Udi Dahan   Udi Dahan – The Software Simplist
Enterprise Development Expert & SOA Specialist
 
  
    Blog Consulting Training Articles Speaking About
  

From CRUD to Domain-Driven Fluency

Friday, February 15th, 2008.

I got a question about how to stay away from CRUD based service interfaces when the logic itself is like that, and I’ve found that this shift in thinking really needs more examples, so I’ve decided to put this out there:

For instance, in an HR system, the process of interviewing candidates – wouldn’t you just insert, update, and delete these Appointment objects?

If I were to put on my domain-driven hat, I would describe those requirements differently – interview appointments have a lifecycle: proposed, accepted, cancelled, etc. It seems that only a user of the role HR Interviewer should be able to make appointments for themselves, so the service layer code would probably look something like this:

using (ISession session = SessionFactory.OpenSession())
using (ITransaction tx = session.BeginTransaction())
{
    ICandidateInterviewer interviewer = session.Get<ICandidateInterviewer>(message.InterviewerId);
    ICandidate candidate = session.Get<ICandidate>(message.CandidateId);

    interviewer.ScheduleInterviewWith(candidate).At(message.RequestedTime);  
    tx.Commit();
}  

The “ScheduleInterviewWith” method accepts an ICandidate and returns an IAppointment. IAppointment has a method “At” which accepts a DateTime parameter and returns void – just changes the data of the appointment. The state of the appointment at creation time would probably be proposed. The appointment object would probably be added to the list of appointments for that interviewer – that’s what will cause it to be persisted automatically.

Later, when the candidate accepts the meeting, we could have the following method on ICandidate – void Accept(IAppointment); that would obviously check that the candidate is the right person for that interview, the appointment’s current state (not cancelled), etc – finally updating its state. What part of this looks like create, update, delete? If that’s what your service layer to domain interaction looks like, do you now know what your messages will be looking like?CRUD seems to be what most of us are familiar with. Moving to domain-driven thinking takes time and practice, but is well worth it. Contrast this with a more traditional O/R mapping solution:

using (ISession session = SessionFactory.OpenSession())
using (ITransaction tx = session.BeginTransaction())
{
    ICandidateInterviewer interviewer = session.Get<ICandidateInterviewer>(message.InterviewerId);
    ICandidate candidate = session.Get<ICandidate>(message.CandidateId); 

    Appointment a = new Appointment(); 

    a.Interviewer = interviewer; 
    interviewer.Appointments.Add(a); 

    a.Candidate = candidate;
    candidate.Appointments.Add(a); 

    a.Time = message.RequestedTime; 

    session.Save(a);  

    tx.Commit(); 
} 

As you can see, we’ve got simpler, more expressive, and more testable code when employing the domain model pattern, than using “just” O/R mapping. I’m not saying that the domain model pattern doesn’t need O/R mapping in the background for it to work. But that’s just it – the persistence gunk needs to be in the background and the business logic needs to be encapsulated.

So, while I’ll agree with Dave that the Domain Model is more lifestyle than pattern, I would argue against these conclusions:

If this post had a point, it’s only to share the idea that Domain Model is a big, big thing. It’s probably overkill in a lot of cases where you have simple applications that have very simple purposes.

As you just saw in the example above, there is no “overkill” to be seen. The domain model in the example wasn’t “a big, big thing”.

The domain model. Use it.

Why not have a better lifestyle?   ;-)

  
If you liked this article, you might also like articles in these categories:


Check out my Best Content If you've got a minute, you might enjoy taking a look at some of my best articles.
I've gone through the hundreds of articles I've written over the past 6 years and put together a list of the best ones as ranked by my 5000+ readers.
You won't be disappointed.

Subscribe to my feedIf you'd like to get new articles sent to you when they're published, it's easy and free.
Subscribe right here.

Follow me on Twitter Follow me on Twitter @UdiDahan.



Something on your mind? Got a question? I'd be thrilled to hear it.
Leave a comment below or email me, whatever works for you.

26 Comments

  1. Amit Says:

    Hi,
    ICandidateInterviewer interviewer = session.Get(message.InterviewerId);
    ICandidate candidate = session.Get(message.CandidateId);

    interviewer.ScheduleInterviewWith(candidate).At(message.RequestedTime);
    tx.Commit();

    Takes a candidate assigns him to interviewer with a time slot.

    Now a level deep, interviewer.ScheduleInterviewWith is certainly going to perform CRUD (CREATE READ UPDATE And Delete over some memory space).
    Isn’t it like CRUD with wrappers.


  2. udidahan Says:

    Amit,

    Of course the interviewer object will be creating an appointment object and adding it to its list. The thing is that that’s encapsulated. If it were to add other objects as well, you wouldn’t see that either.

    You can see that by working entirely in memory that way in the domain model we can more easily unit test those business rules.

    The service layer doesn’t have to explicitly INSERT those objects in the DB. CRUD usually refers to the act of actually working against the DB interfaces – creating an object in memory and connecting it to (and with) other objects is rarely viewed as CRUD.

    Does that make sense?


  3. Nick Says:

    Excellently well-put. It is hard to explain the difference between creating data-oriented domain objects and giving them real responsibilities.

    How do you handle the limitations that you hit when your domain objects need services in order to fulfil their responsibilities? Do you inject dependencies, pass dependencies through with method calls or keep your domain model self-contained and access external services from the calling code?


  4. Mark Says:

    Quick question:

    In the “traditional O/R mapping solution”, we have:

    using (ISession session = SessionFactory.OpenSession())
    using (ITransaction tx = session.BeginTransaction())
    {

    session.Save(a);

    }

    In the “domain-driven” solution, I assume session.Save is called inside:

    interviewer.ScheduleInterviewWith(candidate).At(message.RequestedTime);

    So, how do you have access to the session object here, as its not explicitly passed? Is session effectively an alias to a singleton then (does OpenSession return an existing open session if there is one)? Is this typical when using ORM?


  5. udidahan Says:

    Nick,

    I’ve been seeing that question pop up multiple times on the DDD threads and have just stopped answering it there 🙂

    The Domain Model is a self-contained component – it doesn’t take dependencies on anything else. What it does is raise events that external code can use to make decisions about which external “service” to call.

    Does that make sense?


  6. udidahan Says:

    Mark,

    Session.Save is not called in “interviewer.ScheduleInterviewWith(candidate).At(message.RequestedTime);”

    The domain objects have no persistence code in them whatsoever.

    The O/R Mapper needs to be configured in such a way so that persistence occurs by virtue of the fact that there is an unsaved appointment object in the interviewer’s collection of appointments.

    Does that make sense?


  7. Nick Says:

    Hi Udi,

    Thanks for the answer – I might go and track down some of the earlier posts – always an interesting discussion 🙂

    Nick


  8. Alberto Brandolini Says:

    Definitely well explained.

    I think CRUDs spoil the application, putting business logic in the user behaviour, instead that in the application. But the process of bringing the business logic back into the app is not always straightforward: you need to have smart people to interact with, different skills and motivation and probably some extra time.
    Sometimes this is worth the effort, but some other times a quick collection of CRUDs, maybe implemented fast with Ruby on Rails or Grails is all you need, especially for small applications.

    Alberto


  9. udidahan Says:

    Alberto,

    It looks like there will be a lot more systems to rewrite in the future with the growing popularity of RoR, doesn’t it?

    🙂


  10. Colin Jack Says:

    Good blog entry but I think you’ve been a little unfair with the “before” style code:

    Appointment appointment = new Appointment(message.RequestedTime, a.Candidate);
    interviewer.AddAppointment(appointment);

    Also whilst I like the example you provide I’d also be happy with the service layer calling methods on the Appointment directly such as appointment.Accept() rather than calling ICandidate.Accept(appointment).

    I also think theres really two points you are making here. One is that you think its good to take advantage of the features of the ORM so that when you save an interviewer its appointments are saved, the other is the fluent interface example.

    I’m also interested, do you use fluent interfaces a lot in the domain? So far I’ve only found them useful for simple value objects and entities, particularly creation.


  11. udidahan Says:

    Colin,

    Glad you liked it.

    Yes, I could have done that kind of constructor for Appointment. However, in terms of DDD, I don’t see there being an appointment that could exist without an ICandidate. I also worry about “generic” Accept methods as they may guide people to thinking about the visitor pattern when that’s not what is occuring.

    I’m not sure I’m so much “taking advantage of the features of the ORM” so much as designing a persistent ignorant domain model.

    On the issue of fluent interfaces – it just looks like I did something special. Actually,

    interviewer.ScheduleInterviewWith(candidate)

    returns an IAppointmentThatHasNotBeenScheduled which has a method:

    At(DateTime time);

    So, while I don’t explicitly go looking for how to use fluent interfaces in the domain model, the fact that I use intention revealing interfaces often leads to something that looks fluent. But usually, there is none of the chaining behavior found so often when doing the fluent thing.

    Hope that makes sense.


  12. DDD & Many to Many Object Relational Mapping Says:

    […] From CRUD to Domain-Driven Fluency […]


  13. ryzam Says:

    Do you expose ISession directly in services?..


  14. udidahan Says:

    ryzam,

    I’m not sure what you mean by exposing ISession, but service layer code does make use of ISession directly, yes.


  15. ryzam Says:

    Sorry, my previous question was wrong, actually i would like to ask do you use ISession directly from your services?.. You already answer this thanks.

    But if you are using directly, it seem that your services is taking repository function and how do you test it? What is the advantage to have services direct query/get data from dataaccess framework (for example NHibernate)

    Thanks


  16. udidahan Says:

    ryzam,

    The service layer is inherently integration code and, as such, most suitable for integration testing (rather than unit testing).

    The advantage of services talking directly to ISession is simplicity, and the ability to use the power of the framework chosen (NHibernate).


  17. Andrew Says:

    Hi Udi,

    good post, always like reading your work but have a question, The original example (makes use of the session) looks more like a Unit of work service method than a traditional DDD method, is there anything wrong with the code you posted being placed in the service layer which makes use of the domain model? the reason I ask is I am struggling when thinking in domain methods as most of the domain methods i think of really just model crud behaviour. For example, I am working on some software right now where you basically have an estate which can have a number of sites and all I seem to be modelling is Estate.AddSite, Estate.RemoveSite etc. And the only thing I seem to be putting in my domain object is validation e.g. the Site description cannot be blank…

    Would you class these as domain methods or just service layer methods?
    I think you’re right in terms of this takes a whole different mind set !


  18. udidahan Says:

    Andrew,

    I think that the issue is that the UI you’re supporting is exposing that kind of functionality to the user. DDD applies to UI design as well.

    The code in the post is indeed the implementation of service layer methods.


  19. Andrew Says:

    Hi udidahan,

    Sorry to bother you again, i have read Eric Evan’s book (maybe i should read it again) but I seem to struggle with what would appear in the domain side of things, everything seems to be a service/crud based method of the system. The examples given always seem to fit nicely with business logic (I think I may be interpreting my own system incorrectly) Would you mind suggesting a couple of typical domain methods for the following :

    If i have an estate and this contains regions in the country and these contain houses, the user can add new regions to the estate and houses to regions and view the houses details.

    Does this sound like something that warrents DDD or am I trying to fit something in that just doesnt fit, I cant believe this, as nearly all web based systems are just reflections over data at their core and merely provide facilities for the users to perform basic crud methods on a system. Would you model the crud methods e.g. AddRegion as a domain method or just at the service level?

    Sorry to be a pain, but this is one of the biggest hurdles I always have with DDD, if you can suggest any reading or articles, I would be extremely grateful (where did I put Erics book…)


  20. udidahan Says:

    Andrew,

    That kind of behavior can be built using the Active Record pattern instead of the Domain Model pattern. As you said, it is simple data manipulation and, as such, doesn’t require it. That said, DDD is broader than the Domain Model pattern and there are many other useful elements to it that can still be applicable.


  21. Riana Says:

    Hi Udi,

    This is an old but still very interesting article ! 🙂

    I have just a little question though.

    How do you implement real CRUD based screens as we used to have in many applications ?

    For example, I have an application with which it should be possible to create then register a new Client. Registering a client means here, that I have to enter its infos, address etc .. then save it.

    How do you handle those kind of scenario where your application needs to have a Domain Model (cause it has some complex business logic) but however, certain part of it are just simple CRUD like entering client infos for example. How do to marry both ?

    Thanks Udi, keep the good job on !

    Riana


  22. udidahan Says:

    Riana,

    The trick is to separate the basic CRUD stuff (which can be implemented simply using, for example, datasets) and the stuff requiring the more complex logic. You can look at composition of DDD bounded contexts for more information.


  23. Setya Says:

    Hi Udi,

    Thank you for your nice blog. I’d like to ask what would your code look like if there’s no ORM involved (NHibernate in your case) ?

    Regards,
    Setya


  24. udidahan Says:

    Setya,

    It would probably end up having a bunch of persistence code intermingled with the domain logic – not the most desirable result.


  25. Setya Says:

    Hi Udi,

    In your above example, is it just your intention for clarity sake to expose ISession and ITransaction, or can we just wrap them in a repository class having load(entity) & save(entity) to be invoked from service layer instead ?

    Regards,
    Setya


  26. Setya Says:

    Hi Udi,

    I also want to ask regarding your response to Nick:

    ‘The Domain Model is a self-contained component – it doesn’t take dependencies on anything else. What it does is raise events that external code can use to make decisions about which external “service” to call’

    What if the domain model needs to enforce business validations which depends on external services from legacy system or outside bounded context, I can’t use events for this since event is for something already happened, while validation is preventing it from happening.

    My naive design would be to wrap those external services into a domain service than injecting it as method parameter as I can not find any other way.

    Regards,
    Setya


Your comment...



If this is your first time commenting, it may take a while to show up.
I'm working to make that better.

Subscribe here to receive updates on comments.
  
   


Don't miss my best content
 

Recommendations

Bryan Wheeler, Director Platform Development at msnbc.com
Udi Dahan is the real deal.

We brought him on site to give our development staff the 5-day “Advanced Distributed System Design” training. The course profoundly changed our understanding and approach to SOA and distributed systems.

Consider some of the evidence: 1. Months later, developers still make allusions to concepts learned in the course nearly every day 2. One of our developers went home and made her husband (a developer at another company) sign up for the course at a subsequent date/venue 3. Based on what we learned, we’ve made constant improvements to our architecture that have helped us to adapt to our ever changing business domain at scale and speed If you have the opportunity to receive the training, you will make a substantial paradigm shift.

If I were to do the whole thing over again, I’d start the week by playing the clip from the Matrix where Morpheus offers Neo the choice between the red and blue pills. Once you make the intellectual leap, you’ll never look at distributed systems the same way.

Beyond the training, we were able to spend some time with Udi discussing issues unique to our business domain. Because Udi is a rare combination of a big picture thinker and a low level doer, he can quickly hone in on various issues and quickly make good (if not startling) recommendations to help solve tough technical issues.” November 11, 2010

Sam Gentile Sam Gentile, Independent WCF & SOA Expert
“Udi, one of the great minds in this area.
A man I respect immensely.”





Ian Robinson Ian Robinson, Principal Consultant at ThoughtWorks
"Your blog and articles have been enormously useful in shaping, testing and refining my own approach to delivering on SOA initiatives over the last few years. Over and against a certain 3-layer-application-architecture-blown-out-to- distributed-proportions school of SOA, your writing, steers a far more valuable course."

Shy Cohen Shy Cohen, Senior Program Manager at Microsoft
“Udi is a world renowned software architect and speaker. I met Udi at a conference that we were both speaking at, and immediately recognized his keen insight and razor-sharp intellect. Our shared passion for SOA and the advancement of its practice launched a discussion that lasted into the small hours of the night.
It was evident through that discussion that Udi is one of the most knowledgeable people in the SOA space. It was also clear why – Udi does not settle for mediocrity, and seeks to fully understand (or define) the logic and principles behind things.
Humble yet uncompromising, Udi is a pleasure to interact with.”

Glenn Block Glenn Block, Senior Program Manager - WCF at Microsoft
“I have known Udi for many years having attended his workshops and having several personal interactions including working with him when we were building our Composite Application Guidance in patterns & practices. What impresses me about Udi is his deep insight into how to address business problems through sound architecture. Backed by many years of building mission critical real world distributed systems it is no wonder that Udi is the best at what he does. When customers have deep issues with their system design, I point them Udi's way.”

Karl Wannenmacher Karl Wannenmacher, Senior Lead Expert at Frequentis AG
“I have been following Udi’s blog and podcasts since 2007. I’m convinced that he is one of the most knowledgeable and experienced people in the field of SOA, EDA and large scale systems.
Udi helped Frequentis to design a major subsystem of a large mission critical system with a nationwide deployment based on NServiceBus. It was impressive to see how he took the initial architecture and turned it upside down leading to a very flexible and scalable yet simple system without knowing the details of the business domain. I highly recommend consulting with Udi when it comes to large scale mission critical systems in any domain.”

Simon Segal Simon Segal, Independent Consultant
“Udi is one of the outstanding software development minds in the world today, his vast insights into Service Oriented Architectures and Smart Clients in particular are indeed a rare commodity. Udi is also an exceptional teacher and can help lead teams to fall into the pit of success. I would recommend Udi to anyone considering some Architecural guidance and support in their next project.”

Ohad Israeli Ohad Israeli, Chief Architect at Hewlett-Packard, Indigo Division
“When you need a man to do the job Udi is your man! No matter if you are facing near deadline deadlock or at the early stages of your development, if you have a problem Udi is the one who will probably be able to solve it, with his large experience at the industry and his widely horizons of thinking , he is always full of just in place great architectural ideas.
I am honored to have Udi as a colleague and a friend (plus having his cell phone on my speed dial).”

Ward Bell Ward Bell, VP Product Development at IdeaBlade
“Everyone will tell you how smart and knowledgable Udi is ... and they are oh-so-right. Let me add that Udi is a smart LISTENER. He's always calibrating what he has to offer with your needs and your experience ... looking for the fit. He has strongly held views ... and the ability to temper them with the nuances of the situation.
I trust Udi to tell me what I need to hear, even if I don't want to hear it, ... in a way that I can hear it. That's a rare skill to go along with his command and intelligence.”

Eli Brin, Program Manager at RISCO Group
“We hired Udi as a SOA specialist for a large scale project. The development is outsourced to India. SOA is a buzzword used almost for anything today. We wanted to understand what SOA really is, and what is the meaning and practice to develop a SOA based system.
We identified Udi as the one that can put some sense and order in our minds. We started with a private customized SOA training for the entire team in Israel. After that I had several focused sessions regarding our architecture and design.
I will summarize it simply (as he is the software simplist): We are very happy to have Udi in our project. It has a great benefit. We feel good and assured with the knowledge and practice he brings. He doesn’t talk over our heads. We assimilated nServicebus as the ESB of the project. I highly recommend you to bring Udi into your project.”

Catherine Hole Catherine Hole, Senior Project Manager at the Norwegian Health Network
“My colleagues and I have spent five interesting days with Udi - diving into the many aspects of SOA. Udi has shown impressive abilities of understanding organizational challenges, and has brought the business perspective into our way of looking at services. He has an excellent understanding of the many layers from business at the top to the technical infrstructure at the bottom. He is a great listener, and manages to simplify challenges in a way that is understandable both for developers and CEOs, and all the specialists in between.”

Yoel Arnon Yoel Arnon, MSMQ Expert
“Udi has a unique, in depth understanding of service oriented architecture and how it should be used in the real world, combined with excellent presentation skills. I think Udi should be a premier choice for a consultant or architect of distributed systems.”

Vadim Mesonzhnik, Development Project Lead at Polycom
“When we were faced with a task of creating a high performance server for a video-tele conferencing domain we decided to opt for a stateless cluster with SQL server approach. In order to confirm our decision we invited Udi.

After carefully listening for 2 hours he said: "With your kind of high availability and performance requirements you don’t want to go with stateless architecture."

One simple sentence saved us from implementing a wrong product and finding that out after years of development. No matter whether our former decisions were confirmed or altered, it gave us great confidence to move forward relying on the experience, industry best-practices and time-proven techniques that Udi shared with us.
It was a distinct pleasure and a unique opportunity to learn from someone who is among the best at what he does.”

Jack Van Hoof Jack Van Hoof, Enterprise Integration Architect at Dutch Railways
“Udi is a respected visionary on SOA and EDA, whose opinion I most of the time (if not always) highly agree with. The nice thing about Udi is that he is able to explain architectural concepts in terms of practical code-level examples.”

Neil Robbins Neil Robbins, Applications Architect at Brit Insurance
“Having followed Udi's blog and other writings for a number of years I attended Udi's two day course on 'Loosely Coupled Messaging with NServiceBus' at SkillsMatter, London.

I would strongly recommend this course to anyone with an interest in how to develop IT systems which provide immediate and future fitness for purpose. An influential and innovative thought leader and practitioner in his field, Udi demonstrates and shares a phenomenally in depth knowledge that proves his position as one of the premier experts in his field globally.

The course has enhanced my knowledge and skills in ways that I am able to immediately apply to provide benefits to my employer. Additionally though I will be able to build upon what I learned in my 2 days with Udi and have no doubt that it will only enhance my future career.

I cannot recommend Udi, and his courses, highly enough.”

Nick Malik Nick Malik, Enterprise Architect at Microsoft Corporation
You are an excellent speaker and trainer, Udi, and I've had the fortunate experience of having attended one of your presentations. I believe that you are a knowledgable and intelligent man.”

Sean Farmar Sean Farmar, Chief Technical Architect at Candidate Manager Ltd
“Udi has provided us with guidance in system architecture and supports our implementation of NServiceBus in our core business application.

He accompanied us in all stages of our development cycle and helped us put vision into real life distributed scalable software. He brought fresh thinking, great in depth of understanding software, and ongoing support that proved as valuable and cost effective.

Udi has the unique ability to analyze the business problem and come up with a simple and elegant solution for the code and the business alike.
With Udi's attention to details, and knowledge we avoided pit falls that would cost us dearly.”

Børge Hansen Børge Hansen, Architect Advisor at Microsoft
“Udi delivered a 5 hour long workshop on SOA for aspiring architects in Norway. While keeping everyone awake and excited Udi gave us some great insights and really delivered on making complex software challenges simple. Truly the software simplist.”

Motty Cohen, SW Manager at KorenTec Technologies
“I know Udi very well from our mutual work at KorenTec. During the analysis and design of a complex, distributed C4I system - where the basic concepts of NServiceBus start to emerge - I gained a lot of "Udi's hours" so I can surely say that he is a professional, skilled architect with fresh ideas and unique perspective for solving complex architecture challenges. His ideas, concepts and parts of the artifacts are the basis of several state-of-the-art C4I systems that I was involved in their architecture design.”

Aaron Jensen Aaron Jensen, VP of Engineering at Eleutian Technology
Awesome. Just awesome.

We’d been meaning to delve into messaging at Eleutian after multiple discussions with and blog posts from Greg Young and Udi Dahan in the past. We weren’t entirely sure where to start, how to start, what tools to use, how to use them, etc. Being able to sit in a room with Udi for an entire week while he described exactly how, why and what he does to tackle a massive enterprise system was invaluable to say the least.

We now have a much better direction and, more importantly, have the confidence we need to start introducing these powerful concepts into production at Eleutian.”

Gad Rosenthal Gad Rosenthal, Department Manager at Retalix
“A thinking person. Brought fresh and valuable ideas that helped us in architecting our product. When recommending a solution he supports it with evidence and detail so you can successfully act based on it. Udi's support "comes on all levels" - As the solution architect through to the detailed class design. Trustworthy!”

Chris Bilson Chris Bilson, Developer at Russell Investment Group
“I had the pleasure of attending a workshop Udi led at the Seattle ALT.NET conference in February 2009. I have been reading Udi's articles and listening to his podcasts for a long time and have always looked to him as a source of advice on software architecture.
When I actually met him and talked to him I was even more impressed. Not only is Udi an extremely likable person, he's got that rare gift of being able to explain complex concepts and ideas in a way that is easy to understand.
All the attendees of the workshop greatly appreciate the time he spent with us and the amazing insights into service oriented architecture he shared with us.”

Alexey Shestialtynov Alexey Shestialtynov, Senior .Net Developer at Candidate Manager
“I met Udi at Candidate Manager where he was brought in part-time as a consultant to help the company make its flagship product more scalable. For me, even after 30 years in software development, working with Udi was a great learning experience. I simply love his fresh ideas and architecture insights.
As we all know it is not enough to be armed with best tools and technologies to be successful in software - there is still human factor involved. When, as it happens, the project got in trouble, management asked Udi to step into a leadership role and bring it back on track. This he did in the span of a month. I can only wish that things had been done this way from the very beginning.
I look forward to working with Udi again in the future.”

Christopher Bennage Christopher Bennage, President at Blue Spire Consulting, Inc.
“My company was hired to be the primary development team for a large scale and highly distributed application. Since these are not necessarily everyday requirements, we wanted to bring in some additional expertise. We chose Udi because of his blogging, podcasting, and speaking. We asked him to to review our architectural strategy as well as the overall viability of project.
I was very impressed, as Udi demonstrated a broad understanding of the sorts of problems we would face. His advice was honest and unbiased and very pragmatic. Whenever I questioned him on particular points, he was able to backup his opinion with real life examples. I was also impressed with his clarity and precision. He was very careful to untangle the meaning of words that might be overloaded or otherwise confusing. While Udi's hourly rate may not be the cheapest, the ROI is undoubtedly a deal. I would highly recommend consulting with Udi.”

Robert Lewkovich, Product / Development Manager at Eggs Overnight
“Udi's advice and consulting were a huge time saver for the project I'm responsible for. The $ spent were well worth it and provided me with a more complete understanding of nServiceBus and most importantly in helping make the correct architectural decisions earlier thereby reducing later, and more expensive, rework.”

Ray Houston Ray Houston, Director of Development at TOPAZ Technologies
“Udi's SOA class made me smart - it was awesome.

The class was very well put together. The materials were clear and concise and Udi did a fantastic job presenting it. It was a good mixture of lecture, coding, and question and answer. I fully expected that I would be taking notes like crazy, but it was so well laid out that the only thing I wrote down the entire course was what I wanted for lunch. Udi provided us with all the lecture materials and everyone has access to all of the samples which are in the nServiceBus trunk.

Now I know why Udi is the "Software Simplist." I was amazed to find that all the code and solutions were indeed very simple. The patterns that Udi presented keep things simple by isolating complexity so that it doesn't creep into your day to day code. The domain code looks the same if it's running in a single process or if it's running in 100 processes.”

Ian Cooper Ian Cooper, Team Lead at Beazley
“Udi is one of the leaders in the .Net development community, one of the truly smart guys who do not just get best architectural practice well enough to educate others but drives innovation. Udi consistently challenges my thinking in ways that make me better at what I do.”

Liron Levy, Team Leader at Rafael
“I've met Udi when I worked as a team leader in Rafael. One of the most senior managers there knew Udi because he was doing superb architecture job in another Rafael project and he recommended bringing him on board to help the project I was leading.
Udi brought with him fresh solutions and invaluable deep architecture insights. He is an authority on SOA (service oriented architecture) and this was a tremendous help in our project.
On the personal level - Udi is a great communicator and can persuade even the most difficult audiences (I was part of such an audience myself..) by bringing sound explanations that draw on his extensive knowledge in the software business. Working with Udi was a great learning experience for me, and I'll be happy to work with him again in the future.”

Adam Dymitruk Adam Dymitruk, Director of IT at Apara Systems
“I met Udi for the first time at DevTeach in Montreal back in early 2007. While Udi is usually involved in SOA subjects, his knowledge spans all of a software development company's concerns. I would not hesitate to recommend Udi for any company that needs excellent leadership, mentoring, problem solving, application of patterns, implementation of methodologies and straight out solution development.
There are very few people in the world that are as dedicated to their craft as Udi is to his. At ALT.NET Seattle, Udi explained many core ideas about SOA. The team that I brought with me found his workshop and other talks the highlight of the event and provided the most value to us and our organization. I am thrilled to have the opportunity to recommend him.”

Eytan Michaeli Eytan Michaeli, CTO Korentec
“Udi was responsible for a major project in the company, and as a chief architect designed a complex multi server C4I system with many innovations and excellent performance.”


Carl Kenne Carl Kenne, .Net Consultant at Dotway AB
“Udi's session "DDD in Enterprise apps" was truly an eye opener. Udi has a great ability to explain complex enterprise designs in a very comprehensive and inspiring way. I've seen several sessions on both DDD and SOA in the past, but Udi puts it in a completly new perspective and makes us understand what it's all really about. If you ever have a chance to see any of Udi's sessions in the future, take it!”

Avi Nehama, R&D Project Manager at Retalix
“Not only that Udi is a briliant software architecture consultant, he also has remarkable abilities to present complex ideas in a simple and concise manner, and...
always with a smile. Udi is indeed a top-league professional!”

Ben Scheirman Ben Scheirman, Lead Developer at CenterPoint Energy
“Udi is one of those rare people who not only deeply understands SOA and domain driven design, but also eloquently conveys that in an easy to grasp way. He is patient, polite, and easy to talk to. I'm extremely glad I came to his workshop on SOA.”

Scott C. Reynolds Scott C. Reynolds, Director of Software Engineering at CBLPath
“Udi is consistently advancing the state of thought in software architecture, service orientation, and domain modeling.
His mastery of the technologies and techniques is second to none, but he pairs that with a singular ability to listen and communicate effectively with all parties, technical and non, to help people arrive at context-appropriate solutions. Every time I have worked with Udi, or attended a talk of his, or just had a conversation with him I have come away from it enriched with new understanding about the ideas discussed.”

Evgeny-Hen Osipow, Head of R&D at PCLine
“Udi has helped PCLine on projects by implementing architectural blueprints demonstrating the value of simple design and code.”

Rhys Campbell Rhys Campbell, Owner at Artemis West
“For many years I have been following the works of Udi. His explanation of often complex design and architectural concepts are so cleanly broken down that even the most junior of architects can begin to understand these concepts. These concepts however tend to typify the "real world" problems we face daily so even the most experienced software expert will find himself in an "Aha!" moment when following Udi teachings.
It was a pleasure to finally meet Udi in Seattle Alt.Net OpenSpaces 2008, where I was pleasantly surprised at how down-to-earth and approachable he was. His depth and breadth of software knowledge also became apparent when discussion with his peers quickly dove deep in to the problems we current face. If given the opportunity to work with or recommend Udi I would quickly take that chance. When I think .Net Architecture, I think Udi.”

Sverre Hundeide Sverre Hundeide, Senior Consultant at Objectware
“Udi had been hired to present the third LEAP master class in Oslo. He is an well known international expert on enterprise software architecture and design, and is the author of the open source messaging framework nServiceBus. The entire class was based on discussion and interaction with the audience, and the only Power Point slide used was the one showing the agenda.
He started out with sketching a naive traditional n-tier application (big ball of mud), and based on suggestions from the audience we explored different solutions which might improve the solution. Whatever suggestions we threw at him, he always had a thoroughly considered answer describing pros and cons with the suggested solution. He obviously has a lot of experience with real world enterprise SOA applications.”

Raphaël Wouters Raphaël Wouters, Owner/Managing Partner at Medinternals
“I attended Udi's excellent course 'Advanced Distributed System Design with SOA and DDD' at Skillsmatter. Few people can truly claim such a high skill and expertise level, present it using a pragmatic, concrete no-nonsense approach and still stay reachable.”

Nimrod Peleg Nimrod Peleg, Lab Engineer at Technion IIT
“One of the best programmers and software engineer I've ever met, creative, knows how to design and implemet, very collaborative and finally - the applications he designed implemeted work for many years without any problems!

Jose Manuel Beas
“When I attended Udi's SOA Workshop, then it suddenly changed my view of what Service Oriented Architectures were all about. Udi explained complex concepts very clearly and created a very productive discussion environment where all the attendees could learn a lot. I strongly recommend hiring Udi.”

Daniel Jin Daniel Jin, Senior Lead Developer at PJM Interconnection
“Udi is one of the top SOA guru in the .NET space. He is always eager to help others by sharing his knowledge and experiences. His blog articles often offer deep insights and is a invaluable resource. I highly recommend him.”

Pasi Taive Pasi Taive, Chief Architect at Tieto
“I attended both of Udi's "UI Composition Key to SOA Success" and "DDD in Enterprise Apps" sessions and they were exceptionally good. I will definitely participate in his sessions again. Udi is a great presenter and has the ability to explain complex issues in a manner that everyone understands.”

Eran Sagi, Software Architect at HP
“So far, I heard about Service Oriented architecture all over. Everyone mentions it – the big buzz word. But, when I actually asked someone for what does it really mean, no one managed to give me a complete satisfied answer. Finally in his excellent course “Advanced Distributed Systems”, I got the answers I was looking for. Udi went over the different motivations (principles) of Services Oriented, explained them well one by one, and showed how each one could be technically addressed using NService bus. In his course, Udi also explain the way of thinking when coming to design a Service Oriented system. What are the questions you need to ask yourself in order to shape your system, place the logic in the right places for best Service Oriented system.

I would recommend this course for any architect or developer who deals with distributed system, but not only. In my work we do not have a real distributed system, but one PC which host both the UI application and the different services inside, all communicating via WCF. I found that many of the architecture principles and motivations of SOA apply for our system as well. Enough that you have SW partitioned into components and most of the principles becomes relevant to you as well. Bottom line – an excellent course recommended to any SW Architect, or any developer dealing with distributed system.”

Consult with Udi

Guest Authored Books



Creative Commons License  © Copyright 2005-2011, Udi Dahan. email@UdiDahan.com