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With two time intervals, the stream time (TimeInterval) and the prediction time, we have two temporal dimensions for each stream element. We denote this as a bitemporal stream.

Lifted Expressions

Lifted expressions are normal expressions with at least one temporal attribute involved.

Theoretical Foundation

Expressions are a core element of queries. They are used in map, select, and join operators. Typically, an expression uses one or more attributes from the stream element(s). An example could be attribute1 + attribute2 > 42. A goal of the temporal feature is that this works with temporal attributes in the same way it does with non-temporal attributes. This is done with the lifting approach (a term from the moving object algebra). If at least one attribute of an expression is temporal, the output of the expression will also be temporal. This can be denoted with a second order signature.

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real × treal → treal [+]

treal × treal → treal [+]

Handling of Lifted Expressions in Odysseus

Operators

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Map

Text

Select

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