I agree, Vital Ventura is a really impressive example. It’s being pulled off via Ajax, you don’t see the url change because it is happening behind the scenes. You can install the Firebug extension for FireFox to watch the HTTP requests on pages such as this. The urls are pretty easy to create in WordPress 3.1. The following links work on this site:

3 Bookmarks about javascript
?topics=javascript

2 Bookmarks from WP Hardcore
?source=wp-hardcore

1 Bookmark about javascript from WP Hardcore
?topics=javascript&source=wp-hardcore

I’m pretty sure that complex queries (such as the ones you suggested) are not supported via url string. Otto has a great post about advanced taxonomy queries in 3.1. These examples work really well when used with query_posts() but fail when passed via GET.

The following query was constructed using Otto’s tutorial and is meant to retrieve all posts about Accessibility and The Dashboard but not about Media.

tax_query[0][taxonomy]=topics&tax_query[0][terms][]=dashboard&tax_query[0][terms][]=accessibility&tax_query[0][field]=slug&tax_query[0][operator]=IN&tax_query[1][taxonomy]=topics&tax_query[1][terms][]=media&tax_query[1][field]=slug&tax_query[1][operator]=NOT%20IN

It will work if used inside query_posts() but will not work at all if appended to the url.

I visited the sample sites you referred to in your article;
http://popcritics.com/
http://vitalventure.gmri.org/activities/
and of course wordpress.tv

Among these 3, the vitalventura ( http://vitalventure.gmri.org/activities/ ) really took the custom taxonomies to the next level by providing **filter by multiple terms/taxonomies** functionality. I don’t know how they are pulling this off though. No clue as the URL does not change..

For example, one can visit this page ( http://vitalventure.gmri.org/activities/ ) and then check boxes titled as “Five” and “Six” from the Grade Level Taxonomy and the check box titled “A. Unifying Themes” term from the “SCIENCE & TECHNOLOGY THEMES” custom taxonomy, and as a result, you will get to see the activities filtered down by FIVE, SIX & A. UNIFYING THEMES. If one had to create a unique link ( to put it into the custom menu for example ), would that be possible to build an SEO and developer friendly query string and WP does the rest?

Other sites, are doing it all one dimensional. Once you click on a term under any given taxonomy, you only get a vertical view of all posts that’s been tagged ( or should we say clever tagged ) by that term. and the URL is easy to figure out; you are gonna get something like http://vitalventure.gmri.org/?grade=5

Can I custom crft a URL, so that WP automatically gives me the results of all posts from Categories Cat1 and Cat2, which are also tagged under Places ( a custom taxonomy ) as Place1 and Place2, and also been tagged under People ( yet another custom taxonmy ) as People1 and on top of all that, are also tagged ( general tag taxonomy ) as Tag1 or Tag2. Can such a URL be craftable sometihng like

yoursite.com/?places=place1,place2&people=people1,tag=tag1,tag2,category=cat1,cat2 Or is this too much of a stretch of imagination? if so, how will WP know where to use “AND” and where to use the “OR” from the query string? How would you about something like that?

Sport
– basketball
– soccer
– baseball
– football

In this example, if you were to create Media Type with Videos, Articles, Pod Casts, Picture Gallery etc, would you use Media Type as a seperate taxonomy ( just like Sport being a separate taxonomy ) and then Videos, Pod Casts etc as terms on Media Type

or…

would you create a category ( right next to Bloopers ) and add Media Type as a category and Videos, Pod Casts as Sub category? Which one is going to give you the faceted navigation?

To be honest with you it is rather hard for me to follow the rest of your post, But I’ll do my best to respond. If I were creating a site that was essentially a sports magazine. I would first think about all of the categories that I would like to create. These might be “Interviews”, “Game Highlights” and “Bloopers”. I would then create these as categories. IMHO categories should be used to define the main organizational structure of a website. My sports site might only ever have these three categories, if I decide to add more, it is simple. Most sites that I have created have fewer than 10 categories.

The next thing that I would do is to create a custom taxonomy named “Sport” I would then add to this taxonomy the following terms (which we can refer to simply as “sports”): basketball, soccer, baseball and football. These are the sports that I plan on writing about so there is no need to ad more.

I would not use tags at all, this is just me though :)

Now we have two taxonomy systems that we can use to organize our posts:

Category
– Interviews
– Game Highlights
– Bloopers

Sport
– basketball
– soccer
– baseball
– football

Now if I were to write a post about about how Kobe Bryant tripped over his shoelaces and did a swan dive into the cheerleaders, I would “put” the post in the “Bloopers” category and assign it to sport called “basketball”.

At this stage I might wonder if my magazine could be organized better. It might be a good idea to create another taxonomy for “players” or better yet “athletes”. I would then add Kobe Bryant to the athletes taxonomy and associate the aforementioned post with the Kobe Bryant athlete because the post is mostly about him.

What benefits does this have over using a complex category system with many hierarchical associations? Well, in WordPress 3.1 you will be able to query for multiple taxonomies at the same time So you could easily find all interviews with Michael Jordan as a basketball player – this would be a separate list from all interviews of Michael Jordan as a baseball player. The possibilities are only limited to your imagination and organizational skills.

I should have coined the question differently. Sorry about the use of the word “category”. Here is my second attempt asking it in a different way. This is all in an effort to understand the killer difference in between wordpress’s out of the box hierarchical taxonomy called “category” and any custom taxonomy that the user may choose to create to do the somewhat same thing.

Here we go:

Let’s assume that WP does NOT come with any hierarchical taxonomy. So, “Add Category” button does not appear on the dashboard.

And when a user is in need of creating a post, WP ask him/her to create a taxonomy system to put the post in. So he comes up with a name; “Section” ( notice I deliberately pick this word for the question purposes since the word “section” is a synonym of the word “category” just to make a point that his intentions is the same in creating that particular “bucket”. ), so he picks the word “section” exactly to mean “category”. But in order to do this, he goes in the functions.php and add that register_taxonomy code along with the necessary. And, as a resolt, on the admin dashboard, he now sees the link “Add a section”. He then names the section ( the section custom taxonmy ) as “Topics” and then he starts dumping some posts. To complete our small case, let’s say
he adds a post in regards to “David Beckham’s coming to LA”. Because he *must” classify this post into a pocket ( WP will force him to do so ), he finds himself creating some sub buckets.. One way would be to take this parth; Topics > Sports > Soccer. And for that, he creates the following sub hierarchies. Topics > Sports > Soccer. And then he puts the post in it and then tags it as “Beckham”. Then he goes on to the next post which happens to be dealing with say, “Kobe”. For that, he creates the Topics > Sports > Basketball bucket and then he tags the post under “Basketball” as “Kobe”.

At this point, I’d like to ask maybe simple but terminology-wise important question;

What’s the name of his main custom taxonomy?
Is it “Section” or or is it “Topics”?

How about the items captioned as “Sports” and “Soccer”, “Basketball”?
Are they taxonomies too? Or are they better called “sub custom taxonomies”?
Or should we call them as “Terms” or even better “Terms under custom taxonomy of Soccer” or perhaps, “Terms under custom taxonomy of Topics”. I’d really appreciate it if you could clarify this simple stuff first.

With that, let me ask the main question.

Let’s assume that he did not go for the custom taxonomy path since he thought the good old “category” approach is just perfect for what hw wants to do. This apprach is the familiar approach anyway, cause it is always there and it is the instinctive one. But, …. I’d like you to compare this with the custom taxonmy way. Functionality wise what would be the short comings with choosing one as opposed to the other?

For that, I will make the example as close as possible to the above example. In this scenario, once he clicks the “Add a Category” link on the dashboard and he names it as “Topics”. Let’s pause for a moment here and get this out of the way? Did he created a category called “Topics” or did he create a term called “Topics” under a taxonomy which comes built in with WP as “Categories”. Believe, seeing the things in the right way makes a hell of a difference in understanding these matters. Forgive me everybody, if this level of questioning you think is not needed here. For me, it is. Going on, he a creates a sub category called “Sports” and then two siblings under the “Sports” as “Basketball” and “Soccer”. After that, he categories the Beckham post obviously under the Soccer category while tagging it as “Beckham”.

Now, what are the key differences in these drastically two different approaches? – where the intent is obviously the same.

If the good old built in taxonomy category approach is better than creating the custom taxonomy called “Section”, then, when do creating custom taxonomies starts yielding some advantages over the cats?

Let’s add the Media type into the equation. Maybe that’s going to help.

Let’s say the post about the Beckham was a video and the Kobe’s one was an article. And the site owner decides to also provide a Faceted Navigation option into his site, to capture a different mind-setted crowd from his audiuence whi may be interested in seeing his site from a Media Type point of view such as let’s see what videoes does this site has?
The intent here is to create a “faceted navigation” without duplicating any data and harvesting the same data for different point of views. Going back to our first example, (where he created the custom taxonomy called section” ), he opts in for another one, another custom taxonomy and he names that one as “Media”. And then, he creates the 2 sub hierarchies as “Video” and “Articles” right beneath. ( He can do so because with register_taxonomy, he specified hierarchial as “TRUE” ). And while he was creating the Beckham post, he *not only* classifies it under the “Section custom taxonomy” as topics > sports > soccer *but also* classifies it as “Media” custom taxonomy as Video.

Now let us compare/contrast this with the category way.

He could have certainly ( and most instinctively likely ) to go with creating a category. Because in our example two above, our guy did not deal with any custom taxonomy, he had added “Topics” as a category right from the get go. With that in mind, he now finds himself adding another top level category ( right at the same level as “Topics” ) and then he names it as “Media” and then he creates two sibling sub categories beneath “Media” as “Video” and “Articles”.

If were to compare these approaches, what do you say? They almost seem identical semantically. But WP wise, what are consequences in differences?

I’m very sorry about this long post. I hope it will prove to be a useful one.

I’ll try to answer your other question to the best of my ability, but I will use a custom hierarchical taxonomy named Topic as an example and compare/contrast with categories.

1. Categories are required. This means that every post you publish must be in a category. If one is not chosen, WordPress will add the post to the default category. Topics are not required therefore, if you forget to assign a topic to your post, WordPress will do nothing.

2. Categories are intended to be used to organize posts. It is is your best interest not to hack WordPress into sharing the categories with other post types (pages, attachments, custom…). Custom taxonomies however can be applied across post_types allowing you to share terms.

3. The url structure is very similar:

Category: /category/code-snippets/
Topic: /topic/jquery/

In my opinion, custom taxonomies are best used to achieve a higher level of abstraction in organization than possible using categories and tags alone.

If I create a custom taxonomy called “category” or “Categories”. what would be the technical differences ( the pro’s and con’s ) when that particular custom taxonomy is compared with the built in “categories” that come with WP out of the box?

URL’s wise, functionality wise… what do you say?

how does that work?
Denis