1. Models and Reality: Master Program Execution with DCI
UML China 2010
19-Sep-18
Models and Reality: Master Program Execution with DCI
UML China 2010
Trygve Reenskaug
Dept. of Informatics
University of Oslo
heim.ifi.uio.no/~trygver/themes/babyide
©2010 Trygve Reenskaug
UML-China 2010
:30

2. Two commonly believed Fallacies
UML China 2010
Two commonly believed Fallacies
19-Sep-18
End users cannot understand modern programs
FALSE BECAUSE: Object Models are understandable
BUT: Code must implement user mental model
Programmers cannot read modern programs
FALSE BECAUSE: Object systems can be coded to be readable and checkable
BUT: Code must describe program runtime structure
©2010 Trygve Reenskaug
UML-China 2010
:30

3. Reality program execution creates value
UML China 2010
Reality program execution creates value
19-Sep-18
IDE
Personal plans
Project control
Calender
Accounting
©2010 Trygve Reenskaug
UML-China 2010
:30

4. End User System Experience
UML China 2010
End User System Experience
19-Sep-18
End User mental model
domain model (what the system IS)
use cases
(what the system DOES)
Runtime
(objects and interactions)
Chasm
Compile time
(classes, superclasses)
class model
code
Programmer mental model
©2010 Trygve Reenskaug
UML-China 2010
:30

5. Plan The User’s mental model Object Orientation CRC Cards
UML China 2010
Plan
19-Sep-18
The User’s mental model
Object Orientation
CRC Cards
Lean and Agile
The Programmer’s mental model
Defect removal
Conclusion
©2010 Trygve Reenskaug
UML-China 2010
:30

6. Object-Orientation: networks of communicating objects
UML China 2010
Object-Orientation: networks of communicating objects
19-Sep-18
Alan Kay:
Each Smalltalk object is a recursion on the entire possibilities of the computer.
Thus its semantics are a bit like having
thousands and thousands of computers all hooked together by a very fast network
The essence of object orientation
is the interchange of messages
that takes place in the space between the objects
©2010 Trygve Reenskaug
UML-China 2010
:30

7. True Object Orientation Objects as participants in commnication
UML China 2010
True Object Orientation Objects as participants in commnication
19-Sep-18
receive
methods
memory
receive
methods
memory
receive
methods
memory
©2010 Trygve Reenskaug
UML-China 2010
:30

8. End User performs a Money Transfer What the System DOES
UML China 2010
End User performs a Money Transfer What the System DOES
19-Sep-18
©2010 Trygve Reenskaug
UML-China 2010
:30

9. End User’s Mental Model What the system DOES
UML China 2010
End User’s Mental Model What the system DOES
19-Sep-18
Customer
Bank
FromAccount
ToAccount
transfer ( amount, fromAccount, toAccount)
transfer (...)
deposit (...)
©2010 Trygve Reenskaug
UML-China 2010
:30

10. Three Use Case Executions Money Transfers
UML China 2010
Three Use Case Executions Money Transfers
19-Sep-18
use case execution
use case execution
use case execution
Class ATM
Class SavingsAccount
Class CheckingAccount
©2010 Trygve Reenskaug
UML-China 2010
:30

11. Name the objects by the roles they play in the Interaction
UML China 2010
Name the objects by the roles they play in the Interaction
19-Sep-18
662454
136585
748534
995124
254967
245872
554782
221483 ID
use case executions
ATM
SavingsAccount
CheckingAccount
---
Class
Bank FromAccount
ToAccount
Bank
FromAccount
---
Role
©2010 Trygve Reenskaug
UML-China 2010
:30

12. CRC Class – Responsibility – Collaboration
UML China 2010
CRC Class – Responsibility – Collaboration
19-Sep-18
Wikipedia: Sloppy thinking
CRC cards are usually created from index cards on which are written:
The class name
Its Super and Sub classes (if applicable)
The responsibilities of the class.
The names of other classes with which the class will collaborate to fulfill its responsibilities.
Author
©2010 Trygve Reenskaug
UML-China 2010
:30

13. CRC Candidate – Responsibility – Collaboration
UML China 2010
CRC Candidate – Responsibility – Collaboration
19-Sep-18
CRC cards are usually created from index cards on which are written:
The role name.
The responsibilities of the roles (and the objects that play them).
The names of other roles with which the role will collaborate to fulfill its responsibilities.
Author.
Candidate role – Responsibility -- Collaboration
Wirfs-Brock; McKean: Object Design. Roles, Responsibilities, and Collaborations
©2010 Trygve Reenskaug
UML-China 2010
:30

14. role name = FromAccount
UML China 2010
CRC Cards Example
19-Sep-18
role name = Bank
responsibility =
To serve the customer with a transfer of funds
collaborators = FromAccount
role name = FromAccount
responsibility =
To transfer funds from this account to its collaborator
collaborators = ToAccount
role name = ToAccount
responsibility =
To receive funds as part of a funds transfer
collaborators = none
©2010 Trygve Reenskaug
UML-China 2010
:30

15. Summary Object Models are understandable
UML China 2010
19-Sep-18
End user mental model explains how the system works.
End user mental model is an object model:
Objects
Can store data
Can handle received messages
Can send messages to other objects
Objects interact to to achieve a use case
Objects are named by the role they play in the interaction
©2010 Trygve Reenskaug
UML-China 2010
:30

16. Coplien, Bjørnvig: Lean Architecture ISBN: 978-0-470-68420-7
UML China 2010
Coplien, Bjørnvig: Lean Architecture ISBN:
19-Sep-18
Building Software as if people mattered
No waste Get it right the first time! Be prepared for changes!
Lean Principle: ”everybody, all together, from early on.”
System architecture shall reflect the end user's mental model.
Architecture has two parts: What the system IS: Its state What the system DOES: Its behavior
Architecture a skeleton program
©2010 Trygve Reenskaug
UML-China 2010
:30

17. Plan The Programmer’s mental model The Chasm betweenCode and Execution
UML China 2010
Plan
19-Sep-18
The User’s mental model
Object Orientation
CRC Cards
Lean and Agile
The Programmer’s mental model
The Chasm betweenCode and Execution
What the system IS – What the system DOES
Separation of concerns: Contexts with Roles
DCI: Data – Context – Interaction
Defect removal
Conclusion
©2010 Trygve Reenskaug
UML-China 2010
:30

18. Gamma, Helm, Johnson, Vlissides: Design Patterns
UML China 2010
Gamma, Helm, Johnson, Vlissides: Design Patterns
19-Sep-18
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 p.22, 23]
©2010 Trygve Reenskaug
UML-China 2010
:30

19. The Essence of Object Orientation
UML China 2010
The Essence of Object Orientation
19-Sep-18
a class reveals everything about how an instance will handle an incoming message and reveals nothing about its collaborator or why the message was sent.
an object by itself is not interesting
the essence of object orientation is that objects communicate to achieve a common goal
We need explicit code that clearly specifies the Contexts, i.e., the networks of communicating roles
©2010 Trygve Reenskaug
UML-China 2010
:30

20. Class Hierachy is Irrelevant for program execution
UML China 2010
Class Hierachy is Irrelevant for program execution
19-Sep-18
Object
Wikipedia: Code refactoring is the process of changing a computer program's
source code without modifying its external functional behavior.
copy
Shape
center area
F_Circle
F_Polygon
Circle
Polygon
copy
center area radius
copy
center area vertices
radius
vertices
©2010 Trygve Reenskaug
UML-China 2010
:30

21. The Chasm between End User and Programmer
UML China 2010
The Chasm between End User and Programmer
19-Sep-18
End User mental model
domain model (what the system IS)
use cases
(what the system DOES)
Runtime
(objects and interactions)
Chasm
Compile time
(classes, superclasses)
class model
code
Programmer mental model
©2010 Trygve Reenskaug
UML-China 2010
:30

22. Use Case Context and Roles
UML China 2010
Use Case Context and Roles
19-Sep-18
BankTransferContext
Environment
role Bank
role ToAccount
transfer ( amount, fromAccount, toAccount)
role FromAccount
transfer (..)
deposit (..)
Customer
role methods
©2010 Trygve Reenskaug
UML-China 2010
:30

23. Each Use Case Is Executed in a Context
UML China 2010
Each Use Case Is Executed in a Context
19-Sep-18
Context-2
Use case-2
Context-1
Use case-1
Use case-3
Context-3
Role binding +Role Method injection
©2010 Trygve Reenskaug
UML-China 2010
:30

24. Three Perspectives Data – Context - Interaction
UML China 2010
Three Perspectives Data – Context - Interaction
19-Sep-18
Compile time
Data, Context, Interaction
Object model
code
Data – What-The-System-IS Implementation of user’s domain model Dumb, dumb classes and superclasses without interaction code.
Context – The Roles Participating in a Use Case Roles and role structure Select objects to play the roles. Inject role methods into selected objects (or their classes) Trigger Interaction.
Interaction – What-The-System-DOES Role Methods direct the execution of the Use Case
©2010 Trygve Reenskaug
UML-China 2010
:30

25. Programmer’s Mental Model Data Perspective
UML China 2010
Programmer’s Mental Model Data Perspective
19-Sep-18
End User
domain model
Conceptual schema
«realize»
Class attributes
+ local methods
«instantiate classes to object»
data objects
©2010 Trygve Reenskaug
UML-China 2010
:30

26. Programmer’s Mental Model Context Perspective
UML China 2010
Programmer’s Mental Model Context Perspective
19-Sep-18
End User
use cases
Environment
use case
Context
Role
Role
Role
Bind roles to objects
data objects
©2010 Trygve Reenskaug
UML-China 2010
:30

27. Programmer’s Mental Model Interaction Perspective
UML China 2010
Programmer’s Mental Model Interaction Perspective
19-Sep-18
Class definitions
Context Role Method definitions
package babydemo3.model;
import babydemo3.model.Model;
import babydemo3.model.collaboration.*;
import babydemo3.model.algorithm.*;
import babydemo3.model.data.*;
import java.util.*;
import java.awt.Color;
public class Model extends Observable {
private NetBase netBase;
private Resource resource;
public Model() {}
public Resource resource() {}
public void reset() {}
public void addActivity(String name, Integer duration, Color color) {}
public void addDependency(String predName, String succName) {}
public void frontloadNetwork(Integer startWeek) {
RoleB.frontload(startWeek); setChanged();
notifyObservers("ACTIVITY"); }
RoleA>> public void frontloadNetwork(Integer startWeek) {
RoleB.frontload(startWeek); setChanged();
notifyObservers("ACTIVITY"); }
RoleB>>public void frontload(Integer startWeek) {
// reset all
for (Activity act : AllActivities) {
act.setEarlyStart(null);
} // frontload all
Activity frontloader;
while (CurrentContext.rebind(); Activity != null) {
Integer earlyStart = startWeek;
for (Activity pred : Predecessors) {
earlyStart = Math.max(earlyStart, pred.earlyFinish() + 1);
Activity.setEarlyStart(earlyStart);
package babydemo3.model.algorithm;
import babydemo3.model.Model;
import babydemo3.model.data.Activity;
import babydemo3.model.collaboration.FrontloadCollab;
public class Case {
private Plan model; }
public void frontload(Integer startWeek) {
// reset all
for (Activity act : AllActivities) {
act.setEarlyStart(null);
} // frontload all
Activity frontloader;
while (CurrentContext.reselect(); Activity != null) {
Integer earlyStart = startWeek;
for (Activity pred : Predecessors) {
earlyStart = Math.max(earlyStart, pred.earlyFinish() + 1);
Activity.setEarlyStart(earlyStart);
inject role methods
©2010 Trygve Reenskaug
UML-China 2010
:30

28. Programmer’s Mental Model The Whole Story
UML China 2010
Programmer’s Mental Model The Whole Story
19-Sep-18
End User
use cases
domain model
Conceptual schema
Environment
use case task
realize
Context
Role
Role
Class attributes
+ local methods
+ role methods
Inject role methods
Role
«instantiate classes to objects»
«bind roles to objects»
data objects
interaction
©2010 Trygve Reenskaug
UML-China 2010
:30

29. Plan Defect removal Lean: Get it right the first time
UML China 2010
Plan
19-Sep-18
The User’s mental model
Object Orientation
CRC Cards
Lean and Agile
The Programmer’s mental model
The Chasm betweenCode and Execution
What the system IS – What the system DOES
Separation of concerns: Contexts with Roles
DCI: Data – Context – Interaction
Defect removal
Lean: Get it right the first time
Chunkable, readable code. BabyIDE.
Software Peer Review
Conclusion
©2010 Trygve Reenskaug
UML-China 2010
:30

30. Edsger W. Dijkstra on Bugs
UML China 2010
Edsger W. Dijkstra on Bugs
19-Sep-18
"Program testing can be used to show the presence of bugs, but never to show their absence!“
"Simplicity is prerequisite for reliability.“
©2010 Trygve Reenskaug
UML-China 2010
:30

31. Peer Review Datamation Magazine ca. 1967
UML China 2010
Peer Review Datamation Magazine ca. 1967
19-Sep-18
It’s hard to find bugs in own code
It’s fun to find bugs in other people’s code
Coder learns from reviewer’s comments
Reviewer learns by reading the code
Wikipedia: savings exceeds costs by 4 to 1".
Get it right the first time!
Test to confirm no blunder! --- but execute all statements
Code must be Chunkable! Readable!
©2010 Trygve Reenskaug
UML-China 2010
:30

32. Code must be Chunkable! Readable!
UML China 2010
Code must be Chunkable! Readable!
19-Sep-18
DCI Separation Of Concerns:
Data: Data classes greatly simplified; realize ’pure’ data model.
Context: One Context for each use case, isolated from other Contexts.
Interaction: Roles only meaningful within their Context Role to object binding done within one chunk of methods. The Role Methods specify system behavior
©2010 Trygve Reenskaug
UML-China 2010
:30

33. BabyIDE DCI Integrated Development Environment
UML China 2010
BabyIDE DCI Integrated Development Environment
19-Sep-18 2 1 3 4
©2010 Trygve Reenskaug
UML-China 2010
:30

34. Plan Conclusion The User’s mental model Object Orientation CRC Cards
UML China 2010
Plan
19-Sep-18
The User’s mental model
Object Orientation
CRC Cards
Lean and Agile
The Programmer’s mental model
The Chasm betweenCode and Execution
What the system IS – What the system DOES
Separation of concerns: Contexts with Roles
DCI: Data – Context – Interaction
Defect removal
Lean: Get it right the first time
Chunkable, readable code. BabyIDE.
Software Peer Review
Conclusion
©2010 Trygve Reenskaug
UML-China 2010
:30

35. Conclusion – 1 of 4 DCI = Readable Code
UML China 2010
Conclusion – 1 of 4 DCI = Readable Code
19-Sep-18
The DCI paradigm:
Work with program in different perspectives
D ata Classes for what the system IS
C ontext for the network of communicating roles
I nteraction for what the system DOES
©2010 Trygve Reenskaug
UML-China 2010
:30

36. Conclusion – 2 of 4 DCI = Changeable Code
UML China 2010
Conclusion – 2 of 4 DCI = Changeable Code
19-Sep-18
Data perspective compact; system state only.
Role/object selection separates system state and system behavior.
Existing Contexts can be changed independently.
New Contexts can be added to realize new funtionality.
©2010 Trygve Reenskaug
UML-China 2010
:30

37. Conclusion – 3 of 4 End User Mental Model = Code
UML China 2010
Conclusion – 3 of 4 End User Mental Model = Code
19-Sep-18
End User mental model
domain model (what the system IS)
use cases
(what the system DOES)
Runtime
(objects play roles)
instantiate data classes to objects
context selects objects to play roles inject role methods
Chasm Bridged!
Compile time
(Data, Context, Interaction)
Object model
code
Programmer mental model
©2010 Trygve Reenskaug
UML-China 2010
:30

38. Conclusion – 4 of 4 State of DCI
UML China 2010
Conclusion – 4 of 4 State of DCI
19-Sep-18
DCI Implementation examples in Smalltalk/Squeak, C++, Java, C#, Ruby, Scala, Python. Real applications in Java (Qi4j, Rickard Øberg).
New DCI Programming Language being developed.
BabyIDE Squeak Demo version available Basic technology is freely available for toolmakers
For now: Read the “Lean Architecture” book Read Wikipedia article Never forget the end user of your code Never forget the reader of your code DCI Community at
©2010 Trygve Reenskaug
UML-China 2010
:30

39. Comments? Questions? UML China 2010 19-Sep-18 ©2010 Trygve Reenskaug
:30

40. More reading UML China 2010 19-Sep-18
mailto:
Coplien, J.O., Bjørnvig, G; Lean Architecture for Agile Software Development; Wiley, Chichester, UK, 2010; ISBN
Reenskaug, T; Wold, P.;, Lehne, O. A.: Working With Objects; Manning, Greenwich, CT 06830;1996; ISBN ; (Prentice Hall ISBN ). This book is out of print. An early .pdf version kan be downloaded free from [web page]
Important Web resources: Kay on object orientation: The DCI defining reference: A technical article: More online resources:
Reenskaug, T.: Programming with Roles and Classes; the BabyUML Approach; Chapter in Klein, A.D.; Computer Software Engineering Research; Nova Science Publishers, New York, 2007; ISBN-13: ;pp.45-88; [web page]
Reenskaug, T,: The BabyUML discipline of programming (where A Program = Data + Communication + Algorithms). SoSym 5,1 (April 2006). DOI: /s x. [web page]
Wirfs-Brock, R.; McKean, A.; Object Design. Roles, Responsibilities, and Collaborations. ISBN 0‑201‑37943‑0; Addison-Wesley; Boston, MA, 2003.
Andersen, E. P.; Conceptual Modeling of Objects. A Role Modeling Approach. D.Scient thesis, November 1997, University of Oslo. [web page]
Gamma et.al. (GOF) Design Patterns; ISBN ; Addison-Wesley, Reading, MA
©2010 Trygve Reenskaug
UML-China 2010
:30