© Trygve Reenskaug 2008UMLChina Slide 1 20 November 2015 The Common Sense of Object Oriented...

© Trygve Reenskaug 2008UMLChina Slide 1April 20, 2023

The Common SenseThe Common Senseof of Object Oriented ProgrammingObject Oriented Programming

Trygve ReenskaugDepartment of InformaticsUniversity of Oslo

UMLChina, December, 2008

http://folk.uio.no/trygver/


Plan for talkPlan for talk1958- My first programs

Software engineering in focus

1960- Ship CAD/CAMShip designer in focus

1970- Distributed computingBusiness organization in focus

1978- MVCUser experience i focus

1980- Role modelingModeling processes in focus

1997- BabyUML- DCI paradigmObject oriented programming in focus

2008- BabyIDEHabitable programming tools in focus


Autokon Autokon (1960 -)(1960 -)

Ship Design and ManufactureShip Design and ManufactureMental model

Flame cutter

Computer

http://heim.ifi.uio.no/~trygver/2003/HiNC/hinc-18final.pdf


What it is All AboutWhat it is All AboutBuild Tools for the End UsersBuild Tools for the End Users

Program

mentalmodel

magic

commands

presentations


System DistributionSystem Distributionreflects organization structure reflects organization structure

http://heim.ifi.uio.no/~trygver/1973/iccas/1973-08-ICCAS.pdf


View

MVCMVCModel – View – Model – View – ControllerController (1 of 2)(1 of 2)

Model

User

magicmentalmodel

Illusion of magic:User works with own Mental Model


MVC makes a ToolMVC makes a ToolController Coordinates ViewsController Coordinates Views

Model

User View

Controller

*1

magicmentalmodel

Illusion of magic:User works with own Mental Model


Modeling Use Case with RolesModeling Use Case with Rolesa business organizationa business organization

Ruth(President)

Ann(Consultant)

Bill(Dispatcher)

Joyce(Sales clerk)

Douglas(Marketing manager)

Kim(Methodologist)

Peter(Technical author)

Elsie(Programmer)

Eve(Software Manager)

John(Cashier)

Bill(Bookkeeper)

Joe(Paymaster)

Adam(Chief Accountant)


Modeling Use Case with RolesModeling Use Case with Rolessample expense account processsample expense account process

Ruth(President)

Ann(Consultant)

Bill(Dispatcher)

Joyce(Sales clerk)


Kim(Methodologist)


Elsie(Programmer)


John(Cashier)

Bill(Bookkeeper)

Joe(Paymaster)


6:5:

4:3: 2: 1:


Modeling with RolesModeling with Rolesthe role abstractionthe role abstraction

Ruth(President)

Ann(Consultant)

Bill(Dispatcher)

Joyce(Sales clerk)


Kim(Methodologist)


Elsie(Programmer)


John(Cashier)

Bill(Bookkeeper)

Joe(Paymaster)


6:5:

4:3: 2: 1:

Cashier

Bookkeeper Traveler

Authorizer

Reenskaug et.al.: Working with objects. The OOram Software Engineering Method.Manning 1996; ISBN 1-884777-10-4.

6:5:

4: 3:2: 1:

Interaction

Context

Data


Gamma, Helm, Johnson, Vlissides:Gamma, Helm, Johnson, Vlissides:Design PatternsDesign Patterns

An object-oriented program's run-time structure often bears little resemblance to its code structure.

• The code structure is frozen at compile-time; it consists of classes in fixed inheritance relationships.

• The run-time structure consists of rapidly changing networks of communicating objects.

…, it's clear that code won't reveal everything about how a system will work.

[GOF] Gamma, E; Helm, R; Johonson, R; Vlissides, J: Design Patterns; ISBN 0-201-63361-; Addison-Wesley, Reading, MA. 1995. p.22, 23


The DCI ParadigmThe DCI ParadigmSystem state and System behaviorSystem state and System behavior

D ata The data classes- What the system IS

C ontextThe roles and their connectors- The stage where things happen

I nteractionThe players interact to achieve a use case- What the system DOES and how it does it


““Rapidly changing networks of Rapidly changing networks of communicating objects”communicating objects”

ID=442

ID=993

ID=784

ID=351ID=436

http://heim.ifi.uio.no/~trygver/assets/animate-arrows.mpeg


Edsger W. DijkstraEdsger W. Dijkstrafrom “GOTO considered harmful”from “GOTO considered harmful”

• our powers to visualize processes evolving in time are relatively poorly developed.

• shorten the conceptual gap between the static program and the dynamic process,

• make the correspondence between the program (spread out in text space) and the process (spread out in time) as trivial as possible.


magic

Programmer Centered Programmer Centered ProgrammingProgramming

Program

mentalDCI

model

BabyIDE

Programmer Computer


BabyIDE screendumpBabyIDE screendumpInteraction perspectiveInteraction perspective

A B

C D


ConclusionConclusionDCI = Readable CodeDCI = Readable Code

The DCI paradigm:Work with program in different perspectives

• D ata Classes for what the system IS

• C ontext for seeing the Roles and Objects

• I nteraction for what the system DOES

Dijkstra’s ideal:make the correspondence between

the program (spread out in text space) and

the process (spread out in time) as trivial as possible.


State of BabyIDE ProjectState of BabyIDE ProjectDCI

Squeak mechanism readyImplementations in C++, Ruby, Scala, Python in progress. Java is difficult.

BabyIDESqueak Demo version availableSqueak Alpha version soon

Professional IDEBasic technology is open, I hope professional toolmakers will pick it up.

For now:No general tools availableThink about the reader of your codeTry Mediator pattern!


That’s all.

Thank you for listening.

Comments, Questions?

http://heim.ifi.uio.no/~trygver/


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Oslo, Norway.

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© Trygve Reenskaug 2008UMLChina Slide 1 20 November 2015 The Common Sense of Object Oriented...

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