I recently signed up for Jeremy Keith’s podcasting web app, Huffduffer. The sign-up form has
received a lot of buzz because of its “Mad Lib”-style design,
but what interested me was that after I created my account, I saw the
following in the lower right-hand corner of my profile page:
Huffduffer took the one web site URL I provided it with
(louissimoneau.com) and found just about every profile of mine, from every
social network or web application I’ve ever used. It’s not apparent in the
figure, but those links point to my profiles on those sites. How is this
possible?
Digging around through a number of Jeremy’s blog posts, I found that
he’s using the Google Social Graph API to gather this data. My web site
points to my Twitter, Last.fm, and FriendFeed profiles, and those in turn
(mainly FriendFeed) link out to all my other profiles. Google is able to
follow these links and know that they refer to other instances of me through
clever use of the XFN microformat (more on this a bit later).
Jeremy’s implementation, though definitely cool, is a little blunt.
Some people may object to having every single one of their web identities
listed on their profile, and as Google’s spider is relying on cached data,
some of the information may be out of date. For example, I deleted
interblag.tumblr.com years ago and it has since been picked up by another
individual.
I thought it might be a cool idea to try and develop a slightly more
sophisticated version of this functionality, and at the same time learn a
bit about how the Social Graph API works its magic. I’ll be using Ruby on
Rails for this implementation, but as the code is very simple you should be
able to adapt it easily to whichever platform you’re comfortable
with.
Before we go any further, it’s a good idea to step back and try to
figure out how this functionality is possible in the first place. How does
Google know that those other sites are also “me”? The answer is
microformats. If you’re a real HTML nerd or have a penchant for semantic
code, you’ll already know about microformats, but for the rest of us
here’s a quick catch-up course.
Microformats are just that: mini formats, which happen to sit inside
the larger format of HTML. HTML lacks a way, for instance, of indicating
that a link is pointing to a web site of an individual you’ve met in
person—that is, there’s no “met” attribute that would let you do:
<a href="http://somesite.com" met="true" />
This code, of course, is invalid. Fortunately, HTML has a few
attributes that can be co-opted for this purpose. class is the most obvious, but for links and
anchors we also have rel. For
example:
<a href="http://somesite.com" rel="met" />
This snippet of code, unlike the previous one, is perfectly valid.
This in and of itself may be of little value: at best you could use CSS to
give a different style to links pointing to people you’ve met. But if web
developers across the world agree on a way of
representing this information, suddenly the range of possibilities
explodes: a web spider can crawl links between people who’ve met each
other and construct a map of these relationships.
There are currently microformat standards for everything from
addresses (hCard) to friendships (XFN) to tags (rel-tag), as well as a
number of others currently in the draft stage.
Google is using the microformat standards XFN
(eXtensible Friend Network) and FOAF (Friend of a
Friend) to crawl networks of links. These links point to people
represented by URIs, and it’s the relationships between these people that
Google is attempting to figure out. FOAF is a slightly more complicated
format that involves creating a separate file detailing all your
friendships using XML; that’s unnecessary for our implementation so we’ll
just focus on XFN.
The most basic use of XFN is using rel=”me” in a
link to denote that the site being linked to belongs to the same person as
the site we’re on.
There is, of course, a problem here: this microformat data is only
present if a person has bothered to put it there. And only a small
percentage of web site owners even know what microformats are, let alone
use them on their sites. Well, the good news is that several large sites
and applications add XFN to links automatically. Last.fm and FriendFeed,
for example, both use this standard when you add links to your other
sites. So you may have a social graph without even being aware of
it.
WordPress blogs also make it easy to mark up links in this way.
Scroll down the page when adding a new link to your WordPress blog and
you’ll see the following:
Hence, even without widespread knowledge of microformats, it turns
out that there are a significant number of marked-up XFN links out in the
wild for the Google Social Graph API to spider.
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