copyright © 2015 curt hill software development paradigms what do you need to know?

Copyright © 2015 Curt Hill

Software Development Paradigms

What do you need to know?

Introduction

• Most of this should be a review from previous courses

• We will consider briefly the following:– Waterfall model– eXtreme Programming (XP)– Scrum

• You should know something already on all of these topics


Waterfall Model

• This is a classic engineering model • Predates software engineering in

its use by other engineering disciplines


Waterfall Model


RequirementsDesign

Unit Implementation

Operation & Maintenance

System Integration

Waterfall Problems

• Works better for very large projects– Must have solid managerial support

• Many such projects are canceled before rolling out the product

• The volatility of requirements• Technical debt accumulates and is

not visible until late in the project


Technical Debt

• Unfinished work that is required by a design– Most often seen in projects that are

released early

• Like financial debt this accrues interest making changes more difficult later– Prevents or makes more difficult

enhancements


Waterfall Debt• We do not see the problems early

enough– Requirements were insufficient– Design was poor– Early code was not good

• These problems come home to roost at the end of the project – This is when it is most difficult to

change

• About 18% of real world projects are using Waterfall


Alternatives• Agile, iterative, evolutionary are now

much more common• The idea is quickly develop small code

bases that deal with just the basics• Add one feature at a time• We prepare for failure by being ready

to junk the whole mess if it does not satisfy the users

• All stakeholders review


eXtreme Programming (XP)

• One of the first agile methodologies• Goals to produce high quality

software and increase programmer productivity

• XP has a set of:– Activities– Values– Rules– Principles


XP Activities

• Coding – duh!• Testing

– Unit tests– Acceptance tests

• Listening– To the business experts and each

other

• Designing– Overall structure of the system


XP Values 1• Communication

– Between the business experts and every member of the XP team

• Simplicity– Find the simplest solution – it can be

made more complicated later

• Feedback– System: unit and integration tests– Customers: acceptance tests– Team: to the customers on

requirements Copyright © 2015 Curt Hill

XP Values 2

• Courage– Design for today, not tomorrow– Be fearless in refactoring, not

allowing a poor design to hold things back

• Respect– For self: believe that you can produce

high quality code– For others: do nothing that will cause

impediments for rest of team


XP Rules• Frequent small releases• Code unit tests before the unit• Pair programming• Only one pair integrates code at a

time• No release unless code passes all

unit tests• Finding a bug tests are improved• Collective code ownership


XP Principles• Feedback

– Frequently and promptly to keep project on track

• Simplicity– Often we are asked to consider the future– XP rejects, as the future is unpredictable

• Change– Is inevitable– Accept and move on from there


Scrum• An agile development process• A process framework to manage

software development• It defines scrum teams with:

– Roles– Events– Artifacts– rules

• Its approach is not incompatible with XP

• What is scrum named after?


Scrum Team• Three distinct roles:

– Product Owner– Development Team– Scrum Master

• Teams are self-organizing• Should have all the skills needed to

accomplish their goal• Products are produced incrementally• Each increment should produce a

workable product


Terminology• Product Backlog

– Prioritized list of the features needed in the product

• Sprint – A time period that sees the production of a

new or improved workable product– This is intending to implement a Sprint Goal– Typically less than a month

• Sprint Backlog– Those features intended to be implemented

in this sprint


Product Owner

• Creates and manages the Product Backlog– The only one to do so

• Sole interface with the business– Should be a business expert, not

necessarily a development expert

• Makes sure the Development team understands the items in the backlog


Development Team• Do the work of development• Organize and manage their own

work– Self organizing

• Cross functional– All the skills necessary must be

present in the team

• No:– Sub-teams– Titles– No ranking in importance


Scrum Master• Interface between the team and

nearly everyone else• Insulates the team from outside

pressures• Assists the Product Owner in

managing the Backlog and facilitating events

• Assists the team in a coaching fashion• Not a project manager


Events

• The sprint• Sprint Planning

– A meeting that determines what can be delivered and this will be done

• Daily Scrum– A short meeting to synchronize

activities

• Sprint Review– Final meeting in the Sprint to determine

what has and has not been done


XP and Scrum• Scrum is an agile management

methodology, while XP is an agile engineering methodology

• Duration of increments– XP 1-2 weeks, Scrum 2-4

• Work goals– XP in customer defined order, Scrum

has some choice

• Goal changes are disallowed in Scrum but possible in XP


Finally

• System development methodologies vary substantially

• Traditional methodologies do well with good specifications and solid organizational support

• Agile methodologies can do well where these are absent– Many software development projects are

knowledge acquisition projects which tends to favor the agile approach


copyright © 2015 curt hill software development paradigms what do you need to know?

Documents

curt hillcopyright

curt hillalternativesagile

curt hillintroduction

curt hillxp values

curt hillxp activitiescoding

curt hillwaterfall debtwe

poorearly code

small code bases