[XML-DEV Mailing List Archive Home] [By Thread] [By Date] [Recent Entries] [Reply To This Message] Notations and MIME types
W. Eliot Kimber scripsit: > Unless I've misunderstood something, a MIME type is still an indirection to > the definition of that MIME type. I.e., "text/xml" is a pointer to the RFC > that establishes that MIME type. That's true, but it's not a *flexible* pointer. Neither you nor IETF is free to change the binding of "text/xml"; if XML changes, a new MIME type (which includes the parameters as well as the type/subtype information) must be registered. MIME parameters, BTW, are essentially a method of registering related MIME types en masse: e.g. registering "text/plain" with a "charset" parameter essentially registers "text/plain;charset=us-ascii", "text/plain;charset=utf-8" and so on for all the charsets in the charset registry. > But then a problem is: where do I go to > figure out what RFC a given MIME type maps to? IANA keeps that information in the MIME-type registry. > What if the MIME type is an > "x-*" MIME type, what do I do then? Nothing. This is the moral equivalent of a notation with a "file://" system identifier. > Note that the external ID for a > notation could, in theory be a MIME type: > > <!NOTATION xml SYSTEM "urn:mime:text/xml" > Indeed. > It's clear that I need to write a paper > clearly outlining what notations are for and how they are best put to use. Exactly. > Perhaps part of the problem is that in the Web world we have tended to > remove the need for such a generalized mechanism by hard-coding knowledge > of the semantics of everything? But you can't do that forever, and MIME > only seems to make the problem worse Not worse, perhaps not sufficiently better. > by requiring that all interchangable > types be registered before they can be used. Notations don't require that > because the external ID of a notation can be anything (including MIME types > or their RFC documents). One advantage of MIME types over notations is that they contain declarative information. Unless your program is AI-complete, the only thing you can do with the external ID of a notation is try to use a local table ("mailcap", the Win32 registry) to find an engine to process the data, and communications with that engine are crude: you typically can only request it to render the data in some default manner. A MIME-aware system can take more intelligent action even if it does not have a local resource for processing a specific MIME type, due to the structuring provided by MIME-type syntax. A MIME object of type "text/plain;charset="8859-8-e" can be rendered as ASCII plain text, with loss of information, even if the charset "8859-5-e" is unknown locally. A corresponding notation N1 defined by the external ID "urn:rfc:rfc1555#8859-5-e" leaves a similarly equipped notation-aware processor completely clueless. -- John Cowan http://www.ccil.org/~cowan cowan@c... You tollerday donsk? N. You tolkatiff scowegian? Nn. You spigotty anglease? Nnn. You phonio saxo? Nnnn. Clear all so! 'Tis a Jute.... (Finnegans Wake 16.5) xml-dev: A list for W3C XML Developers. To post, mailto:xml-dev@i... Archived as: http://www.lists.ic.ac.uk/hypermail/xml-dev/ To (un)subscribe, mailto:majordomo@i... the following message; (un)subscribe xml-dev To subscribe to the digests, mailto:majordomo@i... the following message; subscribe xml-dev-digest List coordinator, Henry Rzepa (mailto:rzepa@i...)
|
PURCHASE STYLUS STUDIO ONLINE TODAY!Purchasing Stylus Studio from our online shop is Easy, Secure and Value Priced! Download The World's Best XML IDE!Accelerate XML development with our award-winning XML IDE - Download a free trial today! Subscribe in XML format
|