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

Images – Where do they go ?

Posted in General

After going through several articles and posts and comments about images, I’ve decided to devote some space to the issue here. The treatment will be done at system-wide levels, meaning with an eye on all the *ilities. The debate is between saving images to the/a database vs saving them to disk. My choice is disk. Here’s why.

First of all, some history. Once upon a time, the way all web apps handled images was with the <img> tag using the “src” attribute to point to the relative location of the image on the server’s disk.

Over time, the idea of keeping all entity information together spread, and we began saving images to the database, and then returning them to the client by streaming them over HTTP. We began using the “src” attribute of the <img> tag to point to .aspx pages or .ashx handlers which would return the image to us. Thumbnails and zoomed in images were created on the fly by these techniques and everything worked. But not for long. These techniques begin to break down when the load increases.

What are the problems that occur when saving images to the database ? Well, for starters, if you save the image in the same table as you store the rest of the entity’s information ( for instance your employees table ) you will most likely overrun the page size for the row causing it to be split over multiple pages. This adversely affects performance. ( Note: if you do decide to go this route, I suggest creating a separate image table where you have an Id and the image itself. Then, from your entity table – employees – use a foreign key to the image table. )

Although the previous problem adversely affects the performance of the database engine, this next problem is more of a gotcha. When saving images to disk on the server, the client is able to cache them by itself to its own disk. This reduces the web server load over time as it has less bytes to serve. When images are referenced by “GetImage.ashx?EmployeeId=12”, although you can cache the bytes retrieved from the database in memory on the web server, the client doesn’t cache them to its disk. This further reduces the scalability of the system.

Finally, consider the issue of multiple sizes of images – thumbnails, zooms, etc. Although these can be dynamically generated quite comfortably with “GetImage.ashx?EmployeeId=12&Width=100&Height=100”, this increases ( per request ) the number of CPU intensive operations needed. A prefered alternative is to automatically generate all the image sizes required once, save them to disk, and serve them like any regular image.

Personally, I use an Imaging service for all of these needs – saving the original image to disk, generating thumbnails, getting the path of an image for a given entity ( eg. employee ) and a given size ( eg. zoom ).

Finally consider the case where you have a large volume of images to serve. Better to have a single server, with ultra-fast disk access + Raid, which serves all images. This server, when separated from the database server, would greatly increase the manageability of the server farm and make diagnosing performance problems much easier.

To conclude, although an interesting capability, saving images to the database begins to pale when compared to alternatives under load. Don’t get me wrong, for small systems it may be the simplist 🙂 thing to do, but, time and time again, that small system you built 2 years ago is required to scale and support much more than you originally intended. And, its really not that hard to work the “old fashioned” way. ( Note: run-time generated graphs based on data should not be moved to disk. )

Posted on Saturday, December 27th, 2003.

SOA & Persistence – Its all about Services

Posted in SOA

I’ve been contemplating the move to SOA style development for some time now, but recently I’ve taken the plunge. I’m talking, of course, about giving up OO as a way of life. Not everything is an object.

I have a lot to say on the subject, but my main focus will be on the impact SOA has for developing a system. That’s right. One system. Not how to connect different systems using XML Web Services.

On that note, I’d just like to debunk a myth I ran into recently a la 15 Seconds : Realizing a Service-Oriented Architecture with .NET. The following image appears to be “common knowledge” when talking about SOA. Anyone see the problem ?

Hint: its between the Business Objects and the Data/Persistence.


The problem is that persistence is ( or at least should be ) a service. The business objects themselves should not be aware of their persistence. Rather, the services above should use the persistence service in order to perform the work needed.

Instead of: myCustomer.Update();

Should be: Persistence.Update( myCustomer );

Why is this important ? Because it contributes to a separation of concerns ( see Agile Management – http://www.agilemanagement.net/Articles/Weblog/Separationofconcerns.html ). Obviously, putting the knowledge of persistence ( or, for that matter, anything else ) into business objects creates bloated objects that need to know everything about what can be done with them. I’m sure that this will just further inflame the great O/R mapping debate ( see “Futility of Object-Relational Technologies” and “GENerative Object Mapping Layer” ) but it is still true.

Coming up next:

How to do persistence with SOA.

Posted on Tuesday, December 23rd, 2003.

This Consulting Business

Posted in Consulting

Several times in the career of a “programmer” one considers opening up shop and becoming his own boss – becoming a Consultant ( the capital C stands for the extra money consultants demand ). Brady brings up some interesting issues budding consultants often encounter. Robert offers some really great advice from his own consulting process. I especially appreciate the value of using escrow services. (Update: Robert adds some more advice here ) I’d like to share what little experience I’ve gained over the years in the hope that some other consultant just starting out may save himself some grief.

From my experience, the main skills area that needs improvement in programmer-turned-consultants is project management. This area deals with everything around the actual product/system developed. Development really isn’t the problem. Bottom line – first and foremost, READ ! Anything and everything about project management, contracts, RFPs, and all other things relevant in some way to the project. The hard part is always implementing all the great accumulated wisdom out there.

The most critical thing to remember is: It Takes Time.

Not pure programming, in the zone, 100% productivity time. Time to develop relationships with stakeholders. Time to go through the RFP/RFI process. Time to negotiate. Time to travel ( a lot of people when starting out forget to take this into account when budgeting – it IS time spent on the project, and should be measured – at the very least). Time to meet with users. Time to learn the terrain. Time to reconcile differing views. Time to play politics. … Time.

Obviously there isn’t enough room here to go over all the skills and techniques of project management and consulting, however, I would be remiss if I didn’t come full circle from time to money.

First of all, unless you have a signed contract, signed detailed project description document, etc… no project will be done in 2 months. Once you have all those things, AND there are NO mid-project changes, then you have a case of “contract programming” mentioned in the comments of Brady’s entry, which has a chance of being done in 2 months.

However, there are end-project activities which have to take place, installation, training, support ( yes, even if you didn’t include it in your offer, if you don’t give some support for the bugs that will doubtlessly come up, the project will be labeled a failure. ), meeting with the major stakeholders to see that they’re happy, … you might as well not have done the project.

So, in essence, once you’re a consultant, work != programming. In the vast majority of cases non-programming.Time > programming.Time. Its this mindset that has to take hold. This particularly becomes difficult when a potential client comes to you with a project that sounds exactly like something you just did. It happened to me recently. A client asked for a system that I just finished rolling out at a different client, and I thought: Easy money. Well, the politics there were like nothing I’d ever seen. The project took even longer than at the first client, even though the code had already been written !

Bottom line: Everything is a project, and must be treated as such.

Now, getting to money. Money is important, and so is when you get it ( see Robert first post about milestones ) and making sure that you get it ( Escrow a la Robert ). And, don’t forget taxes. For one-person shops that aren’t overflowing with projects, deferring a payment to a new fiscal year can make a big difference to your net income, and may buy you a favor with the client if you play your cards right.

Of course, no discussion about money and consulting would be complete without raising the issue of hourly vs flat-fee pricing. Most clients prefer fixed price offers, since they fit with their yearly budget planning.

Many consultants I’ve met use hourly fees, but billable hours is a fickle measure that varies from project to project. Personally, I have certain issues with the hourly pricing model – note that I’m referring to the invoice the client receives. When charging hourly, the client will obviously want to know what you did on an hourly basis. Try explaining to the client to pay you $X/hour for having lunch with the head of computing services to make sure that he was pleased with the effect the project had on his department.

Fixed price offers allow a consultant to roll up many project expenses that are often difficult to collect from clients in an hourly model. For those who are skilled in project management, this model often works well. However, the risk involved in under-estimating scope, or time required, may adversely impact the bottom line.

Recently, after reading this great article on Value-Based fees, I’ve had great success in this model. In a nutshell, you, in cooperation with the client, assign value to each deliverable, and price it. This model handles scope creep very elegantly. For lack of space, I suggest you go read the entire article. Moreso, the “Million Dollar Consultant” has a whole page of tips for those going the consulting route. Highly recommended.

To sum up, to succeed in consulting one has to treat it as a whole different career path to be learned and lived. Think “Career Calculus” by Eric Sink. More importantly, consultants are PEOPLE people, not computer people. Soft skills rule.

Posted on Monday, December 15th, 2003.

On Prototypes

Posted in Projects

Prototypes. They’re everywhere. Sometimes they grow into full-fledged systems. Sometimes they’re thrown away. But they can be considered a project in their own right. I’ve decided to write this entry after reading Fabrice’s thoughts on the same subject. Before getting into my own thoughts on the matter, I’d like to quickly sum up the main points I found there, including the comments posted.

The main issue originally revolved around web apps, and whether HTML or ASP.NET should be used for prototypes. Powerpoint, Visio, Paper – yes that stuff that comes out of printers, Photoshop, Illustrator, and Denim were all brought up. Arguments for and against were made. Before I pick a side, I thought I’d return to the basics.

A prototype, by definition, should be thrown away. The lessons learned, obviously, should not.

I bring this point up as it is the most basic. When thinking about prototypes, the last thing that should concern us is if we can “reuse” pieces of it for the actual system. Now, if the point of the prototype is to learn, and learning is most facilitated by short feedback loops (tons of research back this up, think pavlov), we should be looking for the “technology” that allows for the quickest feedback.

What do I mean by feedback ? What the client thinks about what we’re doing. And what’s the fastest form of “do something, get feedback” ? Talking. What we need is a way to actually DO the prototype WHILE talking to the client. This pretty much reduces the number of contending technologies down to 1. Paper.

Paper prototyping, when done well, brings to light SO many issues and unspoken assumptions in SO little time, that, from my experience, it just doesn’t make sense to go any other route. There is so much information out there on paper prototyping that I can’t even begin to list it here. Just google it.

So, how can paper prototyping be done well ? Well, it requires preparation, and, obviously, lots of paper. Plan for about a 1 hour sessions at a time with the client, no more. These sessions are VERY tiring. If possible, try to get someone to write down everything that came up during the session, and what resolutions were reached. This person should not be involved in the session beyond being an observer.

Now, let’s consider the alternative. Using a computer + some software, be it Visio, Photoshop, whatever. The problem with these approaches is that we get to focused on what we’re building, and lose focus of the lessons we should be learning. These approaches obviously increase the time between a decision we make about the system, and getting the client’s reaction. It therefore also increases the time we waste when we get a decision wrong.

The Agile world has already come to this conclusion and makes every attempt to get a real, live customer/client/user on-site for the development of the actual system. When building actual systems, obviously, paper can’t be used. But where it can, and it’s most appropriate, it should.

To sum up, when a prototype is done, we should know more about the real system that we’re building than when we started. Short feedback loops with our clients is what gives us the most information. And paper is the medium most suited to short feedback loops when dealing with prototypes.


Six Signs That You Should Use Paper Prototyping from Java.Net

Sign 1. There are many different ideas about the design

Sign 2. You find yourself defending a particular design

Sign 3. There are parts of the design you’re unsure about

Sign 4. You’re changing the way that the users perform a task

Sign 5. The concepts or terminology are new to the users

Sign 6. You’re feeling uncreative

Posted on Thursday, December 11th, 2003.

SOA vs? XP – well, maybe A vs XP might be more appropriate

Posted in Architecture

There’s a building buzz about SOA. I don’t think that anyone can argue with that. Also, I believe that for large systems, SOA will become the new paradigm. Don’t take my word for it, the PAG group at Microsoft have recently began rolling out ShadowFax, the still emerging definition of what Microsoft sees as SOA’s future.

Now, as a developer, I am pro TDD, using it constantly and consistently. I have been thinking a lot about XP as a way of developing systems in teams. The success stories have been increasing over time, and XP appears to be a valid development methodology in its own right. Not only XP of course, the entire Agile camp ( XP, Scrum, DSDM, etc ) has been raising some serious concern in “heavy” development shops.

What interests me is the mesh/meld of Architecture ( yes, with a capital A ) and agile methods. It would appear that the two, although not entirely opposed, don’t quite fit. Agile methods allow the system’s architecture to unfold as the system is built, keeping it as supple as possible. The architecture camp, of which SOA is a member, define the system’s architecture up front. Of course, small intra-service development efforts could occur before or in parallel to the architecture definition process, however, their effect on it would be minimal at best.

From a historic perspective, I think that where SOA comes in, Agile methods have yet to be introduced, or, if they have been already introduced, the data as to the success of agile over non-agile are inconclusive at best. Very Large Systems ( once again, capitalized ), like those developed for financial institutions, the military, and government have seen very little agile action at the project-wide scale. These systems have multi-year development+deployment schedules. I have recently done a stint at one such project. Waterfall, although not called by name due to recent bad press, is still used, but under the guise of tailoring some other development process.

On these large-scale development projects is where SOA will have the short-term largest impact. This is for the simple reason that project architectures are all different, but there’s nearly always only one development methodology for the company. The entrance barriers to SOA are much, much lower than any agile method.

I would be very interested in hearing any accounts of the SOA-Agile mix. Any thoughts would definitely be appreciated.

Also, “small-scale” SOA sounds like an interesting idea. How relevant is SOA to not-so-large systems ? As a standalone developer, I’d like to know what improvements SOA can bring me over OOA and other alternatives. I’m always looking for ways to be more productive and increase quality at the same time. TDD has recently done exactly that. Some of XP’s practices have also contributed. SOA looks promising. Its the integration of these behaviours that interests me today.

Tell me what you think !

Posted on Sunday, December 7th, 2003.

Mistake #1

Posted in Architecture

I haven’t yet found a mistake of mine that I want to publish, but it just so happens that I came across someone else’s ( luckily ).

On Udi Dahan’s Projects you can find information about the projects that I’ve currently got underway – 5 ( +1 that I’ll have to take on later ).

On one of the projects, Accounting System, I am charged with taking a project that’s finished development ~95% and taking it to production. The developer took me through the system, and I realized that this was not the architecture that I had envisioned when told: “This is a good system. Well architected, stored procedures, and C# code that calls it. ASP.NET pages using code-behind. Its practically finished.”

You can see what kind of monster I’ve inherited here.

To all you DBAs out there who want to develop systems, I tell you this: Do NOT put all the system into the database just because you can ! Even the dreaded “3-tier architecture” is better than that.

Just so the rest of you get an idea of what I’m talking about, think about putting all possible logic into the DB. Calling a stored procedure is all you ever do from the UI besides basic GUI event handling stuff. The SP then does everything – checks business rules, sends email, calls webservices, performs calculations – you name it.

And WHY did they do this ?! So that they could change the functionality of the system without recompiling it ! Let’s see, toss out all the *abilities ( maintainability and all the others ) , get ability to change system without recompile. Hmm… That’s like trading diamonds for glass.

Now, here’s the best part: For the project to be profitable, I’ll have to work by the same conventions ! ugghh…

Final thought: “It works” isn’t an excuse.

Well, I guess that my mistake in this whole process was assuming. Assuming that what I consider well architected, and what someone else considers well architected are two different things. Or, more generally, miscommunication. Even though I was told what to expect “Well architected, stored procedures, and C# code that calls it…”, I didn’t verify what this exactly meant. And even worse – I gave an estimate based on my assumption.

Lesson to be learned ( for me – and I’m only writing this so that I can berate myself more harshly the NEXT time it’ll happen ): Actively search for the hidden assumptions that I make when listening to someone. Make them explicit. Verify them with the speaker.

Final note: although I’ve heard this piece of advice many times before, and, like most things, is just common sense, it wasn’t REAL until it happened to me.

Posted on Saturday, November 29th, 2003.


Posted in General

Once upon a time I thought I had something to say. When I said it, it was received quite well.

Today, I have read and heard what so many others have to say, and I feel that everything’s been said. Not only that, but they say it so much better than I ever could. Is there any point in saying something that’s already been said elsewhere ? What if you haven’t seen it elsewhere yet ? Well, in that case I’m still pretty sure that I’ll just be re-hashing ( at best ) what my betters have already said.

So, what’s left to be said ?

Only one thing.

My mistakes. Maybe from my mistakes, other can spare themselves. This, IMHO, can be my greatest contribution to the community.

I thus set out to let the world know of my screw-ups, and what I learned from them ( since, as many already know, you don’t learn much at all from success ). This will be my mission.


I just found this article on Fool.com about the 12 simple secrets of Microsoft management. Point 4 states: “Require Failure” as follows:

“At most companies, to succeed is good, but to fail is unacceptable. This type of policy means that, as a risk/reward scenario, the risk of failure vastly exceeds the reward of success. Thus, most companies suffer from a workforce that pursues a course of failure avoidance. In contrast, at Microsoft, failure is expected, and even required because risking failure is the only way to push the envelope. As a result, Microsofties relentlessly pursue success without fear of failure. And if they fail, they understand that the key is to fail quickly and not waste time. “

This is great. It turns out that I’ve been doing things the Microsoft way all along.

Posted on Thursday, November 27th, 2003.

Busy busy BUSY

Posted in Projects

Things have been quite frantic recently ( for a glimpse of what’s going on see Udi Dahan’s Projects under the categories ) so I haven’t had much time for blogging. I know that everyone gets bogged down in work now and again, and apologizes for not blogging, but I’m actually quite happy that business is going so well that a large portion of my time can now be billable. If this keeps up, I’ll have to reconsider non-work blogging.

So, although I doubt that this will be my “last” entry, I will probably be going into a dry spell.

Posted on Wednesday, November 26th, 2003.

Udi Dahan's Projects

Posted in Projects

Recently I’ve started thinking about other potential uses for blogging and rss in general. One thought that came to my mind is the use of a blog for managing projects. Before I get into the managing projects thing, I guess that I should give a little background about myself. I am a standalone programmer / consultant. This really means that I am a team of one. I meet with clients, market my services, sign the contracts, meet with the users, dig for requirements, decide on architecture, design the UI, code the system ( test first ), deploy, manage user expectations, etc… Not only that, but I do this on several projects at the same time. This is what I mean by managing projects. I need a way to be most effective at doing all of these things. Just think of the possibilities if all of the stakeholders on a project had an rss aggregator. Communicating status on an ongoing basis would be simple. Mocking up a UI and getting the users comments would be simple. If you could get wiki technology integrated, you could work on all sorts of requirements docs/xp stories/whatever simply. To make a long story short, its all about effective asynchronous communication. Anyway, after all of these thoughts I came to a decision. Just do it. Try it. What’s the worst thing that could happen ? It’ll flop, and I’ll stop it pretty quick. On the other hand, maybe it really could be good for something, even a subset of the things listed above. Maybe other things that I didn’t think of. Maybe the project stakeholders will come up with other ways to use this technology. So… I am officially anouncing the opening of Udi Dahan’s Projects, the blog that will change the way we work – well, the way I work. The first experiment of its kind – that I know of. Tell me what you think ! How can blogging be used to manage projects, or, more generally, to improve the way projects are run ? Any ideas, crazy ones are exactly what I’m looking for, on other uses for this technology ? Am I totally wrong and going on the path to destruction ?

Posted on Thursday, November 20th, 2003.

Architecture, Business Rules, and Aspects, oh my !

I’ve been reading a lot from the agile management blog lately, and I came upon this entry about implementing business rules with aspects. If you haven’t yet read this previous entry about the division of the system architecture not only along system lines, but also along “risk of change” lines, then I suggest you read it first.

First of all, I would like both developers and managers to read the previous entry because of its profound meaning. We CAN and should separate different parts of the system having differing levels of risk. Once again, “3-tier architectures” don’t address these issues. So, if we are dividing the architecture along risk lines as well, then obviously the UI would be the riskiest – having the highest probability to change – over the life of the project.

However, business rules are often considered quite stable. Why ? Because their time-line of change is often stretched out over many project life-times – rather obvious really, business rules deal with the business, not the project. During development of the project we are often given the requirements in such a way that it is difficult to know what is domain knowledge and what is a business rule. It takes effort to separate out what are the business rules – what has changed in the past, and what will change in the future.

For example, in an academic project I performed some time ago, I was given a set of requirements including: 1. A student can register to a given course once in a semester. 2. A student can register to a project in a semester. Which is the business rule, which is the domain ? In this case (1) is the domain, and (2) is the rule – “a project” meaning “only one project” as I later found out. This rule changed sometime after my second alpha to “A student can register to only one project alone in a semester, but several projects in the same semester as long as they have a partner for each of those projects.”

As it is apparent, I, as a developer, have to take into account these risk/change factors and change my architecture accordingly. Ever since that project I have always created a business rules layer separate from the infamous “BL” ( Business Logic ).

Now, getting to the issue of implemeting using aspects. I am a big proponent of AOP, however I often find alternative implementations to be more desirable. Most of the examples given for the use of AOP including logging, transactions, security and others that can be made part of a framework, as .Net has done in many cases. Many have pushed Java’s superiority because of AspectJ, and although .Net doesn’t have an Aspect.Net yet ( although various developments are under way ), I have yet to miss it. Clemens Vasters has done some truly incredible stuff in the use of attributes in .Net for implementing AOP stuff. I’ve always thought that attributes should be used that way. I find that there is one basic flaw in the conclusion to using aspects for connecting business rules to systems. The entire white paper is here. ( Yes, its a pdf unfortunately – only good for print really, Jakob Nielsen thinks so too. ) The basic premise is that I’m building an entire system in an OO manner, which I’ve stopped doing some time ago for these reasons. Clemens has great insights on this as well, see them here.

When using an SOA, your UI, or any other system needing services for that matter, will be sending messages to the guts of your system – the “BL” for you hardcore 3-tier-guys. Let’s call the thing receiving messages in this case the Gateway. All the gateway does is receive messages ( like “Register student number 12 to course number 15 in semester 21” ) and pass them on to the appropriate handler. The word “handler” hear is used like in the term “event handler” for a reason: The receipt of a message is an event. In the white-paper the authors refer to these events as a problem that has to be dealt with. Why ? Because when working in an object oriented fashion, you would have to intercept the call to: new Student(12).RegisterToProject(93); in order to handle the event, ie check/activate a business rule. Aspects are great for this sort of thing. However, when working in a service-oriented fashion, you would send a message of type “RegisterStudentToProject” with the parameters StudentID and ProjectID as above. No need to intercept any call since it has to first go through the gateway. The gateway would then pass the message to the business rules engine which would then find and activate the appropriate rules before and after the actual call to register the student.

The rules engine does something like this:

If ( ActivateBusinessRulesForMessageAndReturnTrueIfCanMakeCall(myMessage) )

The business rules themeselves are implemented in a separate layer than the engine. The mapping between rules and messages is also done in a layer separate from both the engine and the rules. Once we have a layer for each of these, we have architecturally separated the parts that change more often in the system from the rest of it. One can also move to a more dynamic model. One in which you define a language for defining rules, and the mapping to messages as well. Thus, changes could be made by changing a configuration file instead of recompiling any part of the system.

Note that when you have lots of rules and the order for activating them matters, you should move to a commercial rule engine instead of implementing your own. You’ll see that performance becomes an issue as the number of rules increases.

I hope that I’ve managed to introduce yet another strength of the SOA over the pure OO paradigm. Tell me what you think ! Where does the SOA fall short ? Where does the OOA beat the SOA ? Am I full of it ?

Posted on Friday, November 14th, 2003.


Don't miss my best content


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
Chapter: Introduction to SOA    Article: The Enterprise Service Bus and Your SOA

97 Things Every Software Architect Should Know

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