Two System Architectures: MVC and DCA

© Trygve Reenskaug 2006 MVC & DCA - ROOTS 2006 Slide 113.04.2006 16:32

Two System Architectures:Two System Architectures:MVC and DCAMVC and DCA

Trygve ReenskaugDepartment of InformaticsUniversity of Oslo

[email protected]://www.ifi.uio.no/~trygver

Spinoff from Spinoff from the BabyUML projectthe BabyUML projectfor for Readable ProgramsReadable Programs


an Activity Network Planningan Activity Network Planningexampleexample


Projectactivities

actDactB

actCactA

Projectresources

Usertools

My ProblemMy Problem

Undisciplined communication → Spaghetti

ClassClass

Class

actB

Class + superclasses + methods → Noodles


BabyUML Goal:BabyUML Goal:Readable ProgramsReadable Programs

The price of reliability is the pursuit of the utmost simplicity

(C.A.R. Hoare, 1980 Turing Award lecture)


The BabyComponent =The BabyComponent =an object encapsulating other objectsan object encapsulating other objects

network «Component»

resource «Component»

tool «Component»

network «Component»

resource «Component»

tool «Component»


Baby ComponentsBaby ComponentsUniverse of DiscourseUniverse of Discourse

demoData

resource

network

«component» babydemo

tool

«Interface»Observer

«Interface»DemoDataIntf

«Interface»NetworkIntf

«Class»ActivityDescr

«Interface»ResourceIntf


The BabyDemo programThe BabyDemo programdemodata + network + resource + tooldemodata + network + resource + tool

+IDE


Baby ComponentsBaby ComponentsDivide and Conquer: the toolDivide and Conquer: the tool

demoData

resource

network

«co

mp

on

en

t» ba

by

de

mo

tool







Model – View - ControllerModel – View - Controllerbridge gapbridge gap Mental Model – ComputerMental Model – Computer

ModelUser

mental model

computer model


Model – View - ControllerModel – View - ControllerMultiple Views on same ModelMultiple Views on same Model

ModelUser

mental model

computer model

Run Demo

View

1

**


Model – View - ControllerModel – View - ControllerTool = Controller + ViewsTool = Controller + Views

ModelUser

View

Controller

*1

*

*

Tool

mental model

computer model

Run Demo


MModelodel V Viewiew C ControllerontrollerRoles and ResponsibilitiesRoles and Responsibilities

Model Store domain information

View Present and edit domain information

Controller Build, manage and co-ordinate Views


Example: babydemo.toolExample: babydemo.toolClass structureClass structure

Java.awt.Component java.applet.Appletjava.awt.Panel

Controller

ResourceViewButtonsView

java.awt.Button ActivityView

GanttViewDependencyView


Example: babydemo.toolExample: babydemo.tool visual hierarchy visual hierarchy (associations)(associations)

Controller

ResourceViewButtonsView

java.awt.Button ActivityView

GanttViewDependencyView

1 111

1

*

1111

*


Example: babydemo.toolExample: babydemo.toolMVC collaboration structureMVC collaboration structure

model.observed

view, observer: ResourceView

button: java.awt.Button

Tool

controller,observed, observer

view, observer: ButtonsView

view, observer: DependencyView

view, observer: GanttView

view, observer: ActivityView


The Anatomy ofThe Anatomy ofbabyDemo.toolbabyDemo.toolcontroller : Controller

view :DependencyViewview

:ActivityView

heim.ifi.uio.no/~trygver/2006/roots-2006/babyExample4.html


MVCMVCSynchronized SelectionSynchronized Selection

Usera view

actionPerformed()

observer*

pointAndClickMouse

controller

present

update()

selectedObject

selectionEvent()

notifyObserver()


MVCMVCtool componenttool component

+IDE


Baby Components: the networkBaby Components: the networkDivide and ConquerDivide and Conquer

demoData

resource

network

«co

mp

on

en

t» ba

by

de

mo

tool







The Simple ComponentThe Simple Componentindisciplined internalsindisciplined internals

façademethod

façademethod

receive message

actB

actA actC actD


The Declarative ComponentThe Declarative ComponentMember Objects in micro databaseMember Objects in micro database

addDependency()

actDactC

actDactB

actCactA

actA actB actC actD

babyBase with Member Objectsand Member structure

newActivity()

newActivity()

addDependency()

babyBase interfacevoid 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)


DCADCAseparate the whole from the Detailsseparate the whole from the Details

Inward-lookingmethods and fields

Outward-lookingmethods and fields

Componentlooks outward

Member Objectslook inward

Member Object


Three simple operationsThree simple operations


a DCA Component

The DCA ComponentThe DCA ComponentDData + ata + CCommunication + ommunication + AAlgorithmlgorithm

MaestroMethod

MaestroMethod

receive message

micro “database” with Member Objects and structure

actA actB actC actD

Data

Algorithm

Communication

?


The DCA ComponentThe DCA Componentinvisible babyBaseinvisible babyBase

addDependency()

actDactC

actDactB

actCactA

actA actB actC actD

babyBase with Member Objectsand Member structure

newActivity()

babyBase interfacevoid newActivity

(String actName , …) void addDependency

(String predNam , String succNam) Set<ActivityIntf> allActivities

() privateprivate Activity activityNamed

(String actNam)privateprivate Set<ActivityIntf> predecessorsOf

(String actName) privateprivate Set<ActivityIntf> successorsOf

(String actName)

maestroonly

babyBaseonly


public ActivityDescr public ActivityDescr activityDescriptorFor activityDescriptorFor (String actName)(String actName)

another Maestro Method

receive message

babyBase actDactC

actDactB

actCactA

actA actB actC actD

activityDescriptorFor(“actC”)

public class ActivityDescr { public String name; public Integer earlyStart, earlyFinish, duration, rank; public Color color; public Set<String> predecessors, successors;

public class ActivityImpl implements ActivityIntf { MemberBase babyBase; private String name; private Integer earlyStart, duration, rank = 0; private Color color = Color.gray;

Which activity?What are preds, succs??


DescrCollab

activity successors predecessors * *

algorithmalgorithm activityDescriptorFor()activityDescriptorFor()needs both predecessors and successorsneeds both predecessors and successors

roles


public public ActivityDescr ActivityDescr activityDescriptorFor activityDescriptorFor (String actName)(String actName)

MaestroMethod

receive message

micro“database” actDactC

actDactB

actCactA

actA actB actC actD

activityDescriptorFor(“actC”)

actB

actA actC actD

Data

Algorithm

Collaboration =Communication

context

actA actB actC actD


DescrCollab


“9.3.4 CollaborationUseA collaboration use represents the application of the pattern described by a collaboration to a specific situation involving specific classes or instances playing the roles of the 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.”

UML 2.1: CollaborationUML 2.1: Collaboration

BabyUMLCollaboration

BabyUMLQuery

+


Bind roles to Member Objects with queriesBind roles to Member Objects with queries

ActivityDescriptorCollab


DescrCollab


define successors (String actNam) asselect succfrom dependencieswhere pred.name = actNam

define query activity (String actNam) asselect actfrom activitieswhere act.name = actNam

define predecessors (String actNam) asselect predfrom dependencieswhere succ.name = actNam


Algorithm Algorithm (maestro)(maestro)ActivityImpl:: activityDescriptor()ActivityImpl:: activityDescriptor()


D C AD C ADDataata CCommunicationommunication AAlgorithmlgorithm

Data(MemberBase)

A MemberBase maintains the member objects and their structure

Communication(Component façade method)

Component operation realized by

1. establishing a collaboration of roleplaying objects

2. triggering role interaction

Algorithm(Member Object method)

Member object methods implement detailed algorithms


babydemobabydemo Universe of Discourse Universe of Discourseinterface interface NetworkIntfNetworkIntf


actB

actA actC actD

maestro methodmaestro methodvoidvoid frontload frontload (Integer firstWeek);(Integer firstWeek);

another Maestro Method

babyBase

receive message

actDactC

actDactB

actCactA

actA actB actC actD

frontload ( )

frontloaderpredecessors *frontCollab

define query frontActivities asselect actfrom activitieswhere

act.earlyStart.isNiland (

select succfrom dependencieswhere

pred = actand

pred.earlyStart.notNil) isEmpty

actB

actA actC acD

frontload (1)

actB

actA actC actD

actB

actA actC actD

actB

actA actC actD

actA actB actCactB actDactCactB


babyBase.FrontCollabbabyBase.FrontCollabprotected 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; } } } } }


The DCA ComponentThe DCA ComponentDData + ata + CCommunication + ommunication + AAlgorithmlgorithm

FaçadeMethod

receive messagea DCA Component

Algorithms implemented as Methods in Member Objects

Data structure and objectscontained in micro ”database”

actA actB actC actD

Façade Method

1. creates Collaboration by binding Roles to Member Objectsthrough dynamic Queries.

2. triggers Communication as message interaction between Roles

FaçadeMethod

roleX roleY

actDactCactB


• 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.

Summary and ConclusionSummary and Conclusion““make it so simple that there are obviously no deficiencies”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.


The EndThe End

More info at http://heim.ifi.uio.no/~trygver

Claim: MVC and DCA make for self-documenting code


More reading ….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.pdfhttp://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 2003-6http://www.simula.no/publication_one.php?publication_id=601


ZZZTheZZZThe babydemo Componentbabydemo ComponentUniverse of DiscourseUniverse of Discourse

demoData

resource

network


tool

«Interface» ResourceIntf

«Interface» DemoDataIntf

«Interface» NetworkIntf



Divide and ConquerDivide and Conquerthethe networknetwork ComponentComponent

«Class» DemoData

DemoDataIntf

«Class» resource

ResourceIntf

«DCA-component»network

NetworkIntf


«MVC-component»tool

Applet



babydemo.babydemo.NetworkIntfNetworkIntf+IDE


public void public void newActivitynewActivity(String actName , Integer duration, Color color);(String actName , Integer duration, Color color);

MaestroMethod

newActivity()

receive message

babyBase with Member Objects and structure

actA actB actC actD


public void public void addDependencyaddDependency(String fromName , String toName);(String fromName , String toName);

addDependency

MaestroMethod

receive message

babyBase actDactC

actDactB

actCactA

actA actB actC actD


babydemo.babydemo.NetworkIntfNetworkIntf


maestro methodmaestro methodpublic public List<String> activityNames()List<String> activityNames()


babydemo.babydemo.NetworkIntfNetworkIntf

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Two System Architectures: MVC and DCA

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