RDC records certain types of reported associations between pairs of entities. It also requires the reporting of the relation timestamps, i.e. of the time when a relation is reported as existing. For the first round of RDC, we take a conservative approach to associating times with relations, and require that the text evidence be found within the predication of a relation mention. Thus, we treat only Class A (explicit) relations, and only those that include explicit temporal evidence.
The text evidence of a timestamp may be in the form of a temporal phrase that is an adjunct to the predicate ("Bush's Saturday visit to Manhattan", "Rumsfeld became U.S. Secretary of Defense again in 2001"). A more general timestamp may be present in the form of a finite verb that heads the predication of the relation. A large proportion of Class A relation mentions will contain neither a time adjunct phrase nor a finite verb, and will therefore be assigned null temporal attribute values.
There may be more than one time at which a particular relationship is reported as having existed, i.e., there may be more than one timestamp on a relation. For example, a document may note that John Doe was LOCATED at Las Vegas June and August in 2001, or that Jane Doe had the ROLE of Technical Director for SPAWAR Systems Center in 1998 and 2000. The two different times referenced in each example are not evidence of different underlying relations; they are different attribute values for the same underlying relation.