Taxonomies and Classification for Organizing Content

Prentiss Riddle

INF 385E

9/21/2006

What is a taxonomy?

A hierarchical classification system in which categories are subdivided to create finer distinctions.

• animal– vertebrates

• mammals– cat– dog

• reptiles

– invertebrates

• vegetable• mineral

Not all classification systems are taxonomies

Richard Saul Wurman’s LATCH• Location• Alphabet• Time• Category• Hierarchy

Any of these can be expressed as a taxonomy or not.

(Well, maybe not the alphabet...)

A quibble about definitions

• We commonly use “taxonomy,” “hierarchy” and “classification system” interchangeably but in fact they’re distinct (if overlapping) terms

• In particular, a hierarchy can be linear– the “H” in Richard Saul Wurman’s LATCH– elephant > horse > dog > mouse– Maslow’s hierarchy of needs

• A “folksonomy” is not a taxonomy!

Why taxonomies?

Taxonomies in our heads• Fundamental to cognition• Observed in children from an early age• Long before Linnaeus and Darwin: “folk

taxonomies”

Why taxonomies?

Taxonomies in the world• Genealogy, phylogeny

• Command structures, org charts, territories

• Filesystems, domain names, URLs

/var/www/people/faculty.php

www.ischool.utexas.edu

http://www.ischool.utexas.edu/people/faculty.php

This suggests the use of taxonomies in IA

• Taxonomies in support of browsing

• Taxonomies in support of search

But that’s problematic...

Problematic in the world

• The world is complicatedWho here has had cataloguing?LC Subject Headings, LC Classification, Dewey...

• The world is even more complicated– Lattices and networks, not trees– Multiple kinds of relationships– Fuzzy boundaries

Problematic in our heads

• The taxonomies in our heads don’t match the world

• The available taxonomies may not be what’s important anyway– The user doesn’t care about the org chart!

(The mantra of enterprise IA)

– The user doesn’t care about the filesystem

Cautious use of taxonomies• Tempered by understanding and testing users• Enlist users in creating taxonomies

– Techniques like card sorting

• Functional or “folk” etymologies preferred over official ones– A gardening site might classify plants by temperature, sun and water needs, not by botanical classification

• Make official taxonomies available behind the scenes for use by experts (departmental admins, biology wonks)

Taxonomies in support of browsing

“Umbrella architecture”(Rosenfeld & Morville)

E.g., familiar hierarchical menu structures

Taxonomies in support of browsing

Not always ideal...

Taxonomies in support of browsing

...but better than chaos.

• Supports breadcrumbs• If the users don’t know

your taxonomy, gives them a fighting chance to learn it.

Browsing very large taxonomiesYahoo began as a taxonomy company

...although at some point it became a search (and content) company

Taxonomies in support of search

Search results can include a link to a category

Taxonomies in support of searchAnd searches can be limited to a category

Beyond taxonomies

Taxonomies on steroids

Taxonomy + controlled vocabulary

= thesaurus

A thesaurus usually has a taxonomy embedded in it

Relationships in a thesaurus

• Some of the links in a thesaurus express hierarchy and links across it– Broader term (BT)– Narrower term (NT)– Related term (RT)

• Some express the controlled vocabulary– Preferred term (PT)– Variant term (VT)– Use (U)– Used for (UF)

Not just synonyms

• A thesaurus is not just for synonym ringscat = feline = kitten= kittycat

• It’s also for key relationships across the hierarchy

“Nice pants! How about a shirt?”

In a sense, Amazon’s many suggestion features and much of Google Adwords are a set of RT links in a thesaurus

Faceted classification

A problem inherent in taxonomies is, what gets divided first?– History - U.S. - War - 1812– War - History - U.S. - 1812– U.S. - History - 1812 - War

Or in more familiar terms:– Wine - Red - California - Dry - 1999- Under $25– Wine - Under $25 - Red - Dry - California - 1999– etc.

Facets are independent hierarchies

• Facets work in parallel– In the subject classification example: facets for

topic, time, place, etc.– In the wine example: facets for type, origin, price,

manufacturer, etc.

• A particular item will be at the intersection of several facets

• Facets can simplify classification systems both for creators and users

Folksonomies

• Fun, powerful, interesting but a misnomer: not taxonomies at all

• Tagging systems in use in popular “web 2.0” sites– www.flickr.com– del.icio.us

• Personal keyword metadata aggregated for searching and browsing

• The result is not a hierarchy, not really a classification system, certainly not a taxonomy