MVC and DCA:
Two complimentary
system architectures.
Trygve Reenskaug
Department of Informatics
University of Oslo
trygver@ifi.uio.no
http://heim.ifi.uio.no/~trygver/2006/09-JavaZone/
MVC and DCA: JavaZone 2006
© Trygve Reenskaug 2006
2016.05.29
Slide 1
The BabyUML Project
The essence of object orientation is that
objects interact to accomplish some desired
The pricefunctionality.
of reliability is the
pursuit of the utmost simplicity
BabyUML
Goal:
(C.A.R.
Hoare, 1980 Turing Award lecture)
Answer explicitly
– What are the objects?
– How are they interlinked?
– How do they interact?
Do more – type less
MVC and DCA: JavaZone 2006
© Trygve Reenskaug 2006
2016.05.29
Slide 3
Model – View - Controller
mental
model
User
computer
data
Model
View
View bridges gap between
user Mental model and
Computer data
MVC and DCA: JavaZone 2006
© Trygve Reenskaug 2006
2016.05.29
Slide 4
Model – View - Controller
mental
model
User
Controller
computer
data
*
1
View
*
*
Model
View
View bridges gap between
user
Mental
model
and
Controller creates and coordinates
Computer
data Run Demo
multiple
Views
MVC and DCA: JavaZone 2006
© Trygve Reenskaug 2006
2016.05.29
Slide 5
MVC Demo
http://heim.ifi.uio.no/~trygver/2006/09-JavaZone/babyExample4.html
MVC and DCA: JavaZone 2006
© Trygve Reenskaug 2006
2016.05.29
Slide 6
The Anatomy of
MVC Demo
controller
:Controller
panelView
:DependencyPanel
:ActivityView
http://heim.ifi.uio.no/~trygver/2006/09-JavaZone/babyExample4.html
MVC and DCA: JavaZone 2006
© Trygve Reenskaug 2006
2016.05.29
Slide 7
MVC
example
Synchronized Selection
focusView
User
pointAndClickMouse
controller
actionPerformed()
activityView*
selectionChanged()
isSelected()
present
MVC and DCA: JavaZone 2006
© Trygve Reenskaug 2006
2016.05.29
Slide 8
MVC
example
Synchronized Selection
class Controller {
Activity
selection;
inputView
controller
leafView*
User
public void actionPerformed (ActionEvent e) {
pointAndClickMouse
ActivityView source = (ActivityView) e.getSource();
selection = source.activity();
actionPerformed()
for (ActivityView
view : activityViews) {
selectionChanged()
view.selectionChanged();
}
isSelected()
repaint();
}
public boolean isSelected (Activity act)
{
present
return ( selection == act );
}
MVC and DCA: JavaZone 2006
© Trygve Reenskaug 2006
2016.05.29
Slide 9
Model – View - Controller
controller
MVC and DCA: JavaZone 2006
Model
© Trygve Reenskaug 2006
2016.05.29
Slide 10
the Model
as a single Object
illustration copied from
The Java Tutorial
Copyright 1995-2005
Sun Microsystems, Inc.
methods
(behavior)
derived attributes
owned
attributes
(state)
MVC and DCA: JavaZone 2006
© Trygve Reenskaug 2006
2016.05.29
Slide 11
the DCA Model Component
Data + Collaboration + Algorithm
Algorithms
Collaborations
Data
netBase
activities
dependencies
member
Objects
(behavior)
MVC and DCA: JavaZone 2006
(derived attributes)
(external data view)
© Trygve Reenskaug 2006
2016.05.29
resource
allocations
(owned attributes)
(base data)
Slide 12
DCA
netBase – UML schema
Data
Activity
name
earlyStart
successor
earlyFinish
*
DependencyPanel
duration
Dependency
color
netBase
activities
dependencies
allocations
GanttPanel
resource
*
predecessor
ResourcePanel
MVC and DCA: JavaZone 2006
© Trygve Reenskaug 2006
2016.05.29
Slide 14
DCA
netBase - Java
public class Activity {
private Integer earlyStart, earlyFinish, duration;
private String name;
private Color color = Color.gray; ….
activities
netBase
public class BabyBase extends Observable implements Observer {
private Set<Activity> activities;
private Set<MemberDependency> dependencies;
dependencies
Java as schema language
resource
allocations
public class MemberDependency {
private Activity predecessor, successor; ...
Data
(state)
MVC and DCA: JavaZone 2006
© Trygve Reenskaug 2006
2016.05.29
Slide 15
First DCA example
DependencyPanel layout + collaboration
activities
dependencies
DependencyPanel
network
Base
layout Algorithm
allocations
(behavior)
GanttPanel
Collaboration
(external data view)
resource
Base
Data
(state)
ResourcePanel
MVC and DCA: JavaZone 2006
© Trygve Reenskaug 2006
2016.05.29
Slide 17
DCA ex.1: DependencyPanel
responsible for layout Algorithm
layout Algorithm
Model
(behavior)
private void addActivityViews() {
activities
// Compute gridX, gridY, x0, y0, buttonExtent
for (int rank=0; rank <= rankedCollab.maxRank(); rank++) {
// compute xPos, yPos
for (Activity act : rankedCollab.activityListAtRank(rank)) {
dependencies
ActivityView actView = new ActivityView(controller,
act, 24) ;
DependencyPanel
add (actView);
yPos = yPos + gridY;
network
// misc. computations
layout Algorithm
GanttPanel
Base
(behavior) }
}
}
allocations
Collaboration
(external data view)
resource
Base
Data
(state)
ResourcePanel
MVC and DCA: JavaZone 2006
© Trygve Reenskaug 2006
2016.05.29
Slide 18
DCA ex.1:
RankedCollab
Query
Model
define activityListAtRank(Integer rank) as
select act
from DependencyPanel
activities act
where rank(act) = rank
dependencies
(external data view)
allocations
resource
rankedCollab
GanttPanel
netBase
activities
Data
(state)
ResourcePanel
MVC and DCA: JavaZone 2006
© Trygve Reenskaug 2006
2016.05.29
Slide 20
DCA ex.1:
RankedCollab
Java
Model
public List<Activity>
activityListAtRank (Integer rank) {
List<Activity> activityListAtRank
= new ArrayList<Activity>();
dependencies
DependencyPanel
for (Activity
act : bBase. allActivities()) {
if (rankOf(act)layout
== rank) {Algorithm
}
GanttPanel
return activityListAtRank ;
}
rankedCollab
(external data view)
allocations
resource
}
activityListAtRank.add(act);
(behavior)
netBase
activities
Data
(state)
ResourcePanel
MVC and DCA: JavaZone 2006
© Trygve Reenskaug 2006
2016.05.29
Slide 21
Second DCA example
frontloading
Model
activities
Algorithms
(behavior)
dependencies
network
Base
allocations
Collaborations
(external data views)
resource
Base
Data
(state)
MVC and DCA: JavaZone 2006
© Trygve Reenskaug 2006
2016.05.29
Slide 22
D
CA ex.2: frontloading
query - frontloader
Model
activities
Algorithms
DependencyPanell
define
frontloader as
(behavior)
dependencies
network
(select act
Base
from Activities act
allocations
where act.earlyStart == null
GanttPane
and (for all pred in predecessors(act): Collaborations
l
pred.earlyStart != null)
resource
(external data views)
Base
) someInstance
BabyDataBase
(state)
ResourcePane
l
MVC and DCA: JavaZone 2006
© Trygve Reenskaug 2006
2016.05.29
Slide 23
D
CA ex.2: frontloading
Java - frontloader
Model
activities
public Activity frontloader() {
for (Activity act : netBase.allActivities())A
{ lgorithms
if (act.earlyStart() == null) {
(behavior)
dependencies
Set<Activity>
predSet = predecessorsOf(act);
DependencyPanell
private
boolean areAllDone(Set<Activity>
actSet) {
if (areAllDone(predSet))
{
network
boolean
allPredsDone
=
true;
frontloader = act;
Base
for
( Activity
pred : actSet) {
return
(frontloader);
allocations
} if (pred.earlyStart() == null) {
GanttPane
}
allPredsDone = false;
Collaborations
}
l break;
resource
(external data views)
return }null;
Base
}
}
BabyDataBase
(state)
return allPredsDone;
}
ResourcePane
l
MVC and DCA: JavaZone 2006
© Trygve Reenskaug 2006
2016.05.29
Slide 24
DCA ex.2: frontloading
frontload algorithm - Java
Model
activities
public void frontload (Integer startWeek) {
// reset all
for (Activity act : frontloadCollab.resetters()) {
act.setEarlyStart (null);
}
DependencyPanell
Algorithms
(behavior)
dependencies
// frontload all
network
Activity frontloader;
Base
while ((frontloader = frontloadCollab.frontloader()) != null) {
allocations
Integer earlyStart = startWeek;
for (Activity pred : frontloadCollab.frontPredecessors()) {
GanttPane
ollaborations
earlyStart =
l Math.max(earlyStart, pred.earlyFinish() + 1);(external data views)
resource
Base
}
frontloader.setEarlyStart(earlyStart);
Baby ataBase
}
(state)
}
C
D
ResourcePane
l
MVC and DCA: JavaZone 2006
© Trygve Reenskaug 2006
2016.05.29
Slide 26
Second DCA example
compute earlyFinish
Model
activities
Algorithms
(behavior)
dependencies
public Integer earlyFinish() {
if (earlyStart != null) {
network
Base
return (earlyStart + duration – 1);
allocations
} else {
Collaborations
return null;
resource
(external data views)
}
Base
Data
}
(state)
MVC and DCA: JavaZone 2006
© Trygve Reenskaug 2006
2016.05.29
Slide 27
MVC – DCA
Critique
• MVC
– separate Model and View
• when GUI and Model are deployed on different machine.
• when the application code is complex.
– write several View classes for the same Model class
• when the user needs to see the Model from several perspectives.
– write a Controller class to create and coordinate the Views
• when the user needs to see them simultaneously.
• DCA
– simplify Data with a baby database
• when the data structure is complex.
– separate out data queries in Collaboration classes
• if Algorithms need to see data from different perspectives.
– create a separate Algorithm class
• if the Algorithm spans several member objects.
MVC and DCA: JavaZone 2006
© Trygve Reenskaug 2006
2016.05.29
Slide 28
The BabyUML Project
Status
The essence of object orientation is that
objects interact to accomplish some desired
The pricefunctionality.
of reliability is the
pursuit of the utmost simplicity
BabyUML
Goal:
(C.A.R.
Hoare, 1980 Turing Award lecture)
Answer explicitly
What are the objects? Database definition
How are they interlinked? Collaboration
How do they interact? Algorithm
Do more – type less Remains to be done
MVC and DCA: JavaZone 2006
© Trygve Reenskaug 2006
2016.05.29
Slide 29
More reading
http://www.ifi.uio.no/~trygver
mailto: trygver ‘at’ ifi.uio.no
dca-demo example code:
http://heim.ifi.uio.no/~trygver/2006/09-JavaZone/BabyProject-2/
Trygve Reenskaug: Original MVC notes from Xerox PARC
http://heim.ifi.uio.no/~trygver/1979/mvc-1/1979-05-MVC.pdf
http://heim.ifi.uio.no/~trygver/1979/mvc-2/1979-12-MVC.pdf
Charles Antony Richard Hoare: The Emperor's Old Clothes. 1980 Turing Award lecture. Comm.ACM 24, 2 (Feb. 1981)
Trygve Reenskaug: The BabyUML discipline of programming
(where A Program = Data + Communication + Algorithms).
SoSym 5,1 (April 2006). DOI: 10.1007/s10270-006-0008-x.
http://heim.ifi.uio.no/~trygver/2006/SoSyM/trygveDiscipline.pdf
Unified Modeling Language: Superstructure. Version 2.1.
Object Management Group (OMG) document ptc/06-04-02. http://www.omg.org
Cattell, Barry: The Object Data Standard: ODMG 3.0.
Academic Press, London, 2000. ISBN 1-55860-647-4
Erik Arisholm and Dag Sjøberg: A Controlled Experiment with Professionals to Evaluate the Effect of a Delegated
versus Centralized Control …,
Simula Research Laboratory Technical Report 2003-6
http://www.simula.no/publication_one.php?publication_id=601
Reenskaug, Wold, Lehne: Working With Objects.
This book is out of print. A .pdf version kan be downloaded free from
http://www.ifi.uio.no/~trygver
Donald A. Norman: The Design of Everyday Things.
Doubleday/Currency 1990. ISBN 0-385-26774-6
MVC and DCA: JavaZone 2006
© Trygve Reenskaug 2006
2016.05.29
Slide 30