Udi Dahan   Udi Dahan – The Software Simplist
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How to create fully encapsulated Domain Models

Friday, February 29th, 2008.

image Update: The new and improved solution is now available: Domain Events, Take 2.

Most people getting started with DDD and the Domain Model pattern get stuck on this. For a while I tried answering this on the discussion groups, but here we have a nice example that I can point to next time.

The underlying problem I’ve noticed over the past few years is that developers are still thinking in terms of querying when they need more data. When moving to the Domain Model pattern, you have to “simply” represent the domain concepts in code – in other words, see things you aren’t used to seeing. I’ll highlight that part in the question below so that you can see where I’m going to go with this in my answer:

I have an instance where I believe I need access to a service or repository from my entity to evaluate a business rule but I’m using NHibernate for persistence so I don’t have a real good way to inject services into my entity. Can I get some viewpoints on just passing the services to my entity vs. using a facade?

Let me explain my problem to provide more context to the problem.

The core domain revolves around renting video games. I am working on a new feature to allow customers to trade in old video games. Customers can trade in multiple games at a time so we have a TradeInCart entity that works similar to most shopping carts that everybody is familiar with. However there are several rules that limit the items that can be placed into the TradeInCart. The core rules are:

1. Only 3 games of the same title can be added to the cart.
2. The total number of items in the cart cannot exceed 10.
3. No games can be added to the cart that the customer had previously reported lost with regards to their rental membership.
    a. If an attempt is made to add a previously reported lost game, then we need to log a BadQueueStatusAddAttempt to the persistence store.

So the first 2 rules are easily handled internally by the cart through an Add operation. Sample cart interface is below.

   1:  class TradeInCart{
   2:      Account Account{get;}
   3:      LineItem Add(Game game);
   4:      ValidationResult CanAdd(Game game);
   5:      IList<LineItems> LineItems{get;}
   6:  }

However the #3 rule is much more complicated and can’t be handled internally by the cart, so I have to depend on external services. Splitting up the validation logic for a cart add operation doesn’t seem very appealing to me at all. So I have the option of passing in a repository to get the previously reported lost games and a service to log bad attempts. This makes my cart interface ugly real quick.

   1:  class TradeInCart{
   2:      Account Account{get;}
   3:      LineItem Add(
   4:          Game game, 
   5:          IRepository<QueueHistory> repository, 
   6:          LoggingService service);
   7:   
   8:      ValidationResult CanAdd(
   9:          Game game, 
  10:          IRepository<QueueHistory> repository, 
  11:          LoggingService service);
  12:   
  13:      IList<LineItems> LineItems{get;}
  14:  }

The alternative option is to have a TradeInCartFacade that handles the validations and adding the items to the cart. The façade can have the repository and services injected though DI which is nice, but the big negative is that the cart ends up totally anemic.

Any thought on this would be greatly appreciated.

Thanks,
Jesse

As I highlighted above, the thing that will help you with your business rules is to introduce the Customer object (that you probably already have) with the property GamesReportedLost (an IList<Game>). Your TradeInCart would have a reference to the Customer object and could then check the rule in the Add method.

Before I go into the code, it looks like your Account object might be used the same way, but your description of the domain doesn’t mention accounts, so I’m going to assume that that’s unrelated for now:

   1:  public class Customer{
   2:   
   3:      /* other properties and methods */
   4:   
   5:      private IList<Game> gamesReportedLost;
   6:      public virtual IList<Game> GamesReportedLost 
   7:      { 
   8:          get
   9:          {
  10:              return gamesReportedLost;
  11:          }
  12:          set
  13:          {
  14:              gamesReportedLost = value;
  15:          }
  16:      }
  17:  }

Keep in mind that the GamesReportedLost is a persistent property of Customer. Every time a customer reports a game lost, this list needs to be kept up to date. Here’s the TradeInCart now:

   1:  public class TradeInCart
   2:  {
   3:      /* other properties and methods */
   4:   
   5:      private Customer customer;
   6:      public virtual Customer Customer
   7:      { 
   8:          get { return customer; }
   9:          set { customer = value; }
  10:      }
  11:   
  12:      private IList<LineItem> lineItems;
  13:      public virtual IList<LineItem> LineItems
  14:      {
  15:          get { return lineItems; }
  16:          set { lineItems = value; }
  17:      }
  18:   
  19:      public void Add(Game game)
  20:      {
  21:          if (lineItems.Count >= CONSTANTS.MaxItemsPerCart)
  22:          {
  23:              FailureEvents.RaiseCartIsFullEvent();
  24:              return;
  25:          }
  26:   
  27:          if (NumberOfGameAlreadyInCart(game) >=
  28:              CONSTANTS.MaxNumberOfSameGamePerCart)
  29:          {
  30:              FailureEvents
  31:                .RaiseMaxNumberOfSameGamePerCartReachedEvent();
  32:              return;
  33:          }
  34:   
  35:          if (customer.GamesReportedLost.Contains(game))
  36:              FailureEvents.RaiseGameReportedLostEvent();
  37:          else
  38:              this.lineItems.Add(new LineItem(game));
  39:      }
  40:   
  41:      private int NumberOfGameAlreadyInCart(Game game)
  42:      {
  43:          int result = 0;
  44:   
  45:          foreach(LineItem li in this.lineItems)
  46:              if (li.Game == game)
  47:                  result++;
  48:   
  49:          return result;
  50:      }
  51:  }
  52:   
  53:  public static class FailureEvents
  54:  {
  55:      public static event EventHandler GameReportedLost;
  56:      public static void RaiseGameReportedLostEvent()
  57:      {
  58:           if (GameReportedLost != null)
  59:               GameReportedLost(null, null);
  60:      }
  61:   
  62:      public static event EventHandler CartIsFull;
  63:      public static void RaiseCartIsFullEvent()
  64:      {
  65:           if (CartIsFull != null)
  66:               CartIsFull(null, null);
  67:      }
  68:   
  69:      public static event EventHandler MaxNumberOfSameGamePerCartReached;
  70:      public static void RaiseMaxNumberOfSameGamePerCartReachedEvent()
  71:      {
  72:           if (MaxNumberOfSameGamePerCartReached != null)
  73:               MaxNumberOfSameGamePerCartReached(null, null);
  74:      }
  75:  }

image Your service layer class that calls the Add method of TradeInCart would first subscribe to the relevant events in FailureEvents. If one of those events is raised, it would do the necessary logging, external system calls, etc.

As you can see, the API of TradeInCart doesn’t need to make use of any external repositories, nor do you need to inject any other external dependencies in.

One thing I didn’t do in the above code to keep it “short” is to define the relevant custom EventArgs for bubbling up the information as to which game was reported lost or already have 3 of those in the cart. That is something that definitely should be done so that the service layer can pass this information back to the client.

Here’s a look at Service Layer code:

   1:  public class AddGameToCartMessageHandler :
   2:      BaseMessageHandler<AddGameToCartMessage>
   3:  {
   4:      public override void Handle(AddGameToCartMessage m)
   5:      {
   6:          using (ISession session = SessionFactory.OpenSession())
   7:          using (ITransaction tx = session.BeginTransaction())
   8:          {
   9:              TradeInCart cart = session.Get<TradeInCart>(m.CartId);
  10:              Game g = session.Get<Game>(m.GameId);
  11:   
  12:              Domain.FailureEvents.GameReportedLost +=
  13:                gameReportedLost;
  14:              Domain.FailureEvents.CartIsFull +=
  15:                cartIsFull;
  16:              Domain.FailureEvents.MaxNumberOfSameGamePerCartReached +=
  17:                maxNumberOfSameGamePerCartReached;
  18:   
  19:              cart.Add(g);
  20:   
  21:              Domain.FailureEvents.GameReportedLost -=
  22:                gameReportedLost;
  23:              Domain.FailureEvents.CartIsFull -=
  24:                cartIsFull;
  25:              Domain.FailureEvents.MaxNumberOfSameGamePerCartReached -=
  26:                maxNumberOfSameGamePerCartReached;
  27:   
  28:              tx.Commit();
  29:          }
  30:      }
  31:   
  32:      private EventHandler gameReportedLost = delegate { 
  33:            Bus.Return((int)ErrorCodes.GameReportedLost);
  34:          };
  35:   
  36:      private EventHandler cartIsFull = delegate { 
  37:            Bus.Return((int)ErrorCodes.CartIsFull);
  38:          };
  39:   
  40:      private EventHandler maxNumberOfSameGamePerCartReached = delegate { 
  41:            Bus.Return((int)ErrorCodes.MaxNumberOfSameGamePerCartReached);
  42:          };
  43:      }
  44:  }

It’s important to remember to clean up your event subscriptions so that your Service Layer objects get garbage collected. This is one of the primary causes of memory leaks when using static events in your Domain Model. I’m hoping to find ways to use lambdas to decrease this repetitive coding pattern. You might be thinking to yourself that non-static events on your Domain Model objects would be easier, since those objects would get collected, freeing up the service layer objects for collection as well. There’s just on small problem:

The problem is that if an event is raised by a child (or grandchild object), the service layer object may not even know that that grandchild was involved and, as such, would not have subscribed to that event. The only way the service layer could work was by knowing how the Domain Model worked internally – in essence, breaking encapsulation.

If you’re thinking that using exceptions would be better, you’d be right in thinking that that won’t break encapsulation, and that you wouldn’t need all that subscribe/unsubscribe code in the service layer. The only problem is that the Domain Model needs to know that the service layer had a default catch clause so that it wouldn’t blow up. Otherwise, the service layer (or WCF, or nServiceBus) may end up flagging that message as a poison message (Read more about poison messages). You’d also have to be extremely careful about in which environments you used your Domain Model – in other words, your reuse is shot.

Conclusion

I never said it would be easy 🙂

However, the solution is simple (not complex). The same patterns occur over and over. The design is consistent. By focusing on the dependencies we now have a domain model that is reusable across many environments (server, client, sql clr, silverlight). The domain model is also testable without resorting to any fancy mock objects.

One closing comment – while I do my best to write code that is consistent with production quality environments, this code is more about demonstrating design principles. As such, I focus more on the self-documenting aspects of the code and have elided many production concerns.

Do you have a better solution?

Something that I haven’t considered?

Do me a favour – leave me a comment. Tell me what you think.

  
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68 Comments

  1. Nuno Lopes Says:

    Hello,

    Started commenting the ideas presented regarding modeling the domain, but it started to be too long. So I stopped, put together the ideas contrasting and complementing the one presented here on an article in my Blog.

    Just started blogging my mind away last weekend so please fill free to point out some deadlocks of mine, I can only learn and share.

    Here it is:

    http://movablesharp.blogspot.com/


  2. udidahan Says:

    Nuno,

    > Consider a Web Application where this service is in assembly that is directely referenced.

    It doesn’t work like that. The web app would send a message to a different process which would run the above service layer.

    You can find out more about nServiceBus on the site http://www.NServiceBus.com. Take a look at the overview section.


  3. Nuno Lopes Says:

    I see, now I understand. Thank you very much for your answer Udi.

    I reviewed the post in my blog as the English was really bad. If you care to read it (or re-read it) Udi and pass on some comments would be really a learning experience.

    It mainly addresses the Domain Model for the example you used but in a different and better way (at least IMHO).

    What may interest you is that I may be wrong but my approach to the Domain Model and the way you propose Domain Errors to be reported back to the caller don’t mingle that well. At least I don’t see a recurring technique to apply them. Especially when Domain Objects call each other services to perform their activity.

    That is why I don’t like how errors are reported.

    Nuno
    PS: Has you may have guessed already, English is not my mother language, so I’ll try to be carefull so that my impressions can get across without much effort.


  4. udidahan Says:

    Nuno,

    Your English is perfectly understandable – no worries 🙂

    I did go through some posts on your blog – looks like good stuff. Welcome to the conversation.


  5. Domain Events - Salvation Says:

    […] It started by looking for how to create fully encapsulated domain models. […]


  6. Thomas Says:

    Check out this summray of Craig Larman’s view on this:
    http://blogbustingbeats.wordpress.com/2009/07/07/405/


  7. udidahan Says:

    Thomas,

    I read through the post and it describes Craig Larman’s view on *Problem Domain Object Models*, not the Domain Model software artifact I’m describing in this post – I’m afraid it’s a bit of an apples to oranges comparison.

    I do think that more developers should know about the kind of modeling you describe in your post, though.

    Thanks for the link.

    — Udi


  8. Paul Linton Says:

    I really liked your ‘Make Roles Explicit’ talk and found your web site as a result. The method you describe here to handle Domain events seems like it will fix a particular problem I have in my Domain where an action on a Customer should cause various Accounting action to take place.
    Can you clear up for me a couple of questions?
    In DomainEvents there is a comment next to the Container declaration “as before”, I can’t find the earlier reference.
    I assume IContainer is some DI container (StructureMap?) which raises the question of “Where does the DomainEvents class live”? If it goes in the Domain then the Domain depends on the DI container, if it goes in a Service layer then the Domain depends on that service layer. Or is IContainer some abstraction of DI defined in the Domain?
    Will I be in a state of sin if I call the Handles interface IHandle (seems to fit the IWashDishes thought process)?


  9. udidahan Says:

    Paul,

    Don’t worry about the “as before” as the code was taken from an article in which it was developed bit by bit.

    The DomainEvents class is infrastructure, below both the Serivce Layer and the Domain Model.

    On the name IHandle, might I suggest maybe IHandleDomainEvents instead.

    Thanks for your comments.


  10. Richard Says:

    Domain events?? Events are evil. The Specification Pattern works a lot better than this solution proposed, and exceptions are enough. No need to create this domain event thing.. why the need to reinvent the wheel??


  11. udidahan Says:

    Richard,

    I respect that that is your opinion.


  12. caesar.guok Says:

    Hi, Udi,
    I’v met some problemns, when I want to do some Domain Patten practices.
    Maybe someone before talked about this topic.
    Refer to your code, if some rules in the domain model were not passed, how can I stop the next tx.commit() operation? Because the values include in the model object aren’t what the business progress need.
    And then, if I create a series of model, but as you mentioned, the model objects shouldn’t be entity objects which depends on database. How can I do a convertion between model objects and entity objects?

    Thanks in advance.

    Yours Caesar


  13. udidahan Says:

    Caesar,

    Read up on some of my CQRS stuff in which I explain that commands that could fail should not be sent by clients in the first place.


  14. raminxtar Says:

    Very nice article & sample.
    If all that we want to do is to return error codes from domain/service layer, what do you think about this approach:

    class TradeInCart
    {

    OperationResult Add(Game g,out LineItem li){}
    }
    class DomainOperationResult
    {
    public bool IsSuccessful{get;set;}
    public string ErrorMessage{get;set;}
    }

    No need to exceptions or events subscription plus more explicit interface of the domain object


  15. raminxtar Says:

    please change DomainOperationResult -> OperationResult in my post
    OperationResult may be similar to your ValidationResult class.
    BTW is there a downloadable version of your sample code?


  16. Ali Shahzad Says:

    I’m also wondering about the pros and cons of returning a simple OperationResult object from Add method. It probably violates some Command Query Separation principle, but makes the code much simpler as long as the caller does not make further calls on the cart object based on the returned value

    Any ideas?


  17. plalx Says:

    I know this is old, but as far as I can tell, the fact that you are reaching out to another aggregate (customer) to enforce the following invariant means it could be violated if there’s concurrency involved, no?

    if (customer.GamesReportedLost.Contains(game))
    FailureEvents.RaiseGameReportedLostEvent();


  18. udidahan Says:

    Plalx,

    You’re absolutely right – this example doesn’t make use of higher-level service boundaries to isolate the relevant parts of the Game from Customer.


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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



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