• Otherwise a tool can be used

• Critical Path => min possible schedule

6 weeks3 weeks

5 weeks Critical PathTasks

Non-CriticalPath Tasks

Developing a PERT Chart Step 3 - Analyzing the Critical

Path


What if the MinimumSchedule is Too Long?

• You must find a way to cut the schedule

• Begin with tasks on the critical path– Try to divide them into smaller tasks

that can be done simultaneously– Assign more resources - do them faster– Cut functionality or defer until later

• Note that when you do this you might create a different critical path


Developing a PERT ChartStep 4 - Resource Requirements

• Determine the resource requirements of each task:– Equipment, facilities, etc.– Key personnel– Total labor effort (staff days, etc)– May also show minimum and maximum

reasonable allocations, i.e., 8 staff weeks: • minimum 2 weeks (4 people)• maximum 8 weeks (1 person)


Resources• Write this information on the index card

or post-it-note• Vary labor totals or types of personnel

assigned to different tasks in order to meet schedule needs

8 staff weeks:2 weeks, 4 people

8 staff weeks:4 weeks, 2 people

8 staff weeks:2 weeks, 3 senior people

These options mayreduce the critical

path or even removethis task from the

critical path


Scheduling Tools can ...… find critical path/shortest schedule… find minimum and total effort levels… do simulation of schedule to

determine likely outcomes when exact duration are indefinite

… assist in “what if” analysis of possible alternatives

… revise schedules with minimal effortSample tools: Microsoft Project®,

Primavera®


“Schedule from the back” conceptMinimal execution times for each task

Assuming adequate staff, task E must be started at least 7 weeks before final integration, whereas task A must be started at least 11 weeks before!

Using PERT Charts to Decide on Development Sequence

Final Integration4 weeks

C1 week

D3 weeks

F4 weeks

E2 weeks

B6 weeks

A2 weeks


Shopload Shows Resource Needs

and Allocation by Time PeriodWeek 1 2 3 4 5 6Person A 1 1 1 .5 1Person B 1 1 1 1

etc. etc. etc. etc. etc. etc. etc.Total

People2 3 5 4 4.5 3

SpecialEquip-ment A

1 2 2 1

SpecialEquip-ment B

1 1 2 1


Suggested Notationfor Post-it Notes

Yellow– Normal Tasks

Pink or Red – External Tasks that You

Depend OnBlue

– External Tasks that Depend on You


Schedule for Project P(sample)

J F M A M J J A S O N D


• Gizmo hardware must arrive by June 1– We must watch their schedule

• Joe and Mary must be available 100% for this project

• Integration must wait until Sept 15• Programmers must all be available to start

on March 1• At least three test sets must be available

during the month of August

Critical Dependencies, Issues, Assumptions, and Lessons

Learned (sample)


Steps of Detailed Scheduling1) Task Dependency and Flow

– Shows dependencies, but not timing2) Task Duration

– Shows minimum schedule length– Identifies the critical path

3) Critical Path Analysis– Determines what must change if the

schedule is to be reduced


Steps of Detailed Scheduling4) Resource Requirements

– Shows manpower loading, cash flow, etc.

5) GANTT Chart – Shows relative timing– But not the dependencies

6) Network Chart – Combines GANTT and PERT


GANTT Charts• These are devised from the same

data used in a PERT chart, but show the relative time phasing of the tasks instead of the dependencies

• Each “activity” box is sized to be proportional to the length of time it takes

• The boxes are lined up, usually in the order of execution, to show what is happening at what time


Sample Gantt ChartVertical line

represents current date

Task 2

Task 3

Task 6

Task 5

Task 1

Task 7

Task 4


Task 6

Task 5

Task 7

Does Task 6 depend on Task 5? Can Task 5 finish on time?

Gantt Chart does NOT tell you ...… task dependencies

… significance or impact of schedule slips… whether it is realistic to expect you to meet

the schedule… critical path


Network Charts

Copyright © 1995-2003, Dennis J. Frailey, All Rights ReservedDay 3, Part 1, 4/19/2003Jan Feb Mar Apr May Jun Jul Aug

Network Chart --Combining the Pert and

Gantt•Horizontal width indicates schedule length •Arcs indicate dependencies•Horizontal position indicates scheduled

time and task parallelismTask A

Task CTask B

Task D

Task E


Network Chart Summary• Tells you the duration of tasks and

their interdependencies. • Shows Critical Path• Can be color coded to show different

parts of the project– Software in blue, mechanical in red,

etc.• But it still cannot tell you if the

schedule is realistic


Project Management and Scheduling Tools

• Most such tools can show a PERT or GANTT chart

• More capable tools will show a network chart, which is hard to do by hand

• But tools take a lot of work to enter data and the data changes a lot in the early steps of detailed scheduling


Recommendations Regarding Management/Scheduling Tools• Do a PERT chart by hand and work

through the fundamental relationships• Then use a tool after things have

settled down• Select a tool carefully

– Some cannot handle the complexity of a very large project

– But the most capable tools are harder to use


Using Network or Pert Charts to Establish a Schedule

Earliest Completion Date– Tells you how soon you can complete– Tells you the earliest you can start each task

Latest Start Date– Tells you how late you can start and still meet

the deadline– Tells you the latest you can start each task

Critical Chain Analysis– Adds analysis of critical resource needs– Can help you manage to meet short cycle time


Earliest Completion Date

A, C, E, F can slip without hurting schedule

E4 weeks


G3 weeks

D6 weeks

A3 weeks

B4 weeks

C2 weeks

F2 wks

17 weeks min.

Earliest Start DateLater Start Date


Latest Start Date

• A, C, E, F can start late without hurting schedule• B, D, G, Final must start as shown, since on critical

path


G3 weeks

D6 weeks

A2 weeks

B4 weeks

C2 weeks

F2 wk

E4 weeks

17 weeks min.

Earlier Start DateLatest Start Date


Critical Chain Analysis&

Slack Management


• A Critical Resource is a resource that is required on each of two or more tasks– A piece of

equipment– An individual with

unique skills• If shared, each task

gets only part time use

?

Youare essential

to myproject

Myproject willfail without

you

Critical Resources


• If two tasks need a resource, one must give it up or both must run slower

• But it is tempting to fantasize that you can share resources without such high waste

Sharing a Resource MeansLess Efficiency

Percent Use AvailabilityWaste

100% 85% 15%50%+50% 40%+40% 20%33%+33%+33% 25%+25%+25% 25%25%+.... 17.5%+.... 30%


Using Critical Resources• If the resource is critical, it is also

known as a constraint• The fundamental rule of constraint

management is that you should maximize the efficiency of the constraint

• Which means you avoid overusing constraints and wasting time on inefficient sharing


If Task B needs a resource that is also needed by Task A then Task B is on the

Critical Chain

The Critical Chain• The critical chain consists of all

tasks using resources that are needed on the critical path

Task A

Task CTask B

Task D

Task E


Critical Chain Analysis• Start with Latest Start Date schedule • Mark critical path tasks as “on the

critical chain” & identify resources needed for these tasks

• If also needed elsewhere in parallel tasks, mark those tasks as “critical chain” tasks

• Reschedule those tasks earlier, so there is no conflict of resources

• This may change the critical path!


Conventions for Critical Chain Analysis

ConflictEarlier Start Date

Latest possible

Start Date

NormalTasks

Critical Pathand

Critical Chain

Critical Chainbut Not

Critical Path

CriticalPath Tasks


Example of Critical Chain Analysis

G and F need the same critical resourceSo F and its predecessors (E, C) must be started

sooner

A3 weeks


G3 weeks

D6 weeks

B4 weeks

E4 weeks

C2 weeks

F2 wk

17 weeks min.


A Further Example

• A and C cannot proceed in parallel• This changes the critical path and lengthens

the schedule!

H4 wks

G3 wksA

3 wks

E4 wks

C2 wks

F2 wks

B4 wks

D6 wks 18 weeks

minimum

Suppose A and C need the Same Critical Resource


Other Schedule Management Techniques

• Do more careful monitoring of critical path and critical chain tasks

• Start critical chain tasks as soon as you can - to provide maximum risk control

• DO NOT allow people to include slack time in their task schedules. All slack should be held in reserve by a higher level manager


Example of Slack Management Problem


G3 weeks

E4 weeks

C2 weeks


G3 weeks

E4 weeks

C2 weeks

Plan: C and E allow slack to reduce risk

Actual: C and E wait until last possible minute to start


What Might Really Happen


G5 weeks

E4 weeks

C2.5 weeks

Reality: C and G slip a little bit …

C’s slip is absorbed by E’s slackBut G’s slip causes the whole project to slip 2 weeks


Slack Management


G5 weeks

E4 weeks

C2.5 weeks

Actual - Slack can be applied to any task that slips, so the project stays on schedule


G3 weeks

E4 weeks

C2 weeks

Plan: C and E have no slack

Slack - 4 wks


• Critical path analysis identifies what tasks must be shortened to shorten the overall schedule

• Adding resource requirements enables you to decide on sequencing and when to schedule tasks and resources

• GANTT shows relative timing but not dependencies, flow

• Network chart shows both, but requires a more capable tool

Summary Schedule Estimation &

Planning


• Critical Chain shows resource conflicts between critical path tasks & other tasks

• Critical Resources must be managed to avoid impact on critical path

• Critical Chain Analysis shows which tasks must be started earlier in order to avoid resource conflicts

• Slack Management gives maximum risk control and shortest cycle time

SummarySchedule Estimation &

Planning


1) Brassard, Michael, The Memory Jogger Plus+, Goal/QPC, Methuen MA, 1989.

2) Goldratt, Eliyahu M. & Jeff Cox, The Goal, (North River Press, 1984.) Also Theory of Constraints and It’s Not Luck.

3) Thayer, Richard H., ed., Software Engineering Project Management, IEEE Computer Society Press, 1994.

4) U. of West Florida, PERT Home page, http://www.uwf.edu/~coehelp/studentaccounts/rnew/perthome.html

ReferencesSchedule Estimation &

Planning

copyright © 1995-2003, dennis j. frailey, all rights reserved day 3, part 1, page 1 4/19/2003 day...

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