Udi Dahan   Udi Dahan – The Software Simplist
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Visual Cobol, Enterprise Processes, and SOA

Wednesday, April 23rd, 2008.

There’s a fairly intense discussion going on these days amongst the SOA illuminati. In the hopes that people will see me standing beside them and conclude that I too know something, I’ve decided to chip in.

Jim brought the concept of cohesion to the regular SOA discussions around loose coupling in his post Anemic Service Model, which I think, all in all, is a very good idea.

Naïve Service Composition

image Jim first calls out a common anti-pattern that seems to have become quite rampant – I’d call it naïve service composition if only the things being composed could even be called services. And I think the tone being set is correct – a service needs to meet a stronger set of criteria than just being able to be composed. Multiple services sharing the same logical data store (in that the same actual rows/data elements are managed by multiple services) probably means there’s an encapsulation problem here. I agree with Jim sentiment here:

“On the one hand we’re inclined, and indeed encouraged by the SOA brigade, to think of this architecture as a good fit for purpose because it is very loosely coupled. Since every component or service is decoupled from every other component or service it should be possible to arrange and re-arrange them in a Lego-style in a myriad of useful ways. Building out “business services” from some more fundamental set of services is how the books tell us to do it. In fact we could even do that quite easily with point-and-[click] BPM tools, ruling out such overheads as developers and change management along the way. Right?”

MVC? There are, like, 6 of them!image

However, I disagree with some of the conclusions that Jim draws from that point. Jim states “build your services to implement business processes”, and that services are “just an instance of MVC”. I’m going to leave alone the MVC statement since there are like 6 documented kinds of MVC not including the Front Controller stuff that the web guys are now calling MVC. I’m going to focus on the business process advice. JJ also doesn’t seem to agree with this advice. As Savas has already taken issue with the tone of JJ’s response, I’ll keep my focus on the content.

Visual Cobol

First of all, in my previous conversations with Jim he had already denounced the procedural nature of composing higher-level business processes out of smaller services which implement small bits of common activities. Visual Cobol was how he described it. In JJ’s follow-up post, he called out the necessary aspect of autonomy that jives with Jim’s cohesion principle.

I’m a bit concerned about the way JJ tends to version what SOA means over time. It might make it impossible to have intelligent design discussions without tagging each sentence with “as SOA meant in 2006”. I acknowledge that the accepted meaning of SOA by various vendors has changed over the years. However, I’ve found that meanings rooted in decades of computer science tend to last and provide value that outlasts much of the industry-buzzword-bingo (SOA 2.0 anyone?).

Cohesion, Business Domains, and Business Processes

image My view of the original cohesion principles Steve discusses in his 2005 article Old Measures for New Services takes a business spin to Functional Cohesion:

A service should be responsible for one business domain.

If we jump off from this point, we’ll see that certain business processes which occur entirely in one business domain are fully encapsulated, whereas those macro-processes which cross many domains (like Order to Cash) cross multiple services – they do not become a service since that would break the “one business domain” rule. Given that services are loosely coupled, avoiding temporal coupling leads to services raising events. Thus, macro-processes are really just a series of events of various services where each service does its own internal business processes.

Enterprise Processes >> Business Processes

I think that maybe some of the difficulty in discussing concrete SOA guidance has to do with granularity. I’ve started calling those macro-processes something different from business processes, and that may just bring me full circle to Jim’s guidance.

An Enterprise Process is any process which involves multiple business domains.

Under that definition, a service may be responsible for multiple business processes in the same business domain. But still, one business process is usually not a service by itself.

Business Components & Autonomous Components to the Rescue

image Finally, by introducing the additional levels of decomposition of business components and autonomous components I’ve found that we can focus the discourse on one concern at a time. My presentation on the topic can be found here. The 30 second pitch is this:

Business domains are inherently partitionable – data and rules. A business component represents one partition. An example of this is the domain of Sales being partitioned by strategic and non-strategic customers. Although the data structure might be similar or the same, the actual rows/data elements are not shared. Rules around discounts are different.

Within a business component, different activities should not interfere with each other. An autonomous component represents one activity. In our example, reporting on orders from strategic customers should not interfere with accepting their orders. As such, those activities should have different messages coming in on different endpoints. Each endpoint could have different characteristics, like durability. Losing a request for a report when a server restarts isn’t a big deal, however not a good idea for orders.

For more information you could check out these episodes from my podcast:

Business and Autonomous Components in SOA

Using Autonomous Components for SLAs in SOA

Questions and comments are always welcome.

  
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6 Comments

  1. Jim Webber Says:

    Hey Udi,

    I recognise that helicopter picture 🙂

    Jim


  2. udidahan Says:

    It’s called “reuse” 🙂


  3. Weekly Links 1 « Davy Brion’s Blog Says:

    […] Using nServiceBus From Developer to Technical Manager The Technical Manager The Problem Preventer Visual Cobol, Enterprise Processes, and SOA Should you TDD when flying solo? Funding Open Source Projects Got var? Programming “in” […]


  4. Jean-Jacques Dubray Says:

    Udi:

    for the record, I am not versioning SOA even though I understand how this point came across. For me there is pretty much one what to do SOA (after all nobody ever came up with the concept OO 2.0). I was just trying to point out to a community of people that left Web Services technologies somewhere in 02, 03 or 04 (because Web Services technologies where iffy and pretty much a burden for what they were trying to achieve), that after 05 things have accelerated.

    It is clear to me that we have available an Inter-Action oriented Asychronous Peer-to-Peer application model to do SOA. I don’t want to call that SOA 2.0, at best we were at SOA 0.5 in 2004 :-). If only we could focus the discussion on a programming model and avoid talking about general things all the time…

    On another note, I like some of the ideas that you develop in this section: Business Components & Autonomous Components to the Rescue

    Yes, Partition at the record level, rather than at the entity level (but the question still remains)

    Yes, we clearly have “Service Containers”, “Services” and “Endpoints”. You could certainly introduce a certain form of cohesion for colocating services in the same Service Container (sharing similar QoS, native invocations between them…)

    Yes, we should be very careful in not associating related aspects such as reporting and resource lifecycle under cohesive principles

    JJ-


  5. udidahan Says:

    JJ,

    I’m glad that you also see value in bringing more concreteness to the conversation using Business Components & Autonomous Components. Although I haven’t directly gotten into “Service Containers”, I’d be interested in hearing your thoughts on how they connect with the above components.


  6. SOA, EDA, and CEP a winning combo Says:

    […] Related Content SOA and Enterprise Processes […]


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