SOA is about decomposing your existing architecture down to fundamental components: services, data, and processes, then redefining the architecture so that you're addressing most of the data and system behavior using sets of well-defined services. Thus, you can configure solutions and -- more important -- reconfigure solutions as needed to support the business. The reconfiguration aspect of SOA provides agility -- simply put.
Cloud computing, at its essence, is leveraged by SOA as services that happen to exist outside of the firewall, typically. These services become part of the service portfolio and are mixed and matched, typically with on-premise services, to create the required business solutions. These services can be storage, database, information, or application services, all delivered out of the cloud using well-defined APIs or services. Again, this is very much simply put.
They are clearly linked, and any investment made in SOA carries over nicely to cloud computing.
This article, "Debunking the myths about SOA's relationship to the cloud," was originally published at InfoWorld.com. Read more of David Linthicum's Cloud Computing blog and follow the latest developments on cloud computing at InfoWorld.com.