title: Weekly summary table; how to reference the time dimension
body: <p>We're thinking about adding a weekly summary table to our little data warehouse. We have a classic time dimension down to the daily level (Year/Month/Day) with the appropriate Week/Quarter/etc. columns.</p>
  
  <p>We'd like to have the time key in this new weekly summary table reference our time dimension. What's the best practice here—have the time key reference the id of the first day in the week it represents? Or the last day? Or something entirely different?</p>