An example of this is when a service provider accesses multiple back-end systems with different timeout requirements, but only determines at run time which back-end is invoked.

此类示例包括服务提供程序访问多个带有不同超时需求的后端系统，但仅在运行时才确定调用哪个后端系统。

youdao

Next time, we will create a Web service that shields front end PHP code from the back end MySQL system in which the account information is stored.

下次我们将创建一个Web服务，它对前端PHP代码隐藏了存储账号信息的后端MySQL系统。

youdao

Now that you've seen the back-end service that the Web application will use, it is time to look at the front end that USES it.

既然我们已经了解了Web应用将使用到的后台服务，接下来我们将了解它使用到的前台。

youdao

Instead, their customer service agents spend most of their time bridging a digital divide between the consumer and those back-end systems only the agents can reach.

FORBES: The Future Of Customer Service: Lessons From Your Barber