For example, the optimizer does not know the values of host variables or parameter markers (if these are contained in the query) until the query is executed.
例如，优化器到执行时才会知道主机变量或参数标记的值(如果查询中包含的话)。
Or an RPC application may simply want to query the supported protocol sequences by the host.
RPC 应用程序只需查询主机支持的协议序列。
The subscriber (client) simply needs to use WS-Polling to periodically query its SOAP messaging host for any messages waiting to be delivered to it.
订户（客户机）只需使用 WS-Polling 周期性地查询其 SOAP 消息传递主机，以获得等待传递给它的任何消息。
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