Saturday, July 09, 2005


Sean McGrath (Propylon) thinks purpose-agnosticism to be one of the really useful bits of SOA. He refers to a posting he made to the Yahoo SOA group in June 2003, where he wrote:
The real trick with EAI I think, is to get purpose-agnostic data representations of business level concepts like person, invoice, bill of lading etc., flowing around processing nodes.

The purpose-agnostic bit is the most important bit. OO is predicated on a crystal ball - developers will have sufficient perfect foresight to expose everything you might need via an API.

History has shown that none of us have such crystal balls.

Now if I just send you the data I hold, and you just send me the data you hold - using as thin an API as we can muster - we don't have to doubleguess each other.
Propylon has been implementing this idea in some technologies for the Irish Government.
However, Sean believes that purpose agnosticism can only be pushed so far. He cites the service example “test for eligibility for free telephone allowance”, which is evidently purpose-specific. Thus there are some areas where very prescriptive messages (which Sean calls "perlocutionary") are more appropriate.

Let's push this example back a little. Why does B need to know if a particular customer is entitled to a free telephone allowance? Only because it alters the way B acts in relation to this customer. We should be able to derive what B needs to know from (a model of) the required variety of B's behaviour. Let's suppose B delivers a telephone to the customer and also produces an invoice. And let's suppose the free telephone allowance affects the invoice but not the delivery. Then we can decompose B into B1 and B2, where only B2 needs to know about the free telephone allowance, allowing us to increase the decoupling between B1 and A. Furthermore, the invoice production may draw upon a range of possible allowances and surcharges, of which the free telephone allowance is just one instance.

On a cursory view, it appears that the technologies Sean has been building for the Irish Government support a programme of deconfliction - using some aspects of SOA (or whatever you want to call it) to separate sociotechnical systems into loosely coupled subsystems. If this is done right, it should deliver both IT benefits (productivity, reuse) and business benefits. This is all good stuff.

Joined-Up Services - Trust and Semantics

But the deconfliction agenda leads to a new set of questions about joined-up services - what emerges when the services interact, sometimes in complex ways? How do you impose constraints on the possible interactions? For example, there may be system-level requirements relating to privacy and trust.

One aspect of trust is that you only give data to people who aren't going to abuse it. Look at the current fuss in the US about data leakage and identity theft involving such agencies as ChoicePoint. The problem with Helland's notion of trust is that it deals with people who come into your systems to steal data, but doesn't deal with people who steal data elsewhere. So you have to start thinking about protecting data (e.g. by encryption) rather than protecting systems. (This is an aspect of what the Jericho Forum calls deperimeterization.) Even without traditional system integration, an SOA solution such as PSB will presumably still need complex trust relationships (to determine who gets the key to which data), but this won't look like the Helland picture.

A further difficulty comes with the semantics of the interactions. If we take away the assumption that everyone in the network uses the same reference model (universal ontology), then we have to allow for translation/conversion between local reference models. As Sean points out elsewhere, this is far from a trivial matter.

Technology Adoption

My expectation is that the deployment of technologies such as the Public Service Broker will experience organizational resistance to the extent that certain kinds of problem emerge out of the business requirements. In my role as a technology change consultant, I am particularly concerned with the question of technology adoption of SOA and related technologies, and how this is aligned with the business strategy of the target organization. I invite readers of this blog to tell me (in confidence) about the adoption of SOA in their organizations, or their customers' organizations, and the specific barriers to adoption it has encountered.

See also

Collaboration and Context (January 2006) Context and Purpose (February 2006)
Context and Presence (Category)

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