Nowadays, when we integrate different systems together inside a company, Service Oriented Architecture (SOA) is the first choice.
But is it a really good choice? SOA is based on messaging to transfer request and response. Messaging gives us decoupling advantage, but also unreliability.
Let's suppose one case: System A sends message to System B for data update. What will happen if the message is lost for some reason (out of buffer, system failure, etc.)? Should we build shake-hand protocol between A and B to make sure the message is successfully delivered?
How about the old way -- to use a bridge table in a shared database? System A can add a new record into the bridge table for data update; System B can query the bridge table periodically (or to use database notificatione, like SQL Server 2005) to get the update. In this way, we can guarantee the update "message" is delivered from A to B.
If you think there is delay for this solution, SOA messaging also has delay. We can adjust query period for performance issues.
I am not saying SOA is bad. I just want to say when you integrate systems, old way may be a better choice than SOA.