Udi Dahan   Udi Dahan – The Software Simplist
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Non-functional Architectural Woes

Tuesday, January 12th, 2010.

Non-functional architecture
As I sit here in the lounge at Bogota airport waiting for my delayed flight, I remembered something interesting that came up in my 2-week training/consulting in Cali. It’s not a question that came up, or anything like that. It was that I suddenly noticed a pattern in many of my consulting and training clients over the past years. And as I thought about it, I realized that it was prevalent in our industry as a whole – in the literature, on the web, everywhere.

It’s how people think about functional and non-functional requirements.

The problem with categorization

There’s nothing wrong with categorizing requirements as either functional or non-functional.

The problem is that people project that categorization from the problem domain to the solution domain as well.

There is an impression that architecture and technology choices are, to a large extent, based on non-functional requirements, and only on non-functional requirements.

Here are some examples:

Extensibility: Workflow/BPM engine , DSL, Plug-in framework, etc
Scalability: Message/Service Bus, Database (NoSQL camp, I’m looking at you too), etc
High Availability: See scalability

Too many times have I noticed architects so focused on these issues that they all but ignore the functional requirements and the business objectives of the stakeholders.

Not to place an unfair portion of the blame there, the vendors have been perpetuating the above fallacies to sell more and/or new products. Given the enormous influence of the big vendors (conferences, training, etc) it isn’t any wonder that architects in the field use the vendors’ “best practices”.

The problem that arises from this kind of thinking is a shoe-horning of functional requirements into the architecture decided upon entirely in the context of non-functional requirements.

Functional Earthquakes

Stable architecture cannot be created based entirely on non-functional requirements. There are functional requirements that can shake the foundation of a technically-oriented architecture.

Let’s take the canonical layered architecture with its normalized database. Now we get a new requirement in the form of:

“As a supplier, when I log-in, I want to see on my home page my most recent purchase orders, grouped by highest value retailer (total historical purchase order value), sorted according to requested time of delivery.”

In order for a developer to implement this according to the architectural guidelines of normalization and layering here’s what they do: join retailers who have an agreement with the supplier (join between supplier, retailer, and agreement tables), join the purchase orders and their lines, (ignoring tax for now), sum the line value and group by retailer, and use as an input to the purchase order table joining again, filter in last 24 hours, sort by time of delivery.

So, in our normalized database, we have many millions of purchase orders, hundreds of millions of lines, that we’re joining against each other as well as several other tables.

After this new feature has been implemented, any time a supplier sees their home page, the system stops accepting purchase orders until the home page has been rendered several minutes later.

Can we really say that our architecture is stable if a single functional requirement can undo all of it’s non-functional properties?

Obviously not – but the question the architect (and his boss) are asking is, how did this happen? And if it happened once, can it happen again?

Lessons Learned – sorta

So a reporting database is introduced so that all complex queries like those performed above won’t prevent the system from accepting new purchase orders. A nightly batch moves data from the normalized DB to the reporting DB. Sounds good – non-functionally.

And then a new requirement comes in for handling rush-orders.

So we do an hourly batch. But now these batches start to cause hiccups to our transactional system, which gets backed up, and when released, allocates many more threads to deal with the pending load, and the increased concurrency in the databases sharply increases the number of deadlocks, further backing up the system, until the system becomes effectively unavailable.

Can this be happening again? A functional requirement undoing all of our technically elegant non-functional architectural decisions?

Now what?

The technology is blamed. We should have never counted on SQL Server to handle our kind of *enterprise* requirements. Let’s move to Oracle – it’s *unbreakable*. (Several months and functionalities later) We should have never counted on a database to handle our kind of enterprise requirements. Let’s introduce an *Enterprise Service Bus*. (Several months and functionalities later) We should have never counted on our internal IT to host this. Let’s move to *The Cloud*. (Several months and functionalities later, looking at the bill from our cloud provider) We should have never used .NET for our application because it requires the more expensive Windows cloud. Let’s rewrite on Linux to reduce our cloud costs.

By this time, all the people who originally worked on the project aren’t there anymore. And the cycle continues with limited memory of where we started and how we got here.

Soon, soon, we’ll find that non-functional silver bullet that will make all of our problems go away.

These are not the droids you are looking for

They really aren’t.

If we want our architecture to be stable, we need to base it on stable abstractions. The only thing is that there aren’t any inherently stable abstractions in the solution domain (as we’ve had the chance to witness). That really only leaves one other place to look for them – in the problem domain, also known as the functional requirements.

But functional requirements change all the time! Wasn’t that what got us into this mess to begin with?

Indeed, but in between the functional requirements and behind them is something that is quite stable: the stakeholders business objectives.

The supply chain will continue to strive to optimize itself. To shorten the time for an order to be fulfilled. To decrease the amount of inventory that a retailer holds. To choose the best set of suppliers for our product catalog. To recognize which retailers give me the most business and serve them better. To identify high potential retailers – big retailers (like Walmart) who aren’t buying as much from me as other retailers.

This is how the business has been done for decades and will continue to be done for decades more.

If we could find a way to capture those stable elements and represent them as core elements in our architectural structure, and then balance the non-functional requirements within those functional contexts, maybe, just maybe, our architecture will stand the test of time.

More to come…

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  1. Bjarte Says:

    The process of jumping between different technical solutions to fulfil the non-functional requirements while the functional requirements are changing is probably one of the most common ways to spend too much money on a software project.

    I’m looking forward to the post where you will reveal how we connect the dots between the business goals and our architecture 😉

    Thx for another great post.

  2. DaRage Says:

    Problem domain, solution domain reminds of Object Thinking book of David West. Lately I’ve been noticing more post like this one calling for the return to the basics of object-oriented ideas.

  3. David Nelson Says:

    “…in between the functional requirements and behind them is something that is quite stable: the stakeholders business objectives.”

    I envy you the industries and environments you work in where the business objectives have actually remained stable over the course of even a single software project. That has certainly not been my experience.

  4. Kamran Saleemi Says:

    Definitely one of your most incisive posts …

  5. udidahan Says:


    Glad you liked it.

  6. udidahan Says:


    Indeed – we have to walk before we run 🙂

  7. udidahan Says:


    I think we need to differentiate between the “business objectives” for the software project, and the actual business objectives of the stakeholders – usually expressed in language not related to software at all.

    If you could describe your environment, maybe I could help identify a stable stakeholder objective?

  8. Steve Degosserie Says:

    Very interesting article as always. Do you think DDD (focus on the problem domain first) & Strategic Design (identify & focus on what brings the most business value) provide a partial answer to his problem ?

  9. Gary A Says:

    It all goes back to what you consider a requirement is:

    The requirement ‘As a supplier, when I log-in, I want to see on my home page my most recent purchase orders,..’ is a software requirement. It’s something the sofware must do.

    The business requirement is something like ‘To shorten the time for an order to be fulfilled.’ Or business objective.

    The input to architecture decisions are the business requirements – not the software requirements, which come later once you’ve determined what the solution is.

    Too often we just don’t do business requirements. Or we take software requirements from users and call them business requirements because they cme from the business. That’s where the problem is.

  10. udidahan Says:


    It sounds like we’re very much in agreement.

    I’d say that ‘shortening the time for an order to be fulfilled’ is an ongoing business objective that is the spirit behind many specific software requirements that we may get.

    The question that I intend to address in my next post is how we take this business objectives (requirements) and capture them in our software architecture.

    Thanks for your comments.

  11. Jean-Jacques Dubray Says:


    >> the only thing is that there aren’t any inherently stable
    >> abstractions in the solution domain (as we’ve had the chance to
    >> witness).

    That’s because you rely on vendors for these abstractions. I think it is time to develop a stable (Architecture independent – not just technology independent) set of Solution Abstractions.

    I have described how to go about that in a generic way here: http://www.infoq.com/articles/mop

    The problem with traditional approaches, UML, EMF or now SSM is that somehow they are anchored in OO, i.e the concept of “Class” is at the center of the M3 layer. I was hoping SSM would change that, but they did not. The irony and tragedy is that none of the “solution abstraction” can be efficiently described with an OO foundation.

    So if you go int the problem space and try to create abstractions there, you’ll run into the exact same problem because all models are built on sand, i.e. OO.

  12. Jean-Jacques Dubray Says:


    I have developed a more elaborate response here: http://www.ebpml.org/blog/212.htm


  13. Bogdan Nedelcu Says:

    Very deep you thoughts are.

    Shall we ever be able to represent business knowledge in a structured/programmable way or shall we always concentrate on the ability to change our software according to the always changing functional requirements.

    We, as humans, are able to represent in our minds the concepts, the domain, we are able to expose parts of it to the outside world, but even the most skilled of us are in difficulty to well formalize these concepts.

    Indeed business is done in the same way for decades, business as a whole. Some business objectives are the same and some are very particular. It is why extracting the architectural artifacts from the functional requirements is difficult.

    Is it true that one business objective resembles to its business area, but is somehow particular ? Is it true the more you add businesses objectives together the more they look like the whole ? Is that why we can easily formalize business theory and hardly manage to formalize a running business ?

    These were my questions. One could answer that the solution is related to fractal theory.

    Looking forward to “more to come…”

  14. Jean-Jacques Dubray Says:

    >> shall we always concentrate on the ability to change our software
    >> according to the always changing functional requirements.
    This sounds easier that the former, and possibly good enough

    >> but even the most skilled of us are in difficulty to well formalize
    >> these concepts.
    This comes from the fact that the current modelling paradigm is “OO” based and surprisingly does not integrate behavior. All models are reduced to elements with attributes and references to each other. “Behavior” is strangely left to be under the hood in the metadata interpreter or compiler. So you are left to describe “behavior-less” models (on the problem or solution side). This is wrong.

  15. Jean-Jacques Dubray Says:

    I don’t know if you have seen that post too: http://friends.praxeme.org/2009/08/get-out-of-the-immaturity-model-part-2/

    I think that’s fairly relevant to what you are attempting to achieve.


  16. Bogdan Nedelcu Says:

    @Jean-Jaque when speaking about difficulty to formalize I am not necessarly refering to OO concepts, rather to put in any kind of theoretical model a certain business case. I’m not sure a programming language is a solution to this problem, nor the current business modelling tools, nor that it is even possible.
    Let’s see what Udi has to say about that.

    I detailed my ideas here http://www.dependnet.ro/blog/post/2010/01/17/Business-Objectives-as-key-architectural-pillars-doubled-by-fractal-inspiration.aspx

  17. Steve Says:

    At what point does accountability of the crazy req start? They can’t live in a vacuum of not understanding the impact their req have on the system

    I’m playing a bit of devils advocate here…

  18. udidahan Says:


    > Is it true that one business objective resembles to its business area, but is somehow particular ?

    Business objectives can usually be sourced to a single stakeholder – someone who is measured a certain way by the organization around them. Our goal is to find them.

    > Is it true the more you add businesses objectives together the more they look like the whole ?

    Not exactly sure what you mean by this, but I’m feeling that the answer is no. We need to find which objectives go to different stakeholders, and then decouple their implementations in software.

    > Is that why we can easily formalize business theory and hardly manage to formalize a running business ?

    I don’t think that we can easily formalize business theory, but agree that there is difficulty in modeling (let alone formalizing) a running business. The larger the business, the more likely it’s undergoing some reorganization, merger, acquisition, entrance into a new market, exit from some other market, etc. The goal is to identify those elements and segregate their implementations from those parts which represent more stable parts of the business.

    Hope that answers your questions.

  19. udidahan Says:


    After reading your post and the comments above, I think that this quote can serve as a kind of summary of your position (please correct me if I’ve over-simplified):

    “This particular rash of BPM products built their business on the fallacy that you could somehow build solutions directly from ‘problem-side abstractions’.”

    Note that in my post, I didn’t say to build the solution DIRECTLY from the “problem-side abstractions”. I said that we need to capture certain *stable* elements of the problem domain and have them represented explicitly in the solution domain. At that point, we can continue with good solution domain practices and avoid many of the situations described in my post.

  20. udidahan Says:


    “At what point does accountability of the crazy req start?”

    I do believe your horns are showing, Mr. Devil’s advocate 🙂

    Are those requirements really that crazy? If we had developed the system differently and it were easy for us to implement those requirements, would they not be crazy then? Is it the business’ fault that they didn’t give us these requirements up-front?

    OMG – are we going back to big requirements up-front to avoid these problems?

    We’re going to find the right balance between all these things – hang in there 🙂

  21. Kyle Szklenski Says:

    This was another great post, as usual. I’m looking forward to the next one on this topic as well. This is one of the biggest problems that I run into with clients today.

    When working with other programmers, it’s often the case that they tend to think that it’s more important what specific tools you’re using, rather than how you use them and what you use them for. For example, someone once told me that it’s important to be *really* good with ReSharper, because it will help you build your designs effectively. I’m a RS ninja, and I categorically disagreed with him – that is, I told him why it neither helps nor hurts a design, and should *not* help or hurt design. It would be good to have tools to help design, but it’s still fundamentally a human problem, I think. Naturally, that same person said that it’s only if you’re using TypeMock that you can really design a real system.

    Finally, I’ve found lately an MVVM craze that forgets the first piece of the pattern: the model. The models are trash, but they have these “elegant” view-models that make it easy to tie themselves in knots.

    Sorry, this turned into a bit o’ the rant. Good post, Udi. 🙂

  22. udidahan Says:


    Glad you liked it.

  23. mohan Says:

    what is the real time examples of functional and non functional requirements?

  24. udidahan Says:


    What do you mean by “real time” ?

  25. A CQRS Journey – with and without Microsoft Says:

    […] The effects of this lack of alignment may be felt only much later in the project, when we get a requirement that just doesn’t fit the architecture we’ve set up. I’ve blogged about the symptoms of this problem about 2 years ago in my post Non-functional architectural woes. […]

  26. Tom Gilb Says:

    Of course quality and performance requirements are major architecture drives, along with constraints (costs, legal, culture).

    If someone wants some free deep technology on this see my downloads at gilb.com

    Real Architecture. Slides for Javazone Sept. 8 2011
    http://vimeo.com/28763240 Video

    Video of Javazone Presentation

    If someone is deeply serious, email me and I’ll send you a free digital copy of my CE book which has all the language tools to deal with this.

  27. udidahan Says:


    I like your “Real Architecture” slides.

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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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