02291: System IntegrationWeek 9

Hubert Baumeisterhuba@dtu.dk

DTU ComputeTechnical University of Denmark

Spring 2018

Contents

Principles of Good Design

Software Development Process

Project Introduction

DRY principle

DRY principleDon’t repeat yourself”Every piece of knowledge must have a single, unambiguous,authoritative representation within a system.”The Pragmatic Programmer, Andrew Hunt and David Thomas

I codeI documentationI build stystem

Example: Code Duplication

Example: Code Duplication

Companynamec-address-streetc-address-cityprintAddress

Addressstreetc i typrintAddress

Companyname

Personnamecpr-number

works at

home address

address

Personnamecpr-numberhome-address-streethome-address-cityprintAddress

works at

DRY principle

I Techniques to avoid duplicationI Use appropriate abstractionsI DelegationI InheritanceI Classes with instance variablesI Methods with parameters

I Refactor to remove duplicationI Generate artefacts from a common source. Eg. Javadoc

KISS principle

KISS principleKeep it short and simple (sometimes also: Keep it simple,stupid)

I simplest solution firstI Strive for simplicity

I Takes time!!I refactor for simplicity

Antoine de Saint Exupery”It seems that perfection is reached not when there is nothingleft to add, but when there is nothing left to take away”.

YAGNI principle

YAGNI principleYou ain’t gonna needed it

I Focus on the task at handI E.g. using the observer pattern because it might be needed

→ Two different kinds of flexibilityI make your design changeable

I tests, easy to refactorI design for change

I Use good OO principlesI High cohesion, low couplingI Decentralized control

→ Both are needed, but focus on the first before introducingnot needed constructs for the second

Low Coupling

High coupling

A B

D E

C

F

Low coupling

A

B

D

E

C

F

Low Coupling

High coupling

A B

D E

C

F

Low coupling

A

B

D

E

C

F

High Cohesion

Low CohesionPerson

namecpr-numbercompanyNamework-address-streetwork-address-cityhome-address-streethome-address-city

High Cohesion

Addressstreetcity

Companyname

Personnamecpr-number

works at

home address

address

High Cohesion

Low CohesionPerson

namecpr-numbercompanyNamework-address-streetwork-address-cityhome-address-streethome-address-city

High Cohesion

Addressstreetcity

Companyname

Personnamecpr-number

works at

home address

address

Law of Demeter

Law of DemeterI ”Only talk to your immediate friends”I Only method calls to the following objects are allowed

I the object itselfI its componentsI objects created by that objectI parameters of methods

I Law of Demeter = low coupling→ delegate functionality→ decentralised control

Computing the price of an order

Order

calculate pricecalculate base pricecalculate discounts

Productnameprice

Customernamediscount info

OrderLinequantity

*

1

1

Computing the price of an order

Order

calculate pricecalculate base pricecalculate discounts

Productnamepriceget price for quantity

Customernamediscount infocalculate discount

OrderLinequantitycalculate price

*

1

1

Layered Architecture

Eric Evans, Domain Driven Design, Addison-Wesley, 2004

Example Vending Machine

Two different presentation layers

I Swing GUI

I Command line interfaceCurrent Money: DKK 5

0) Exit1) Input 1 DKK2) Input 2 DKK3) Input 5 DKK4) Select banana5) Select apple6) Cancel

Select a number (0-6): 5Rest: DKK 2Current Money: DKK 0Dispensing: Apple

Architecture

«abstract»Observable

VendingMachineUI VendingMachineTextUI

«enumeration»Fruit

APPLEBANANA

VendingMachine

dispensedItem : FruitcurrentMoney : inttotalMoney : intrestMoney : int

input(money : int)select(f : fruit)cancel()...

Observable

Presentation LayerPresentation Layer

Application Layer

«delegate»

Observer

«delegate»

«delegate»

Observer

Contents

Principles of Good Design

Software Development Process

Project Introduction

Success rate for software projects 2000—2008

Sheet1

Page 1

2000 2002 2004 2006 2008

succeeded 28% 34% 29% 35% 32%

failed 23% 15% 18% 19% 24%

challenged 49% 51% 53% 46% 44%

2000 2002 2004 2006 2008

0%

20%

40%

60%

80%

100%

120%

challenged

failed

succeeded

CHAOS Summary 2009 Report

I Succeeded: 32%I Failed: 20%I Challenged: 48% (over

time, over budget, lots ofdefects, low customersatisfaction. . . )

Failed or challengedI AmandaI RejsekortetI Obamacare WebsiteI German road toll systemI Denver airport baggage

systemI . . .

Scaling software development

Small hutI one personI no special knowledge

SkyscraperI not possible with one

personI special knowledge: static,

electricity, water, waste,elevator, . . .

Types of software (Lehmann)

I s-type: mathematical function, sorting: completespecfication

I p-type: real world problems, e.g., chess: modelling the realworld

I e-type: embeded into socio-technical systems.Requirements change as the environment changes.System changes the environment: e.g., operating system

I Continuing ChangeI Increasing ComplexityI Conservation of Organisational Stability (invariant work

rate)I Continuing GrowthI Declining Quality

Activities in Software Development

I Understand and document what the customer wants:Requirements Engineering

I How to build the software: DesignI Build the software: ImplementationI Validate: Testing, Verification, Evaluation→ Waterfall

Waterfall process

I 1970: Winston W. Royce how not to develop softwareI 1985: Waterfall was required by the United States

Department of Defence

Example: Empire State Steel Construction

From The EmpireState Building by JohnTauranac

From Building the Empire State by Willis,1998

I Kept the budgetI Was finished before

deadlineI Built in 21 month (from

conception to finishedbuilding) (1931)

→ Basic design in4 weeks

I Fast-track construction

→ Begin theconstructionbefore the designis complete

→ create a flow

Delays in waterfall processes

D I TA

Time

Features

Release date

Implementation by layers and not functionality

Costs of changing requirements: Waterfall

I Changed / new requirements change the design andimplementation

I Cost of change not predictable→ Avoid changing/new requirements if possible

→ Good for s-type projects, not applicable to p-type ande-type projects

Iterative Processes: E.g. Rational Unified Process(1996)

Agile Software Development Methods (1999)I Extreme Programming (XP) (1999), Scrum (1995–2001),

Lean Software Development (2003), . . .I Kanban (2010): not a method; tool to improve processes

Functionality

TimeAD IT

AD ITR

AD ITR

AD IT

R

AD IT

R

AD IT

R

F 1

F 2

F 3a

F 8

F 4

F 5

F 6

RAD IT

1. Iteration

Database / Infrastructure Layer

Presentation Layer

Application Layer

Domain Layer

UserStory

UserStory

UserStory

I Highest priority user storyfirst

I If delayed: importantfeatures are implemented

Problem in Software Engineering (Recap)

I Liggesmeyer 1998

Changing Requirements: Agile Methods

Scott Ambler 2003–2014 http://www.agilemodeling.com/artifacts/userStory.htm

I Cost of changeI New / changed requirements not done yet: zero costsI Changed requirements already done: the cost of a

requirement that can not be implemented

Resource Triangle

Plan Driven

D I TA

Time

Features

Release date

Agile

Database / Infrastructure Layer

Presentation Layer

Application Layer

Domain Layer

UserStory

UserStory

UserStory

eXtreme Programming (XP)I Kent Beck 1999I 12 Practices

Kent Beck, Extreme Programming 1st ed.

Scrum

Working incrementof the software

Sprint Backlog SprintProduct Backlog

30 days

24 h

file:///Users/huba/Desktop/Scrum_process.svg

1 of 1 /18.3.13 24:16

Wikipedia

I Robert Martin (Uncle Bob) about ”The Land that ScrumForgot”http://www.youtube.com/watch?v=hG4LH6P8Syk→ History about agile methods, the agile manifesto, and

Scrum and its relationshop to XP

Lean Software Development

I Lean Production:I Value for the customerI Reduce the amount of waste in the production processI Generate flow

I Waste: resources used which do not produce value for thecustomer

I time needed to fix bugsI time to change the system because it does not fit the

customers requirementsI time waiting for approvalI . . .

Generating flow using Pull and Kanban

WIP = Work in Progress Limit

1324

A T IWork Item DoneDQueue WIP Queue QueueQueue WIP WIP WIP

8

7

9

10

5

6

BlahComposite

Leaf Assembly4 2 3

3 3 3 3

Flow through Pull with Kanban

I Process controlling: local rulesI Load balancing: Kanban cards and Work in Progress

(WIP) limitsI Integration in other processes

Figure from David Anderson www.agilemanagement.net

Online Kanban Tool: Trello

I www.trello.com: Electronic Kanban board useful foryour project

I Kanban board the exam project example https://trello.com/b/CqzwTiRT/02291-example-lean

I Another https://trello.com/b/4wddd1zf/kanban-workflow

Process for the exam project

1. Create workflows2. Create use case diagrams3. Select 6 use cases4. Determine basic (intended) architecture5. Pair modelling: 2 people work together→ https:

//trello.com/b/CqzwTiRT/02291-example-lean

I Meet often to coordinate the designI Update your plan, use cases, detailed use cases,

acceptance tests, etc. as needed→ Important for grading: models have to be consistent with

each other6. Check the acceptance tests and use case realization for all

use case scenarios

Important!

Report structure 6= project structureI Report structure: waterfall (by technique)I Project structure: agile (by user case scenario)

Contents

Principles of Good Design

Software Development Process

Project IntroductionDescription of the toll systemTaskOrganization

Exam Project: Model of a Toll System

I ReportI 45 min group presentation

A detailed project description can be found on CampusNet

Toll Lane

Toll Lane

Cash Register

Credit Card Reader

Printer

Single Ticket Reader

Toll Lane ComputerTouchscreen

Bank

))) (((

Antenna

1)

1)1)

1)

3) 2)

1) Only normal check-in lane2) Only normal check-out lane3) Only express lane (check-in and check-out)

Barrier

1,2,3)

1)

Toll Station

Toll Lane

Toll Station

Toll Lane

Toll Lane

Toll Lane

::

Station Server Station Client

Enterprise

Toll Station

Enterprise

Toll Station

Toll Station

Toll Station

::

Enterprise ServerEnterprise Client

Webserver

Functionality

I Check-inI Express Lane with toll tagI Normal Lane using a single ticket with cash / credit card

I Check-outI Express Lane with toll tagI Normal Lane using a ticket

I Buy Toll TagI Show ReportsI Change RateI Notify CustomersI Adminstration

Tasks

I TasksI Analyse the requirementsI Acceptance testsI Design the system: Components, Interfaces, PSM’s,

Classes, LSM’s, OCL constraintsI Use case realizations as sequence diagrams

I General remarksI Abstract from any physical implementation, e.g. embedded

system, communication protocol, . . .I Abstract away from any concrete user interface

representation: Application layer functionalityI Focus on the 6 use cases you have chosen

Evaluation Criteria

Evaluation CriteriaHow well are the learning objectives in the course descriptionaccomplished by each participant.

I Danish law: Be able to evaluate everybody individuallyI Two aspects:

a) to give a fair evaluation to each of youb) to be able to detect possible differences

→ For each section, diagram etc. name who did it (at mosttwo names)

I Make sure that everybody did something of everythingI In the project presentation: Everybody should have

I read the project reportI be able to explain each part of the model

Evaluation Criteria (cont.)

I Correct use of UML diagrams and OCL constraintsI Understandability of the designI Correct use case realizations that are consistent with the

LSM’s, PSM’s, classes, interfaces, etc.I Correct implementation of componentsI Correct object life cycle state machineI Appropriate abstraction level of the design

Organization

I Start: TodayI End: Wednesday 2.5I Upload the report as PDF and with the correct name on

Campus Net using the assignment moduleI Project presentations

I Mon 28.5—Tue 29.5I 45 min: around 10 min slides presentation; rest is Q&A

I Teaching assistants and I are available for questions /clarifications

I More detailed specification of the problem is on CampusNetI Lectures continueI No specific exercises, but exercise session 8:15—10:00 will

be kept for questions

Project: Rules on Cheating

Rules for Quoting (from Study Handbook Sect. 3.9)”. . . The rules regarding citations and references to sources inwritten assignments are that citations must be indicated byquotation marks at the start and end of the citation and thesource of the citation must be referred to either in parenthesesor in a note to the text. When not citing directly but basing thediscussion on a specific source, the source must be referredto either in parenthesis or a note to the text. . . . ”

→ Usual rules for referencing sources: sources must benamed

Course

I 2 more lecturesI Week 10: Model-driven architecture (MDA) and Agile

modellingI Week 11: Verification of models: Model checkingI Week 12: No lectureI Week 13: No lecture