Principle:
create fact tables with the most granular data possible to support analysis of
the business process.
In
Data warehousing grain refers to the level of detail available in a given fact
table as well as to the level of detail provided by a star schema.
It
is usually given as the number of records per key within the table. In general,
the grain of the fact table is the grain of the star schema.
Facts: Facts must be consistent with
the grain.all facts are at a uniform grain.
- Watch for facts
of mixed granularity
- Total sales for
day & montly total
Dimensions: each dimension
associated with fact table must take on a single value for each fact row.
- Each dimension
attribute must take on one value.
- Outriggers are
the exception, not the rule.
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