Considering a +rdf+xml Media Type Convention

Status of this Document

This is a collection of thoughts by ericP.

Parallels With +xml Media Types
Evolution Path
Counter Arguments

Parallels With +xml Media Types

RFC 3023 contains a set of arguments for a +xml media suffic convention. The RDF column may as well go away 'cause the parallels are pretty obvious.

Question	XML answer	RDF analog
1. Why not /xml? (Why not /rdf?)	XML defines new datatypes opaquely handle-able by mime processor	RDF also defines new datatypes
2. Why not follow /vnd.?	subtree is orthogonal from whether the media type uses XML syntax allows XML document types to be identified within any subtree	same applies for RDF
3. Why not use xml/?	top-level MIME determines content type, not syntax	...
4. Why not sniff for XML?	breaks HTTP HEAD and (e.g. IMAP4 Content-Type selection)	...
5. Why not use a parameter?	XML-ness of media is invariant; parameters are not invariant practically, no dispatches by media type	... RDF apps seem to follow same trend
6. application/xml; Content-Feature=iotp?	really breaks given no dispatches by media type tree negotiation, e.g. image/xml Content-Feature=svg???	...
7. special (higher-priority) parameter, e.g. application/iotp; $superclass=xml?	combines previous two problems how is it different? is superclass already known?
8. Why not use Content-Disposition?	requires bilateral upgrades practically, no dispatches by media type
9. Why not use Alternative-Content-Type?	requires bilateral upgrades more common API support to set Content-Type than to set arbitrary headers
10. Why not use conneg (e.g., accept-features: (syntax=xml))?	Conneg is still in the oven.
11. How about three levels, e.g. text/xml/rdf?	MIME explicit about kind/specific media tree. Need to follow 2048 registration tree convention for IETF, vendor and personal trees (i.e. can't use '/'s in subtree)
12. Why use '+'?	can't use tspecials '.' already use in registration tree convention choice whittled down to '+'
13. difference between text/foo and text/foo+xml?	by conventional (at the time) infrastructure, completely different xml variants may include new semantics [should make a decision here, the designers or world can adjust when semantics change]
14. And when then next encoding comes along?	follow convention, use application/foo+rdf+xml for XML and application/foo+rdf otherwise
15. Must I use the '+xml'?	you don't have to should leave space for unanticipated generic processing utility

Counter Arguments

The principal contested use of +rdf+xml that I can see is that it may be more useful to reserve it for the subset of XML documents with a fixed XML schema so that XML processors can really make use of it. For example, a document learning that ericP-foaf.rdf is application/foaf+rdf+xml could look for a stylesheet associated with that document's content model. If this is a goal, we should not use application/powder-s+rdf+xml for POWDER-S as there is no defined XML schema for it.

Evolution Path

Following the recommendation of point 14, text/ical+rdf+xml and text/ical+rdf+ttl may be useful somday.

CVS Log

$Log: Overview.html,v $
Revision 1.3  2008/12/05 16:32:44  eric
~ slightly prettier

Revision 1.2  2008/12/05 16:31:30  eric
+ note that RDF analog column in danger

Revision 1.1  2008/12/05 16:23:44  eric
moved

Revision 1.2  2008/12/05 16:10:53  eric
+ Table of Contents

Revision 1.1  2008/12/05 16:06:54  eric
created

ericP
$Id: Overview.html,v 1.3 2008/12/05 16:32:44 eric Exp $