January 27, 2006

Why I use the word “MOLAP”

“MOLAP” stands for “Multidimensional OLAP.” It’s almost exactly what Ted Codd was referring to in the white paper where he introduced the term “OLAP.” Relational advocates correctly point out that relational tables are NOT “two-dimensional;” rather, every column in a table represents a dimension.

(If that’s not obvious, think of rows in a table as n-tuples, and n-tuples as akin to vectors. Then think back to the linear algebra segment at the beginning of your Calculus of Several Variables class. Vector spaces? Dimensions? I rest my case.)

Despite all that, I’m comfortable with the “M” in MOLAP, because a dimension in a MOLAP hypercube is a lot more complex than a dimension in a relational table. The latter is itself — well, if there’s a sort order, it’s typically one dimensional. But the analog in a MOLAP cube can be a whole rich and complex hierarchy.

So yes — MOLAP is inherently more multidimensional than ROLAP, atlhough one can of course do something equivalent to a single hypercube by creating a whole lot of different tables.


One Response to “Why I use the word “MOLAP””

  1. Historical notes on analytics — terminology | Software Memories on January 17th, 2012 3:08 am

    […] A particular non-relational DBMS architecture that I prefer to refer to as MOLAP (Multidimensional OLAP). […]

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