There are many good reasons to combine Software-as-a-Service (SaaS) and Service-Oriented Architecture (SOA). SaaS is about delivering a single piece of software to many users, and SOA is about building software that's flexible and reusable. Together, you get a SaaS solution that uses SOA technologies to more quickly adjust to changing market conditions and customer needs. Some vendors, in fact, have made SaaS a part of SOA by building a SaaS framework that exposes defined business processes for integration within SOA applications. But you can take it a step further by using SOA as a way to connect an enterprise to an externally hosted SaaS application. Whether SOA is acting as a foundation for a SaaS application or serving as a means of connecting corporate assets to that SaaS application, one thing is clear: These two software concepts are anything but mutually exclusive.

Read more about the combination of SOA and SaaS:
- read the article at InformationWeek

ALSO:
- read this on getting the most out of SOA
- this on what SOA is all about
- this on SaaS: A view from the trenches
- and this on SaaS hitting the mainstream