Temporal representation and reasoning in the medical record are difficult due to: (1) the diversity of time expressions; (2) the complexity of determining temporal relations among events (which are often left to inference); (3) the difficulty of handling the temporal granularity of an event; and (4) general issues in natural language processing (e.g., ambiguity, anaphora, ellipsis, conjunction).
the signals used for reconstructing a timeline can be both domain-specific and complex, and are often left implicit, requiring significant domain knowledge to accurately detect and interpret.