- From: Philip Jägenstedt <philipj@opera.com>
- Date: Tue, 19 Jan 2010 02:35:06 +0100
- To: "Ian Hickson" <ian@hixie.ch>
- Cc: "Toby Inkster" <tai@g5n.co.uk>, "HTMLWG WG" <public-html@w3.org>
On Tue, 19 Jan 2010 02:14:41 +0100, Ian Hickson <ian@hixie.ch> wrote: > On Mon, 18 Jan 2010, Philip Jägenstedt wrote: >> On Sun, 17 Jan 2010 20:47:29 +0100, Toby Inkster <tai@g5n.co.uk> wrote: >> > Cyclical references amongst blank nodes cannot be represented in >> > Microdata. In Turtle an example might be: >> > >> > @prefix foaf: <http://xmlns.com/foaf/0.1/> . >> > _:bob foaf:knows _:jon . >> > _:jon foaf:knows _:bob . >> > >> > In RDFa it can be expressed quite simply: >> > >> > <p xmlns:knows="http://xmlns.com/foaf/0.1/knows" >> > about="_:jon" rel="knows:" rev="knows:" resource="_:bob"> >> > Jon and Bob know each other. >> > </p> >> > >> > To express the same semantics in Microdata would require assigning a >> URI >> > to at least one of the people. Certainly it's possible for a script to >> > assign a URI on the fly, but committing to maintaining the meaning of >> > that URI long-term is harder, which is why blank nodes are so >> frequently >> > used in RDF. >> > >> > I believe, this could be addressed by allowing @itemid to contain a >> > blank node name, and providing a way for @itemprop to specify a blank >> > node as its value. >> >> Right, if there's an actual need then it's easy to hardwire the _:foo >> syntax to create blank nodes in the RDF extraction algorithm. Currently >> the algorithm ignores item types which aren't absolute URIs. Is _:foo an >> absoute URI, or is it not a URI at all? > > Looped references are one of the features that were explicitly deferred > to > the next version, because there simply weren't use cases that needed it. > I > designed the mechanism that one would use to do it back when first > writing > the Microdata section, I just didn't include it. What mechanism did you have in mind and does it still hold, so that it's possible to add in the future should it actually be needed? I have no particular desire for it, but I'd like to know what "plan B" is and that it doesn't break things. -- Philip Jägenstedt Core Developer Opera Software
Received on Tuesday, 19 January 2010 01:35:25 UTC