【摘要】 论文提出一种数据流管理系统中支持实时性查询的数据流操作语言PQL。PQL以SQL₉9为蓝本,引入了时间戳、快照窗口、标记窗口、滑动窗口以及连续查询等一系列相关概念,对数据流连续查询中的近似查询和查询的实时性也给出了充分的语法和语义支持。PQL充分地实现了数据流的操作特征,它不仅可以实现数据流上的选择、投影、连接等操作,支持物理时间和逻辑时间两种时间戳,而且可以实现数据流与关系表的连接操作。更多还原

【Abstract】 This paper proposes a language that can support real-time query on data streams.We call it Power Query Language.PQL based on SQL₉9 and imports timestamp,snapshot window,landmark window,sliding window and continuous query.A query defined by PQL can be an approximate query and contains a deadline.It not only implements select-project-join query on data streams,but also supports physical timestamp and logical timestamp and also can join a data stream with a table.更多还原