Dw design fact_tables_types_6

DATA WAREHOUSING Multi Dimensional Data Modeling. Fact Table Types

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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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Transaction-grained fact tables are often richly dimensional and usually have only a single fact (the amount of the transaction).

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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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Periodic snapshots are appropriate for long running processes that extend over many reporting periods.

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Accumulating snapshots, are used for short processes that have a definite beginning and end, such as an order being filled.

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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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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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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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The Data Warehouse Toolkit.Second Edition.The Complete Guide to Dimensional Modeling.Ralph Kimball.Margy Ross