  TimeML is an XML-based schema for annotating temporal information over
discourse. The standard has been used to annotate a variety of resources and is
followed by a number of tools, the creation of which constitute hundreds of
thousands of man-hours of research work. However, the current state of
resources is such that many are not valid, or do not produce valid output, or
contain ambiguous or custom additions and removals. Difficulties arising from
these variances were highlighted in the TempEval-3 exercise, which included its
own extra stipulations over conventional TimeML as a response.
  To unify the state of current resources, and to make progress toward easy
adoption of its current incarnation ISO-TimeML, this paper introduces
TimeML-strict: a valid, unambiguous, and easy-to-process subset of TimeML. We
also introduce three resources -- a schema for TimeML-strict; a validator tool
for TimeML-strict, so that one may ensure documents are in the correct form;
and a repair tool that corrects common invalidating errors and adds
disambiguating markup in order to convert documents from the laxer TimeML
standard to TimeML-strict.
