Pragmatic Architecture

By Bob Bunsonrbunson@munichreamerica.com

Software Architecture is…

The Approach

Simulation of software development project Fictitious system from Concept to Code Oriented around the software architect

The purpose of this exercise is to demonstrate: Architecture considerations Architecture activities The realization of architecture in code

Roles

My role Architect

Your candidate roles Architect reviewer Architect

apprentice Coder on future

iterations Passive observer

What I* mean by Architecture

The critical decisions that define a system

The decisions that are hard to change

*By “I”, I really mean the actual thought leaders in the industry

Tax Calculator - Business Requirements

Produce a free tax calculator so that people can compute their taxes, plus their late penalties, so that they can pay the IRS

Tax Calculator - Non-Functional Requirements

Design for testability Run on all modern browsers Maintainability Productivity should

not decrease as the application grows

All errors logged High performance All pages should

display in .6 seconds Simple enough to demonstrate

Brush up on Architecture

Tax Calculator - Architecture Principles

Interesting, but small No technology distractions Interoperability

Tax Calculator - An Expanded Principle

No Technology Distractions Statement

During a presentation on basic application architecture, the introduction of new or trendy technologies should be avoided

Rationale New, trendy, or controversial technologies has the

potential to distract the audience and potentially impede the presenter from communicating about the foundations of architecture

Implications Increased focus on the primary topic Lost opportunity to learn a new technology in preparing

for the presentation

Tax Calculator - Architecture Constraints

All ETL must use SQL Server Integration Services

.NET platform Coding based on Microsoft naming

conventions and “Clean Code” guidelines

Tax Calculator - Risk Assessment

Congress will change the tax laws retroactively prior to the presentation

Internet could be unreliable during this presentation

Web Forms and Test Driven Development don’t work well together

Risk Management Principles

Open communication

Integrated with the audience

Tax Calculator - Risk Management Strategy

“Web Forms and TDD causes too much friction” Microsoft created

ASP.NET MVC for a reason

To mitigate, create a prototype to evaluate the ease and intuitiveness (avoid the need to be clever and creative) of writing tests and code

Tax Calculator - Prototyping Goals

Explore variations of the model-view-presenter pattern (Supervising Controller, Passive View)

Introduce a few anticipated scenarios such as working with Session State

Prototyping

Why Mitigate risk Communicate concepts Understand technology

What Throw away Evolutionary

Architecture Patterns

Web Presentation Patterns Model View Controller Model View Presenter Page Controller

Domain Logic Patterns Transaction Script Domain Model Table Module

Tax Calculator – Architecture Tradeoffs

“Design for Testability” vs. “No Technical Distractions” ASP.NET MVC better for testability But would violate principle of “No

Technical Distractions” “Performance” vs. “Simple Enough to

Demonstrate” vs. Usability AJAX would improve performance and user

experience, but would Add to the complexity of the system

Tax Calculator – Technology Selections

ASP.NET Web Forms Nunit Visual Studio Web Server Windows Vista WatiN for Acceptance Testing

Tax Calculator – Key Design Decisions and Justifications

Use of ASP.NET Web Forms over ASP.NET MVC Supports principle of “No Technology

Distractions” Use of NUnit over MSTest

Would get kicked out of Alt.Net if I used MSTest Domain Model over Dataset

Preference of a domain model which encapsulates behavior and data to support potentially complex tax calculations over DataSets

More easily testable

Tax Calculator – More Key Design Decisions

Model View Presenter Desire to keep behavior out of code-

behind to support principle of Testability Introduce Rhino.Igloo open source

tool to abstract HTTP Context for easier testing Prototyping uncovered obstacles

associated with creating unit tests without dependencies on Session, Request, Response, etc.

Modeling with UML

Why Model

Martin Fowler: UML as Sketch UML as Blueprint UML as a

Programming Language

Reverse Engineering Forward Engineering

Tax Calculator – Class Diagram

No Best Practices

Context Tradeoffs, constraints, and the real world

exist Effective architecture

Factors in context Applies patterns when they apply Leverages experience (own and others)

There is no ideal best architecture

Tax Calculator – Aspects of Code Discussion

Realization of the software architecture in code

Testability of the layers Object oriented principles in practice Few thorny topics Prioritized until we run out of time Give “architect reviewers”

something to do when the code falls short in any area

Tax Calculator – Code Preview

Testing▪ Readable, descriptive tests▪ Arrange, Act, Assert▪ Test Doubles – visualize where a mocking

framework might help▪ Differentiate between unit tests and

acceptance tests

Tax Calculator – Code Preview Application

Dependency Injection - visualize where an Inversion of Control container might help

Model View Presenter Domain model Validation Error Handling Layer super types Testable code

Tax Calculator – Code Preview

UI can also support architecture principles Separation of Concerns: HTML and CSS Maintainability: Master page, Layer

super type Interoperability: XHTML User Experience: At least the potential of