Martin:
IMO - SOA is potentially a specialization of a combination of many
things - interface based design (IBD), component architecture (CA), OO
methodology etc. It seems to possess some elements of these things.
The questions we need to answer are "How can we describe it as
architecture?" and "is it sufficiently different from other existing
architecture reference models to warrant existence as a concept?". If
it is architecture, then surely it must be describable as architecture.
My $0.02 worth:
Services are core, but not sufficient by themselves to represent a new
class of architectural paradigm. What else is needed for services to be
bound to in a true P2P environment? Some way for the services to be
discoverable (Advertising) and some mechanism to describe all aspects of
a service (Service Description) that would be required in order to
invoke the service. Additionally, knowing what invoking the service
meant (contract) and knowing the data that is passed in and optionally
returns from a service invocation (Data Model) are all core. There are
a lot of questions we need to answer around this including whether or
not semantics of the data model is an important aspect.
What is outside the core definition? Messaging, Security, BPM, QoS and
any other items that is probably present in most SOA's but not all.
This may seem very controversial at first but follow the logic.
If I build something and that is "Service Oriented" architecturally,
does it have to have a "message"? No - the service itself has a
mechanism that allows a service consumer to bind to it to invoke the
service but it doesn't actually have to be invoked for it to be "service
oriented architecture". Does a car have to be driven on a road before
it is a car? The answer is likewise "no". An application only has to
be architected to utilize the concepts surrounding a service in order to
be utilized by service consumers when it is implemented. The reference
model therefore would not have a core messaging component. Any
architecture developed using the reference model will likely have
messaging as a component and over half will likely employ some form of
security.
Summary:
Following this core model, SOA is definable as architecture (as a
reference model) and is sufficiently distinct to warrant existence. It
has a unique combination of components that work together to facilitate
services being present, discoverable and invokable.
Duane Nickull
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Senior Standards Strategist - Adobe Systems, Inc. - http://www.adobe.com
Vice Chair - UN/CEFACT Bureau Plenary - http://www.unece.org/cefact/
Adobe Enterprise Developer Resources - http://www.adobe.com/enterprise/developer/main.html
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