一个门只是一个消息，图形表示为一端连接序列图的框架边缘，另一端连接到生命线。
A gate is merely a message that is illustrated with one end connected to the sequence diagram's frame's edge and the other end connected to a lifeline.
Rails构建于一门优秀语言（Ruby）和坚实的相关配套设施之上，是一个强大的web框架。
Rails is a strong web framework, built on an excellent language (Ruby), and surrounded by a solid ecosystem.
因为是箭头的线连接到图的框架，而箭头连接到生命线，所以 getBalance 消息是一个入口门。
The getBalance message is an entry gate, because it is the arrowed line that is connected to the diagram's frame with the arrowhead connected to a lifeline.
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