Sorry for raising my voice here, but some of us are really working hard to show that SemWeb technologies don't have to be complicated, and unfortunately, the new CommonTag effort seems to send exactly the opposite message.
Don't get me wrong, a widely used tagging ontology would be great. We do have 3 (or 4? 5?) tagging vocabularies already, but none really caught up, possibly because tagging is meant to be simple and the proposed solutions apparently weren't easy enough. CommonTag is promoted as being "simple" and "easy", but after looking at the examples in the QuickStart Guide, I'm not so sure:
- The snippets are really off-putting (not only for Non-RDFers). Do I really need multiple nested HTML nodes to create something as simple as a tag?
- Couldn't the term names be more intuitive? What could a ctag:Tag be? The actual tag or an intermediate resource that is then, err, tagged? A person ctag:tagged a resource, right? Ah, no.
- Why aren't the term names at least consistent? "ctag:taggingDate" follows noun-role, "ctag:tagged" is a dunno, "ctag:means" is a present-form verb, "ctag:isAbout" sort-of follows the hasPropertyOf anti-pattern.
- The vocabulary introduces aliases for well-deployed terms such as rdfs:label and dct:created, which makes its use in practical settings expensive (it'll ease things on the author side, though).
To be a little more constructive: Using the vocabulary doesn't have to lead to the complicated markup seen in the examples. I'm sure they'll soon get better snippets from someone in the RDFa community. And apart from that, there is also a handy term in the RDF Schema which might just be what you are looking for: "ctag:isAbout". It lets you directly point from a resource (default is the page) to a Linked Data identifier (e.g. from DBPedia), without the need for all those intermediate nodes (which lead to triple bloat and slow down SPARQL queries). CommonTag-consuming apps will have to implement some form of inferencing to handle "isAbout", but as the term is in the spec, I assume they plan to.
Granular modeling of tags is apparently tricky, but shouldn't there be some sweet spot? Something a little more expressive than rel-tag but less complex than a fully spec'd Tag ontology? xFolk looks promising, or maybe the CommonTag group members could have agreed on formalizing and supporting "scoped rel-tag" (rel-tags with an optional RDFa "about" container). Most rel-tag-to-RDF converters have some form of scoping already anyway (because tags can apply to reviews, pages, vcards, etc.). That would have been a cool outcome after 1 year of stealth work.
I may as well just over-stress the simplicity aspect here. Maybe CommonTag is "simple enough" for web publishers. There are some initial supporters, and for RDFers, the nested structures and bnodes will most probably be acceptable. So let's see how things evolve.
<#me> ctag:isAbout dbpedia:Semantic_Web .still doesn't sound right for a rich tag, and the domain is "ctag:TaggedContent" which sounds wrong for non-textual resources, too. (dct:relation is the best I could find so far for tagging things with things, but Dublin Core is coming from a publishing context and is therefore often recommended for describing publications only).