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
3
4. Transaction-grained fact tables are often
richly dimensional and usually have only a
single fact (the amount of the transaction).
4
5. Periodic snapshot records are generally
repeated each reporting period as long as the
thing being measured (like the account) is in
existence.
5
6. Periodic snapshots are appropriate for long
running processes that extend over many
reporting periods.
6
7. Accumulating
snapshots, are
used for short
processes that
have a definite
beginning and end,
such as an order
being filled.
7
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
8
9. The simplest implementation of an
accumulating snapshot does not give you
intermediate points in the history of, for
example, an order.
9
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.
10
11.
12.
13. The Data Warehouse Toolkit.Second
Edition.The Complete Guide to Dimensional
Modeling.Ralph Kimball.Margy Ross
