[whatwg] Trying to work out the problems solved by RDFa
Toby A Inkster
mail at tobyinkster.co.uk
Thu Jan 1 07:24:50 PST 2009
The use cases for RDFa are pretty much the same as those for
For example, if a person's name and contact details are marked up on
a web page using hCard, the user-agent can offer to, say, add the
person to your address book, or add them as a friend on a social
networking site, or add a reminder about that person's birthday to
If an event is marked up on a web page using hCalendar, then the user-
agent could offer to add it to a calendar, or provide the user with a
map of its location, or add it to a timeline that the user is
building for their school history project.
Providing rich semantics for the information on a web page allows the
user-agent to know what's on a page, and step in and perform helpful
tasks for the user.
So why RDFa and not Microformats?
Firstly, RDFa provides a single unified parsing algorithm that
Microformats do not. Separate parsers need to be created for
hCalendar, hReview, hCard, etc, as each Microformat has its own
unique parsing quirks. For example, hCard has N-optimisation and ORG-
optimisation which aren't found in hCalendar. With RDFa, a single
algorithm is used to parse everything: contacts, events, places,
cars, songs, whatever.
Secondly, as the result of having one single parsing algorithm,
decentralised development is possible. If I want a way of marking up
my iguana collection semantically, I can develop that vocabulary
without having to go through a central authority. Because URIs are
used to identify vocabulary terms, I can be sure that my vocabulary
won't clash with other people's vocabularies. It can be argued that
going through a community to develop vocabularies is beneficial, as
it allows the vocabulary to be built by "many minds" - RDFa does not
prevent this, it just gives people alternatives to community
Lastly, there are a lot of parsing ambiguities for many Microformats.
One area which is especially fraught is that of scoping. The editors
of many current draft Microformats would like to allow page
authors to embed licensing data - e.g. to say that a particular
recipe for a pie is licensed under a Creative Commons licence.
However, it has been noted that the current rel=license Microformat
can not be re-used within these drafts, because virtually all
existing rel=license implementations will just assume that the
license applies to the whole page rather than just part of it. RDFa
has strong and unambiguous rules for scoping - a license, for
example, could apply to a section of the page, or one particular image.
RDFa was largely borne of looking at Microformats, looking at what
was successful about them, considering problems with them, and
finding ways to resolve those problems.
1. It has been discussed in hAudio, figure, hRecipe and others.
Toby A Inkster
<mailto:mail at tobyinkster.co.uk>
More information about the whatwg