What do slowly changing dimensions (SCDs) represent to a database designed for decision-support?
What will be an ideal response?
A database designed for decision-support will normally store data that can be several years old. During
that time the business is likely to change and this may impact on the corporate data. The star schema
has to continually evolve to support the business and this means that it is important to identify and
accommodate these changes where necessary.
Many dimension attribute values are not fixed but change over time e.g. an employee may change
department. Dimensions that have changeable attribute values are called slowly changing dimensions
(SCDs).
This requires the identification of dimensions and attributes to be tracked and decisions made on how
they are to be tracked as not all changes are significant.
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