This document discusses Domain Driven Design (DDD). It provides an overview of DDD, including that it focuses on removing translation barriers between a domain, development team, and software design. It also describes common building blocks of domain models such as entities, value objects, factories, repositories, and services. Additionally, it discusses refactoring a model to gain deeper insight, including making implicit concepts explicit.
We often relate Domain-Driven Design with the content of Eric Evans' book; however even this book suggests looking outside for other patterns and inspirations: analysis patterns (Accounting, Finance), domain-oriented use of design patterns (the Flyweight pattern), established formalisms (e.g. monoids) and XP literature in particular (e.g. the patterns on the c2 wiki and OOPSLA papers).
The world has not stopped since the book either, and new ideas keep on emerging regularly. And you can share your own patterns as well.
In this session, through examples and code we'll go through some particularly important patterns which deserve to be in your tool belt. We'll also provide guidance on how best to use them (or not), at the right time and in the right context, and on how to train your colleagues on them!
This talk was delivered at the PHPers meetup in Wroclaw, 10 August 2015.
I presented a set of techniques which help you transition from a legacy codebase to DDD. I focused more on the strategic DDD patterns like bounded contexts.
The main idea in such refactorings is to:
1. List all your (potential) bounded contexts
2. Decide which ones are deserving the DDD tactical patterns
3. Decide which ones can stay as CRUD
4. Communicate between the BCs via events
Imagine a team developing to a specific business domain. We use languages to communicate with the client, company and within the team. We also use programming languages to develop the software. And still, we want our code to express, no only a correct syntax for that language, but the knowledge of the business domain in which we are developing.
And if it was possible to capture the business meaning and transforme it into a language?
This talk is about DSLs, it's architecture, business use, and also how to implement and test them.
How I Learned to Stop Worrying and Love Legacy Code.....Mike Harris
Legacy Code. I never wrote it; everybody else did!
How many times have you waded through an ageing, decaying, tangled forrest of code and wished it would just die?
How many times have you heard someone say that what really needs to happen is a complete rewrite?
I have heard this many times, and, have uttered that fatal sentence myself.
But shouldn’t we love our legacy code?
Doesn’t it represent our investment and the hard work of ourselves and our predecessors?
Throwing it away is dangerous, because, before we do, we’ll need to work out exactly what it does, and we’ll need to tweeze out that critical business logic nestled in a deeply entangled knot of IF statements. It could take us years to do, and we’ll have to maintain two systems whilst we do it, inevitably adding new features to them both. Yes we get to reimplement using the latest, coolest programming language, instead of an old behemoth, but how long will our new cool language be around, and who will maintain that code, when it itself inevitably turns to legacy?
We can throw our arms in the air, complaining and grumbling about how we didn’t write the code, how we would never have written it the way it is, how those that wrote it were lesser programmers, possibly lesser humans themselves, but the code still remains, staring us in the face and hanging around for longer that we could possibly imagine. We can sort it out, we can improve it, we can make it testable, and we can learn to love our legacy code.
You have to deliver ambitious new features but your codebase is a huge mess of legacy technologies, with no test?
It is very tempting to throw it all away and rewrite everything from scratch, but is it wise when you consider the associated cost, risk and delayed time-to-market?
Through an experience report, we'll show a "Strangler Application" strategy where only carefully selected areas of legacy code are rewritten. Agile development techniques like BDD or TDD remain necessary, with some adjustments.
We'll also describe step by step the overall thinking process you can use to deal with large legacy code bases efficiently.
First presented at Agile France 2013, and in countless Brown Bag Lunches since, a best-seller!
Video (In French) here: http://www.infoq.com/fr/presentations/code-legacy
We often relate Domain-Driven Design with the content of Eric Evans' book; however even this book suggests looking outside for other patterns and inspirations: analysis patterns (Accounting, Finance), domain-oriented use of design patterns (the Flyweight pattern), established formalisms (e.g. monoids) and XP literature in particular (e.g. the patterns on the c2 wiki and OOPSLA papers).
The world has not stopped since the book either, and new ideas keep on emerging regularly. And you can share your own patterns as well.
In this session, through examples and code we'll go through some particularly important patterns which deserve to be in your tool belt. We'll also provide guidance on how best to use them (or not), at the right time and in the right context, and on how to train your colleagues on them!
This talk was delivered at the PHPers meetup in Wroclaw, 10 August 2015.
I presented a set of techniques which help you transition from a legacy codebase to DDD. I focused more on the strategic DDD patterns like bounded contexts.
The main idea in such refactorings is to:
1. List all your (potential) bounded contexts
2. Decide which ones are deserving the DDD tactical patterns
3. Decide which ones can stay as CRUD
4. Communicate between the BCs via events
Imagine a team developing to a specific business domain. We use languages to communicate with the client, company and within the team. We also use programming languages to develop the software. And still, we want our code to express, no only a correct syntax for that language, but the knowledge of the business domain in which we are developing.
And if it was possible to capture the business meaning and transforme it into a language?
This talk is about DSLs, it's architecture, business use, and also how to implement and test them.
How I Learned to Stop Worrying and Love Legacy Code.....Mike Harris
Legacy Code. I never wrote it; everybody else did!
How many times have you waded through an ageing, decaying, tangled forrest of code and wished it would just die?
How many times have you heard someone say that what really needs to happen is a complete rewrite?
I have heard this many times, and, have uttered that fatal sentence myself.
But shouldn’t we love our legacy code?
Doesn’t it represent our investment and the hard work of ourselves and our predecessors?
Throwing it away is dangerous, because, before we do, we’ll need to work out exactly what it does, and we’ll need to tweeze out that critical business logic nestled in a deeply entangled knot of IF statements. It could take us years to do, and we’ll have to maintain two systems whilst we do it, inevitably adding new features to them both. Yes we get to reimplement using the latest, coolest programming language, instead of an old behemoth, but how long will our new cool language be around, and who will maintain that code, when it itself inevitably turns to legacy?
We can throw our arms in the air, complaining and grumbling about how we didn’t write the code, how we would never have written it the way it is, how those that wrote it were lesser programmers, possibly lesser humans themselves, but the code still remains, staring us in the face and hanging around for longer that we could possibly imagine. We can sort it out, we can improve it, we can make it testable, and we can learn to love our legacy code.
You have to deliver ambitious new features but your codebase is a huge mess of legacy technologies, with no test?
It is very tempting to throw it all away and rewrite everything from scratch, but is it wise when you consider the associated cost, risk and delayed time-to-market?
Through an experience report, we'll show a "Strangler Application" strategy where only carefully selected areas of legacy code are rewritten. Agile development techniques like BDD or TDD remain necessary, with some adjustments.
We'll also describe step by step the overall thinking process you can use to deal with large legacy code bases efficiently.
First presented at Agile France 2013, and in countless Brown Bag Lunches since, a best-seller!
Video (In French) here: http://www.infoq.com/fr/presentations/code-legacy
Watch the video online: http://vimeo.com/79181633
Even in an agile world, specifications often go too far and describe solutions with too much details; all these premature decisions constraint the implementation and remove opportunities. There is a remedy: refactoring the specs, even before refactoring the code.
In the TDD cycle, refactoring is the art of restructuring the code to make it simpler, without changing its behavior at runtime. A key part of refactoring is to recognize and extract duplications.
Refactoring is very useful at the code level, and it is even more powerful when applied during business analysis or functional architecture. We will show how the practice of refactoring directly "at the business domain level" can simplify the problem, and therefore the resulting implementation code, by orders of magnitude. This means much less code to write, to test and to maintain, and much less defects as a result.
We will introduce 5 patterns on how to refactor at the business-domain level, such as "Make It Systematic" and "Degenerate Case". We will also explain some limits and the required mindset.
This approach of refactoring has been used on several real-world projects and is derived in particular from DDD and from Specification by Example.
Leveraging more then DDD Lite in the startup projectThomas Jaskula
Short presentation about how Domain Driven Design help me with my startup project. A lightweight CQRS approach was used (commands separated from queries without other ceremony).
One of the main advantages of PHP is that it allows you and your company to build up projects in no time and with immediate feedback and business value. Sometimes, however, fast growth and unprevented complexities could make your codebase more and more difficult to manage as time passes and new features are added.Domain Driven Design can be an elegant solution to the problem, but introducing it in mid-large sized projects is not always easy: you have to deal with difficulties at technical, team and knowledge levels. This talk focuses on how to approach the change in your codebase and in your team mindset without breaking legacy code or stopping the development in favor of neverending refactoring sessions.
A Practical Guide to Domain Driven Design: Presentation Slidesthinkddd
Tonight I presented on Domain Driven Design to the Alt.Net group in Sydney at the invite of Richard Banks.
As a follow up, attached are the slides I used, feel free to distribute and use on the Creative Commons Licence
Introduced by Eric Evans in 2004 via his Blue Book, Domain Driven Design (DDD) has received tremendous positive feedbacks from many developers & communities over the years. On the other hand, we have to admit that DDD has since not been widely used in the trenches or within most of our development projects... How can we explain such failure in its diffusion? Is DDD in itself difficult or is it just the way people used to present it which makes it hard to grasp and inaccessible? Through our various (more or less successful ;-) experiences, we will try to highlight what DDD is using a simple and more accessible approach. The opportunity for us is to show you how helpful it can be for your day-to-day projects. Wouldn't be the perfect time for all of us to ease the DDD onboarding for beginners and to reboot DDD for experts?
How to succeed in software development. Following agile methodology principles helps to achieve much better results. Know more about eXtreme Programming, one of the famous agile software development methodology.
Learn how to write better code. Follow key software development principles like KISS, DRY, YAGNI, and SOLID. Know how to choose better names, structure your code, write methods, and design classes.
This presentation shows the concept of a Domain Specific Language in Ruby. A language that aims to solve specific problems, as opposed to general purpose languages that are used to software development in general. A simple syntax language, so natural to read, write and above all things, be easy to understand both for the computer as a human being. Expressing yourself in a language means that the point on semantic is more important to solve specific problems than to their interpreter to know what is going on.
A very high-level introduction to scaling out wth Hadoop and NoSQL combined with some experiences on my current project. I gave this presentation at the JFall 2009 conference in the Netherlands
My presentation from the GoMobile2016 convention. In y talk I described what i call the next revolution in customer brand communication on the mobile channel. I believe Whatsapp new strategy of basing it's business model on facilitating customer - brand communication along with FB messenger doing the same thing is going to change everything. Again.
Watch the video online: http://vimeo.com/79181633
Even in an agile world, specifications often go too far and describe solutions with too much details; all these premature decisions constraint the implementation and remove opportunities. There is a remedy: refactoring the specs, even before refactoring the code.
In the TDD cycle, refactoring is the art of restructuring the code to make it simpler, without changing its behavior at runtime. A key part of refactoring is to recognize and extract duplications.
Refactoring is very useful at the code level, and it is even more powerful when applied during business analysis or functional architecture. We will show how the practice of refactoring directly "at the business domain level" can simplify the problem, and therefore the resulting implementation code, by orders of magnitude. This means much less code to write, to test and to maintain, and much less defects as a result.
We will introduce 5 patterns on how to refactor at the business-domain level, such as "Make It Systematic" and "Degenerate Case". We will also explain some limits and the required mindset.
This approach of refactoring has been used on several real-world projects and is derived in particular from DDD and from Specification by Example.
Leveraging more then DDD Lite in the startup projectThomas Jaskula
Short presentation about how Domain Driven Design help me with my startup project. A lightweight CQRS approach was used (commands separated from queries without other ceremony).
One of the main advantages of PHP is that it allows you and your company to build up projects in no time and with immediate feedback and business value. Sometimes, however, fast growth and unprevented complexities could make your codebase more and more difficult to manage as time passes and new features are added.Domain Driven Design can be an elegant solution to the problem, but introducing it in mid-large sized projects is not always easy: you have to deal with difficulties at technical, team and knowledge levels. This talk focuses on how to approach the change in your codebase and in your team mindset without breaking legacy code or stopping the development in favor of neverending refactoring sessions.
A Practical Guide to Domain Driven Design: Presentation Slidesthinkddd
Tonight I presented on Domain Driven Design to the Alt.Net group in Sydney at the invite of Richard Banks.
As a follow up, attached are the slides I used, feel free to distribute and use on the Creative Commons Licence
Introduced by Eric Evans in 2004 via his Blue Book, Domain Driven Design (DDD) has received tremendous positive feedbacks from many developers & communities over the years. On the other hand, we have to admit that DDD has since not been widely used in the trenches or within most of our development projects... How can we explain such failure in its diffusion? Is DDD in itself difficult or is it just the way people used to present it which makes it hard to grasp and inaccessible? Through our various (more or less successful ;-) experiences, we will try to highlight what DDD is using a simple and more accessible approach. The opportunity for us is to show you how helpful it can be for your day-to-day projects. Wouldn't be the perfect time for all of us to ease the DDD onboarding for beginners and to reboot DDD for experts?
How to succeed in software development. Following agile methodology principles helps to achieve much better results. Know more about eXtreme Programming, one of the famous agile software development methodology.
Learn how to write better code. Follow key software development principles like KISS, DRY, YAGNI, and SOLID. Know how to choose better names, structure your code, write methods, and design classes.
This presentation shows the concept of a Domain Specific Language in Ruby. A language that aims to solve specific problems, as opposed to general purpose languages that are used to software development in general. A simple syntax language, so natural to read, write and above all things, be easy to understand both for the computer as a human being. Expressing yourself in a language means that the point on semantic is more important to solve specific problems than to their interpreter to know what is going on.
A very high-level introduction to scaling out wth Hadoop and NoSQL combined with some experiences on my current project. I gave this presentation at the JFall 2009 conference in the Netherlands
My presentation from the GoMobile2016 convention. In y talk I described what i call the next revolution in customer brand communication on the mobile channel. I believe Whatsapp new strategy of basing it's business model on facilitating customer - brand communication along with FB messenger doing the same thing is going to change everything. Again.
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Here is the slide deck I used for a quick presentation to share my experiences and thoughts how starting with customer outcomes can help a small, cross-functional team do faster product delivery and gain necessary traction essential for early validation and subsequent growth.
Information Interviews (Informational Meetings) are key for job search success. Tied to networking and target marketing. This RochesterWorks! Job Strategy Group presentation includes participant strategies for requesting these meetings.
Following on from the success of last year, this annual event for London's architect community will have architectural innovation as a theme this year, and particularly CQRS. At the DDD eXchange we will feature leading thinkers and architects who will share their experience and Eric Evans is the programme lead.
The importance to be Driven
There are many buzzwords and acronyms to describe how the software should be designed. TDD (Test Driven), BDD (Behaviour Driven), DDD (Domain Driven) are the most well known. In this speech we'll run thought all these techniques comparing each one of those with TDD and finding what are the common concepts. An exercise will show to the students how different the code will be using different design methodologies as driver.
Following on from the success of last year, this annual event for London's architect community will have architectural innovation as a theme this year, and particularly CQRS. At the DDD eXchange we will feature leading thinkers and architects who will share their experience and Eric Evans is the programme lead.
Envisioning the Future of Language WorkbenchesMarkus Voelter
Over the last couple of years, I have used MPS successfully to build interesting (modeling and programming) languages in a wide variety of domains, targeting both business users and engineers. I’ve used MPS because it is currently the most powerful language workbench, lots of things are good about iz, in particular, its support for a multitude of notations and language modularity. But it is also obvious that MPS is not going to be viable for the medium to long term future; the most obvious reason for this statement is that it is not web/cloud-based. In this keynote, I will quickly recap why and how we have been successful with MPS, and point out how language workbenches could look like in the future; I will outline challenges, opportunities and research problems. I hope to spawn discussions for the remainder of the workshop.
Domain-driven design is a collaborative process involving both domain experts and software practitioners that attempts to address issues of complexity in software. This process is described in the book Domain-Driven Design written by Eric Evans. Domain-driven design starts with the assertion that complexity is in the domain, not in the technology. Accordingly, we must let technology play a supporting role.
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Up to speed in domain driven design
1. Up to Speed in
Domain Driven Design
Rick van der Arend
rvdarend@sogyo.nl
2. Agenda
What is Domain Driven Design?
An example of a domain model
The building blocks of a domain model
Refactoring towards deeper insight
What has been learned since the book?
Wrap-up
SOFTWARE INNOVATORS 2
4. DDD in one sentence
Domain Driven Design is a style of software
development which focuses on removing translation
barriers between domain, development team and
design of working software using a ubiquitous
language supported by a well refined livingmodel.
5. Translation barriers
Team talks to users and experts (if lucky)
Write software that behaves as requested
Names get translated back and forth
Concepts diverge without anyone noticing
SOFTWARE INNOVATORS 5
?
7. Origins of the acronym DDD
Eric Evans wrote the book that gave the
acronym DDD an impulse in 2005. Aptly named:
Domain Driven Design
“Tackling Complexity in the heart of software”
9. Domain model
SOFTWARE INNOVATORS 9
Parallel to the equator
Parallel to the earth axis
Orthogonal to the sun’s plain of movement Turning during the year
10. From Phased to Iterations
Analysis Design Build
Iteration Iteration
Test
11. Start with the Model, don’t stop
SOFTWARE INNOVATORS 11
Iteration Iteration
Domain Model
effort as part
of an iteration
14. Entities & Value objects
Entities have an unmistakeable identity
Value objects are indentified by.. their value
a Person
a Name
an Address
This depends on.. of course.. Context!
15. Factories , Repositories, Aggregates
Factories create, Repositories store
The unit of work they work on is an aggregate
The thing they create of find and hand over will
be a reference to the aggregate root
16. Services
Services encapsulate... well… Services
They are not part of the core domain, but linked
Objects change into other objects
17. Layers.. and more
UI > domain model > Data access
SOFTWARE INNOVATORS 17
Or.. domain model depends on nothing
19. Refactoring towards deeper insight
Use patterns when appropriate
Make Unit Tests
Better yet, do TDD
Better yet, do BDD
DRY and YAGNI
But: all a bit technical
20. Making Implicit Concepts explicit
Listen to Language
Scrutinize Awkwardness
Contemplate Contradictions
Read the Book
Try, Try again
Model the less-than-obvious: constraints,
processes, commands, relations, etc.
23. Strategic Design: context rules!
Be aware of different contexts
Make a context map
See how different bounded contexts relate
Shared Kernel, Customer/Supplier development
teams, Conformist, Separate Ways, Partner
Use an anti-corruption layer
24. Context Maps step-by-step
1. What models (or BBoM) do we know of? (draw
blob each and name it.)
2. Where does each apply? (Boundary in words.)
3. Where is information exchanged? (Connect)
4. What is the relationship?
(Upstream/downstream? Partner? Etc.)
26. Highlights that Evans learned
Building blocks are overemphasized
But domain events added as a new type of block
General advice
▫ Don’t spread modeling too thin
▫ Focus on the core domain
▫ Clean, bounded context (CM steps available)
▫ Iterative process
▫ Don’t bore your domain experts
27. Domain events taken further
Greg Young has been promoting the idea of
Command and Query separation
28. Techniques to explore
Exploratory Modeling (xM)
Model Driven Development environments
Language Workbenches
Naked Objects and other such platforms
SOFTWARE INNOVATORS 28
30. Summary
DDD highlights aspects of software design
It focuses on the ‘core domain’ and uses a
ubiquitous language, based on a domain model
The ubiquitous language brings out flaws
A Domain Model is normally made up of certain
types of building blocks
Thinks about context too: take control where and
whenever possible
31. Resources for Further study
http://www.domaindrivendesign.org
Numerous articles on http://www.infoq.com
http://www.slideshare.net/devnology/unleash-
your-domain-with-greg-young
32. DDD in C#
Jimmy Nilsson applied it to a C# context. His
book is has an informal tone, but a bit noisy.
Applying DDD and Patterns
With Examples in C# and .NET