Databases Reference
In-Depth Information
Aggregating the Flight Data table
When aggregating data, the first step is always to define which dimension fields will
be left out and which ones will be kept in the summarized table. We should analyze
this question by looking at the data from the ground up, that is, by reviewing each
dimension from the most granular to the most general. The following list shows the
most important dimension fields in the
Flight Data
table, sorted by granularity:
•
Airport
(
Origin
and
Destination)
•
City
•
State
•
Country
•
Aircraft Type
•
Aircraft Group
•
Airline / Carrier
•
Carrier Group
•
Region
•
Month
•
Quarter
•
Year
If we analyze how removing each dimension would individually affect the result
of the summarization process, we can find that the most impact would come from
removing the
Airport
dimensions, both Origin and Destination, since those are the
ones with the greatest granularity. At the same time, we can say that the
Airport
dimension does not add much value to the analyses we are looking to deliver in our
document, so it's a good choice to leave it out.
Dropping dimensions from the data directly impacts the
analyses that can be made in the resulting QlikView document.
Therefore, the decision to leave out certain fields for the sake of
summarization should always be discussed with the end user.
We could remove additional dimensions, for example,
Aircraft Type
or
Carrier
, but
as we move up the detail ladder to the most general dimensions, those dimensions
become more and more important to accomplish different analyses.
