Temporal Expression

Definition

A temporal expression is a syntactic construct used, e.g., in a query that evaluates to a temporal value, i.e., an instant, a time period, a time interval, or a temporal element.

Key Points

Advanced by Gadia [1], a temporal expression is a convenient temporal query language construct.

First, any temporal element is considered a temporal expression. As Gadia uses a discrete and bounded time domain, any subset of the time domain is then a temporal expression. Next, an attribute value of a tuple in Gadia’s data model is a function from the time domain to some value domain. Likewise, the attribute values of a tuple are valid during some temporal element. To illustrate, consider an (ungrouped) relation with attributes Name and Position. An example tuple in this relation is:

$$ \begin{array}{l} \left(\left\langle \left[4;\;17\right]\; Bill\right\rangle,\;\left\langle \left[4;\;8\right] Assistant,\right.\right.\\ \quad \left.\left. \left[9;\;13\right]\;...