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From: mouse@mcgill-vision.UUCP (der Mouse)
Newsgroups: sci.crypt,comp.sys.ibm.pc,comp.sources.wanted
Subject: Re: Need information on data compression algorithms
Message-ID: <743@mcgill-vision.UUCP>
Date: Sun, 26-Apr-87 08:44:40 EDT
Article-I.D.: mcgill-v.743
Posted: Sun Apr 26 08:44:40 1987
Date-Received: Sun, 3-May-87 18:39:20 EDT
References: <528@savax.UUCP> <635@ttidca.UUCP> <4542@columbia.UUCP> <1323@ihdev.ATT.COM>
Organization: McGill University, Montreal
Lines: 31
Xref: mnetor sci.crypt:359 comp.sys.ibm.pc:3718 comp.sources.wanted:1072

In article <1323@ihdev.ATT.COM>, pdg@ihdev.ATT.COM (Joe Isuzu) writes:
> In article <4542@columbia.UUCP> metzger@garfield.columbia.edu.UUCP (Perry Metzger) writes:
>> Look folks, as we all know from being cryptographers [...] that the
>> redundancy of english is NEVER estimated [...] at more than 75%, so
>> thus it is impossible to compress it beyond that in general.

> Unless you take symbolic representation into account.  Say you
> numbered the (2^14)-1 words, and used that to replace just the
> absolute matches (forgetting about endings etc),

What you appear to be suggesting is not just compressing English text
but representing it at a higher level.  If you "compress" beyond the
point of discarding all redundancy you are losing information; in other
words, there will be distinct input texts which compress to the same
compressed text, which means it will be impossible to correctly
regenerate both of them from the compressed text.  For example, in
English there are often two (or more) ways to represent the same
concept.  We are not interested in merely storing ideas (or if we are,
we should be explicit in admitting it), we want to compress text and
then uncompress to the exact same sequence of bytes.

Alternatively, your posting could be taken to mean that you believe
there is more than 75% redundancy in English.  In the case of Usenet
postings I fear you are correct - maybe your software would improve
netnews performance! -- what's that?  You don't have this implemented?
Then how do you know it works?  Go ahead and try it; I suspect you will
find it doesn't compress by as much as you think it will.

					der Mouse

				(mouse@mcgill-vision.uucp)