Software Project Management Task Estimating and Scheduling

Sequencing to Estimating/Scheduling

Gantt Charts

Resource Management

Activity Duration EstimatingAfter defining activities and determining sequence,

the next steps are estimating and mapping to a calendar

“Bottom-up” Estimating Estimate each activity individually and sum as you go

• Some folks add an “overhead” fudge factor

Scheduling Map tasks onto fixed points in time Typically represented using Gantt Charts

Course Technology, 1999

Bottom-up EstimatingHow do you construct per task estimates?

Weighted average formula: optimistic time + 4X most likely time + pessimistic time

6

Example: Suppose you had a task you estimate at 10 days, but have some

risk associated with it?

Weighted Calculation:

8 workdays + 4 X 10 workdays + 24 workdays = 12 days

6

where 8 = optimistic time, 10 = most likely time, 24 = pessimistic time

When constructing your schedule, consider the risk factor associated with the worst case!

Course Technology, 1999

PERT Example RevisitedThe dates as shown here are the result of some

probabilistic estimate

Prepare Material forBusiness Management

98/29/95 9/4/95

Conduct the BusinessManagement Review

109/5/95 9/11/95

RD Approved by IS Dir,DMA Dir, Cust Sponsor

119/11/95 9/11/95

Approval to Proceed toNext Stage

129/11/95 9/11/95

RequirementsDefinition (Analysis)

18/1/95 9/11/95

Prepare for Analysis

28/1/95 8/7/95

Analyze the CurrentSystem

48/8/95 8/14/95

Develop and EvaluateAlternative Solutions

68/15/95 8/21/95

Plan the Next Stage

88/22/95 8/28/95

Reaccess ApplicationArchitecture

58/8/95 8/14/95

Outline Transaction,Security and Training

78/15/95 8/21/95

Define SystemRequirements (Business)

38/8/95 8/14/95

ITDE(0.3),ITI

ITDBA(0.3) ITDBA(0.3)

For example, Task 4 with a 6 day estimate mayhave had best, expected, worst estimates of 1, 7, 8

Gantt ChartsGantt charts

Provide a standard format for displaying project schedule information

Lists project activities and their corresponding start and finish dates in a calendar format

Start with your WBS and refine

Symbols include: A black diamond: milestones or significant events on

a project with zero duration Thick black bars: summary tasks Lighter horizontal bars: tasks Arrows: dependencies between tasks

Course Technology, 1999

Sample Tracking Gantt Chart

white diamond: slipped milestonetwo bars: planned and actual times

The actual color and pattern may vary by tool

Course Technology, 1999

Schedule “Slack”

Slack - flexibility in your schedule Free slack or free float is the amount of time an activity

can be delayed without delaying the early start of any immediately following activities

Total slack or total float is the amount of time an activity may be delayed from its early start without delaying the planned project finish date

Formula 1:• The buffer in your plan can be computed as the total calendar

time minus the critical path duration

Formula 2:• The buffer can be calculated as the latest date by which you

can start minus the earliest date on the calendar you can start

Slack time = available time - real time

Slack = latest start time - earliest start time

Example

Free and Total Float or Slack for Project XTask Start Finish Late Start Late Finish Free

Slack Total Slack

A Mon 8/3/98 Mon 8/3/98 Wed 8/5/98 Wed 8/5/98 0days 2days B Mon 8/3/98 Tue 8/4/98 Mon 8/3/98 Tue 8/4/98 0days 0days C Mon 8/3/98 Wed 8/5/98 Wed 8/5/98 Fri 8/7/98 0days 2days D Tue 8/4/98 Fri 8/7/98 Thu 8/6/98 Tue 8/11/98 2d 2d E Wed 8/5/98 Tue 8/11/98 Wed 8/5/98 Tue 8/11/98 0d 0d F Wed 8/5/98 Mon 8/10/98 Fri 8/14/98 Wed 8/19/98 7d 7d G Thu 8/6/98 Thu 8/13/98 Mon 8/10/98 Mon 8/17/98 0d 2d H Wed 8/12/98 Wed 8/19/98 Wed 8/12/98 Wed 8/19/98 0d 0d I Fri 8/14/98 Mon 8/17/98 Tue 8/18/98 Wed 8/19/98 2d 2d J Thu 8/20/98 Mon 8/24/98 Thu 8/20/98 Mon 8/24/98 0d 0d

Course Technology, 1999

Computing Early and Late Times

Forward Pass: determine early start (ES) and early finish (EF) times for each task Work from left to right Adding times in each path Rule: when several tasks converge, the ES for the

next task is the largest of preceding EF times

Backward Pass: determine the last finish (LF) and last start (LS) times Start at the end node Compute the bottom pair of numbers Subtract duration from connecting node’s earliest start

time

Example: Compute ES, EF, LS, LF

Example: Solution

Scheduling

Make Schedule Trade-offs Knowing the critical path helps you make trade-offs Consider all inputs to your schedule

• Estimates - You cannot violate the constraints of the PERT– Change dependencies (F-S, S-S, etc.)– Change estimates once given

• Resourcing• Outsourcing• Other constrained resources

So what tradeoffs?• Remember the diamond!!!

– Scope - can you reduce what you have to deliver (& therefore do?) – Quality - skimping on quality implies you can work “faster”– Time - can you extend the due date and open up slack?– Cost - can you invest in more resources?

Time

Quality

Scope

CostExpectations

Project Schedule Shortfalls

If a project is falling behind, think of the “levers” you can pull: Add more time Add more people - Beware the “Mythical Man Month”! Revise expectations Address the critical path!

Techniques: Shortening durations of critical tasks for adding

more resources or changing their scope Crashing tasks by obtaining the greatest amount of

schedule compression for the least incremental cost Fast tracking tasks by doing them in parallel or

overlapping them - implies modifying dependenciesCourse Technology, 1999

Shortening Project Schedules

Overlappedtasks

Shortenedduration

Original schedule

Course Technology, 1999

Project Resource OrganizationDepends on backgrounds & work styles of team members

Extroverts: tell their thoughts Introverts: ask for suggestions Intuitives: base decisions on feelings Rationals: base decisions on facts, options

Resource Staffing Mapping skill types to functional needs and support Sophisticated models understand skill level, experience Responsibility Assignment Matrix (RAM) and/or Skills Matrix (SM)

RAMA resource planning tool

Who does What Can be for both planning and tracking Identify authority, accountability, responsibility Who: can be individual, team or department Can have totals/summary at end of row/column

SMAnother resource planning tool

•Resources on one axis, skills on other•Skills can high level or very specific•Cells can be X’s or numeric

RAM Examples

RAM withstakeholder

Simple RAM

Skills Matrix (SM)

Resource Plan – Staffing Levels Resource Staffing Levels:Looks kinda like your EVA eh?

GANTT Chart View:per person, per task

Matrix View:

4/7 11/7 18/7 25/7 1/8 8/8 15/8 22/8 29/8 5/9 12/9 19/9

T4

T8 T11

T12

T1

T3

T9

T2

T6 T10

T7

T5

Fred

Jane

Anne

Mary

Jim

Name DEP Proj1 Proj2 Proj3 Proj4 Proj5 0% 50%

Joe Eng 50% 0% 50%

Sue Eng 50% 0% 50%

Bob Eng ? 25% 75% 100%?

Bill Eng 100% 100%

Row Ops 0%

Julie Ops 0%

Cindy Eng 33% 33% 33% 100%

Tim Eng 100% 0% 100%

Barry Ops 0%

Miles Eng 33% 33% 0% 67%

Paula Ops 0%

Peter Eng 100% 33% 133%

Total 200% 133% 83%? 83% 91% 108% 700%

Issues and Summary

WBS - Project and Task Scope

Task Activity Networks, Precedence Charts, PERT Task dependencies and duration estimates

Scheduling, Gantt - Map to “real-time” Considers all constraints on the project May have slack to reduce risk (but at what cost?)

Resource Planning• Pick your model (RAM or SM), pick your view• Track – living document throughout your project!

Issues Granularity Resilience to change Too much work when it falls out of date anyway?