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Archive for the ‘NHibernate’ Category

Query Objects vs Methods on a Repository

Wednesday, March 28th, 2007

Given that we have some interface/class that we use to communicate with the persistence mechanism, in NHibernate terms this would be ISession, although that could be wrapper by some more technology-agnostic interface like IDbConversation – holding the generic methods: Insert, Update, Delete, GetById<T>, GetAll<T>, etc.

What design issues are better handled by option one (query objects) or option two (methods on a repository)?

Option 1:

No custom repository per persistence type. All calls are done on IDbConversation. Fetching objects with custom queries is done like so:

IList<T> IDbConversation.PerformQuery(IQuery<T> query);

and then specific classes implement IQuery<T>, for instance, GetCustomersWithOutstandingDebtForLastQuarter which implements IQuery<ICustomer>. This implementation is responsible for translating the query into the appropriate representation for the persistence framework – say a chain of ICriteria in terms of NHibernate.

This results in loose coupling between queries, such that changing the interface of one would not touch code used by another.

By putting all queries in the same parent namespace “Queries”, we get the nice intellisense support of typing “IList<ICustomer> customers = this.IDbConversation.PerformQuery(Queries.” and getting the list of available options.

Option 2: (the more common)

One custom repository per persistence type. The repository talks with IDbConversation. The repository exposes methods for custom queries.

IList<Customer> CustomerRepository.GetCustomersWithOutstandingDebtForLastQuarter();

The repository translates the query to the specific persistence framework.

This results in less moving parts. In order to find a specific query you just type “this.CustomerRepository.” and the list of available methods shows up with intellisense.

Since all code is in the same class, changing the implementation/interface of one query/method may cause unintended side effects.

As you can probably tell, I’m for option one. It also fits nicely with my fetching strategy design, which I’m going to post the detailed design for shortly.

What are your thoughts?

[Also posted on the Domain Driven Design group here.]

Better Domain-Driven Design Implementation

Tuesday, March 6th, 2007

I just ran into a great example for explaining DDD in Ayende’s post “Entities, Services, and what goes between them”. Let’s just jump right into the code:

public class Order
       public virtual Money CalculateCost()
              Money cost = Money.Zero;
              foreach (OrderLine line in OrderLines)
                     cost = cost.Add(line.Cost);   

              cost = cost.Add(this.ShippingCosts);
              return ApplyTaxes(cost);


public class OrderService
       public virtual Money CalculateCostForOrder(int orderId)
              Order order = Repository<Order>.FindOne(
                     (Where.Order.Id == orderId).ToDetachedCriteria()
                           .SetFetchMode(“OrderLines”, FetchMode.Eager));

               return order.CalculateCost();

I’d like to improve this already great code.

First of all, the fact that the OrderService just calls the CalculateCost method on the Order object is great. What is interesting is how it knows that the implementation of that method requires the OrderLines to be fetched. From a performance perspective, this is absolutely correct. We want to hit the database only once, so eager fetching is good. What I would like to do is to take this knowledge a collocate it with who should know it.

Well, the class that absolutely knows about the fact that OrderLines are required for the CalculateCost method is the Order class. However, the OrderService is the one that needs to make use of the fetching strategy, so there needs to be some way for us to communicate this. I usually use an interface to represent a role that (9 times out of 10) has a single fetching strategy.

The two common cases where fetching strategy differs is when fetching the object “for read” – in other words, to show data to the user, and the other is “for write” – in essence calling methods on the object which change its state. The third, somewhat less common case is “for calculation” which is described above. We could model these as IOrderInfo, IOrder, and IOrderCalculator respectively – with each of them exposing the relevant properties, methods, and events. By and large, we would have one class implement all these interfaces, but this isn’t a hard and fast rule.  

Now, imagine that there was an interface called IFetchingStrategy. Also, imagine we had a factory which created objects implementing it based on some type we gave them – let’s call that IFetchingStrategyFactory. In it we could find that under the type IOrderCalculator was a fetching strategy describing eager loading for OrderLines. Our generic repository could go to the IFetchingStrategyFactory automatically, without the service getting involved. This would simplify the service code:

public class OrderService
       public virtual Money CalculateCostForOrder(int orderId)
              IOrderCalculator order = Repository<IOrderCalculator>.FindOne(
                     (Where.Order.Id == orderId));
              return order.CalculateCost();

But the issue here isn’t just simplicity, but the Single Responsibility Principle – or that each class should have only one reason to change. Should the fetching strategy change, the OrderService class would not have to change.Moving forward with this, we realize that when OrderLines are loaded for an IOrderCalculator, they don’t need their connection to the Product. In which case, it might make sense for us to have a separate class, OrderCalculator, and not just Order. OrderCalculator would contain a list of OrderLines, but not as IList, but rather IList<IOrderLineForCalculation>. Using a sufficiently intelligent O/R mapper, we could map the class OrderLine with a fetching strategy as well, so that when it is requested as IOrderLineForCalculation, the Product association would not be traversed. Of course, when using simpler O/R mappers we might have to create a new class.  

This may seem like a lot of trouble to go to. It actually isn’t. It’s pretty much just a different way to package the code you already wrote. Yes, there are more interfaces, and probably more classes, but the amount of business logic code is the same. I’ve been able to keep performance high with this design, but increase its maintainability. I measure maintainability as both the amount of time, and number of changes that need to be made by a programmer familiar with the design. Learnability (?) is often called maintainability, but I think that it’s something else. This design may not be as learnable– meaning it would take a given programmer longer to learn this design than the previous one. I submit that the increased maintainability outweighs the increased learnability substantially.  

I would love to see some standardization around these principles, making it easier to change O/R mapping tools and decreasing the learning curve for developers changing tools. In my opinion, these principles are key to moving the implementation and adoption of Domain-Driven Design and O/R mapping forwards, specifically in handling the problematic performance perception in data-driven environments like most enterprises.

Product-Driven Architecture and O/R Mapping

Thursday, February 22nd, 2007

Published in Developer.com

Summary: The single, most important trap to watch out for when choosing an object-relational mapping tool is this: “Product-Driven Architecture”. PDA is a term I use to describe a set of symptoms that I’ve seen in projects over the years. In these projects, entire teams would spend months agonizing over product comparison tables, debating the importance and rankings of various features, all without a coherent architecture.

Continue reading.

Dataset – O/R mapping rumble at TechEd MVP Dinner

Thursday, November 9th, 2006

So, last night I was at the MVP dinner in TechEd and everything was nice. We had a nice meal, conversation was nice, weather was… nice. And then the volume started to rise, slowly at first, so as you don’t quite notice it. After a bit, you kind of stop talking and look around. And then I hear it…

<WWF announcer voice>
Are you ready… to RUMBLE !?!?
</WWF announcer voice>

It was Datasets vs. O/R mapping, a slight twist on the infamous datasets vs. custom objects debate, all over again. They pulled me in, kicking and screaming, I swear, I really do. The lines were drawn, maintainability, performance, all the things that architects like to philosophize about in terms of other people’s work.

Anyway, I won’t give you the play-by-play ‘cause we were there almost all night. I’ll just cut to the chase.

First things first – any comparison of solutions without the context of a problem leads nowhere, fast, and stays there. So the first question I asked (when I got the chance to speak) was “are we talking about querying/reporting here?” and the answer was something like “well, yeah, but a lot of other things too”. So my suggestion was that we discuss the solutions in terms of two contexts – querying/reporting and OLTP.

What I mean by OLTP is the data-updating kind of work that you do on certain items. Examples of this include “insert order”, “change customer address”, and “discount product”. Querying/reporting doesn’t change data, and often involves dealing with large sets of data pulled from different kinds of entities (in ERD terms).

Luckily, my suggestion to deal with them separately was accepted. Secondly, I proposed that an object model (specifically implementing the Domain Model pattern) designed for OLTP would perform poorly when used for querying/reporting – simply because it wasn’t designed for it. The structure of a domain model is such that it makes it possible to define / implement business rules in one place. That’s possible, not easy.

Well, the dataset people weren’t going to just hand me the OLTP side of the equation without a fight, so they mentioned how easy it was to just “AcceptChanges”, and that my way was much more complex. My rebuttal came in the form of a question (are you seeing a pattern here?): Do you just swallow DbConcurrencyExceptions are do you throw all the user’s changes away when it happens? I didn’t quite make out the answer since there was a lot of mumbling going on, but I’m pretty sure they had one. I mean, you can’t develop multi-user systems using datasets without running into this situation.

The example that clinched OLTP was this. Two users perform a change to the same entity at the same time – one updates the customer’s marital status, the other changes their address. At the business level, there is no concurrency problem here. Both changes should go through. When using datasets, and those changes are bundled up with a bunch of other changes, and the whole snapshot is sent together from each user, you get a DbConcurrencyException. Like I said, I’m sure there’s a solution to it, I just haven’t heard it yet.

Now, here’s where things get interesting. I didn’t say that using a domain model automatically solves this problem. Rather, I described how each client could send a specific message, one a ChangeMaritalStatusMessage, the other a ChangeAddressMessage, to the server – in essence, giving the server the context in which each bit of data is relevant. The server could just open a transaction, get the customer object based on its Id, call a method on the customer (ChangeMaritalStatus or ChangeAddress), and commit the transaction. If two of these messages got to the server at the same time, the transactions would just cause them to be performed serially, and both transactions would succeed. The important part here is not losing the context of the changes.

When we talked about querying/reporting, things seemed quite a bit clearer. Datasets, or rather datatables seemed like a fine solution – most 3rd party controls support them out of the box. One guy mentioned that datasets performed poorly for large sets of data and that by designing custom entities for the result set, he could improve performance and memory utilization by, like, 70%. To tell you the truth, I think that if you need the performance, do it, if not, just use datasets. There isn’t much of an issue of correctness.

Just as an ending comment, in response to something someone said about scalability, I asked if they were reporting against the live OLTP data. The response was “yes”. Well, there’s a database scalability problem if I ever saw one. OLTP works most correctly when employing transactions that have an isolation level of serializable. The problem with them is that they lock up the whole table, or get blocked when a table scan is going on. Querying often results in a table scan. You can see the problem. Anyway, a common solution to this problem is to just reduce the isolation level, a quick fix that improves performance almost immediately. You take one hit in that your reports may be showing incorrect data, especially if they do aggregate type work. You might take another hit if your OLTP transactions need to do aggregate type work themselves. That second hit is pretty much unacceptable. A different solution is to accept the fact that the heaviest querying can usually show data that isn’t up to date up to the second.

In such a solution, you would have another database for reporting. It wouldn’t be just a replica of the OLTP database, but rather a lot more denormalized – which is a really not nice way of saying designed for reporting. You could then move the data from your OLTP database to the reporting database in some way (more to come on this topic) and you increase the scalability of your database. Just to define that a bit better – your OLTP database will be able to handle more transactions per unit of time, and reports will run faster, meaning that you will both improve their latency and the number of queries that can be handled per unit of time.

Anyway, I was pretty tired after all that, but if I had to sum it up I’d say something like this: before debating solutions, define the problem, you get a lot more insight into the solutions and you get it faster. That’s just win-win all around.

DDD – why bother?

Saturday, October 7th, 2006

Domain Driven Design (DDD), alongside its growing popularity, is experiencing some growing pains. The Domain Model pattern, documented in the Patterns of Enterprise Application Architecture book, is at the heart of DDD yet the division of responsibility between it and other DDD patterns like Service Layer isn’t quite clear. To make matters worse, the value of the Domain Model pattern relative to simpler code-generation techniques remains vague. The one thing that has reached a wide consensus is that it requires a higher level of skill to employ these techniques than continue using the widespread procedural programming practices. There is one overwhelming reason to do it anyway, though, and that is that it is the cheapest way to get a system up and running right. The reasoning behind this has to do with business rules.

An exceedingly large number of systems are being built and modified today in order to support business rules. Beyond just computerizing the management of data in the enterprise, today’s systems are required to computerize the business processes that use that data, and these processes are built upon business rules.

A rule is composed of two main elements, a clause and an action. The clause defines under what circumstances the action is to be activated. An example of a rule employed in the business environment might be “if the customer is a preferred customer, then give them a 5% discount on all orders”. The rich behavior of an enterprise is governed by these interacting rules. Consider the result of adding another business rule like “if the customer has ordered $100,000 or more in the last year, then they are to be considered a preferred customer”. If a customer is not preferred, but then sends in a new order that puts them over the limit, how is the system to behave? Conversely, what if a preferred customer cancels an order bringing them under the limit?

I’ve seen too many projects that have been tasked with implementing these kinds of behaviors yet were unable to get the system running right. Customers that should have gotten discounts didn’t in some cases, and those that should not have enjoyed a discount did at times. After much time was spent trying to track down what part of the code was wrong, changing some code, testing, over and over again, an executive decision was made to put the system into production as is. The harm to the business was deemed cheaper in this case then not putting the system in production. Is it any wonder that business is skeptical of IT’s ability to handle the agile enterprise of the future where, not only will the business rules be more complex, they will be changing all the time.

The Domain Model pattern encapsulates these business rules in such a way that they will be run even when not directly invoked. This is especially critical when one rule triggers another. Intelligent use of OO principles when designing the domain can help you altogether avoid the jump in complexity found in Business Rules Engines.

Finally, we need to understand that supporting techniques like Object/Relational (O/R) mapping are but a means, and not the end. The discussions around DDD often get mired down in the relative costs of O/R mapping and procedural code generation. Persistence is a solved problem, a technical problem that has no meaning to business. Is it not time to raise the discussion to the level of business? If the only problem you are trying to solve is the manipulation of data in a database, then don’t bother with DDD and its descendents. It won’t make your life any easier. If, on the other hand, business has gotten sick of IT deciding for them how to run their business; if you are the one tasked with building the right system, you just won’t be able to do it unless you build the system right – DDD won’t be a bother, but a necessity.

SQL Injection attacks & O/R mapping

Saturday, September 30th, 2006

You’ve probably never thought of SQL Injection Attacks and O/R mapping in the same context. I know I haven’t, that is, until today. I saw Scott’s post on how to “Guard Against SQL Injection Attacks” and started wondering how long it’s been since I’ve given it any thought. Then I realized that it was around the same time I switched to O/R mapping.

Since data received from the user is put in domain objects, and then those objects are mapped to tables (or views) in the database, the O/R mapper just handles it all for me. I assume that all the mappers out there use parameterized SQL, but I know for sure that NHibernate does (from peeking at the logs every once in a while).

Anyway, just wanted to mention this added side benefit of moving to the Domain Model pattern – no more SQL injection worries.

To map, or not to map?

Saturday, March 11th, 2006

I had this discussion with Clemens when he was last here in Israel – his position, as was so eloquently stated here, was against, while I was pro. The question he raised “To map, or not to map?” he himself answered, “to map”. The question remaining was how to map; write the sql yourself, or let some tool write/generate it for you.

The overarching question is: what do you REALLY gain by O/R mapping?

(As an aside, among the comments of his post are those using the acronym ORM. Please stop – that acronym is already taken by Object Role Modeling.)

I’ve been using O/R mapping techniques on mission critical projects for some time now, and if I wanted to compare it to what I did before, it would not be to writing all the sql by hand. I don’t remember ever doing that – there was always code generation involved. Because, let’s face it – there’s a lot of drudgery involved for things that aren’t performance critical. No reason to do THAT by hand.

So, for me, the ONE THING that O/R mapping gives me better than what I did before is this:

O/R mapping gets me better object-oriented business logic.

That’s it.

Like Clemens said, if you “don’t know SQL and RDBMS technology in any reasonable depth”, don’t expect to get good performance. Obviously this is true for any technique. But I guess that empirically speaking, the percentage of people without said knowledge is larger in the group where you don’t HAVE to write sql.

So, I’ll bet you’re asking yourself, “if that’s all Udi gets from O/R mapping, why does he keep doing it?” Or maybe you’re asking yourself “should I get a beer? This is getting long…”

The fact of the matter is that I don’t know a better way to write business logic than by using OO techniques. I grant that data is important, but the reason that many applications are built is business logic – there’s something that this new system can/should do, that the old systems couldn’t (often using the same data).

If I could sum up my understanding of Clemens position, it would be this:

A lot of developers probably aren’t experienced, or knowledgeable enough the use O/R mapping well. Therefore writing the sql yourself is better.

While I agree with the first statement, and I think that the same could be said about communication, threading, .net and many other things, I don’t think that the conclusion logically follows.

So, I guess I would sum up my position like this:

If you would like to develop a persistent domain model, O/R mapping techniques will probably help you. If you would like your solution to perform well, you should probably learn how databases work, as well as what the O/R mapping tool does under the covers.

Ultra scalability for the web

Saturday, December 10th, 2005

On one of the discussion lists I linger in, the following question was raised:

I have a client who wants me to use nHibernate for a ASP.NET Portal we are creating with Visual Basic 2005. Approx. 250,000 users, as many as 40,000 actives at the same time. Does nHibernate introduce significant overhead? Are there known issues?

I figure that the answer I gave there would be valuable to a larger audience, so here it is:

1. No, NHibernate does not introduce significant overhead.
2. Not that that will make any difference for the load described above.

Unless you architect for that level of load, any data access strategy will require very expensive hardware. For example, what better way to handle load than preventing the users from hitting your servers at all? This can be done by generating xml files for data, which are referenced by html pages statically. Look and feel should be done by separate css files. There’s nothing better than using the entire internet as your cache. Manage the expiration of these xml files from the caches of ISPs all over the web. This kind of solution will also enable you to expand your site to Akamai networks much easier, further increasing scalability.

NHibernate gives you the ability to write object oriented business logic in a persistent environment. If your site is light on logic, you might not get much benefit from using an O/R mapper. This has nothing to do with handling very high levels of load.

While the internet places inherent constraints on our ability to develop certain solutions, at the same time we can take advantage of “the rules of the net” – how content is transferred, to handle the highest levels of load. You would be hard pressed to come up with a better, more resilient solution if you were to architect it from scratch.

O/R Mapping meets Mission Critical

Monday, July 4th, 2005

After listening to a recently uncovered gem – polymorphic podcasts the topic of O/R mapping was raised yet again. I will be writing on this topic more in depth in other forums soon, but I wanted to give the executive summary here: O/R mapping is problematic.

The underlying assumption of O/R mapping is based on mapping objects to tables. However, for mission critical systems, the whole idea of updating or deleting rows from the database goes against basic principles. In a not-so-recent podcast from Ron Jacobs, Clemens Vasters described the kind of database design often utilized in high-end systems. There he describes timestamping data with a validity period creating “insert-only databases” – these enable the highest levels of performance and scalability, not to mention regulatory compliance. However, the familiar semantics of updating and deleting entities provided by O/R mapping do not seem to support these scenarios.

But all is not lost! There are solutions. I’ll be posting these solutions in the afore-mentioned forums soon.

Code from First Agile Israel Meeting

Tuesday, February 1st, 2005

The code I presented at the Agile Israel meeting can be downloaded here. It’s just a small sampling of how much code you DON’T have to write when using O/R Mapping.


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“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.”

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