Re: Britannica data format?

Subject: Re: Britannica data format?
From: Paulo S. L. M. Barreto (pbarretonw.com.br)
Date: Sun Dec 26 1999 - 17:07:18 CST

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>[Jim Gillogly] wrote:
>>> I note that the data is prejudiced toward 0-bits, suggesting it's not
>>> one of the most aggressive compression algorithms.
>
>Ben [Laurie] wrote:
>> That's in the nature of Lempel-Ziv (at least, until you fill its
>> compression table).

A compression table is used in the LZ78 variants, like LZW. How do you know
it's not an LZ77-type algorithm, like the one (deflate) used in gzip? The
compression FAQ lists tens (or is it hundreds?) of variants.

As for the challenge, it's interesting to notice that only 65 values are
used, and the last code is one of those that occur only once. This suggests
it's a kind of base-64 encoding (64 data codes plus a terminator), and
indeed it may be simply this (i.e. no encryption, only encoding) since
there's a heavy unbalance in the frequency table (e.g. code 71 appears 12
times).

Paulo.

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