Architecture Category for Udi Dahan's Blog

Udi Dahan – The Software Simplist
Enterprise Development Expert & SOA Specialist

Blog

Consulting

Training

Articles

Speaking

About

Archive for the ‘Architecture’ Category

Decoupling layers – upside down

Friday, June 10th, 2005

Every once in a while I run into a question about how code from a “lower layer” can call code in an “upper layer”. This comes up a lot around the DDD groups where you see people trying to work around the idea that repositories are above entities when they want/need an entity to call into a repository. Same thing in data access.

Why is it not yet obvious that events (in .net) are the solution?

Just have your “lower layer” objects expose events for what they need from “upper layers” and have objects there register for those events. In the event-handling methods the calls can be made between objects on the upper layer finally returning the result back to the lower layer. As an aside, a lot of people aren’t used to the fact that raising an event can return something – it really is quite useful.

Posted in Architecture | Comments Off on Decoupling layers – upside down

What I want out of Biztalk

Friday, May 27th, 2005

Give me as many of the patterns out of the EIP book as you can and make it run fast. Is that too much to ask?

Posted in Architecture, BizTalk, Development | Comments Off on What I want out of Biztalk

So what if the contract's first?

Thursday, April 14th, 2005

I’ve been following the contract-first stuff going on for the last while in some disbelief. The assertion that “defining” the contract FIRST will somehow make the system better hasn’t even gotten to the sparse anecdotal evidence stage. But, the idea of contract-first is not new – there have been proponents of this school for ages, many of them coming from old-school waterfall methodologies.

In the real world, when developing a new system, or any new piece of code that has an interface for the outside world to interact with it, you don’t know enough to fully define the contract/interface, be it first, second, or third. In most cases, you start with a partial interface, start implementing it, change it, go on with some other parts, return to the first part, change it again, and on, and on, and on. It’s a discovery process where you bounce between interface and implementation many times.

There something hiding behind that concept “contract-first”, and it’s “contract-once”, which I believe is anti-thetical to how software is really built.

There’s no reason web services with wsdl should be any different.

Posted in Architecture | Comments Off on So what if the contract's first?

Last call for IOC

Thursday, April 7th, 2005

After seeing the questions raised after my last installment on IOC, I think that I was wrong to use the UI to illustrate my point. What I was demonstrating was NOT how to do “Model-View-Whatever”, but rather a way to retrieve data from other objects without using IOC. The reason I did this was to refute the claims that to do this in a testable manner required IOC.

Finally, I want to make it clear that I think interfaces are great and that they should be used VERY often. And it’s not that I think IOC has no value. All I was saying was that we can go beyond what IOC gives us by using events and components – well, independent objects would be a better name.

I’ll weigh in on the MVC vs MVP battle some other time 🙂

Posted in Architecture | Comments Off on Last call for IOC

Channel 9 helps me articulate the importance of SOA

Wednesday, April 6th, 2005

Near the end of Jim Gray’s interview on Channel 9 he talks (very shortly) about his disagreement with Don Box pertaining to SOA in general and Indigo specifically. That’s the moment that I found the words to describe why SOA is important.

SOA is about how to build systems that can do distributed, parallel processing effectively.

And, by the way, I lay my chips on the Jim Gray side of the argument. I think that the code that programmers will write will be by and large synchronous (barely any multi-threading) and that system-wide concurrency will be achieved through properly designed messaging interactions. I’ll be giving a webcast about this topic sometime next month – the link will be up when I have it.

Posted in Architecture | Comments Off on Channel 9 helps me articulate the importance of SOA

On the factoring of interfaces

Wednesday, April 6th, 2005

Chris Mackenzie‘s take on “Implementing an Interface in the UI, or the 7-layer system” is based on having an interface for each of our entities in the system. His example focuses on a Person entity, thus having an IPerson interface. Now, the issue of having UI elements implement these interfaces is interesting, but secondary. First, we have to take a look back at what separating an interface from an implementation entails.

A “Person” is more than just their data – our IPerson interface should also contain methods for manipulating Person objects. I would even go so far as to say that we should avoid using the “set” part of properties – all manipulation should be entirely method based. I know that this is OO zealotry, but I’ve found that, more often than not, large blocks of code are written behind “set” properties. This can be easily taken too far.

So, what I propose is to refactor our IPerson interface into 2: an IPersonInfo interface which contains the data-only aspect of a Person as property “get”s only, and an IPerson interface which inherits IPersonInfo and contains the behavioral aspects of a Person – the methods.

What is the good for?

Well, for those cases where we will want UI controls to implement our IPerson interface, it would seem odd to have such a control need to implement a “GiveTwoWeeksNotice” method.

Also, since the IPersonInfo is, in essence, read-only data, we can safely pass it anywhere without worrying that the data in our object will be corrupted somehow.

There is one thing to watch out for, though. The IPersonInfo is really a data transfer object, something of an anti-pattern within a given application boundary. We need to make sure our application doesn’t regress into procedural manipulation of the data. I don’t think there will be too much danger of that for developers used to separating interface from implementation.

So, to end on a positive note, the IPersonInfo can also be effectively used at application boundaries – between client and server for instance. As well, when it comes to persistence, all we’re really interested in is the data – no need to use an IPerson when an IPersonInfo will suffice; but one can consider persistence to databases (and the like) as a kind of application boundary too.

Posted in Architecture | Comments Off on On the factoring of interfaces

Travelling to IOC, and beyond

Monday, April 4th, 2005

One of the points raised in the comments to my previous post was that the method described would not be applicable for retrieving/consuming data/objects.

Let’s take as an example, that we want to populate the list of order items in a grid when an order is selected in the form. Before IOC, we would load our Order object and use the GetOrderItems method. The problem with this, among other things, is testing – our code is tightly coupled to the implementation of the Order class and the OrderItem class.

For testing purposes, it would be most convenient if we could supply an instance of some other class; that way we could test the form in isolation. The next step in our journey would be to separate the interface of the Order class from its implementation so that the form would only need to be dependent on the interface. However, if the form did not have a reference to the concrete implementation of the interface, how could it instantiate the appropriate object in order to use it?

Enter the IOC frameworks. They exist exactly to solve these kinds of problems. In our example, it would be the responsibility of the form to request the instance from the IOC framework, who would, in turn, instantiate the appropriate object and return it to the form. This opens up the opportunity to use mock objects to unit test our form.

So far, so good. But it doesn’t have to end there.

One of the problems with this approach is that we aren’t able to test the system without the UI – there’s all sorts of workflow-ey type logic there, hiding behind button clicks and other abominations 😉

A different approach might be used. Suppose that when the button is clicked on the form requesting that the order items be shown, all the form does is raise an event “OrderItemsRequested”, no more. Well, that would get rid of the logic hiding behind the button, but that logic has to go somewhere. What we would need, also, is for someone to register for the event, so that it could be handled – someone that the form isn’t aware of. Let’s call this class Presenter, for now.

In fact, it would be the Presenter which shows the form, in effect creating a new instance of the form class, and registering for the event. However, what I would much prefer is that the Presenter would just wire up the event of the form to the appropriate sink. However, events are not so aesthetically pleasing for receiving data – I wouldn’t like seeing a delegate like:

public delegate IList OrderItemsRequestedDelegate();

for the event above – it smells. However, what we could do is let the form dictate how it would like to get the data back, in essence letting the form influence the plumbing. The result of this would be a method on the form:

public void SetOrderItems(IList orderItems);

and a corresponding delegate:

public void SetOrderItemsDelegate(IList orderItems);

while the event would now correspond to the delegate:

public void OrderItemsRequestedDelegate(SetOrderItemsDelegate callback);

and so the form would raise it’s event like this:

protected void OnOrderItemsRequested()
{
if (OrderItemsRequested != null)
OrderItemsRequested(new SetOrderItemsDelegate(this.SetOrderItems));
}

Our Presenter is beginning to lose it’s presenting role, why don’t we call it Plumber instead.

So, our Plumber would want to hook up the event from the form to the Order object like so:

Form f = new Form();
Order o = Repositories.OrderRepository.Get(id);

f.OrderItemsRequested += o.GetOrderItems;

(Here we’re using .Net 2.0 delegate inference.)
However, this couldn’t work because the GetOrderItems method on the Order class doesn’t correspond to the signature of the delegate. It almost seems like we’re stuck.

Well, there is a way out.

Remember how in the last post we used events to push processes forwards, well, we can do the same thing again. If the Order class were to return the list of order items with an event, we could change the plumbing a bit and get a nicely decoupled design.

Instead of “GetOrderItems”, let’s call the method “YieldOrderItems”, which, when it is called, will raise an event “OrderItemsReady” when it has the data (possibly on a different thread if it took a long time to get them, consider the ramifications of that (!), re-entrant domain objects – god help us). The event would return the data as a parameter. It’s delegate could, in fact, be the same as “SetOrderItemsDelegate” above (public void SetOrderItemsDelegate(IList orderItems);).

Things are beginning to fall into place. Let’s return to our plumber:

Form f = new Form();
Order o = Repositories.OrderRepository.Get(id);

f.OrderItemsRequested += { o.OrderItemsReady += callback; o.YieldOrderItems(); o.OrderItemsReady -= callback; }

(Here we’re using .Net 2.0 anonymous methods and delegate inference.)
What we’ve done is that when the form requests the order items, it raises it’s OrderItemsRequested event, which registers the delegate raised as the parameter to the Order’s own event. The order is then asked to yield it’s order items, which raises it’s OrderItemsReady event, which calls the delegate on the form, which returns the data to the form to be shown, and finally cleans up.

I know that if there’s anything in the world that goes against the “do the simplest thing” principle, it’s what I’ve just described . It takes a while to digest. It took me quite a while to dream it up, and even longer to become convinced that the dream isn’t really a nightmare.

The real advantage in the approach, beyond the fact that the view and the model are totally decoupled, and that we don’t need to the form in order to test all the functionality, is that the so called Controller logic is embedded in the way we connected the pipes. The flow is not only external to both the view and the model, it does nothing more than hook up what was already there. I’m trying to think of a way to externalize this plumbing to XML files to get to total nirvana.

Anyway, back to IOC. One could definitely make the plumber class independent of the implementations of the concrete form, order, and order item classes by using IOC frameworks. My assertion is that it is not needed nearly as much as it was before, if at all. I can unit test both the view and model in total isolation, without needing mocks – I just register for the events in my tests. This leaves the plumber, who, in essence, doesn’t do anything, there is hardly any behaviour there. We could go the whole nine yards and test him as well, using mocks as needed, but what would we learn that wasn’t already evident from the code? Would we test that the right delegate got to the right place? How could we assert that without duplicating the code under test?

Anyway, to sum up, IOC is great, it makes you think about your code and design in new ways, ways you didn’t think possible before. Events are great, they can take you beyond what you thought possible with IOC. X will be great, etc, etc, … By always striving for better testability, interface versioning, and looser coupling, we will improve the design of our systems, which, after all, is the (software) bottom line.

Remember the agile manifesto:

“We are uncovering better ways of developing software by doing it …”

Posted in Architecture | Comments Off on Travelling to IOC, and beyond

IOC, TDD, and design

Monday, April 4th, 2005

Before tackling another aspect of IOC in .Net, I think it necessary to reiterate a point oft raised in TDD circles:

If it’s hard to test, you should probably take another look at your design.

I think that we have maybe let the “design pendulum” swing to far as a part of the methodology shift XP, and the other agile methods, have brought. Although TDD does guide us to let the design float up out of the code while we are iterating, I feel that we do not have to forget all we have learned about good design over the years.

We can save quite a bit of time by aiming closer to the target. There are also certain “practices” that help; preferring instances to statics is one, separating interface from implementation is another.

Finally, touching back on the IOC point – I think that taking the step to using dependency injection, with or without frameworks, will help us get to better designs faster. I believe it to be a necessary step that should not be skipped. However, to believe that the design continuum ends at IOC is to ignore history – something better always comes along, eventually (usually because the problems we deal with change so that yesterday’s solutions don’t quite cut it anymore).

Posted in Architecture | Comments Off on IOC, TDD, and design

IOC vs .Net, round 2

Wednesday, March 30th, 2005

Quite a lot of people got up in arms after my previous post about the decreased relevance of IOC (Inversion of Control) in .Net. I have to say that the provocation was somewhat intentional, but the logic is still sound.

For those familiar with design based around IOC, it is clear that any dependencies between classes are broken by interfaces. The advantages in terms of testability and lower coupling are well known. I don’t argue these points, but rather I think that they don’t go far enough.

Let’s take as an example a class C1 that is dependent on interfaces I1, I2, and I3. Personally, I prefer constructor based injection to property injection, but it is irrelevant. The problem is always the null value. If for one of the interfaces we receive a null object, then we will be getting NullReferenceExceptions whenever code is run that uses that object. This is something of an annoyance when I only want to test one interaction, even though other interactions may be involved – I can’t just pass in null.

The other solution to the “null problem” is to have class C1 always test for null before using an object. I bet you can smell the stench half way across the ‘net.

Another issue is versioning/extensibility – if I want to have 2 objects of interface I1 in use for C1, well, I have to change my class. Consider wanting to both send voice-mail and email to a user as a result of something in C1. Both the voice-mail and the email implementation would implement the same interface. If it’s true for 2, then it’s true for 3, and K, so by induction we have an extensibility problem. The flip side is that once the class has been written for an arbitrary number of objects, the code that calls it needs to be aware of this. We’re changing the code of the class because of factors totally external to it, this smells of a responsibility problem.

In fact, wouldn’t it be nice to take all this wiring between all our implementation classes and make it so that they wouldn’t need to know about it, or be changed by changes in the wiring?

This could be called making the class independent. Some would call this a component. I wouldn’t get too hung up on definitions. It’s just the evolution of the design.

So, the question remains; HOW do we make our class C1 independent of I1, I2, and I3?

Well, the answer is to look within our class. Why is it that we’re calling the interfaces at these specific places in our code? In essence, we’re notifying the outside world about things that are going on inside.

In the example above with the email and voice-mail, class C1 is really trying to perform functionality that can be called “Notify User” by using the interfaces it has. Suppose that instead of knowing that C1 needs to call two instances of IUserNotifier, it would just raise an event – NeedToNotifyUser. The object that instantiated C1 would be responsible to wire that instance’s event to the appropriate notifiers.

Assuming that there’s a delegate defined: public void NeedToNotifyUserDelegate(IUser user);

Then class C1 would have an event: public event NeedToNotifyUserDelegate NeedToNotifyUser;
And a corresponding method:

protected void OnNeedToNotifyUser(IUser user)
{
  if (NeedToNotifyUser != null)
    NeedToNotifyUser(user);
}

and the interface IUserNotifier would have a method like: void NotifyUser(IUser user);

and the code that instantiated C1 would look similar to:

IUserNotifier emailNotifier = new EmailNotifier();
IUserNotifier voiceMailNotifier = new VoiceMailNotifier();
C1 c = new C1();

c.NeedToNotifyUser += new NeedToNotifyUserDelegate(emailNotifier.NotifyUser);
c.NeedToNotifyUser += new NeedToNotifyUserDelegate(voiceMailNotifier.NotifyUser);

As you can see, we have now made C1 independent of the IUserNotifier interface, externalized the wiring, and handled the issue of nulls quite nicely. Our unit tests of C1 don’t even need to mock up instances of these interfaces anymore.

So, the fact that .Net has delegates/events makes it possible to do away with IOC in many cases, where Java cannot.

If we were to call C1 a component now, then an application built in this manner could be said to have a Component Oriented Architecture. It’s really just a plain old Object Oriented Architecture after some refactoring.

Although it appears that we have in essence removed the dependencies, they are still subtly there, hiding in plain sight. The delegate we defined above has, entirely by accident, the same signature as the methods being wired. The delegate serves as the design-bridge between our implementations.

If, however, all our “components” were developed independently, the chances of this happening are a bit above none and a bit less than zilch. In this case, we would have to create explicit bridge classes that would be used to translate event “calls” on one end, to method calls on the other. This is perfectly acceptable, although not optimal (code wise). The main advantage is that it allows near absolute independent development and testing of each “component”. This can amount to real time savings. Of course, you wouldn’t REALLY want to delay integration until the end 🙂

You might think, then, that we can do away with IOC altogether. There are, however, some cases where it can’t be done, and more where it shouldn’t be done. But that’s a topic for a different post 🙂

Posted in Architecture | Comments Off on IOC vs .Net, round 2

Why IOC is more a Java thing than a .Net thing

Tuesday, March 15th, 2005

I’ve wondered for some time how it is that IOC (Inversion of Control), aka Dependency Injection frameworks were so common in the Java camp, yet hardly mentioned in .Net circles. Just the other day it hit me. In .Net, we have delegates and events, and they are all that we need, in 99.9% of the cases. In fact, when you look at under which circumstances IOC is used in Java, you’ll often see an implementation of raising an event.

Here’s hoping that we don’t see an NIOC or anything.

Posted in Architecture | Comments Off on Why IOC is more a Java thing than a .Net thing

« Previous Entries

Next Entries »

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

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, 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, 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, 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, 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, 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, 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, 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, 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, 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, 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, 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, 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, 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, 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, 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, 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, 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, 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, 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, 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, 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, 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, .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, 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, 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, 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, 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, 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, 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, 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, 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

Article: The Enterprise Service Bus and Your SOA

97 Things Every Software Architect Should Know

Follow me on Mastodon