As James Hendler pointed out in a recent article in AAAI magazine, the current web lacks typed links. I have an easy part-way solution to this problem. As an example, when people link to another site, they might mention that they agree or disagree with the site that they are linking to but a software agent would have to rely on natural language processing of the text surrounding the link to determine how they felt about the linked information. I propose adding a few attributes to <a href=...> links; for example:
<a href=... agreeWith="no">etc.
<a href=... businessPartner="yes">
<a href=... aFriend="yes">
<a href=... paidAdvertisement="yes">
These attributes would be ignored by web browsers, be easy for people to add if there were only a few accepted attributes for link types, and software agents could get some idea what the trust relationships, etc. are for the linked information.
PS. thanks to reader Faried for reminding me that MicroFormats.org already proposes the "rel" attribute that is similar to what I proposed.