It could be the result of the resource adapter receiving some external stimulus from a back-end system. Or it could just be some internal event, possibly even timer driven.

它可以是资源适配器接收到后端系统的一些外部刺激之后的结果，也可以仅仅是一些内部事件，甚至可能是由计时器驱动的事件。

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Large-scale websites are driven by numerous databases, APIs, and other back-end services.

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