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organizations looking to reduce integration costs are increasingly adopting a service-oriented architecture (soa) to maximize their it investment.
the preeminence of web services as a tool that can support a wide range of dynamic business processes has made it the soa tool of choice. web services are easy to build but difficult and expensive to maintain. monitoring and management costs weigh heavily on the roi calculator, and in order to maximize roi enterprises need to keep a keen eye on the support and reliability meter.
in the web services world, an application is typically a chain of services, or "links," woven together in some sequence with a web services front end. the chain itself is weaker than the weakest link in the chain. for example, if an application consists of three service calls, each with a reliability of 0.99, 0.96, 0.97 respectively, the overall application reliability according to the laws of probability and statistics is
application reliability = 0.99*0.96*0.97=0.92
the multiplicative effect of individual services tends to steeply reduce overall application reliability as the number of links in the chain increases.
some of the biggest strengths of web services, the http and soap protocols, are also its weaknesses. http is a stateless protocol that does not guarantee delivery of all the packets to the destination. nor does it guarantee the order of the arriving packets. this makes http an unreliable protocol incapable of meeting the delivery requirement of "exactly once". if there is no bandwidth, the packages are discarded. soap is the wire protocol for web services and has some inherent performance problems. extracting the soap body from the soap envelope is time-consuming. parsing megabytes of xml data with a lot of type information is slow and intensive. to increase the reliability of web services and measure up to the more mature and robust middleware messaging standa... 下一页