In most small sites taxonomy is obvious, but in larger sites, especially those where the expertise of the readership may not be that of the authors, taxonomy design can make the difference between a site being good or bad.

VIEWS Module - with it's powerful taxonomy based Filters - makes taxonomy design even more important than before.

General Rules

1) Unless a Vocab is well known to all anticipated users, and alphabetical (e.g. Countries of the World), try and keep them below 30-40 Terms.

2) If your Vocab has Parent-Child structures, think about dividing it up because it's likely to be going to get too big, and is probably badly designed.

Example (sort from an online arts shop) - Traditional Arts Single Select

Europe
-Lapp
-Sami
-Celtic
Australia
-Aboriginal

This represented the way the shop classified their items.

But as such it prevents some clients saying "show me European Art".

Multiple Select is an option but much better to have two Vocabs - one for Region and one for Culture, make them both multi and a collector could say "What have you got which is Lapp, or Celtic or Chinese?"

3) Too Many Terms

"Perfect" taxonomies are always too complex and you need to fight to make them more manageable. (Esp if you have just cut up a few Parent Child vocabs into several smaller ones each...)

The advantage of VIEWS is that the multiple taxonomy terms start to build context, and that can be captured by views.

There are not many sites that ever need to show more than 3-4 filters to users, even if there are 5-6 more hidden ones .

Plus building them into structure adds even more granularity.

Eg a site for ALL the small towns of America, where people are interested in their little towns stuff, using Book for basic structure:-

Top level - States - 50 items
Off each State - Counties
Off each County - settlements

Click the named settlement and a get a VIEWS screen with filters for News, Culture, Announcements.

(Hidden filters in the Views filter by State/County/Settlement)

Highly non scary - any users can use that to get what they need.

4) Clients are not experts on taxonomy, not even their own

Taxonomy is a communications issue and if there is a budget for the site it's always worth running it past an outsider - but note that they will need to get to understand the purpose of the site and also to an extent the jargon of the subject.

This normally requires a least one decent face to face meeting to force the client to decide what is important, and what can be cut out. (Trust me, these decisions will have to be made, and if they are not, then people are probably not thinking carefully enough.)

5) Taxonomy creates Legacy issues - SO GET IT RIGHT

Once you have a load of tagged data, it's hard to make changes to taxonomy structures (apart from adding terms) without rendering existing nodes much harder to find. Trust me, NO ONE will go back and edit existing data, not in real life, unless there is massive funding for that purpose.

6) Taxonomy is trial and error.

It should be the first thing you do on a site, but by adding test data you'll find flaws, and refine and eventually go live with something that works. In between times you solved the CSS and templating...

I once spent 3 days testing different ways to classify cars for one site - the makes/models complexity of past 20 years is a nightmare, and which there are several ways ot do it, all of which work, some are more userfriendly than others!

Hope this helps.

Ian Dickson - community specialist with a sideline in taxonomy because its the buidling block for EFFECTIVE social software... .