Ongoing time point now is used to state that a tuple is valid from the start point onward. For database systems ongoing time points have far-reaching implications since they change continuously as time passes by. State-of-the-art approaches deal with ongoing time points by instantiating them to the reference time. The instantiation yields query results that are only valid at the chosen time and get invalidated as time passes by. We propose a solution that keeps ongoing time points uninstantiated during query processing. We do so by evaluating predicates and functions at all possible reference times. This renders query results independent of a specific reference time and yields results that remain valid as time passes by. As query results, we propose ongoing relations that include a reference time attribute. The value of the reference time attribute is restricted by predicates and functions on ongoing attributes. We describe and evaluate an efficient implementation of ongoing data types and operations in PostgreSQL.

中文翻译：

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查询结果随着时间的推移仍然有效（扩展版本）

正在进行的时间点现在用于声明元组从起点开始是有效的。对于数据库系统，持续的时间点具有深远的影响，因为它们随着时间的流逝而不断变化。最先进的方法通过将它们实例化为参考时间来处理正在进行的时间点。实例化产生的查询结果仅在所选时间有效，并随着时间的流逝而失效。我们提出了一种解决方案，可以在查询处理期间保持正在进行的时间点未实例化。我们通过在所有可能的参考时间评估谓词和函数来做到这一点。这使得查询结果独立于特定的参考时间，并产生随着时间的推移保持有效的结果。作为查询结果，我们提出了包含参考时间属性的持续关系。参考时间属性的值受持续属性上的谓词和函数的限制。我们描述并评估了 PostgreSQL 中正在进行的数据类型和操作的有效实现。