PermaLinks, Purple Numbers, and the Semantic Web

I recently found the pages on Microformats, which led me to the discussion of "Plain Old Semantic Web" (POSH). (That's by far the best discussion I've seen on the subject. It doesn't even mention the idiotically arbitrary non-distinction between <b> and <strong>, instead focusing on far more important distinctions for semantic processing.)

On the page that talks about using id attributes, it mentions that they function as anchors! (I of course knew of the syntax, but only just know found out about the semantics.) Using them cleans up the HTML considerably,
especially if you use rollover effects for links and forget to close an anchor tag (the rollover applies to
all text from <a name=""... until the next <a...).

The page then goes on to illustrate the addition of a permalink, using a tag at the end of an entry:

  <div class="entry" id="e000501">
  <a href="#e000501" title="Permalink" rel="bookmark">#</a>

(Interestingly, rel="bookmark" is recommended--perhaps because it distinguishes that link from navigational
links. But there is no discussion of the use case that makes it important.)

The hashmark, of course, had its origin in Doug Engelbart's "purple numbers", originally showcased in his 1968 demo! In 2004, or thereabouts, Chris Dent led the charge to bring purple numbers to the web in a big way. The Purple Wiki pages at Eugene Kim's BlueOxen site also used that strategy.

But creating numbers for things gets to be a pain--especially when you make revisions and have to figure out the next available number to use. So someone came up with the "purple pilcrow" (a reversed paragraph mark that turns out to be one of the special characters you can specify with a number). I'm not sure if it was Tim Bray's invention, but he certainly blogs about why using that character makes more sense than a number. (He uses them, too. They're almost invisible. But if you look hard, you'll see them.)

The lost somewhere in the mists of time, someone came up with the idea of using a hash mark . That seems to be
the winning idea, since it is a standard keyboard character that means "number" in many settings. So just in case you were wondering where they came from, now you know!



Hi Eric! Glad to see that you're blogging, and even happier to see that you're bringing attention to purple numbers.

Just to clear up some factual errors, while "purple numbers" as a concept emerged from Doug Engelbart's original hypertext system, they didn't actually become purple until the mid-1990s, and they didn't appear on the web until 2000. I was the first person to write software for generating purple numbers on the web (at Doug's urging), and Chris joined me in the cause in 2002, when we wrote PurpleWiki and started Blue Oxen. A more complete history is at:

Regarding pilcrows and hash marks: The intention behind those characters have nothing to do with the difficulty of generating new numbers. Generating numbers is easy. The problem is with how you display that information to the user. Chris and I were well aware of the intrusiveness of purple numbers, especially as they got larger, but for us, that was a feature, because we wanted to build awareness around the concept of granular addressability. We actually switched to hash marks in PurpleWiki for a while, then actually switched back to the numbers, because people found them useful for human addressability as well. Tim Bray was the first to use pilcrows for display, and Simon Willison's CSS hack popularized them. I actually like Simon's hack a lot.

Posted by Eugene Eric Kim on January 14, 2008 at 06:32 AM PST #

Thanks much for the corrections, Eugene. That's a terrific perspective on what actually happened, and whodunit.

Folks should also know that after working with Doug Engelbart closely for a time, you set up Blue Oxen Associates ( precisely to do research and consultation, focusing on the knowledge processes that are key to collaboration.

Posted by Eric Armstrong on January 14, 2008 at 08:11 AM PST #

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