OPC历史数据服务器提供了一种标准的历史数据访问机制给那些对历史数据感兴趣的用户。
OPC historical data access Server provides a kind of standard mechanism of data access for the users who are interested in historical data.
只有在查询的from子句包含周期规范时，DB 2才会自动且透明地访问历史数据。
DB2 accesses the historical data automatically and transparently only if the FROM clause of the query includes the period specifications.
而对于历史数据，系统提供了静态曲线和在线WEB访问查询。
While as to historical data, the static curve and WEB accessing and inquiring on line are supplied.
而对于历史数据，系统提供了静态曲线和在线WEB访问查询。
While as to historical data, the static curve and WEB accessing and inquiring on line are supplied.
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