Databases Reference
In-Depth Information
Notice that delivery units are not included in the production data. This is because each
delivery unit is always associated with the same delivery segments, irrespective of the
period. Because of this invariant, it is possible to index each delivery segment by its
many delivery units. To calculate the route to a particular delivery unit, the system need
only actually calculate the route to its associated delivery segment, which can be recov‐
ered from the index using the delivery unit as a key. This optimization helps both reduce
the size of the production graph, and reduce the number of traversals needed to calculate
a route.
The production database contains the details of many different delivery periods, as
shown in
Figure 5-15
. This multiperiod graph shows some of the overall complexity
present in the data.
Figure 5-12. Structure of the delivery network for Period 1
