May 26, 2003
blt (Blog Link Types) is a taxonomy of link types for web log links. I developed this selection of link type values to provide a complement to the type taxonomy described by Randall Trigg in Chapter 4 of his 1983 Phd thesis. The need for these additional links stems from a comment of Trigg's in section 4.5.7 of his paper: "At first glance it may seem strange that there are so many more critical link types than supportive ones. The reason for this stems from the relative information yield. A reader seeing a supporting comment, gains very little substantive knowledge (beyond learning that the original author has at least one backer). On the other hand a critique must convey a reason for the disagreement and so imparts to readers another side to the story. Thus it stands to reason that critical links require the richest structure." Web loggers tend to point out things that they like on the web more often than things that they don't like, so web log links need a richer selection of positive link types.
I came up with the types by analyzing about 150 links within a particular weblogging community: the O'Reilly Developer Weblogs. To demonstrate the mechanics of out-of-line link typing, I created an RDF file of types for these links; you can add to or download the collection yourself.
The addition of metadata to existing web links, with optional attribution of that metadata, just screamed RDF to me. Adding qualitative judgements, especially with the optional attribution, to existing web resources really goes back to the roots of the work that inspired RDF.
The namespace document describes the names in the http://www.snee.com/ns/blt namespace, a collection of names for typing links from weblog entries. There are two sets of names: names for the elements used for out-of-line assignment of link types to existing links, and link types themselves.
In-line link typing is easy to add with an attribute of the HTML A element that's been there since HTML's first DTD: the seldom-used REL attribute, which "gives the relationship(s) described by the hyperlink." I've been trying to use this to type the links in my weblog entries lately, and most of the links in this document have them. (Along with Trigg's link types and my blt types, you may find that the REL values enumerated in the XHTML documentation are useful as well.)
And remember: whether using blt, Trigg, or XHTML link types, remember to declare the namespace to help the automated processes that try to use them!
To add link types to existing links, you can use this form. You can download the accumulated type assignments below. You don't have to fill out the "URL for attribution" field, but an attributed link type has more value than an anonymous one. I use my home page address and not a mailto link for to identify myself, because I get enough spam that I really try to avoid putting my e-mail address in a mailto URL.
You can download the RDF data that contains link types that I've assigned and any that people have added using the form above. There are two files to download: linktypes.txt is the basic data file, which isn't well-formed XML; linktypes.rdf is the shell file that is well-formed XML and references linktype.ent as a system entity. Download both, point your parser at linktypes.rdf, and you'll be fine if you're using software that conforms to the XML 1.0 specification.
I'm open to suggestions for link types for the BLT namespace, but I ask two things of any suggestions: