Last week, Yahoo blogged about yet another microformat theyll be indexing: Common Tag. Based on RDFa, Common Tag is . . . well . . . kind of like every other semantic microformat out there.

Common Tag is integrated with Zemanta, Adaptive Blue, Yahoo Search Monkey and several other services. In addition to organizing web pages by their meanings, Common Tag can also bring more related content to publishers, and possibly also greater visibility (the Yahoo connection). Yeah, it looks cool, but its going to take some serious time and effort before theyll see enough widespread adoption to make a difference.

At Search Engine Land, Vanessa Fox points out that this wave of the future is still pretty far off for search engines:

Both Google and Yahoo have told me that they could use metadata in web search in the future, if it proves to be useful and they can safeguard against spamming. So far, this hasnt happened.

She also points out that the parallels between this type of semantic tagging and an earlier version were all familiar with"the meta keywords tag (speaking of spamming!):

The idea of using meta data to tag web pages in order to describe them to search engines isnt new, of course. The meta keywords tag has been around since at least 1995. And its easier to adopt than Common Tag. . . .

Indeed, Yahoo supported the meta keywords tag initially (and to some extent, still does), but when Google launched, they did not. It was too easy for site owners to stuff that tag with anything they wanted, rather than the true focus of the page. Search engines use smarter methods (starting with the content on the page and how external sites link to it) for determining relevance.

Vanessa also points out research that indicates that link anchor text was a better signal for relevance than even the popular tagging site Delicious.

So, seriously, why would Yahoo want to invite what might turn out to be just more spam? Vanessa wonders if theyre getting out of the consumer search business, what with all the microformats theyre pushing these days (hCard, hCalendar, hReview, hAtom, XFN, Dublin Core, Creative Commons, FOAF, GeoRSS, MediaRSS, RDFa, and OpenSearch). Is this indicating a move toward a structured data search or a push for third-party search engines using Yahoo BOSS? What do you think?

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