1 Another group of Patterns Architectural Patterns

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Another group of Patterns

Architectural Patterns

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Patterns

Pattern: A representation of a proven solution.

Problem

Applicable Forces

Solution

ConsequencesBenefits

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Software Architecture

• Architecture is OVERLOADED– System architecture

– Application architecture

• Architecture for this presentation is

• The modules, processes, interconnections, and protocols which constitute the deployed software system.

• Different from the behavioral architecture which describes how the business classes execute the business processes.

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Architecture Specification

• Document which defines in text and diagrams the design, flow and technologies of the design.

• Shows how persistence, communication, and behavior are to be implemented in the system.

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Types of Patterns

• Lowest Level – Programming Patterns– Iterator, if, while

• Design Level – Design Patterns– Factory, builder, --- gang of 4

• Before Design – Architectural Patterns–Martin Fowler- presentation, domain, data

storage, environment

• Analysis Patterns – – used in requirements analysis

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Architectural Layers - Patterns

–Presentation » interactions with the user – HTML, thick client, MVC,

web services

–Domain (Logic) » Business rules, validations, calculations,

verifications

–Data Storage » database

–Environmental» Session management, messaging

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Presentation Architectural Patterns

• Presentation interactions with the user

• No Client

• Thick Client (rich client)

• Thin Client

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Presentation Architectural Patterns

• Model View Controller

• Application Controller

• Input Controller– Page Controller

– Front Controller

• View Controller– Template View

– Transform View

– Two Step View

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Model View Controller

Separation of Presentation (View/Controller) from Domain (Model)

Separation of View and Controller

Model – Domain object

View – Presentation object

Controller – Controller object to handle user request/response

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Application Controller

A centralized point for handling screen navigation and flow of an application.

Application Controller – determines which type of input is needed or which screen.

Input Controller

View

Application Controller

Domain Layer

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Application Controller

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Application Controller

• A single point of control to change program flow and navigation

• May be in mediating layer between the presentation and the domain

• May be reusable across various presentations

• Testable outside the UI framework.

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Front Controller

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Page Controller

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Front vs Page Controller

• Front Controller – Single point for adding behavior

– Can add behavior dynamically (filter pattern)

– Use with more complex applications

• Page Controller – Simple - Input controller per page

– Don’t put controller logic into scriplets – use separate classes

– More prone to duplicate code with this controller

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Template View

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Transform View

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Template vs Transform vs Two Step

• Template View– Follows natural editing notions

– Supports non=programmer editors of HTML

– Needs discipline to avoid scriplets

• Transform View– Can test without server

– Works well with XML

• Two Step View– Easy to make global appearance changes

– Easy to support multiple appearances

– Complex

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Example

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Data Storage

• Need mechanisms to allow RDBMS to communicate in the OO world.

• With OO databases none of these patterns necessary.

• Useful even if non-OO language wants to communicate with RDBMS to make the DB flexible to change in type and to make the data representation protected.

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Data Storage Patterns

• Table Data Gateway

• Row Data Gateway

• Active Record

• Data Mapper

• Structural Patterns– Foreign Key Mapping, Identify Field Association,

Table Mapping, Single Table Inheritance.

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Table Data Gateway

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Row Data Gateway

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Row Data Gateway (2)

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Active Record

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Data Mapper

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Distribution Patterns

• Remote Façade

• Data Transfer Object

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Remote Facade

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Data Transfer Object

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Summary

• No one patterns is an end all

• Patterns are mechanisms to help decompose applications into reusable, maintainable, modules.

• The layers of development help to define the needed patterns

• No pattern is always correct -- fit the application.

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