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[FYI] Machine Tags

From: Karl Dubost <karl@w3.org>
Date: Mon, 5 Feb 2007 12:56:31 +0100
Message-Id: <DAD7737E-E7C3-47D5-8CB6-DAEFAC8AA87B@w3.org>
To: public-rdf-in-xhtml task force <public-rdf-in-xhtml-tf@w3.org>


It is not directly related to RDFa but it has connections

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# What are machine tags?

Machine tags are tags that use a special syntax to define extra  
about a tag.

Machine tags have a namespace, a predicate and a value. The namespace  
defines a class or a facet that a tag belongs to ('geo', 'flickr',  
etc.) The predicate is name of the property for a namespace  
('latitude', 'user', etc.) The value is, well, the value.

Like tags, there are no rules for machine tags beyond the syntax to  
specify the parts of a machine tag. For example, you could tag a  
photo with :

* flickr:user=straup

* flora:tree=coniferous

* medium:paint=oil

* geo:quartier="plateau mont royal"

* geo:neighbourhood=geo:quartier

Flickr has already used machine tags, informally, on a couple of  
occasions :

- When we launched Maps, we provided a way for people who had
"geotagged" their photos to import their location data. This was
done using the "geo:lat=..." and "geo:lon=..." tags.

- When a user tags an event with an upcoming ID (for example :
"upcoming:event=81334") we display a link back to the upcoming.org
site. A similar example is the excellent "Flickr Upcoming Event"
greasemonkey script :


Dan Catt wrote a very good piece about machine tags - he called them  
"triple tags" - last year :


Update : Dan's gone and written another excellent piece about all of  
this stuff now that we've launched machine tags:



# What is the spec for machine tags?

Machine tags are divided in to three parts :

1) A "namespace" :

Namespaces MUST begin with any character between a - z; remaining
characters MAY be a - z, 0 - 9 and underbars. Namespaces are

2) A "predicate" :

Predicates MUST begin with any character between a - z; remaining
characters MAY be a - z, 0 - 9 and underbars. Namespaces are

3) A "value" :

Values MAY contain any characters that a "plain vanilla" tags
use. Values may also contain spaces but, like regular tags, they
need to wrapped in quotes.

Namespace and predicates are separated by a colon : ":"

Predicates and values are separated by an equals symbol : "="

For example :

* flickr:user=straup

* geo:locality="san francisco"


# Why can't I use non-ASCII characters for namespaces and predicates ?

Simple steps, first.


# Can I define another machine tag as the value of a machine tag?

Sure, but it will not be processed as a machine tag itself.


# How do I add machine tags?

By adding tags! No, really.

Machine tags are added *exactly* the same as any other tag whether it  
is done through the website or the API.

When the Flickr supercomputer processes your tags, we take a moment  
to check
whether it is a machine tag. If it is we leverage the powerful Do  
What I Mean engine to, well, do what you mean.


# How do I query machine tags?

Via the API!

Specifically, using the "machinetags" parameter in the  
'flickr.photos.search' method. Like tags, you can specify multiple  
machine tags as a comma separated list.


# Can I query the various part of a machine tag?

Yes. Aside from passing in a fully formed machine tag, there is a  
special syntax for searching on specific properties :

* Find photos using the 'dc' namespace :

{"machine_tags" => "dc:"}

* Find photos with a title in the 'dc' namespace :

{"machine_tags" => "dc:title="}

* Find photos titled "mr. camera" in the 'dc' namespace :

{"machine_tags" => "dc:title=\"mr. camera\"}

* Find photos whose value is "mr. camera" :

{"machine_tags" => "*:*=\"mr. camera\""}

* Find photos that have a title, in any namespace :

{"machine_tags" => "*:title="}

* Find photos that have a title, in any namespace, whose value is  
"mr. camera" :

{"machine_tags" => "*:title=\"mr. camera\""}

* Find photos, in the 'dc' namespace whose value is "mr. camera" :

{"machine_tags" => "dc:*=\"mr. camera\""}


# Is there a limit to the number of machine tags I can query?

Yes. The limit depends on the tag mode (ALL or ANY) that you are  
with. "ALL" (AND) queries are limited to (16) machine tags.  
"ANY" (OR) queries are limited to (8).


# Can I do range queries on machine tags?

No. Not yet, anyway.

It is a hard problem for reasons far too dull to get in to here. It's  
on the list.


# Are machine tag namespaces reserved?

No. Anyone can use a namespace for anything they want.

If you are concerned about colliding namespaces you should consider  
adding an additional machine tag to define your namespace. For example :


Like tags, in general, we expect (hope?) that the community will  
develop its own standards by consensus over time.


# What about all the machine tags that are already in the Flickr  

At the moment, they are still treated as plain old tags.

We have plans to go back and re-import them as machine tags but for  
now, only new tags will be processed as machine tags.

In the meantime, if you re-save a machine from the 'edit this tag'  
page it will be re-imported as a machine tag.


# Is the predicate *really* a predicate?

You are in a dark cave. In the corner is a fire and a man making  
bunny shadows on the wall with his hands. Whether or not it's really  
a 'predicate' depends on how much time you spend on the semantic-web  
mailing list. ;-)

It's close enough to being a predicate that it makes for a good short- 


# Wait, aren't machine tags just RDF?

No, machine tags are not RDF; they could play RDF on television, though.

See also :



# Huh, what is RDF ?

RDF Describes Flickr. That's really all you need to know about RDF.

Karl Dubost - http://www.w3.org/People/karl/
W3C Conformance Manager, QA Activity Lead
   QA Weblog - http://www.w3.org/QA/
      *** Be Strict To Be Cool ***
Received on Monday, 5 February 2007 11:56:58 UTC

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