Tagging in del.icio.us

del.icio.us is a social-­bookmarking application, the first of its kind and in many ways still the best. People use deli.cio.us to keep track of bookmarks, identified by URLs, and to follow other users’ bookmarks. Tagging is an important part of del.icio.us, which pioneered tagging in general and has done much to popularize it.

In the discussion of Flickr, I show how tagging enables textual searching and browsing of nonverbal objects such as pictures. Why would tags be useful in del.icio.us for categorizing web pages, whose primary constituent still tends to be text? Tags capture essentials about a web page that cannot be easily uncovered by full-­text searching. Useful tags might not even involve any of the words that are actually in the text of the web page. Tags often describe the relationship between the bookmark and the user (for example, the tag toread) rather than anything intrinsic to the web page. Nonetheless, you might get to the point in which computer summarization techniques could automatically generate tags for a given web page. For instance, Tagthe.net (http://tagthe.net/) provides such an API.

Note a fundamental difference between tagging in Flickr and del.icio.us: in Flickr, each object being tagged (a photo) has only one set of tags, created by the object’s owner and others granted permission to tag the photo. In del.icio.us, each object (a bookmark) being tagged could belong to many users, each having their own sets of tags. As Thomas Vander Wal explains, “broad” folksonomies such as that of del.icio.us (as opposed to the “narrow” folksonomies, such as Flickr’s) enable one to compare how different people tag the same object.[56]

Chapter 2 documented the URL language of del.icio.us. In this chapter, I describe more about the mechanics of adding tags and the issues of multiple-­word tags and multilingual tags.

Mechanics of Adding Tags in del.icio.us

Without the del.icio.us Firefox plug-­in, you can use the web site’s upload form:

  1. Go to http://del.icio.us/post/, enter the URL (for example, http://www.rubyonrails.org/), and hit the Save button.

  2. You will end up on a page that prompts you for the description, notes, and tags. Note that del.icio.us offers recommended tags and lists your tags, which are tags you have already used in del.icio.us—if any.

With the del.icio.us Firefox plug-­in (http://del.icio.us/help/firefox/extension), it becomes easier to push a link into del.icio.us. You can also use a bookmarklet to put in pages (http://del.icio.us/help/buttons) or get Internet Explorer buttons (http://del.icio.us/help/ie/extension).

Dealing with Case and Multiword Phrases

In contrast to Flickr, del.icio.us tags are single-­word labels. Tags in del.icio.us cannot contain any spaces, but they can contain punctuation. The example given in the documentation (http://del.icio.us/help/tags) is what to do with a multiword phrase such as San Francisco; the suggested tags are sf, san-francisco, SanFrancisco, san.francisco, or “whatever makes sense to you.” Does it matter which of these tags you choose?

Let’s gather some facts about how del.icio.us works with search phrases. There’s some documentation at http://del.icio.us/help/search, but you can also do a little experiment. Let’s look for San Francisco in del.icio.us. If you type San Francisco in the search box, selecting the option to search all of del.icio.us, you go here:


You can limit the domain of the search (to your own bookmarks, to all of del.icio.us, or to the Web). This search “goes through bookmark descriptions, notes, and tags.” You can limit the search to tags via a tag: prefix (tag:sanfrancisco):


What can you learn from this search?

  • The case of tags is preserved in how a tag is displayed (that is, if you enter SanFrancisco, it will stay SanFrancisco). However, searches for tags are case insensitive; that is, if you enter sanfrancisco or SanFrancisco, you still get the same tags (http://del.icio.us/tag/SanFrancisco).

  • On the other hand, punctuation is significant in search as well as in the display. Unlike Flickr, in which punctuation is stripped from the canonical representation of a tag, punctuation does not behave like whitespace.

In del.icio.us, because you can’t have spaces in tags, there are many variations in dealing with multiword tags. Returning to the example of San Francisco and the variants sf, san-francisco, SanFrancisco, and san.francisco for a minute, contrast the syntax of tags in del.icio.us and Flickr:

  • In del.icio.us, San Francisco is not a valid tag because it contains a space. sf, san-fran cisco, SanFrancisco, and san.francisco are all distinct tags.

  • In Flickr, San Francisco is a permissible tag. However, you cannot tag the same photo with any of the following variants (san-francisco, SanFrancisco, and san.francisco) because the punctuation is stripped away to determine the clean version of a tag.

Getting More Information

The http://tech.groups.yahoo.com/group/ydn-del.icio.us/ site is a good place to get answers to developer-­type technical questions. You’ll often see Joshua Schachter, the founder of deli.cio.us, actively answering people’s questions.

[57] http://api.flickr.com/services/rest/?method=flickr.tags.getListPhoto&api_key={api-key}&photo_id=368644336