| This service retrieves information about the temporal persistence of objects in terms of their existence through time. The existence of non-existence of an object is represented via the 'isExtant' property. When confidence in this assertion reaches a threshold level, the object is deemed to exist. When the value of this property switches to false the object is deemed to no longer exist. This form of representation allows the temporal persistence of transient phenomena (e.g. earthquakes) to be determined. |