  When exploring time series datasets, analysts often pose "which and when"
questions. For example, with world life expectancy data over one hundred years,
they may inquire about the top 10 countries in life expectancy and the time
period when they achieved this status, or which countries have had longer life
expectancy than Ireland and when. This paper proposes TimePool, a new
visualization prototype, to address this need for univariate time series
analysis. It allows users to construct interactive "which and when" queries and
visually explore the results for insights.
