Wildcard Machine Tag URLs

This post was originally published on the code.flickr.com weblog in July, 2008.

If you’re not already familiar with machine tags the easiest way to think of them is being like a plain old tag but with a special syntax that allows users to define additional structured data about that tag. In turn the magic space hamsters that run the site have been trained to recognize, index and allow for searches across multiple facets of a given machine tag.

Machine tags have three parts : a namespace which is like a subject or a topic; a predicate which is a like a property of that topic; a value which is … well, a value. For a more thorough introduction to the subject I’d recommend reading the announcement we made in the Flickr API discussion group when machine tags were first added to the site. If you’d like to know even more, after that, there is good collection of links available on del.icio.us.

Which brings us to the part where I tell you that we’ve added the ability to search for machine tagged photos in plain old tag URLs (as well as in tag searches on the Flickr search page) using the facetted query syntax that has always been available in the API. For example :

• All the photos tagged “flickr:user=bees”, aka Cal :

  http://www.flickr.com/photos/tags/flickr:user=bees

That’s a trick, really. You’ve always been able to do this since machine tags are just tags. The New-New means you can be even more granular in what you are looking for. How about :

• All photos with Flickr users :

  http://www.flickr.com/photos/tags/flickr:user=

• Or Upcoming.org users :

  http://www.flickr.com/photos/tags/upcoming:user=

• Or even Facebook users :

  http://www.flickr.com/photos/tags/facebook:user=

• Or simply all users regardless of service (or namespace) :

  http://www.flickr.com/photos/tags/*:user=

• Maybe, all the photos in the flickr namespace :

  http://www.flickr.com/photos/tags/flickr:*=

• But, seriously, back to Cal : Cal, across services (or namespaces) :

  http://www.flickr.com/photos/tags/*:user=bees

• All Cal. All the time :

  http://www.flickr.com/photos/tags/*:*=bees

• And no, you can not do this. No ponies for you if you try :

  http://www.flickr.com/photos/tags/*:*=

The wildcard URL syntax is also available for an individual user’s tags :

• These are all my photos that have been machine tagged with either a Geonames, Places or GeoPlanet (née Where on Earth) locality ID :

  http://www.flickr.com/photos/straup/tags/*:locality=

• Or photos in the George Eastman House’s photostream that were developed using the daguerrotype process :

  http://www.flickr.com/photos/george_eastman_house/tags/photo:process=daguerreotype

Now for the list of caveats and Known-Knowns :

• At the moment it is still not possible to poke around the hierarchy of a given machine tag : all the predicates for a namespace; all the unique pairs of namespace and predicates; that sort of thing. It is On The List [FIX:trade] and hopefully we can offer up something for you to play with, even if it’s just in the API to start with, shortly.

• Values in wildcard URLs should are treated the same way regular tags are in URLs. That is “san francisco” becomes “sanfrancisco” or in machine tag speak : *:*=sanfrancisco.

• In the examples above, I’ve illustrated namespaces that are used to denote one service or another. It is important to remember that there are no rules about what can or should be a namespace. Like tagging, the hope is that the various communities will arrive at and adapt a consensus according to their needs.

In the meantime, kick back and enjoy photos taken by people on their Dopplr trips, photos by people who really really like airplanes or photos by people who are interested in possums (not to mention all manner of marsupials) or whatever else comes to mind!