for telecon: ISSUE-23 @profile order

Currently RDFa Core 1.1 says that when @profile includes multiple
profiles, e.g.

	profile="http://example.com/a http://example.net/b"

these are processed from left to right. This means that if a particular
term or prefix is defined in both profiles, then the definition in the
latter profile "wins".

If we were defining RDFa in isolation, this might make perfect sense,
but @profile is an attribute from HTML 4 and is (at least
theoretically, though often not in practise) used by microformats, so
we need to take into account this historical baggage.

HTML 4 defines @profile as a list but says that only the first URI is
deemed to be significant, the rest being ignored. If we make allow
later profiles to overrule the first profile, then this seems at odds
with HTML 4 - we're saying that later profiles are more significant
than the first.

XMDP, the profile format used by microformats, extends the definition
of @profile by saying that profiles are listed in descending
significance. This means that when a term is defined in two profiles,
the first profile wins. If we do this the other way around, it may
prove an annoyance for people wishing to publish hybrid
RDFa/microformats documents.

It seems apt to mention GRDDL if only in passing. In GRDDL it doesn't
matter which order you process profiles in. That's fine.

Lastly, let's think about human psychology. We tend to employ a
technique called cognitive frontloading - i.e. we get the most important
things out of the way first. That means, if there's a bunch of profiles
I'm going to type into a list, chances are that I'm going to type in the
most important ones first. Given that, it makes sense for us to
allow earlier profiles to override later ones.

So my proposal is for RDFa Core 1.1 to state that profiles are handled
from right to left.

As an aside, we may wish to mention somewhere that implementations
should be free to download and parse the profiles in any order, or
in parallel. What's important is that the terms and prefixes defined in
them are added to the lists of terms and prefixes in the correct order.

-- 
Toby A Inkster
<mailto:mail@tobyinkster.co.uk>
<http://tobyinkster.co.uk>

Received on Wednesday, 26 May 2010 08:47:11 UTC