Databases Reference
In-Depth Information
8
What Is Tim
e Variance?
This discussion of Time Variance in a data warehouse assumes a shared
understanding of data warehousing. If you are unsure of the meaning
and application of such terms as
transaction table
,
fact table
,
dimension
table
, or
entity
, then please have a copy of
Building and Maintaining a Data
Warehouse
handy. These terms and the methods by which we use them are
explained in
Building and Maintaining a Data Warehouse
. So, rather than
try to surmise the meaning and application of data warehouse jargon,
please be ready to reference
Building and Maintaining a Data Warehouse
,
which is a topic on the basics of data warehousing.
Time Variance. This is one of those phrases penned by IT people, for
IT people. It's a bit of shorthand. The phrase
Time Variance
is full of
meaning. Rather than spend ten minutes to define Time Variance every
time we discuss one of the concepts of time in a d ata warehouse, we
simply use the phrase
Time Variance
. Before we define a solution that
delivers Time Variance in a d ata warehouse, we need to have a c om-
mon understanding of time—time in a data warehouse and time in Time
Variance. First, we start with the ubiquitous invisible object in every
Itemset—time.
tIme
Walk into any jewelry store, up to the wristwatch display case, and you'll
see it. It's on the face of every wristwatch. They calculate time in different
ways. Some of them calculate time gears, some with quartz, and some
with a computer chip. They display time in different ways. Some display
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