object architecture design

15.1.2003 Software Engineering 2003Jyrki Nummenmaa

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OBJECT ARCHITECTURE DESIGN

• These slides continue with our example application, based on the simplified OMT-based technique.

• I am not trying to cover all or not even most aspects here.

• We will have other examples to show how things can be done differently.


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What Is Architectural Design?

Choices Made In Architectural Design:• Components• High-Level Design Patterns• Architectural Styles• A Possible Framework Architecture• Processes and Hardware• Processes and Communication• Other Architecture-Related Decisions • -> Some of these issues depend on each other

strongly.


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Why Architectural Design?

• Managing complexity– It is easier to manage complexity, if we divide the

application into reasonable parts.

• Maintainability– Usually a reasonable architecture makes it much easier to

maintain the software.– This may actually be the biggest reason for architectural

design.

• Efficiency– A good architecture enables us to isolate the potential

causes for inefficiency and makes it possible to scale up performance when load increases.


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Input Information For Architecture Design

• Analysis model of the application showing what the system is about and what it should do.

• Hardware environment• Software environment

- possible database management system- communication technologies- programming language – if known- target operating system(s) – if known


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Architectural Design For Example Game Application

• Clearly, it seems reasonable to separate the game logic from the user interface.

• If done suitably, this will also enable multiple client applications with a view to the same game.

• This kind of an approach is actually quite usual.• In fact, so usual, that there is a well-known

architectural solution for this kind of setting, called Model-View-Controller architecture (MVC architecture).

• We will study a variant of MVC from a separate set of slides by Ari Jaaksi, Nokia.


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Design Patterns

• Our design could follow the principles of MVC (or MVC++) directly.

• Another possibility is to copy an existing design idea and modify it to our needs.

• The idea of copying designs like this is the basic idea behind design patterns.

• It has been difficult to reuse code. The idea of design patterns is to reuse ideas.

• In a way, applying the MVC model is reusing the idea. However, there have been efforts to give a fixed format for presenting design patterns.


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Design Pattern Description

• Name• Problem• Solution

– Static: E.g. Class Diagram– Dynamic: E.g. Sequence Diagram

• Strategy– How to implement the pattern

• Consequences– Results and trade-offs


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Design Pattern ”Observer”

• Problem: We want to keep a number of objects (observers) aware of the state of an object (subject)

• This is done by making the observers subscribe to the subject.

• Whenever the subjects state changes, it will publish information about that to all subscribed observers.


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Subject {abstract}

Subject {abstract}

Object {abstract}

Object {abstract}

update() {abstract}update() {abstract}

ConcreteSubjectConcreteSubject

ConcereteObserverConcereteObserver

update()update()

observes

*

registersfor all g in observes { g.update()}

attach(x:Observer)detach(x: Observer)notify()

Class Diagram for Observer Design Pattern


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:ConcreteSubject t1:ConcreteObserver

attach(t1)

update()

t2:ConcereteObserver

attach(t2)

notify()

update()

Changes State

A Sequence Diagram For Observer Design Pattern


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Some observations

• A subject and the respective observers need minimal information on each other.

• In fact, they need to implement the required operations (attach, detach, notify, update), but that’s about that.

• This way, we get a high level of independence in their implementations.


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Subject {abstract}

Subject {abstract}

Object {abstract}

Object {abstract}

update() {abstract}update() {abstract}

GameModelGameModel

GameGUIGameGUI

update()update()

observes

*

registersfor all g in observes { g.update()}

attach(x:Observer)detach(x: Observer)notify()

Applying The Observer Design Pattern

Controller?


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Applying The Observer Pattern

• Apparently, we can use the Observer pattern for the user interface to observe the state of the game.

• Q: How is this different from using the MVC model?A: This model does not include the control part, ie. it is more appropriate for situations, where observing is enough. This way, MVC seems more appropriate for our game example.

• -> Back to the drawing board. The MVC looked better. However, we will look at yet another possibility: components.


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Components - What?

• Component technologies can be seen as packaging technologies

• Independent• Can be used as a building block to build larger

systems – dynamic, ”plug & play” linking• Have a well-defined interface, which hides the

implementation completely• Can be treated as a product of its own• Can be installed separately• Can be implemented with any language, as long as

it implements the necessary interfaces


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Components - Why?

• Object-oriented source-level re-use of code requires same source code language.

• Object-oriented source-level re-use may require understanding of the implementation.

• Building the system from source-level pieces requires that these pieces compile happily with each other.

• We want to avoid the above problems and build binary components with well-defined interfaces.


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ComponentZ

ComponentY

InterfaceX

Component Diagram

implements

uses

Interface – this may also be represented with stereotype <<interface>> for a class.

component


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Component - Interfaces

• An interfaces defines a set of services, which semantically belong together.

• An interface is a contract between the user and the implementor.

• A componenent may implement many interfaces and an interface may be implemented by many components.

• Once an interface is released, it does not change.• If changes are necessary, a new interface is

released.• As a matter of fact, you should know all this.


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Component Technologies

• Microsoft COM & DCOM (distributed COM)• CORBA standard

– several vendors – heavyweight system

• Java Beans


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GameGUI

GameController

GameModel

GameModelInterface

GameControllerInterface

Component Diagram For The Game Application


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User

Choose to take card

Show funds

Card Value

Sequence Diagram for ”Take Card” at Component Level

Pay (1)

Updated funds

Turn Card

Show card value

Add Funds (Value)

Show funds

GameView GameController GameModel

Take card

Show funds

Show card value

Updated fundsShow funds


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: GameClient : GameServer

: GameModel

: GameController

: GUI

<<TCP/IP>>

Deployment Diagram

Processing resource (a device, not a device type)

Component instance Object – ok, this was a componentin an earlier slide, this is just for example

object architecture design

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