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Patterns in Software Engineering Lecturer: Raman Ramsin^ Lecture 8^ GoV Patterns – Architectural

Part 2

1

Sharif University of Technology

Part

Patterns in Software Engineering – Lecture 8

Architectural Patterns: CategoriesArchitectural

Patterns: Categories

„

From Mud to Structure

Layers,

Pipes and Filters, and

Blackboard

„

Distributed Systems

Broker; also

Microkernel and

Pipes and Filters

I

t

ti

S

t

„

I

nteractive Systems

Support the structuring of systems that feature human-computer interaction.

Model-View-Controller and

Presentation-Abstraction-Control

„

Adaptable Systems

Support extension of applications and their adaptation to evolving technology andchanging functional requirements.changing functional requirements.

Reflection and

Microkernel

2

Sharif University of Technology

Patterns in Software Engineering – Lecture 8

Interactive Systems: Model

-View-Controller

Interactive Systems: Model View Controller^ „

Divides an interactive application into three components.

The

Model

contains the core functionality and data.

Views

display information to the user.

Controllers

handle user input.

Controllers

handle user input.

A change-propagation mechanism ensures consistency between the user interface(views and controllers) and the model.

4

Sharif University of Technology

Patterns in Software Engineering – Lecture 8

Interactive Systems: Model

-View-Controller

Interactive Systems: Model View Controller^ „

Context

-

Interactive applications with a flexible human

-computer interface

„

Context

Interactive

applications with a flexible human computer interface.

„

Problem

-

Forces are as follows:

„

Problem

Forces

are as follows:

The same information is presented differently in different windows, for example,in a bar or pie chart.

The display and behavior of the application must reflect data manipulationsimmediately.

Changes to the user interface should be easy, and even possible at run-time.

Supporting different 'look and feel' standards or porting the user interfaceshould not affect code in the core of the application.

5

Sharif University of Technology

Patterns in Software Engineering – Lecture 8

Model-View-Controller: Structure

• Views and Controllers

„

View

components present information to the user.

‰

Each view defines an update procedure that is activated by the change propagationmechanism and retrieves data from the model.

‰

Each view creates a suitable controller.

‰

Views often offer functionality that allows controllers to manipulate the display.

„

Controller

components accept user input as events.

‰

If the behavior of a controller depends on the state of the model, the controller

p

,

registers itself with the model and implements an update operation.

7

Sharif University of Technology

Patterns in Software Engineering – Lecture 8

Model

-View-Controller: Class Structure

Model View Controller: Class Structure

8

Sharif University of Technology

Patterns in Software Engineering – Lecture 8

Model

-View-Controller: Dynamics

• Scenario II

Model View Controller: Dynamics

Scenario II

the MVC triad is initialized

the

MVC triad is initialized.

10

Sharif University of Technology

Patterns in Software Engineering – Lecture 8

Model

-View-Controller: Consequences

Model View Controller: Consequences^9

Multiple views of the same model

9

Multiple

views of the same model

9

Synchronized views

9

'Pluggable' views and controllers

9

Exchangeability of 'look and feel'

g

y

9

Framework potential

8

Increased complexity

8

Potential for excessive number of updates

8

Potential for excessive number of updates

8

Close couplings

11

Sharif University of Technology

Patterns in Software Engineering – Lecture 8

Interactive Systems: Presentation-Abstraction-Control

y

Context -

Development of an interactive application with the

help of agents

„

Problem

Forces are as follows:

Problem

-

Forces

are as follows:

Agents often maintain their own state and data.

Interactive agents provide their own user interface.

Systems evolve over time.

13

Sharif University of Technology

Patterns in Software Engineering – Lecture 8

Presentation

-Abstraction-Control: Structure

Presentation Abstraction Control: Structure^ „

Interactive application is structured as a tree

-like hierarchy of PAC agents.

Interactive application is structured as a tree like hierarchy of PAC agents.

‰

There should be one top-level agent, several intermediate level agents, andeven more bottom-level agents.

‰

Every agent consists of three components:

presentation

abstraction

and

‰

Every agent consists of three components:

presentation,

abstraction, and

control.

Th

T

l^

l PAC

t

„

Th

e

Top-level PAC agent:

provides the functional core of the system;

includes parts of the user interface that cannot be assigned to subtasks.

p

g

„

Bottom-level PAC agents:

represent self-contained semantic concepts on which users of the system canact

such as spreadsheets and charts

act, such as spreadsheets and charts.

„

Intermediate-level PAC agents:

represent either combinations of, or relationships between, lower-level agents.

14

Sharif University of Technology

Patterns in Software Engineering – Lecture 8

Presentation-Abstraction-Control: Structure

• Components

p

16

Sharif University of Technology

Patterns in Software Engineering – Lecture 8

Presentation-Abstraction-Control: Dynamics

• Scenario I

y

„

Cooperation between different PAC agents when opening a new bar

-chart

Cooperation between different PAC agents when opening a new bar chartview of the election data.

17

Sharif University of Technology

Patterns in Software Engineering – Lecture 8

Presentation-Abstraction-Control: Consequences

q

9

Separation of concerns

9

Support for change and extension

9

Support for change and extension

9

Support for multi-tasking

8

Increased system complexity

8

Complex control component

8

Complex control component

8

Efficiency

8

Applicability

19

Sharif University of Technology

Patterns in Software Engineering – Lecture 8

Architectural: Adaptable SystemsArchitectural:

Adaptable Systems

„

Reflection:

p

rovides a mechanism for changing structure and behavior of p

g

g

software systems dynamically.

Supports the modification of fundamental aspects, such as type structures andfunction call mechanisms.function call mechanisms.

An application is split into two parts.

„

A

meta level provides information about selected system properties and makes the software self-awaresoftware self aware.

„

A

base level includes the application logic; its implementation builds on the meta level.

„

Microkernel:

Applies to software systems that must be able to adapt to

„

Microkernel:

Applies

to software systems that must be able to adapt to

changing system requirements.

separates a minimal functional core from extended functionality and customer-specific parts.

serves as a socket for plugging in such extensions and coordinating theircollaboration.

20

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