To understand ETL, one must master the arena of maps.
Maps show the way to transform codes or values in one format (source) into the
desired codes or values of another (destination). Sometimes you’ll hear
crosswalks rather than maps—same thing. Sometimes you’ll hear of transformation
rules or business rules—gets complicated here. The business rules describe
exactly how a value in one format must be transformed. A simple map or
crosswalk might take a code of “1” and make it an “a.” A business rule might
demand that “1” become “a” when referring to a first grader, but “b” when
referring to a second grader, but still “a” if the second grader was socially
promoted, however, “b” if the social promotion occurred in
kindergarten.
One must not underestimate the importance or complexity
of these ETL processes. A special education December child count data
collection from districts to the state education agency might require 50 or more
business rules.
The EduGuru speaks: Remember when the ugly duckling
transformed into the beautiful swan? Our data transform from whatever they need
to be in the school or district database to the “beautiful,” comparable data at
the state level when they pass all the business rules. Be clear. This is not a
fairy tale. This is a dream come true.
*from the movie Napoleon Dynamite
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