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Client-Server -> SOA.... Is it really a transition or a big development ?

Hi,

In all sources related to SOA/ESA by SAP, it is said that, transitioning from Client-Server Arch(CSA) to SOA is the same as transitioning from Mainframe systems to Client-Server Arch.

If we think about Mainframe and CSA, it is obvious that there had been big differences in that transition. Such as, the INTELLIGENT CLIENT concept had appeared to replace the DUMMY CLIENTS, so this had changed the way of IT Business. There would be a main application providing several functionalities(server) and other applications which want to use those functionalities (clients) would connect to the server using some functionalities on its own (that means a client appliction should also have some functionalities in order to at least connect to the server, so that made them different from the DUMMY clients of the mainframe era)

Now, when I look at the differences between SOA and CSA, I cannot see that incompareble differences.Why ? Let me explain :

- One of the most important differences between SOA and CSA is, SOA is vendor and platform independent, so that any application can call any applications functionality as long as they are using Web Services. That is true. But the question arises here : It is still the case that someone is calling some others' functionalities (services), so there is still a client/server mentality, isn't there and We will still be using several client/server programming languages in order to realize the main functionality of the web services but this will be transparent to the user and the integration. The main difference is, SOA is vendor and platform independent. But I don't think this can be commented as a missing feature of CSA. Because the aim of CSA was to make the clients more intelligent and not to make them vendor/platform independent. And also architectures like CORBA and DCOM have also tried to achieve that independency (even though they have restrictions compared to Web Services, one of the main reasons for this is using Web as a transport/communication protocol) but they are still treated as some extensions on top of CSA because they are using CSA beneath. But if we compare Mainframes and CSA, even though I haven't seen manframe ages, I think it is clear that CSA does not use any architectural functionality of Mainframes. They are completely different.. But is SOA and CSA completely different ?

I agree with all reasons why today business needs sth more agile, more flexible and it is becoming clearer day by day that SOA and Web Services provides this environment, BUT, I still cannot make it clear, WHY it is accepted as a transition from CSA and why it is not treated as a big development over CSA while using the main features of it.

Any comments will be appreciated.

Regards

Ahmet Engin Tekin

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    author's profile photo Former Member
    Former Member
    Posted on Oct 12, 2005 at 10:18 PM

    Ahmet,

    I would like to add also my 2 centimes (of euros) to the debate.

    I think the starting point of SOA is the recognition that no single application can be built today in a monolithic architecture, the days of well layered architected systems integrated with other well layered applications are over.

    Today, an application cannot be built without leveraging some data and business logic somewhere. Take the simple example of calculating tax rates on a purchase order in global economies. Why should every company in the world own a component that calculate tax rates. This component would almost need to be updated everyday in a global context because rules and regulations change almost daily at the scale of the world.

    SOA and its associated technologies such as web services enable an application architecture (composite application model) that can leverage services such as Tax Calculation wherever they are, regardless of the technologies in which they were built.

    This requirement is actually profound and is creating the need for new paradigms the most important of which is bring the "message" as the same level of importance as "code" or "data. This is why you see technologies like BPEL taking more importance every day.

    Regarding the C/S debate, nothing says that Web Services have to be invoked in a C/S mode. It is actually quite remarkable that Web Services offer a unified model for C/S or peer-to-peer invocations (please see my web cast below).

    I have given a presentation at the last TechEd in Vienna that you may want to watch where I developed a pattern to reason about the SOA application model. I call this pattern REASC: Resource representation, Event, Activity, Service and Coordinator. I also provide a new view of the Web Service architecture stack based on this pattern.

    The web cast can be found here:

    http://www70.sap.com/community/pub/events/2005_09_teched_us/presentations_02.epx

    It is called "the standards of SOA"

    Cheers,

    Jean-Jacques Dubray

    Standards Architect

    SAP Labs

    Palo Alto, CA

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    • Former Member Former Member

      I would like to add a point concerning transition in the hardware -side.

      It is obvious to us that there doesn't need to be a transition in the hardware- or even in the application infrastructure. Instead, we can move to SOA while using current applications on current HW platforms. All we need to do is describe application functionalities as services and exploit them as web-services through a bus.

      On the other hand, we are talking about a possibility to change our existing application and hardware infrastructure in the long run. We can forget division into ERP, SCM, PDM or whatever and move into grid-computing for improved scalability and reliability. In a way, the transition is so smooth it may not seem like a transition at first.

  • author's profile photo Former Member
    Former Member
    Posted on Sep 28, 2005 at 02:55 PM

    Hi Ahmet

    How would you define an application from the VB-Oracle, Powerbuilder , Pro C-Oracle days. A thick client that held the business logic distributed onto individual end user PCs that interacted with a server which hosted the DB for data. I assume CSA refers to this type architecture. In which case there is a fundamental difference between SOA and CSA . But essentially I think we have moved outof "this kind" of "thick C"SA ages ago with the introduction of app server and web based delivery and limited footprint client namely the browser.

    And thus introducing the "thin C"SA , eventhough multi tiered with business logic in a tier of its own , its still a silo, monolithic , not always integration ready.I think in this context SOA is big shift atleast in the server/integration layer providing granular integration/orchestration ready services and repositories for service registration and discovery.

    Just my thoughts....

    Regards

    Pran

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    • Former Member Former Member

      Sivaraj,

      Yes I've already pointed that considering hardware has become a block for me. Anyways, what you say is not wrong, regarding SOA's transition is from rigid business apps to flexible business prosesses. BUT, as you are probably also aware , in most of the presentations/documents (including SAP), SOA and Web Services are presented as the next step from CSA. If we assume this is not the case, then this post should terminate itself 😊

      Regards

      Ahmet

  • author's profile photo Former Member
    Former Member
    Posted on Oct 10, 2005 at 11:08 PM

    Ahmet,

    This is such an interesting topic that I could not resist staying away from it.

    My two cents and I would like to look at it from a completely different angle. I would rather compare SOA to EAI instead of CSA. Technically I can plug in M/F applications & Client-Server applications to form an SOA in an IT landscape. for e.g. In SAP’s own language, a M/F system or a Non-SAP CSA can talk to XI (using adapters) which inturn can publish/subscribe services. From this perspective, it would be an evolution from Batch mode interfaces (In Mainframes) to “Point-to-Point” interfaces to “EAI” using hub-n-spoke model and then finally to SOA using enterprise bus. After all, we are using web-services to communicate between applications or “blocks of business functionality” if you can call it from an SOA perspective.

    Also I agree with ShivrajÂ’s opinion above that so far all architecture changes have been within the IT domainÂ…This is probably the first architecture change that is extending itself to the business domain.

    Regards

    Vaidy

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