What makes Web services so appealing is that, for all intents and purposes, its an exercise in pure democracy. Anyone can be a creator and consumer of Web services. Anyone with a good idea for a new specification can put it out there for review and adoption. You don't need fancy equipment to be a Web services player. As with open-source, Web services is truly a bottom-up movement.
SOA is seen as the next evolution in Web services. However, there are a lot of steps that need to be taken to get from Web services to SOA. To put it simply, Web services is edgy, hip, and a bit rebellious, but SOA is corporate and conservative. Thomas Erl, writing in recent Weblog on Webservices.Org, brings some clarity to this challenge: that is, SOAs will likely be built with Web services, but building Web services won't make an SOA. Erl, president and chief architect of XMLTC Consulting, warns that the bottom-up approach of building Web services won't automatically put you on the road to SOA. By their nature, Web services are highly distributed, and are most often deployed for point-to-point solutions -- very much a bottom-up approach. Erl notes, however, that "I have yet to see a bottom-up approach that results in anything resembling a service-oriented architecture." By contrast, the top-down approach required for service-orientation "is infused into the business process layer so that services can be modeled in alignment with business models."
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