- From: Donald E. Eastlake 3rd <dee3@torque.pothole.com>
- Date: Tue, 24 Apr 2001 15:24:41 -0400
- To: discuss@apps.ietf.org
And, of course, none of this has to do with ASN.1 but rather to do with BER, PER, DER, etc., i.e., with particular ASN.1 Encoding Rules. One could define a VER (Verbose Encoding Rules) for ASN.1 which was worse than any of the compared alternatives. Similarly, one can define more compact XML encoding rules, e.g., WAP's Binary XML. Donald From: Keith Moore <moore@cs.utk.edu> Message-Id: <200104241917.PAA17760@astro.cs.utk.edu> X-URI: http://www.cs.utk.edu/~moore/ To: Jacob Palme <jpalme@dsv.su.se> cc: Keith Moore <moore@cs.utk.edu>, discuss@apps.ietf.org In-reply-to: Your message of "Tue, 24 Apr 2001 20:29:50 +0200." <p05010407b70b755d01a3@[130.237.150.141]> Date: Tue, 24 Apr 2001 15:17:54 -0400 Sender: moore@cs.utk.edu List-Unsubscribe: <mailto:discuss-request@apps.ietf.org?Subject=unsubscribe> >> >there's more than one kind of typing. in your ASN.1 examples, you don't >> >appear to include the "name" of each datum, whereas in your ABNF and XML >> >examples, you do. >> >> The main principle of efficient coding of protocols is to only send >> the information which varies over time. Information which is static, >> like the names of the fields, is either suppressed or compacted very >> strongly. It is this compacting of this information which is a main >> reason why the ASN.1 encoding got so compact. > >This isn't a feature of ASN.1. It's a feature of encoding the >field names implicitly via their position in the data stream vs. >encoding them explicitly with tags. ASN.1 can do this either >way. For instance, SNMP uses ASN.1 but tags each datum with an OID. > >You can also do positional encoding with RFC 822 headers or XML. >It's just a question of how much of the syntax of the underlying >data that you expose/export into the outer presentation syntax. > >> The disadvantage with this, of course, is that the encoded date is >> much more difficult to read for a human not using a special program. > >That's only one disadvantage of positional encoding. You're making >assumptions about which data is static and which data isn't static >that aren't even appropriate for the examples that you cite, much less >in general. > >> Did you also look at my comparison between RFC822 and XML >> >> RFC822 example: >> From: Father Christmas <fchristmas@northpole.arctic> >> >> XML encoding of the same information: >> >> <from> >> <user-friendly-name>Father Christmas</user-friendly-name> >> <e-mail-address> >> <localpart>fchristmas</localpart> >> <domainpart> >> <domainelement>northpole</domainelement> >> <domainelement>arctic</domainelement> >> </domainpart> >> </from> >> >> The XML encoding uses five times as many characters. > >you could have as easily said: > ><from>Father Christmas <fchristmas@northpole.arctic></from> > >and that would have been a more accurate comparison. The XML version >uses a few more characters, but it's not a huge difference overall. > >Keith
Received on Tuesday, 24 April 2001 15:26:50 UTC