浏览器利用http头，通过相同的服务器端代码来满足不同类型的请求。
Browsers use the HTTP header to satisfy many different kinds of requests with the same server-side code.
有许多不同的方法和服务可用来找到满足接口请求的对象。
There are many different methods and services available to locate objects that will satisfy the request to an interface.
例如，某个请求可能由不同物理位置的多个潜在提供者中的任何一个来满足，而服务请求者不需要意识到这一点。
For example, service requesters need not be aware that a request could be serviced by any of several potential providers at different physical locations.
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