Faceted Classification
November 28, 2001

Lately I've been hearing a lot about Faceted Classification. I'm not sure who was the first to coin it but it's a navigation method that seems to work very well when you have a large list of items you need to classify and browse.

EXAMPLES

Here are some examples of sites that use Facetted Classification:

Epicurious
Wine.com

WHAT IS IT?

Yahoo's Dewey Decimal System approach of highly coordinated taxonomy has a tree structure where each item has a small pigeon hole at the end where the item is classified. Of course any given item can be put into multiple boxes, but in the end it's a dead-end system where you have to climb up the branch again to browse further. This may be suitable if you have a small number of categories, but quickly becomes unweildly and a maintenance nightmare when you have as many items as Yahoo or any decent sized ecommerce site.

In the case of Epicurious the issue is how to classify all the recipes on the site in a way that is easily browsable while at the same time usable. They achieve this by using a facetted approach. Each receipe is given four attibutes (= facets = metadata) - Main Ingredient, Course / Meal,Cuisine, Season/Occasion. (see example) Since each recipe has these facets the search can be refined by each time by one of these facets. You can start on any facet and refine by any facet. It become a very "open-ended" browsing method. This systems also lends itself to easy maintenance and excellent cross referencing.

Consider this:

Facet | # of Terms
Main Ingredients | 30
Cuisine | 16
Course/Meal | 16
Season/Occasion | 13
Total Terms | 85
Total Combinations | 99,840

HOW-TO

- make sure that you have too many items to be listed in a clear tree hierarchical list
- create clear item attributes (facets) that are applicable to all items and use user-facing vocabulary
- store all items in database with the attributes as metadata columns

WORDS OF CAUTION

If you have items that are not readily categorizable or the categories are disputed, this may not be the system to use. Recipes and wines are one thing, assigning attributes to articles produced by an organization may be harder to implement.

RELATED RESOURCES

The Speed of Information Architecture (11/14/2001)
Innovation in Classification (9/23/2001)
Faceted Classification (2000)



Comments

The most important thing to remember when creating facets is that they must be exclusive: a topic (or 'property', or 'value') can not be in facet A and also in facet B.

'cuisine', 'course' and 'season' are good facets because a season is never a course or a cuisine.

'things to do' and 'places to go' or good facets.

'things to remember' and 'activities' are bad facets, because sometimes an activity can be a thing to remember.

Note that *within* a facet, the topics (like Chinese cuisine and Indian cuisine) don't have to be exclusive: a dish can be Chinese-Indian without problems.

Posted by: PeterV on May 28, 2002 08:35 AM
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