Temporal information in newswire articles : an annotation scheme and corpus study.

Many natural language processing applications, such as information extraction, question
answering, topic detection and tracking, would benefit significantly from the ability to
accurately position reported events in time, either relatively with respect to other events or
absolutely with respect to calendrical time. However, relatively little work has been done
to date on the automatic extraction of temporal information from text.
Before we can progress to automatically position reported events in time, we must gain
an understanding of the mechanisms used to do this in language. This understanding can
be promoted through the development of all annotation scheme, which allows us to identify
the textual expressions conveying events, times and temporal relations in a corpus of 'real'
text.
This thesis describes a fine-grained annotation scheme with which we can capture all
events, times and temporal relations reported ill a text. To aid the application of the scheme
to text, a graphical annotation tool has been developed. This tool not only allows easy markup
of sophisticated temporal annotations, it also contains an interactive, inference-based
component supporting the gathering of temporal relations. The annotation scheme and the
tool have been evaluated through the construction of a trial corpus during a pilot study. In
this study, a group of annotators was supplied with a description of the annotation scheme
and asked to apply it to a trial corpus.
The pilot study showed that the annotation scheme was difficult to apply, but is feasible
with improvements to the definition of the annotation scheme and the tool. Analysis of
the resulting trial corpus also provides preliminary results on the relative extent to which
different linguistic mechanisms, explicit and implicit, are used to convey temporal relational
information in text.