Two System Architectures:
MVC and DCA
Spinoff from
the BabyUML project
for Readable Programs
Trygve Reenskaug
Department of Informatics
University of Oslo
trygver@ifi.uio.no
http://www.ifi.uio.no/~trygver
MVC & DCA - ROOTS 2006
© Trygve Reenskaug 2006
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Slide 1
an Activity Network Planning
example
MVC & DCA - ROOTS 2006
© Trygve Reenskaug 2006
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Slide 3
My Problem
Undisciplined communication → Spaghetti
User
tools Class
actA
actC
+ superclasses + methods → Noodles
actB
Project
resources
Project
activities
actD
Class
Class
Class
MVC & DCA - ROOTS 2006
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Slide 4
BabyUML Goal:
Readable Programs
The price of reliability is the pursuit of
the utmost simplicity
(C.A.R. Hoare, 1980 Turing Award lecture)
MVC & DCA - ROOTS 2006
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Slide 5
The BabyComponent =
an object encapsulating other objects
resource
resource
«Component»
«Component»
network
network
«Component»
«Component»
tool
«Component»
tool «Component»
MVC & DCA - ROOTS 2006
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Slide 6
Baby Components
Universe of Discourse
«component» babydemo
demoData
tool
«Interface»
DemoDataIntf
resource
«Interface»
Observer
«Interface»
ResourceIntf
«Interface»
NetworkIntf
network
«Class»
ActivityDescr
MVC & DCA - ROOTS 2006
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Slide 7
The BabyDemo program
demodata + network + resource + tool
+IDE
MVC & DCA - ROOTS 2006
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Baby Components
Divide and Conquer: the tool
demoData
tool
resource
«Interface»
Observer
«Interface»
ResourceIntf
«Interface»
NetworkIntf
network
«component» babydemo
«Interface»
DemoDataIntf
«Class»
ActivityDescr
MVC & DCA - ROOTS 2006
© Trygve Reenskaug 2006
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Slide 11
Model – View - Controller
bridge gap
Mental Model – Computer
mental
model
computer
model
Model
User
MVC & DCA - ROOTS 2006
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Slide 12
Model – View - Controller
Multiple Views on same Model
mental
model
computer
model
Model
User
1
*
View
*
Run Demo
MVC & DCA - ROOTS 2006
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Slide 13
Model – View - Controller
Tool = Controller + Views
mental
model
Controller
computer
model
*
1
User
*
*
Model
View
Tool
Run Demo
MVC & DCA - ROOTS 2006
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Slide 14
Model View Controller
Roles and Responsibilities
Model
View
Store domain information
Present and edit domain
information
Controller Build, manage and co-ordinate
Views
MVC & DCA - ROOTS 2006
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Slide 15
Example: babydemo.tool
Class structure
Java.awt.Component
java.awt.Panel
java.applet.Applet
Controller
ButtonsView
java.awt.Button
MVC & DCA - ROOTS 2006
DependencyView
GanttView
ResourceView
ActivityView
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Slide 16
Example: babydemo.tool
visual hierarchy (associations)
Controller
1
1
1
ButtonsView
DependencyView
1
1
GanttView
1
1
ResourceView
1
*
*
java.awt.Button
MVC & DCA - ROOTS 2006
1
ActivityView
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Slide 17
Example: babydemo.tool
MVC collaboration structure
Tool
controller,
observed, observer
view, observer
: ButtonsView
view, observer
: DependencyView
model.
observed
view, observer
: GanttView
view, observer
: ResourceView
button
: java.awt.Button
view, observer
: ActivityView
MVC & DCA - ROOTS 2006
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Slide 18
The Anatomy of
babyDemo.tool
controller : Controller
view
:ActivityView
view
:DependencyView
heim.ifi.uio.no/~trygver/2006/roots-2006/babyExample4.html
MVC & DCA - ROOTS 2006
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Slide 19
MVC
Synchronized Selection
a view
controller
observer*
User
pointAndClickMouse
actionPerformed()
selectionEvent()
notifyObserver()
update()
selectedObject
present
MVC & DCA - ROOTS 2006
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Slide 20
MVC
+IDE
tool component
MVC & DCA - ROOTS 2006
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Slide 21
Baby Components: the network
Divide and Conquer
demoData
tool
resource
«Interface»
Observer
«Interface»
ResourceIntf
«Interface»
NetworkIntf
network
«component» babydemo
«Interface»
DemoDataIntf
«Class»
ActivityDescr
MVC & DCA - ROOTS 2006
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Slide 26
The Simple Component
indisciplined internals
receive message
façade
method
actA
façade
method
actC
actD
actB
MVC & DCA - ROOTS 2006
© Trygve Reenskaug 2006
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Slide 27
The Declarative Component
Member Objects in micro database
newActivity
()
add
Dependency()
babyBase interface
actA
actB
actC
actD
babyBase
actA actC
with Member Objects
and Member structure
actB actD
MVC & DCA - ROOTS 2006
actC actD
© Trygve Reenskaug 2006
void newActivity
(String actName , …)
void addDependency
(String predNam , String succNam)
Set<ActivityIntf> allActivities
()
Activity activityNamed
(String actNam)
Set<ActivityIntf> predecessorsOf
(String actName)
Set<ActivityIntf> successorsOf
(String actName)
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DCA
separate the whole from the Details
Component
looks outward
Outward-looking
methods and fields
Member Object
Inward-looking
methods and fields
MVC & DCA - ROOTS 2006
© Trygve Reenskaug 2006
Member Objects
look inward
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Slide 29
Three simple operations
MVC & DCA - ROOTS 2006
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Slide 30
The DCA Component
Data + Communication + Algorithm
receive message
a DCA Component
Maestro
Method
Maestro
Method
Communication
?
actA
actB
actC
actD
micro “database”
with Member Objects and structure
MVC & DCA - ROOTS 2006
© Trygve Reenskaug 2006
Algorithm
Data
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Slide 31
The DCA Component
invisible babyBase
newActivity
()
add
Dependency()
babyBase interface
actA
actB
actC
maestro
only
actD
babyBase
actA actC
with Member Objects
and Member structure
actB actD
MVC & DCA - ROOTS 2006
void newActivity
(String actName , …)
void addDependency
(String predNam , String succNam)
Set<ActivityIntf> allActivities
()
private Activity activityNamed
(String actNam)
private Set<ActivityIntf> predecessorsOf
(String actName)
private Set<ActivityIntf> successorsOf
(String actName)
actC actD
© Trygve Reenskaug 2006
babyBase
only
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public ActivityDescr
activityDescriptorFor (String actName)
receive message
activityDescriptorFor
(“actC”)
public class ActivityDescr {
public String name;
public Integer earlyStart, earlyFinish, duration, rank;
public Color color;
another public Set<String> predecessors, successors;
Maestro Method
Which activity?
What are preds, succs??
actA
actB
actC
actD
actA actC
public class ActivityImpl implements ActivityIntf {
MemberBase babyBase;
private String name;
private Integer earlyStart, duration, rank = 0;
private Color color = Color.gray;
actB actD
babyBase
MVC & DCA - ROOTS 2006
actC actD
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Slide 33
algorithm
activityDescriptorFor()
needs both predecessors and successors
DescrCollab
*
predecessors
activity
*
successors
roles
MVC & DCA - ROOTS 2006
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Slide 34
public ActivityDescr
activityDescriptorFor (String actName)
receive message
actA
actC
actD
actB
Maestro
Method
activityDescriptorFor
(“actC”)
DescrCollab
*
predecessors
actA
actB
*
activity
actC
successors
actD
actA actC
micro
“database”
actB actD
MVC & DCA - ROOTS 2006
© Trygve Reenskaug 2006
Collaboration =
Communication
context
Algorithm
Data
actC actD
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Slide 35
UML 2.1: Collaboration
“9.3.3 CollaboratioA collaboration describes a structure of
collaborating elements (roles), each performing a
specialized function,
which collectively accomplish some desired functionality…
Thus, details, such as the identity or precise class of the actual
participating instances are suppressed.”
BabyUML
Collaboration
+
“9.3.4 CollaborationUse
A collaboration use represents
the application of the pattern described
BabyUML
by a collaboration to a specific situation
involving specific classes or instances playing
Query
the roles of the collaboration.”
MVC & DCA - ROOTS 2006
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Slide 36
Bind roles to Member Objects with queries
ActivityDescriptorCollab
DescrCollab
predecessors
predecessors **
activity
activity
successors
successors **
define query activity (String actNam) as
select act
from activities
where act.name = actNam
define successors (String actNam) as
define predecessors (String actNam) as
select succ
select pred
from dependencies
from dependencies
where pred.name = actNam
where succ.name = actNam
MVC & DCA - ROOTS 2006
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Slide 37
Algorithm (maestro)
ActivityImpl:: activityDescriptor()
MVC & DCA - ROOTS 2006
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Slide 38
DCA
Data Communication Algorithm
Data
A MemberBase maintains the member
(MemberBase)
objects and their structure
Communication Component operation realized by
(Component façade 1. establishing a collaboration of
method)
roleplaying objects
2. triggering role interaction
Algorithm
Member object methods implement
detailed algorithms
(Member Object
method)
MVC & DCA - ROOTS 2006
© Trygve Reenskaug 2006
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Slide 42
babydemo Universe of Discourse
interface NetworkIntf
MVC & DCA - ROOTS 2006
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Slide 43
maestro method
void
frontload (Integer firstWeek);
receive message
actA
actC
acD
actD
actB
another
Maestro Method
frontload
frontload (1)
()
frontCollab
*
predecessors
actA
actB
actC
frontloader
actD
actA actC
actB actD
babyBase
MVC & DCA - ROOTS 2006
actC actD
© Trygve Reenskaug 2006
define query frontActivities as
select act
from activities
where
act.earlyStart.isNil
and (
select succ
from dependencies
where
pred = act
and pred.earlyStart.notNil
) isEmpty
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babyBase.FrontCollab
protected class FrontCollab {
ActivityIntf frontloader;
Set<ActivityIntf> predecessors;
FrontCollab() {
// activity that is ready to do : not done and all predecessors done
frontloader = null;
predecessors = new HashSet<ActivityIntf> (0);
for (ActivityIntf act : activities) {
if (act.earlyStart() == null) {
Set<ActivityIntf> preds = predecessorsOf(act.name());
boolean predsDone = true;
for ( ActivityIntf pred : preds) {
if (pred.earlyStart() == null) {
predsDone = false;
break;
}
}
if (predsDone) {
frontloader = act;
predecessors = preds;
break;
} } } } }
MVC & DCA - ROOTS 2006
© Trygve Reenskaug 2006
13.04.2006 16:32
Slide 45
The DCA Component
Data + Communication + Algorithm
receive message
a DCA Component
Façade
Method
Façade Method
Façade
Method
1.
creates Collaboration by binding
Roles to
Member Objects
through dynamic Queries.
roleX
actA
actB
actB
roleY
actC
actC
2. triggers Communication as
message interaction
between Roles
actD
actD
Data structure and objects
contained in micro ”database”
MVC & DCA - ROOTS 2006
© Trygve Reenskaug 2006
Algorithms
implemented as Methods
in Member Objects
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Slide 46
Summary and Conclusion
“make it so simple that there are obviously no deficiencies”
• Reduce coupling by enforcing component encapsulation.
• MVC to separate domain information and presentation
– Model components hold domain information
– Tool gives user direct access to information
• View objects let user see and edit
• Controller object coordinates views
• DCA to organize component internal Member Objects
– Data: Member objects administred by BabyBase that ensured data
integrity
• Conceptual Schema; BabyBase defines universe of discourse.
• External schemas: BabyBase creates collaborations for the external
operations
• (Internal schema is the Member Object classes).
– Communication: Maestro methods in Component object triggers
Member Object behavior
– Algorithms: What’s left in the Member Objects.
MVC & DCA - ROOTS 2006
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Slide 48
The End
Claim:
MVC and DCA make for
self-documenting code
More info at http://heim.ifi.uio.no/~trygver
MVC & DCA - ROOTS 2006
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Slide 49
More reading ….
http://www.ifi.uio.no/~trygver
mailto: trygver ‘at’ ifi.uio.no
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.
Trygve Reenskaug: The BabyUML Discipline of Programming. ECMDA 2005 keynote.
http://heim.ifi.uio.no/~trygver/2005/babyuml/ECMDA2005-keynote.ppt
Edsger Dijkstra: A Discipline of Programming, 1976
Charles Antony Richard Hoare: The Emperor's Old Clothes. 1980 Turing Award lecture. Comm.ACM 24, 2 (Feb. 1981)
[UML] Unified Modeling Language: Superstructure. Version 2.1.
Object Management Group (OMG) document ptc/06-04-02. http://www.omg.org
Trygve Reenskaug: Empowering People with BabyUML:
A sixth GenerationProgramming Language. Opening talk, ECOOP 2004, Oslo.
http://heim.ifi.uio.no/~trygver/2004/ECOOP-04/EcoopHandout.pdf
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
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 Style on the Maintainability of Object-Oriented Software, Simula Research Laboratory
Technical Report 2003-6
http://www.simula.no/publication_one.php?publication_id=601
MVC & DCA - ROOTS 2006
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Slide 50
ZZZThe babydemo Component
Universe of Discourse
«component» babydemo
tool
demoData
resource
«Interface» DemoDataIntf
«Interface» ResourceIntf
«Interface» NetworkIntf
network
«Class»ActivityDescr
MVC & DCA - ROOTS 2006
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Slide 51
Divide and Conquer
the network Component
«component» babydemo
«Class»
resource
ResourceIntf
«MVC-component»
tool
Applet
«DCA-component»
network
NetworkIntf
«Class»ActivityDescr
«Class»
DemoData
DemoDataIntf
MVC & DCA - ROOTS 2006
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Slide 55
+IDE
babydemo.NetworkIntf
MVC & DCA - ROOTS 2006
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Slide 56
public void newActivity
(String actName , Integer duration, Color color);
receive message
newActivity
()
actA
actB
actC
Maestro
Method
actD
babyBase
with Member Objects and structure
MVC & DCA - ROOTS 2006
© Trygve Reenskaug 2006
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Slide 59
public void addDependency
(String fromName , String toName);
receive message
add
Dependency
Maestro
Method
actA
actB
actC
actD
actA actC
actB actD
babyBase
MVC & DCA - ROOTS 2006
actC actD
© Trygve Reenskaug 2006
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Slide 60
babydemo.NetworkIntf
MVC & DCA - ROOTS 2006
© Trygve Reenskaug 2006
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Slide 61
maestro method
public List<String>
MVC & DCA - ROOTS 2006
© Trygve Reenskaug 2006
activityNames()
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babydemo.NetworkIntf
MVC & DCA - ROOTS 2006
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