So what could do is fake Facets in a hierarchy and what you would get is a weird sort of hybrid with some interesting properties.

Example of a well-groomed hierarchy: Classifying Hierarchies

Imagine that you are an incredible-y anal dresser. You fold your clothing with the aid of a straight edge. (I've actually personally witnessed such a thing.) When you launder, you not only separate whites from darks, but as everyone knows, not all darks are created equal and red/oranges, green/blues and yellow/tan/greys are all washed separately as well.

Your organization of clean clothing is even more astounding. The Container Store is your temple and Elfa is the altar at which you worship. Your Closet is a strict 4-level, semantically encoded hierarchy where each level of the hierarchy consistently maps to a Facet of your clothing: Occasion>>Mood>>Anatomy>>Layer

• Notice the (small) size of the vertical scrollbar
• Notice the total # of containers in the Finder window...
• Closet_hierarchy.png:
  

Why would you ever do this? The Faceted Hierarchy provides an efficient and secure guided navigation experience.

• Items are chunked into containers, containers are chunked into container types. All of this chunking provides you with a narrative of your data.
• The semantically pure levels of the hierarchy provide you with a roadmap of the series of decisions you will need to make at each level of the hierarchy
• The semantically consistent levels means that the series of decisions is always the same no matter which branch of the tree you explore
• Each level of the hierarchy is completely filled out, so you're never afraid that you might be missing out on something

As it turns out, our Fashion Nazi has a special gift for constructing hierarchies. The Closet hierarchy is exceptionally designed for the following reasons:

In addition to the semantic purity, the Fashion Nazi has gone one step further to ensure that the semantics themselves are nested in the optimal order

• where optimal is defined as the ability to eliminate as much stuff as possible at each decision point in the hierarchy
  • where decision point is defined as the point at which Fashion Nazi must choose a particular Closet container in order to travel to the next level of the Closet hierarchy
• where the Fashion Nazi is optimizing for getting dressed in the morning

At every level of the hierarchy, Fashion Nazi (FN) wants to encounter only viable options of dress. Therefore, it makes most sense to define the top levels of the hierarchy with semantics such that FN can quickly eliminate most of the containers and only feel obligated to delve into 1 or 2. Anatomy and Layers would be a bad example of what to put at the top of the hierarchy. In order to get fully dressed, FN must dip into every Anatomy container and depending on the season (Summer, Spring/Fall or Winter), nearly every Layer container.

Right off the bat, FN cannot eliminate any branches of the tree. And what's more is that as he dips into each Anatomy container and then each Layer container, he is then confronted with the very thing he expressely did not want from the outset: a whole array of unviable options of dress: For each Body part and Layer, he must repeatedly select from an array of apparel for every Occasion and then for every Mood. OR worse, in the monotony of deciding upon Occasion and Mood over and over again, FN accidentally makes inconsistent Occasion and Mood selections and ends up at the gym with JLo Bling bunny slippers, Teletubby Red track pants and a formal Boardroom blazer.

A different way to put it is that Fashion Nazi never wants to make the same decision twice. With Anatomy and Layer at the top of the tree, you're repeatedly presented with the Occassion and Mood options over and over again: 48 times to be exact. With Occassion and Mood at the top of the tree, you only make those decisions once.

In contrast, Occasion and Mood are great examples of what to put at the top of the hierarchy. Fashion Nazi always knows what occasion he's dressing for and it's usually only 1 occassion. Fashion Nazi is not always sure about his mood, but he can usually narrow it down to 1 or 2. These days, it's been more often JLo Bling and less often Martha Stewart pastels.

Right off the bat, 86% of the tree vanishes and once FN has figured out what kind of mood he's in, he is only ever presented with viable options of dress: Clothing for every part of the body and every layer of dress that is appropriate for the occasion he is attending and the mood he is in.

In other words, not only does this hierarchy chunk data down into containers and then chunk the containers down into container types, they proceed to prioritize the ordering of those container types by way of the fixed parent-child structure to help guide you towards your goal.

• In the Closet hierarcy, you only need to make the Occasion and Mood decisions once and then you're on your way...
• Closet_tree.png:
  

• In the Inverted hierarchy where Anatomy and Layer are at the top of the tree, you must make the Occasion and Mood decision 12x4=48 times!
• Inverted_tree.png:
  

The end result is an efficient and secure browsing experience

• The hierchical organization guides FN towards a coherent outfit, where each piece of clothing is appropriate for the occasion he is attending and conveys a consistent mood.
• As mentioned above, the filled out spectrum of possibility at each level of the hierarchy gives Fashion Nazi the confidence he needs to know that he hasn't overlooked some crucial cache of clothing (ie. underwear).

That's why hierarchies are good at Guided Navigation, because they help you find the right things in the right way.

Faceted Hierarchies are just easier to grok

DDC example

• Case study: DDC
• Notice how the most easily comprehensible parts of the Generalities branch are the ones with "clear semantic encoding".
• This is because you're brain was able to chunk down a big huge list of topics into a hierarchy of 2 or 3 attributes or facets.
• The other sub-areas just smear into an unmemorable list of General sounding things.
• generalities.png: