This document discusses different types of fact tables used in data warehousing: transaction fact tables track discrete processes over time; periodic snapshot fact tables record activity during repeating time periods like months; and accumulating snapshot fact tables overwrite facts as a process progresses, allowing intermediate snapshots of processes like orders. Accumulating snapshots are appropriate for short, definite processes while periodic snapshots work for long-running ones.

1. DATA WAREHOUSING
Multi Dimensional
Data Modeling.
Fact Table Types

2. 2

3.  Transaction
 Track processes at discrete points in time when they
occur
 Periodic snapshot
 is a fact table that records activity during a repeating
predictable time period, like the monthly summary of
a bank account
 Accumulating snapshot
 A snapshot of the most recent state of something and
therefore the dimensional foreign keys and the facts
are, in general, over-written as time progresses
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4.  Transaction-grained fact tables are often
richly dimensional and usually have only a
single fact (the amount of the transaction).
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5.  Periodic snapshot records are generally
repeated each reporting period as long as the
thing being measured (like the account) is in
existence.
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6.  Periodic snapshots are appropriate for long
running processes that extend over many
reporting periods.
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7.  Accumulating
snapshots, are
used for short
processes that
have a definite
beginning and end,
such as an order
being filled.
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8.  For an order, we would usually make a record
for each line on the order, and we would
revisit the record making updates as the
order progressed through the pipeline
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9.  The simplest implementation of an
accumulating snapshot does not give you
intermediate points in the history of, for
example, an order.
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10.  Accumulating snapshots typically have
multiple dates in the fact table representing
the major milestones of the process.
However, just because a fact table has several
dates doesn’t dictate that it is an
accumulating snapshot.
 The primary differentiator of an accumulating
snapshot is that we typically revisit the fact rows
as activity takes place.
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13.  The Data Warehouse Toolkit.Second
Edition.The Complete Guide to Dimensional
Modeling.Ralph Kimball.Margy Ross