What is SOA, how does it resonate with mash-ups ?

SOA, service oriented architecture, is a collection of services that communicate with each other. The services are self-contained and do not depend on the context or state of the other service. They work within a distributed systems architecture.

In mashups, applications are unleashed and integrated in new and interesting ways with other types of applications. That's also the guiding philosophy in SOA, in which applications are broken down into granularized service components that can be mixed and matched with other services as business needs demand. And, theoretically, could be assembled on the fly by the business folks, versus sending work orders to the IT department. And, theoretically, such services can come from outside the walls of the enterprise.

It's important to realize that what SOA brings is the loose coupling between the providers and consumers of Services. Loose coupling means that businesses can change how they consume Services without having to make changes to the implementation of those Services, and vice-versa. Most of today's mashups care little about loose coupling. After all, if Google changes the implementation or location of their Service interface, for example, then developers of the various mashups that leverage one of Google's Services would have to update their mashups.