Databases Reference
In-Depth Information
Our re-designed data model will look as follows, after applying the
appropriate changes:
As you can see, the synthetic key has been removed and the
Payroll
and
Operations
tables are now connected to the
Department
and
Employees
dimension tables indirectly and through the link table.
When designing a data model using this method, we should always consider
the following:
• The link table can become very large depending on the number of possible
combinations that exist between or among the fields it's composed of.
• We must make sure that all of thecombinations that exist in both fact tables
are also in the created link table. If they are not, the association between the
fact tables and the link tables might be "broken" or missing for some records.
• For performance optimization, the link table should not have repeated
records. Only one record per possible combination of values is needed.
• If the link table becomes immense, remember that QlikView needs to
"walk" through the defined path between tables each time it needs to
look for associations. An additional "hop" on this path, especially if it
is through a large table, might slow calculation times for the end user.
