agile development and domain driven design

Jacopo Romeihttp://www.sviluppoagile.it/

Agile development and Domain Driven Design

Jacopo Romei, http://www.sviluppoagile.it/

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Ego sliding Jacopo Romei

PHP since 1999

IT CEO in the past

Freelance agile coach

http://www.sviluppoagile.it/


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Agile development

A family of empirical methodologies


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Agile Manifesto Individuals over tools

Working software over documentation

Customer collaboration over contract deals

Accept change over following plans


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Domain

What does inspire our solutions?


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Driven

Where do we find our solutions?


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Design

What does provide us with solutions?


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Design vs. Process Design principles

Messy reality

DDD is a way to cope with the mess

Agile Dev is a way to cope with the mess


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Manouvrability

Agility means manouvrability


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Shared values Courage

Respect


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Respect

Simplicity

Simplicity is the art of maximizing the amount of work not done


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Respect

Simplicity Communication Feedback


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Respect

Simplicity Communication Feedback

Who

Which

How

Why


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XP and good design Refactoring tries to avoid overengineering

Refactoring can develop underengineering

XP works best with good designers

DDD helps developers being good designers


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Don't ossify, please

Supple, knowledgerich design


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Orthogonality•Orthogonality is a system design property facilitating feasibility and compactness of complex designs.

• Orthogonality guarantees that modifying the technical effect produced by a component of a system neither creates nor propagates side effects to other components of the system.

•Emergent behavior of a system should be controlled strictly by formal definitions of its logic and not by side effects resulting from poor integratio

•Orthogonality reduces testing and development time


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Shared required practices Iterative and incremental development

Close relationship with domain experts

Refactoring


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UX & Agile

Methodology to write user stories


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DDD & Agile

Methodology to (let emerge) design


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Ubiquitous language

One jargon to rule them all


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Ubiquitous language Model as backbone of language in

Code Diagrams Writings Speech


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Ubiquitous language Refactor

Classes Methods Modules

Reflect Real world entities Confusion resolution in conversations Changes in language as changes in model


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Example


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Short example “If we give the Routing Service an origin,

destination and arrival time, it can look up the stops the cargo will have to make and well... stick them in the database”

“The origin, destination and so on... it all feeds into Routing Service and we get back an Itinerary that has everything we need it”

“A Routing Service finds an Itinerary that satisfies a Route Specification”


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Documentation

Agile methodologies value working software over comprehensive documentation


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UML is not enoughUML doesn't convoy the concepts behind a model

UML doesn't convoy what objects are meant to do


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Ubiquitous documentationUML provides some documentation

Code provides some documentation

Ubiquitous language provides some documentation


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Hands-on modelers

Everyone who writes code must feel responsible for the model.


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Hands-on modelers


Everyone contributing to the model must touch the code.


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Hands-on modelers


Everyone contributing to the model must touch the code.

That's a DDD team. That's an agile team.


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Modeling paradigm

Object oriented programming is good to model the way we think about things. OO community

developed lots of critically meaningful concepts.

PHP community: WAKE UP!


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Deadly divide Model can be absent (brrr...)

Model can be overdesigned

Model can be detached from the domain

Suspect correctness

Hard to maintain

Difficult to understand


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Reflection

Software must reflect domain model


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Ubiquity

Software must reflect ubiquitous language


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Building blocks Layered architecture

Services

Entities

Value Objects

Factories

Aggregates

Repositories


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Layers User interface

Smart UI vs. Model Driven Design


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Application

a.k.a. Controller


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Application

a.k.a. Controller

Domain/Model layer


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Application

a.k.a. Controller

Domain/Model layer Infrastructure


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Frameworks

Free choice, but domain layer must be preserved.


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The end, the beginning

No one said agile was easy.

No one said it was a standalone concept.


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What's next

Agile Day 2009


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Jacopo Romei

jacopo [at] sviluppoagile.it

skype: jacoporomei

www.sviluppoagile.it

agile development and domain driven design

Technology