Temporal Data Types

Temporal databases allow one to associate a temporal extent with a real world phenomenon. These temporal extents may represent either events or states. Events correspond to phenomena occurring at a particular instant, for example the time when a car accident occurred. States represent phenomena that last over time, such as the duration of a project.

 

SimpleTime is a generic type that generalizes the Instant and Interval data types. It is an abstract type and thus, when a value associated to SimpleTime is created, the specific subtype (either Instant or Interval) must be specified. A SimpleTime can be used, for example, to represent the time (with a granularity of one day) at which an event such as a conference occurs, where one-day conferences are represented by an Instant and other conferences, spanning two or more days, are represented by an Interval.

An Instant denotes a single point in time according to a specific granularity. It has no duration. An instant can have a special value now, which is used for indicating the current time. Instants are used to represent events,

An Interval denotes a set of successive instants enclosed between two instants. Intervals are used to represent states, for example the duration of project A.

A ComplexTime denotes any heterogeneous set of temporal values that may include instants and intervals.

Finally, Time is the most generic temporal data type, meaning “this element has a temporal extent” without any commitment to a specific temporal data type. It is an abstract type that can be used, for example, to represent the lifespan of projects, where it may be either an Interval or an IntervalSet.