We oldschoolers need to revisit the language we use to talk about dimension structures

Oct 03. 20182 min read
Scott Wiltshire

Back Then …

In the TM1 world many people have for many years been used to saying “hierarchies” when referring to hierarchical dimension structures e.g.

Ancestor > direct children (consolidated) > intermediate consolidations > ultimate leaf descendants

When TM1 was just TM1 and dimensions didn’t have named hierarchies this was OK as it was still clear what we were talking about. But times have changed. TM1 is Planning Analytics now, and Planning Analytics has alternate hierarchies. Old TM1 dinosaurs need to change their ways!

In the Now …

In any technical discussion clear unambiguous terms are essential. Not only do we need to be clear what we mean, the audience must understand what is meant without any extra overhead from guessing or translating what is being said.

To make our communication clear we need to adopt new terminology. The rules for doing this are quite simple.

  • Elements stay elements. No need to change anything here.
  • For internal multi-levelled parent child relationship structures use the term “rollup“. In PA a rollup should never be referred to as a “hierarchy” this is incorrect and only confuses.
  • Wherever we were used to saying dimension simply replace with “hierarchy“. Hierarchies contain rollups. In fact hierarchies are now the containers for elements, rollups, subsets and attributes (not dimensions, that was back then, we need to get to the now).
  • The term dimension should only be used when talking about cube structure. Dimensions in PA are merely a container for hierarchies.

Avoid confusion

I have seen some people try to address the confusion caused by their old habits of referring to rollups as “hierarchies” by adding capitalization to distinguish  “big H” Hierarchies from “little h” hierarchies. This is confusing enough in written language but just doesn’t work in a spoken conversation. Others qualify with adjectives e.g. named hierarchies or alternate hierarchies while still referring to rollups as “hierarchies”. Frankly this isn’t any better. The fact we need to accept is that the old way we were used to using this term is now wrong. There is no need for forced capitalization or extra descriptors. Hierarchies alone is sufficient. In Planning Analytics and OLAP/MDX the term has a specific enough meaning already, let’s just use it and drop the old ways!

It may be difficult at first, but please if you catch yourself saying “hierarchy” when you really mean “rollup” stop and correct yourself. It doesn’t take long to change the habit and the sooner we all do we can stop second guessing each other.

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