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- I think there's something that people are missing in this discussion
- that is basic to the MIME philosophy, so here comes my two cents:
-
- MIME is a standard with a very different philosophy from many other
- standards (ODA, etc.). It has been said, not entirely incorrectly, that
- MIME isn't a format standard at all, but rather a standard for labeling
- and safely encoding data whose format is described by other standards.
- (Indeed, I think a major reason that text/richtext is the most
- controversial content-type is that it almost is the ONLY MIME type of
- which this is not true.) The basic idea of putting the minimum possible
- information in the header field is a natural outgrowth of this
- philosophy, hence the argument that if the information is in the body,
- it should not be duplicated in the headers.
-
- Larry Masinter has pointed out -- quite correctly -- that there are
- situations in which this is undesirable. I find his anonymous ftp
- example quite compelling: I would prefer not to ftp a 50 megabyte file
- only to find out that it is the wrong kind of postscript. I don't
- think, however, that requiring a "full" description of the detailed
- format information is necessarily the right solution, largely because
- defining "full" for any given format is so problematic, and runs the
- danger of being inconsistent with the internal information.
-
- Another part of the MIME philosophy is openness and extensibility. This
- openness, I believe, points the way to a more appropriate resolution of
- the problem. It is worth noting that the MIME standard does not close
- the book on additional parameters in the content-type line. That is,
- MIME says that a PostScript body part should be labelled as
-
- Content-type: application/postscript
-
- It also says, I believe, that unrecognized parameters should be ignored.
- This means that a MIME-conformant implementation will treat the above
- content-type and the following one as equivalent:
-
- Content-type: application/postscript; foo=bar; FavoriteCheese=muenster
-
- Not a very useful example, I'll admit. But this opens the door for
- communities to experiment with what additional parameters might be
- useful. If the wais, gopher, or www communities decided to use MIME as
- the base data representation standard, they could easily specify a few
- additional parameters for situations of concern to those communities.
- Indeed, as has been pointed out, if the transport system is other than
- mail, there are likely to be some diffferent concerns. (Larry's
- anonymous ftp problem, for example, is arguably central to wais and
- relatively peripheral to email.) So it might simply prove to be more
- important to the wais community to have the Postscript Level labeled in
- the header data than it was to the mail community. No big deal. The
- consensus in the mail community (at least as reflected on the ietf-822
- mailing list, which devised MIME) was that such a parameter was not
- particularly necessary or desirable for email use. The WAIS community
- might reach a diametrically opposite conclusion, and can accordingly
- extend MIME to include a few extra parameters, content-types, etc. The
- most useful of these, I conjecture, will eventually find their way back
- into the email world. This kind of evolution is precisely the reason I
- always felt so strongly that MIME needed a path for graceful evolution,
- including the IANA process for registering new content-types, character
- sets, and parameters.
-
- So the bottom line for me is that Larry's concerns have definite merit,
- but I think that they can easily be accomodated as minor extensions to
- MIME. My suggested path for making those extensions is to first try to
- reach a consensus on what extensions are needed for the wais/www/gopher
- communities, and then register those extensions with IANA. If any of
- them prove to be problematic in the sense that they need to be
- universally implemented -- as opposed to only being implemented among
- cooperating software -- the documents defining them can be submitted to
- the IAB standardization process. However, I suspect that official
- standard status will not be necessary in most cases.
-
- I hope that sheds some light on muddy waters... -- Nathaniel
-
-