schedule & effort

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Schedule & effort

Problem

• Our ability to realistically plan and schedule projects depends on our ability to estimate project costs and development efforts

• In order to come up with a reliable cost estimate, we need to have a firm grasp on the requirements, as well as our approach to meeting them

• Typically costs need to be estimated before these are fully understood

1. Figure out what the project entails– Requirements, architecture, design

2. Figure out dependencies & priorities– What has to be done in what order?

3. Figure out how much effort it will take

4. Plan, refine, plan, refine, …

Planning big projects

What are project costs?

• For most software projects, costs are:– Hardware Costs– Travel & Training costs– Effort costs

Aggravating & mitigating factors

• Market opportunity• Uncertainty/risks• Contractual terms• Requirements volatility• Financial health• Opportunity costs

Cost drivers

• Software reliability • Size of application database • Complexity • Analyst capability • Software engineering

capability • Applications experience • Programming language

expertise

• Performance requirements • Memory constraints • Volatility of virtual machine • Environment • Use of software tools • Application of software

engineering methods • Required development

schedule

What are effort costs?

• Effort costs typically largest of the 3 types of costs (hardware, training and effort), and the most difficult to estimate.

• Effort costs include:– Developer hours– Heating, power, space– Support staff; accountants, administrators, cleaners, management– Networking and communication infrastructure– Central facilities such as rec room & library– Social security and employee benefits

Software cost estimation – Boehm (1981)

• Algorithmic cost modeling– Base estimate on project size (lines of code)

• Expert judgment– Ask others

• Estimation by analogy– Cost based on experience with similar projects

• Parkinson’s Law– Project time will expand to fill time available

• Pricing to win– Cost will be whatever customer is willing to pay

• Top-down estimation– Estimation based on function/object points

• Bottom-up estimation– Estimation based on components

Productivity metrics

• Lines of code– Simple, but not very meaningful metric– Easy to pad, affected by prog language– How to count revisions/debugging etc?

• Function points– Amount of useful code produced

(goals/requirements met)– Less volatile, more meaningful, not perfect

Function points

Function points are computed by first calculating an unadjusted function point count (UFC). Counts are made for the following categories (Fenton, 1997):

– External inputs – those items provided by the user that describe distinct application-oriented data (such as file names and menu selections)

– External outputs – those items provided to the user that generate distinct application-oriented data (such as reports and messages, rather than the individual components of these)

– External inquiries – interactive inputs requiring a response – External files – machine-readable interfaces to other systems – Internal files – logical master files in the system

Each of these is then assessed for complexity and given a weighting from 3 (for simple external inputs) to 15 (for complex internal files).

Unadjusted Function Point Count (UFC)

Weighting Factor

Item Simple Average Complex

External inputs 3 4 6

External outputs 4 5 7

External inquiries 3 4 6

External files 7 10 15

Internal files 5 7 10

Each count is multiplied by its corresponding complexity weight and the results are summed to provide the UFC

Object points

Similar to function points (used to estimate projects based heavily on reuse, scripting and adaptation of existing tools)

• Number of screens (simple x1, complex x2, difficult x3)• Number of reports (simple x2, complex x5, difficult x8)• Number of custom modules written in languages like Java/C

x10

COCOMO II Model

• Supports spiral model of development• Supports component composition, reuse, customization• 4 sub-models:

– Application composition model – assumes system written with components, used for prototypes, development using scripts, db’s etc (object points)

– Early design model – After requirements, used during early stages of design (function points)

– Reuse model – Integrating and adapting reusable components (LOC)

– Post architecture model – More accurate method, once architecture has been designed (LOC)

• Computes software development effort as function of program size and a set of "cost drivers”.

• Product attributes – Required software reliability– Size of application database– Complexity of the product

• Hardware attributes – Run-time performance constraints– Memory constraints

Intermediate COCOMO

• Personnel attributes – Analyst capability– Software engineering capability– Applications experience– Virtual machine experience– Programming language experience

• Project attributes – Use of software tools– Application of software engineering methods– Required development schedule

Intermediate COCOMO

• Each of the 15 attributes receives a rating on a six-point scale that ranges from "very low" to "extra high" (in importance or value). An effort multiplier from the table below applies to the rating. The product of all effort multipliers results in an effort adjustment factor (EAF). Typical values for EAF range from 0.9 to 1.4.

Intermediate COCOMO

Example: Twitter repression report

Repressed citizen

UC#1: Report repression

UC#2: Clarify tweet

Concerned public

UC#3: View reports

UC#3a: View on map UC#3b: View as RSS feed

One possible architecture

TwitterTwitterFaçade

GeocoderGeocoder

Façade

Database

Apache+PHP

MappingWeb site

Google maps

RSSWeb service

Tweetprocessor

MySQL

Activity graph: shows dependencies of a project’s activities

1a

1c 2

1b

3a

3b

4

Do Twitter facadeDo Twitter facade

Do geocode facadeDo geocode facade

Design dbDesign db

Do tweet processor Do tweet processor

Do map outputDo map output Do RSS outputDo RSS output

Test & debug mapTest & debug map

Test & debug RSSTest & debug RSSAdvertiseAdvertise

3

Test & debug componentsTest & debug components

Milestone 2: DB contains real dataMilestone 3: DB contains real, reliable dataMilestone 4: Ready for public use

• Filled circles for start and finish

• One circle for each milestone

• Labeled arrows indicate activities– What activity must be performed to get to a

milestone?– Dashed arrows indicate “null” activities

Activity graph: shows dependencies of a project’s activities

• Ways to figure out effort for activities– Expert judgment– Records of similar tasks– Effort-estimation models– Any combination of the above

Effort

• Not a terrible way to make estimates, but…– Often vary widely– Often wrong– Can be improved through iteration & discussion

• How long to do the following tasks:– Read tweets from Twitter via API?– Send tweets to Twitter via API?– Generate reports with Google maps?

Effort: expert judgment

• Personal software process (PSP)– Record the size of a component (lines of code)

• Breakdown # of lines added, reused, modified, deleted

– Record time taken• Breakdown planning, design, implement, test, …

– Refer to this data when making future predictions

• Can also be done at the team level

Effort: records of similar tasks

• Algorithmic (e.g.: COCOMO: constructive cost model)– Inputs = description of project + team– Outputs = estimate of effort required

• Machine learning (e.g.: CBR)– Gather descriptions of old projects + time taken– Run a program that creates a model You now have a custom algorithmic method

• Same inputs/outputs as algorithmic estimation method

Effort: estimation models

1. Assess the system’s complexity2. Compute the # of application points3. Assess the team’s productivity4. Compute the effort

Using COCOMO-like models

Assessing complexity

e.g.: A screen for editing the database involves 6 database tables, and it has 4 views.This would be a “medium complexity screen”.

This assessment calls for lots of judgment.

Pfleeger & Atlee

Computing application points (a.p.)

e.g.: A medium complexity screen costs 2 application points.

3GL component = reusable programmatic component that you create

Pfleeger & Atlee

Assessing team capabilities

e.g.: Productivity with low experience + nominal CASE… productivity = (7+13)/2 = 10application points per person-month (assuming NO vacation or weekends!!!!!)

Pfleeger & Atlee

• It offer many benefits for developers building large-scale systems.

• As spiraling user requirements continue to drive system complexity to new levels, CASE tools enable engineers to abstract away from the entanglement of source code, to a level where architecture & design become apparent and easier to understand and modify.

• The larger a project, the more important it is to use a CASE tool in software development.

CASE (comp aided SE) TOOLS

• As developers interact with portions of a system designed by their colleagues, they must quickly seek a subset of classes and methods and assimilate an understanding of how to interface with them.

• In a similar sense, management must be able, in a timely fashion and from a high level, to look at a representation of a design and understand what's going on. Hence case tools are used

CASE TOOLS

Identify screens, reports, components

TwitterTwitterFaçade

GeocoderGeocoder

Façade

Database

Apache+PHP

MappingWeb site

Google maps

RSSWeb service

Tweetprocessor

MySQL

3GL components - Tweet processor - Twitter façade - Geocoder façade

Reports - Mapping web site - RSS web service

Use complexity to computeapplication points

3GL components - Tweet processor - Twitter façade - Geocoder façade

Reports - Mapping web site - RSS web service

Simple model assumes thatall 3GL components are 10application points.

Displays data from only a few database tables (3? 4?)Neither has multiple sections.Each is probably a “simple” report, 2 application points.

3*10 = 30 a.p.

2*2 = 4 a.p.

30 + 4 = 34 a.p.

• Assume at your company the team has…– Extensive experience with websites, XML– But no experience with Twitter or geocoders– Since 30 of the 34 a.p. are on this new stuff,

assume very low experience– Virtually no CASE support… very low

• therefore calculate the productivity as application points in the “person-months”.

• Note: this assumes no vacation or weekends

Assess the team’s productivity& compute effort

Distribute the person-months over the activity graph

1a

1c 2

1b

3a

3b

4

Do Twitter façade (1.25)Do Twitter façade (1.25)

Do geocode façade (1.25)Do geocode façade (1.25)

Design db (0.25)Design db (0.25)

Do tweet processor (1.00) Do tweet processor (1.00)

Do map output (0.25)Do map output (0.25) Do RSS output (0.25)Do RSS output (0.25)

Test & debug map (0.25)Test & debug map (0.25)

Test & debug RSS (0.25)Test & debug RSS (0.25)Advertise (1.0?)Advertise (1.0?)

3

Test & debug components (3.75)Test & debug components (3.75)

• Divide person-months between implementation and other activities (design, testing, debugging)– Oops, forgot to include an activity for testing and

debugging the components… revise activity graph

• Notice that some activities aren’t covered– E.g.: advertising; either remove from diagram or

use other methods of estimation

The magic behinddistributing person-months

• Ways to get more accurate numbers:– Revise numbers based on expert judgment or

other methods mentioned.– Perform a “spike”… try something out and actually

see how long it takes– Use more sophisticated models to analyze how

long components will really take– Use several models and compare

• Expect to revise estimates as project proceeds

Do you believe those numbers?

Further analysis may give revised estimates…

1a

1c 2

1b

3a

3b







Test & debug RSS (0.25)Test & debug RSS (0.25)

3


• Sort all the milestones in “topological order”– i.e.: sort milestones in terms of dependencies

• For each milestone (in order), compute the earliest that the milestone can be reached from its immediate dependencies

Critical path: longest route through the activity graph

Example: computing critical path

1a

1c 2

1b

3a

3b








3


0.250.25

1.501.50

1.501.50

2.002.00

6.256.25

6.756.75

6.506.507.007.00

Example: tightening the critical path

1a

1c 2

1b

3a

3b





Do map output (0.50)Do map output (0.50)

Do RSS output (0.25)Do RSS output (0.25)



3


0.250.25

1.501.50

1.501.50

2.002.00

2.002.00

2.502.50

2.252.256.256.25

What if we get started on the reports as soon as we have a (buggy) version of the database and components?

• Shows activities on a calendar– Useful for visualizing ordering of tasks & slack– Useful for deciding how many people to hire

• One bar per activity• Arrows show dependencies between activities• Milestones appear as diamonds

Gantt Chart

Example Gantt chart

Gantt chart quickly reveals that we only need to hire two people (blue & green)

• Scheduling with a set of requirements and an architecture?

• In contrast, assume that you are scheduling before you have requirements and an architecture. How much different would that be?

• What are the pros and cons of each approach?

Two ways of scheduling

• Updated vision statement– Your chance for extra credit!!– Thursday presentation: Each team is given 15

minutes to present how their vision has been more clear through this time (power-point presentation)

– You can include your requirements gathering, constraints and other details of your work until now.

– What are your future plans?– You will receive your midterms back tomorrow.

What’s next for you?

schedule & effort

Documents

project costs

types of costs hardware

meeting themtypically

software projects

simple external inputs

reliable cost estimate

project entailsrequirements

complex internal files