What you don’t want to know about SOA

SOA (service oriented architecture) is a big deal, I like it.
But it isn’t the be all and end all of computing. Here are ten
things you need to know about SOA.

1. You can’t sell SOA. SOA allows your company to be more
   flexible. SOA enables the agile enterprise. Oh, yes. But you can’t
   build a business case or cost justification out of flexibility or
   agility, you can only build that based on resolving a business
   issue or issues. In appropriate circumstances SOA may enable a
   business solution to a business problem: that’s all.
2. Even if you could sell SOA you couldn’t because you can’t
   describe to a business person what it is. The truth is that there
   is no good definition of what SOA is. Even as a concept it is
   fragile and different vendors and analysts will give you different
   (and nebulous) definitions. If even the IT industry cannot agree on
   a definition, how can you expect the business to understand it? The
   best that can be said is that it represents a set of enabling
   technologies.
3. Business Process Management (BPM) is not SOA. You can do either
   without the other though doing SOA without BPM might be
   tricky.
4. BPM engines represent a potential bottleneck for SOA. If
   everything is built around BPM and your services have to keep
   referring back to the BPM engine for instructions then that engine
   can become a bottleneck. You may therefore need to have multiple
   such engines with an “engine of engines” for
   orchestration. A better idea might be to have intelligent services,
   where appropriate, which understand their own routing and can
   maintain state information: thereby reducing the calls necessary to
   the engine.
5. BPM isn’t enough anyway. It’s fine for fairly simple processes
   but can become impractical when environments are very complex and,
   especially, where the business is exception-driven. This is the
   role of (complex) event processing (CEP).
6. Most vendors in the SOA space acknowledge the potential role of
   event processing but don’t understand it. For example, I have seen
   SOA presentations where CEP is confused with operational BI-style
   event processing. Certainly there is a place for this in SOA
   (throughput monitoring for example rather than the instance
   monitoring of BAM [business activity monitoring]—though the
   two should really be combined). Oracle, which does understand event
   processing, has CEP at level 5 in its maturity model for SOA: which
   is fine, except that CEP can be implemented totally independently
   of SOA.
7. You don’t need to use SOAP (simple object access protocol).
   Funnily enough, this isn’t as simple as it is supposed to
   be—there are alternatives that are simpler.
8. One of the biggest potential paybacks for SOA is in the ability
   to reuse services. But how do you make this happen? We couldn’t do
   it for objects and we couldn’t do it for components so why do we
   think we can do it for services? We can set up SOA governance and
   implement IT policies and rules but does that mean that developers
   will abide by them? When the pressure is on? When this job has to
   be finished by tomorrow?
9. And talking about governance how is this going to
   work—what is the relationship between SOA and data
   governance, for example? If part of the purpose of governance is to
   establish the ownership of processes and data then that is a
   problem, because ownership implies responsibility and people will
   shy away from the latter if given half a chance. The theoretical
   models put about for governance are all very well but if they can’t
   be applied in the real world (at least some of the time) then we
   need more pragmatic sets of “the best we can reasonably
   get” practices rather than aiming for the ideal all of the
   time.
10. Data is largely ignored (IBM is an honourable exception here)
    by most of those talking about SOA but if SOA is about undoing the
    Gordian knot of spaghetti that most company application
    architectures look like then shouldn’t the same be the case for the
    similarly complex data environment?

There a probably a lot more things that people need to know
about SOA but I have run out of space. Perhaps readers would like
to add some more points?