This isn’t about dimensions performing Romeo or Juliet, but is meant to
indicate that the same dimension can be used to act as multiple, similar dimensions. The obvious example is the time
dimension, which can be used,
or better, must be used to accommodate multiple occurrences of time and date.
Looking at a typical sales fact table, you see order date, ship date, receive
date, return date, and payment date—five dates, one dimension. Physically
speaking, all these dates link to the same date dimension table; logically, of
course, they don’t because you would end up with an empty result set in most
of the cases where multiple date restrictions apply. Take for instance the query
for retrieving the total order value of DVDs ordered in December 2007 that
were not returned within five days after shipment. This query involves three
types of dates, and when all the required date restrictions are being set on the
same date dimension table, you end up with an empty result set, or at least a
result set that doesn’t correctly answer the question. The SQL to illustrate the
correct solution for this looks similar to the query we used when discussing
table aliases (which is basically the same).
Now it’s easy to see that if you apply the last two restrictions to the same
table, this would cause an empty result set; it’s not possible for a date to be
bigger than the same date plus 5 days.
Another example related to the WCM database is the actor and director information. We could combine these two entities in a single role-playing artist or movie_person dimension. A lot of actors become directors later in their career and sometimes even the opposite occurs. Take for instance Quentin Tarantino, who started his career as a director and could later be found acting in his own movies as well.
Another example related to the WCM database is the actor and director information. We could combine these two entities in a single role-playing artist or movie_person dimension. A lot of actors become directors later in their career and sometimes even the opposite occurs. Take for instance Quentin Tarantino, who started his career as a director and could later be found acting in his own movies as well.
