By Daniel Terdiman

Staff Writer, CNET

It may sound like another language, and in a way it is: Flickr is a popular photo-sharing service that allows anyone to view most of the more than 50 million member-submitted images it hosts. Tags, meanwhile, are the searchable keywords the individuals can assign to either their own images or to those of nearly anyone else that say something about the information–the defining characteristic of Flickr and a growing number of other online services.

“In Flickr, tags worked because they were fundamentally social,” said Stewart Butterfield, Flickr’s co-founder. “By agreeing on a tag in advance, users could collectively curate collections of photos in a dead simple way. Now we see people announcing at events, ‘The tag for this is baychi05’ and stuff like that.”

The idea behind tagging may be irresistibly simple, but its ramifications are enormous and complex. For more than a decade, the primary way to categorize and find information on the Internet was through the automated algorithms of search engines, a process at once laborious and highly imprecise. Tagging has quickly gained popularity because it allows human beings to bring intuitive organization to what otherwise would be largely anonymous entries in an endless sea of data.

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Also known as “folksonomies,” tagging systems are usually created by users themselves, rather than site owners, and make many online services far more accessible and useful than they had ever been before. The practice brings a social context to such resources as blogs, shared bookmarking, photography and even books.

Moreover, beyond its practicality, others find a philosophical significance in tagging because it is consistent with the social thinking often associated with the beginnings of the Internet. What many fans of tagging like best is that it is a system that empowers individuals. And after years of users trying to find their way around Web sites using categories defined by a small number of people running those sites, tagging is a huge relief.

Tag, you’re it

“Tagging” is a term used to describe human indexing of material on the Web, which in theory makes content more intuitively found and shared. Tagging systems are also known sometimes as “folksonomies”–a combination of “folk” and “taxonomy”–as well as “shared bookmarking.”

“We’ve had this decades-long program of top-down metadata. People (were asked) to go out and become familiar with one ontology and to make sure data is categorized like this. But people are not very good at this,” said Cory Doctorow, an editor of the technology culture blog BoingBoing and the European outreach coordinator of the Electronic Frontier Foundation. “I think what’s completely right about folksonomies is asking people to do something for their own benefit, to have them organize their own information and then find the accidental or fortuitous positive externalities.”

Because tagging is used as an indexing tool and as a way to search for information, both in discrete databases or across the Internet, some say it is conceivable that the technology could one day give search engines like Google a run for their money.

Brad Hill, an author who has written about search engines, sees tagging at this stage as a tool for collaborative social use, not for universal searching. But he added that tagging could become so deeply embedded in the social fabric that “tag clouds”–large groupings that collectively cover many areas of information–could one day become the first search choice for many people.

“A critical mass of users might be reached where it would make as much sense to go into a gigantic tag cloud as it would to go into a search engine,” Hill said. “It’s an intriguing idea, but it is probably pretty far off.”

Others fear that tagging systems may be hijacked by large corporate interests to the point where their value is lost or diluted.

One Flickr group objected when Yahoo bought the service and promptly announced that all members would be required to have a Yahoo account by sometime next year. Primarily, the group is worried that Yahoo will take their registration information and sell it to advertisers, as the company does with data from its many other services.

“Yahoo is trying to use all its different services to expand its user base,” said Ville Oksanen, who is spearheading the protest. “If the company wants to keep customers happy, they should make it possible for Flickr customers to stay (just) Flickr customers.”

Such sentiments are not uncommon among tagging communities, whose members can be passionately protective of the systems they use. Because of the value they add to information available to everyone, many see tags as one of the rare kinds of metadata large numbers of people have an incentive to create.

“It’s the small element that individuals use for their self-interests,” said “Smart Mobs” author Howard Rheingold, “that aggregates into something that returns value that nobody put into it individually, but everybody put into it.”

Butterfield noted that more than two-thirds of all Flickr images have been tagged by members and can be quickly sifted out of the digital haystack by someone who has an idea what they’re looking for. For example, fans of Nevada’s Pyramid Lake could search on Flickr and discover that 80 images in the database are currently tagged by users with the term “Pyramid Lake.”

Flickr is often cited as an emblem of tagging’s success–especially so since it was purchased by Yahoo. But countless other sites, blogs and services have adopted the practice. Other sites that rely heavily on user-created tags include the social bookmarking service Delicious, the community blog MetaFilter and the blog search site Technorati.

The open-source, free encyclopedia, Wikipedia, defines folksonomies as a “neologism for a practice of collaborative categorization using freely chosen keywords.”

“Now we see people announcing at events, ‘The tag for this is baychi05’ and stuff like that.”

–Stewart Butterfield, co-founder, Flickr

“I’ve got about 400 to 600 diaries a day, and you’ve got this crush of information and people clamoring to organize it,” said Markos Moulitsas, founder of political blog Daily Kos. “It’s a serious problem trying to categorize the amount of information on the site. There are millions of words. How do you organize it?”

The answer came earlier this month with the introduction of tagging on the site. “Unlike categories, which force people to fit their content into a small number of content groupings, tagging allows registered users to categorize not just their own diaries, but those of anyone else’s on the site, with as many keywords as necessary,” Moulitsas informed Daily Kos’ readers with its tagging debut on Oct. 10.

Technorati, a site that indexes blogs, is trying to elevate tagging to the next level. CEO David Sifry explained that his company had recently begun allowing people to tag not only specific blog entries, which had been possible since January, but also to tag entire blogs. Thus, he said, readers can now divine more context about blogs, especially when multiple users tag a site and do so with multiple tags.

A blog might be tagged with the keyword “nanotechnology,” for instance, but because individuals might also assign one blog with tags like “biotech” or “bioinformatics” and another with “cyberlaw” or “antitrust,” it gives searchers information at a glance that can tell them specific things about that site.

“You immediately get to slice and dice what’s going on right at this moment,” Sifry said, “in different communities about that topic.”

It is for reasons like this that John Battelle, author of “The Search,” believes that tagging systems will eventually be subsumed by traditional search engines. “Anything that makes search better is going to be voraciously swallowed up by the larger search players,” he said. “It’s one of a number of reasons why Yahoo bought Flickr. It’s one of a small number of reasons why people are investing in Delicious and Technorati, and it will make search better.”

And because many corporations are beginning to implement tags internally, the question is whether the technology can in and of itself be the basis of a business plan. Kevin Marks, a principal engineer at Technorati, said that probably won’t happen anytime soon, adding that “it’s not so much a product as a feature and a mindset.”

To that end, tags will undoubtedly prove valuable in giving companies new ways to get a handle on the immense amount of information they have to coordinate.

“In a corporate environment, the interests are narrower than all the human interests on the Web and the vocabulary becomes narrower,” said Dave Weinberger, a fellow at the Harvard Berkman Center. “If it’s a plastics company, and someone uses the term ‘mold,’ there’s a much greater chance they’re talking about injectable mold, so the ambiguity problem gets easier too.”

Sifry used the example of an automobile company trying to merge German and American divisions and the attendant problems of information sharing it could cause. By implementing a tagging system which encourages employees to assign multiple tags to documents, the company could begin to build a bridge between documents in German and English that might never be crossed otherwise, he said.

“It makes a linkage between two disparate systems,” Sifry said.

Thomas Vander Wal, the information architect credited with coining the term “folksonomy” noted that he’d heard about a consortium of museums looking to create a tagging project for works of art. He explained the idea would be to give museum patrons the power to assign tags to art and thus to provide more context, through the use of multiple tags, for people trying to understand certain works.

“It’s essentially to figure out the vocabulary that regular people use, or just a cross-section of people would use, to describe art works,” Vander Wal said.

“You immediately get to slice and dice what’s going on right at this moment in different communities about that topic.”

–Dave Sifry, CEO, Technorati

The philosophical concepts behind tagging are even manifesting themselves out of the online world and into the realm of the physical.

Jane McGonigal, who works for 4orty2wo Entertainment, a so-called experience marketing firm, recently undertook a project called the Ministry of Reshelving. She explained that the idea was to challenge the common categorization of the George Orwell classic, “1984.”

Participants across the United States were encouraged to go to bookstores and move copies of “1984” from their traditional “fiction” or “literature” placement to new sections. McGonigal suggested “current events,” “politics,” “history,” “true crime” or even “new nonfiction.”

In each case, those who moved a copy of the book were told to leave behind a leaflet explaining that “1984” had been reshelved and that the Ministry of Reshelving was “dedicated to the proper classification of fiction and nonfiction texts.”

“We called it folksonomy mobs,” McGonigal said, “coordinated acts of re-tagging or reclassification in public spaces.”

McGonigal is also a fan of tagging online and said that on sites like Flickr, tags on photographs are a way for people to show they are interested in the work of others.

“When I go to Flickr and I tag people’s photos, it’s to show them that I care,” she said. “It’s like a hug.”