The Client-to-Service Ratio

It is natural for people to think about their SOA in terms of the number of services that they have created. And as one person joked the other day, every company seem to report having between 200 and 500 services. The criteria for being a service tends to vary significantly - anything from XML over JMS to EJB's to WS-I compliant Web services.

Service Architects love to brag about the number of services - and I let them. Actually, I encourage them to brag. However, I'm quick to challenge these same people with a very simple question:

"200 SERVICES! That's great - but how many clients???"

This simple question usually makes the most pompous architect fall to their knees in shame.

You see, one of the reasons that guys like me go around shouting "SOA, SOA, SOA!" is because we believe that a sharable infrastructure can be used across "applications" to enable a new level of productivity. Yes, we believe in the unicorn called "reuse". The "how many client" question hits at the heart of the share/leverage/reuse debate. I know it - they know it.

Back to my story - I ask the question, "How many clients" - and I stare at their face like a CIA agent looking for twitches. Within seconds, I witness the five phases of panic :-)

Phase 1: "Oh crap. I should know this."
Phase 2: "I better make up a number - I told him 200 services - hence I'll tell him 200 clients!"
Phase 3: "Nope - that won't work - he'd realize that my client-to-service ratio would be 1:1 indicating that I wasn't getting any leverage."
Phase 4: "2:1 seems high at this stage; 1.5:1 seems believable... yea, (1.5 * 200)=300... but I can't tell him 300..."
Phase 5: The Service architect looks me squarely in the eye, head shifted slightly to the left and says "Currently, we have 322 clients."

And I say - "Excellent" followed by a slight grin and a playful stare indicating that I was 100% aware of what had just occurred. I usually then move to relieve the 5 seconds of torture and lies that I just put them through by saying something like, "Well - it is still early; SOA is still evolving and you won't see that number climb until more of the organization adopts it." And my friend gladly take the bait - "Absolutely! Right now, we're just building out the core services - we're confident that the ratio will increase over time."

And I move on to question number 2...