harvard - Dave's Blog

Tag Metadata in Feeds

2008 Aug 25, 10:13

As noted previously, my page consists of the aggregation of my various feeds and in working on that code recently it was again brought to my attention that everyone has different ways of representing tag metadata in feeds. I made up a list of how my various feed sources represent tags and list that data here so that it might help others in the future.

Tag markup from various sources

Source	Feed Type	Tag Markup Scheme	One Tag Per Element	Tag Scheme URI	Human / Machine Names	Example Markup
LiveJournal	Atom	atom:category	yes	no	no	, (source)
LiveJournal	RSS 2.0	rss2:category	yes	no	no	technical (soure)
WordPress	RSS 2.0	rss2:category	yes	no	no	, (source)
Delicious	RSS 1.0	dc:subject	no	no	no	photosynth photos 3d tool (source)
Delicious	RSS 2.0	rss2:category	yes	yes	no	domain="http://delicious.com/SequelGuy/"> hulu (source)
Flickr	Atom	atom:category	yes	yes	no	term="seattle" scheme="http://www.flickr.com/photos/tags/" /> (source)
Flickr	RSS 2.0	media:category	no	yes	no	scheme="urn:flickr:tags"> seattle washington baseball mariners (source)
YouTube	RSS 2.0	media:category	no	no	no	label="Tags"> bunny rabbit yawn cadbury (source)
LibraryThing	RSS 2.0	No explicit tag metadata.	no	no	no	n/a, (source)

Tag markup scheme

Tag Markup Scheme	Notes	Example
Atom Category atom:category xmlns:atom="http://www.w3.org/2005/Atom"	category/@term Required category name. category/@scheme Optional IRI id'ing the categorization scheme. category/@label Optional human readable category name.	term="catName" scheme="tag:deletethis.net,2008:tagscheme" label="category name in human readable format"/>
RSS 2.0 category rss2:category empty namespace	category/@domain Optional string id'ing the categorization scheme. category/text() Required category name. The value of the element is a forward-slash-separated string that identifies a hierarchic location in the indicated taxonomy. Processors may establish conventions for the interpretation of categories.	domain="tag:deletethis.net,2008:tagscheme"> MSFT
Yahoo Media RSS Module category media:category xmlns:media="http://search.yahoo.com/mrss/"	category/text() Required category name. category/@domain Optional string id'ing the categorization scheme.	scheme="http://dmoz.org" label="Ace Ventura - Pet Detective"> Arts/Movies/Titles/A/Ace_Ventura_Series/Ace_Ventura_-_Pet_Detective
Dublin Core subject dc:subject xmlns:dc="http://purl.org/dc/elements/1.1/"	subject/text() Required category name. Typically, the subject will be represented using keywords, key phrases, or classification codes. Recommended best practice is to use a controlled vocabulary.	humor

Update 2009-9-14: Added WordPress to the Tag Markup table and namespaces to the Tag Markup Scheme table.

feed media delicious technical atom youtube yahoo rss tag

Date Time Formats

2007 Sep 27, 2:17Starting on a new simple project I wanted to get the history of my Delicious links. Delicious has an export tool available via the settings section so I thought I'd try that. However, the links aren't exported in XML not even in XHTML but rather in HTML. Shocking. An example:

"Don't Tase Me, Bro!" (UF Student Tasered Remix)

Remix of the 'Don't tase me, bro!' guy getting tasered.At this point I'm already not going to use this file because its in HTML but I'm even more disgusted by those date time values. Raymond Chen of the Old New Thing posted about recognizing timestamps and timestamp sentinel values. From the first blog post and with the use of a calculator for base conversion one can tell that those are UNIX style timestamps counting the number of seconds since 1970.

It reminds me of my hatred for the MIME date time format I developed working on my webpage's server side parsing of atom and RSS. Atom is of course my favorite as Atom uses the Internet date time format described in the following documents. Here's an example of one 2007-09-27T020:50:00.000-08:00

• W3C Recommended Date and Time Format
• IETF: Date and Time on the Internet: Timestamps
• XML Schema dateTime

On the other hand the evil and villainous RSS uses the MIME date time format now described in the more recent IETF MIME standard. Here's an example Thu, 27 Sep 2007 20:50:00 -0800
The Internet date time format has the advantage of being so easy to sort. An alphabetic sort with normal C-style collation rules of strings containing Internet date times will also sort them chronologically. This is not the case for the MIME date time due to the preceding day of the week and the spelled out month name. This also means that when producing these you have to figure out the day of the week and when parsing them you have to match month names rather than just parsing out numbers. Anyway now days if I see mention of a date time in a new proposed standard or spec I be sure to point out the numerous advantages of the Internet date time format.

date xml html feed time technical date-time code atom rss

Commenting Wishlist

2007 May 1, 4:33In the past I've come up with ideas for software and find that the very idea is implemented soon after. So this time rather than getting down about it I'm going to make it work for me. I'll state what I want to use and hope that its magically implemented. In order to uniformly support comments on my website I want a web service with the following features:

• Allow users to view and add comments for any particular URI.
• Use OpenID and optionally Card Space to identify users.
• Use a captcha system that's optionally cute or humorous.
• Has atom or rss feeds of the comments available.
• Doesn't require users to register.
• Doesn't require any extra steps for commenting on a URI that no one has commented on.

I'm going implement this now so no one go off and do it before me so that I can use it without having to do anything...technical homepage