Introduction to Pattern Oriented Analysis and Design (POAD)

Instructor: Dr. Hany H. Ammar Dept. of Computer Science and Electrical Engineering, WVU

Outline  Review of Design Patterns

– The Lifecycle of a Pattern – Examples of Design Patterns

 The Command Pattern  The Observer Pattern  The Strategy Pattern

 Pattern Oriented Development – The Analysis phase – The Design phase – The design refinement phase

 The Feedback Control Example

The Lifecycle of Patterns

Real World Projects

Pattern Mining

Discover Patterns

Incident Occurrence of a Pattern

Preliminary Documentati

on

Document Analyze/Rule of Three

Author Version

Document

Pattern Polishing

Reusable Version

Pattern Reuse

Feedback

Modification

Phase I: MINING

Author World

Phase II: POLISHING

Pattern Community World

Phase III: REUSE

Pattern User World

Legend

Activit y Produc t

(From the Reference “Pattern-Oriented Analysis and Design”, Sherif M Yacoub and Hany H. Ammar Addison-Wesley Inc., 2004)

Review of Design Patterns  Examples of Design Patterns (From the Design

Patterns CD by Gamma et al, Addison-Wesley Inc., 1998 )

The Command Pattern: Encapsulate a request as an object

Review of Design Patterns

The Command Pattern

From the Design Patterns CD by Gamma et al, Addison-Wesley Inc., 1998

Review of Design Patterns Examples of Design Patterns The Observer Pattern: when one object changes state, all its dependents are notified and updated automatically

Model View Controller example

Review of Design Patterns

Examples of Design Patterns The Observer Pattern class diagram

From the Design Patterns CD by Gamma et al, Addison-Wesley Inc., 1998

Review of Design Patterns Examples of Design Patterns

The Strategy Pattern: lets the algorithm vary independently from clients that use it

Pattern Oriented Development

 Design Patterns are used in an ad-hoc strategy for design refinement

 They are also used to address a set of design problems without any guidance of how these patterns can be glued or interface together

 Is there a way to use design patterns as building blocks or as components in the design of systems ?

Pattern Oriented Development

 Pattern Oriented Analysis and Design (POAD)

The process aspects of POAD explains the phases and steps to develop an application design using patterns the POAD process has three phases:

– Analysis – Design – Design Refinement

Pattern Oriented Development

Analysis

Design

Design Refinement

a logical model is developed and patterns are selected

where patterns are glued together to produce a detailed pattern-level

diagram

An initial class diagram, and a more dense and profound class diagram,

and sequence diagrams are developed

Acquaintan ce Pattern

Library

Candidate Patterns

Selection

Selected Patterns

Application Requirements

Requirem ent

Analysis

Required Conceptual

Components

Retrieval

Pattern-Level Diagrams

Constructing Pattern-Level

models

Create Pattern

Instances

Define Pattern

Relationships

Construct Pattern-Level

Diagrams

Constructing models for Pattern-Level with

Interfaces

Pattern-Level with Interfaces Diagrams

Declare Pattern

Interfaces

Identify Relationships

between Pattern Interfaces

Constructing models for Detailed Pattern-Level

Detailed Pattern- Level Diagrams

Selected Patterns

(c) Design

Instantiating Pattern Internals

Domain Specific Detailed Pattern-Level Diagrams

Specializatio n

Concretizatio n

Develop Class Diagrams

Initial UML class diagram

Design Optimization

Reductio n

Merging & Grouping

Optimized class diagram

Detailed Pattern- Level Diagrams(d) Design Refinement

Analysis

Design

Design Refinement

(b) Analysis

(a) Overall POAD

The POAD process a) overall phases, b) analysis, c) design, and d) design refinement

POAD Analysis Phase

 Develop use case diagrams to identify the problems to be solved and the possible breakdown of the application as a set of logical components.

 Acquaintance with relevant pattern databases to get the analyst familiar with existing solutions.

 Retrieval of patterns from the domain specific databases to select a set of candidate patterns in an automated fashion.

 Selection of patterns from a set of candidate patterns for possible inclusion in the design process.

Construct Pattern-Level Models

 Create an instance for each selected pattern by describing the patterns and their constituents in an application specific context

 Define how these instances are related to each other

 The semantic of a dependency relationship used between patterns has a "uses" meaning

The Feedback Control Example

 Block diagram for a feedback control system

Reference Input

Measurement

Feedback Data

Error (Actuating)

Signal Feed forward Elements

Feedback Elements

Plant.+

+

Controlled Output

From Pattern-Oriented Analysis and Design, Sherif M Yacoub and Hany H. Ammar Addison-Wesley Inc., 2004

The Feedback Control Example  POAD Analysis Phase (Pattern Selection)

– The feedforward component implements some sort of a control strategy (instance of Strategy pattern)

– The feedback component receives measurements and applies a feedback control strategy

– In the error calculation component, the feedback controller notifies the error calculation unit with the feedback data (instances of the Observer pattern)

– Data of different types need to be exchanged between the framework components (Measurement, Feedback Data, input data , and error data )

The Feedback Control Example

FeedforwardStrategy

FeedbackObserver

FeedbackStrategy

ErrorObserver

Blackboard

Apply forward control strategy

Manipluate Data

Plant

Apply feedback control strategy

Manipulate Data

Calculate Error

Manipluate Data

Pattern-Level diagram for feedback control system This is an architectural pattern based on the data flow architectural style

The Feedback Control Example

FeedforwardStrategy (from POAD1-Feedback)

FeedbackObserver

(from POAD1-Feedback)

FeedbackStrategy

(from POAD1-Feedback) ErrorObserver

(from POAD1-Feedback)

Blackboard

(from POAD1-Feedback)

Context

Update Notify Context

Update

Notify

setData getData

Pattern-Level with Interfaces

The Feedback Control Example

F e e d f o r w a r d S t r a t e g y ( f r o m P O A D 1 - F e e d b a c k )

< < S t r a t e g y> > F e e d b a c kO b s e r ve r

( f r o m P O A D 1 - F e e d b a c k)

< < O b s e r ve r > >

F e e d b a c kS t r a t e g y ( f r o m P O A D 1 - F e e d b a c k )

< < S t r a t e g y> >

E r r o rO b s e rv er ( f r o m P O A D 1 - F e e d b a c k)

< < O b s e r ve r > >

B l a c kb o a r d ( f r o m P O A D 1 - F e e d b a c k )

< < B l a c kb o a r d > >

C o n te x t

U p d a t e N o t i f y C o n t e x t

U p d a t e

N o t i f y

s e t D a t a

g e t D a t a

C o n c r e t e O b s e r v e r

o b s e r v e r S t a t e

U p d a t e ( )

C o n c r e t e S u b je c t

s u b je c t S t a t e

g e t S t a t e ( )

S ub je c t

A t t a c h ( ) D e t a c h ( ) N o t if y ( )

O b s e r v e r U p d a t e ( ) nn

S u b je c t

A t t a c h ( ) D e t a c h ( ) N o t if y ( )

O b se rv er U p d a t e ( )

C o n c r e t e O b s e r v e r o b s e r v e r S t a t e

U p d a t e ( )

C o n c r e t e S u b je c t s u b je c t S t a t e

g e t S t a t e ( )

nn

C o n c r e t e S t r a t e g y A

A lg o r it h m I n t e r f a c e ( )

C o n c r e t e S t r a t e g y B

A lg o r ith m I n te r f a c e ( )

C on t e xt

C o n t e x t I n t e r f a c e ( )

S t r a t e g y

A lg o r it h m I n t e r f a c e ( )

C o n t e x t

C o n t e x t I n t e r f a c e ( )

S t r a t e g y

A lg o r it h m I n t e r f a c e ( )

C on cr e t e S t ra t eg yB

A lg o r it h m I n t e r f a c e ( )

C on c r et e S t ra t eg y A

A lg o r ith m I n te r f a c e ( )

C o n c r e t e D a t a H o ld e r A C o n c r e t e D a t a H o ld e r B

B la c k b o a r d

s e t D a t a ( )