See

http://www.debian.org/doc/debian-policy

for info about the components of a debian package

=============================================================================

See man sources.list(5), which describes the file /etc/apt/sources.list:
This line:

	deb http://www.math.uiuc.edu/Macaulay2/debian/ distribution component

gets expanded to this URL:

	http://www.math.uiuc.edu/Macaulay2/debian/dists/distribution/component/binary-i386/Packages.gz

to search for package names.

Similarly,

	deb http://http.us.debian.org/debian stable main contrib non-free

gets translated to 

	http://http.us.debian.org/debian/dists/stable/main/binary-i386/Packages.gz

That compressed file contains entries such as this one, separated by blank lines:

    Package: bash
    Essential: yes
    Priority: required
    Section: shells
    Installed-Size: 1848
    Maintainer: Matthias Klose <doko@debian.org>
    Architecture: i386
    Version: 3.1dfsg-8
    Replaces: bash-doc (<= 2.05-1), bash-completion
    Depends: base-files (>= 2.1.12), debianutils (>= 2.15)
    Pre-Depends: libc6 (>= 2.3.6-6), libncurses5 (>= 5.4-5)
    Suggests: bash-doc
    Conflicts: bash-completion
    Filename: pool/main/b/bash/bash_3.1dfsg-8_i386.deb
    Size: 872884
    MD5sum: 85437fb26d035bd4a91ae4bc98bc63d2
    SHA1: 06a42e1679ec3a61a21eef5d329f90c38e9c4885
    SHA256: 7dafebd6c7497b5fddfe31b015f54daac8016190d65512019f8a85813e4bcd9e
    Description: The GNU Bourne Again SHell
     Bash is an sh-compatible command language interpreter that executes
     commands read from the standard input or from a file.  Bash also
     incorporates useful features from the Korn and C shells (ksh and csh).
     .
     Bash is ultimately intended to be a conformant implementation of the
     IEEE POSIX Shell and Tools specification (IEEE Working Group 1003.2).
     .
     Included in the bash package is the Programmable Completion Code, by
     Ian Macdonald.
    Tag: implemented-in::c, interface::shell, role::program, scope::utility, uitoolkit::ncurses

The Filename: entry gives the filename, relative to the URL, i.e., the file is at

    http://http.us.debian.org/debian/pool/main/b/bash/bash_3.1dfsg-8_i386.deb

=============================================================================

For ubuntu releases, take a look here:

    http://security.ubuntu.com/ubuntu/dists/

    There you see these releases:

	dapper		6.06
	hardy		8.04
	intrepid	8.10
	jaunty		9.04
	karmic		9.10
	lucid		10.04

=============================================================================

A debian archive is an archive made with the "ar" program, with three files in it, in a certain order:

    % ar tv /home/25/dan/local/to/Macaulay2/Downloads/macaulay2-0.9.91_i686-Linux-usr-2_all.deb
    rw-r--r-- 1000/1000       4 Oct 11 21:07 2006 debian-binary
    rw-r--r-- 1000/1000  216297 Oct 11 21:07 2006 control.tar.gz
    rw-r--r-- 1000/1000 7790785 Oct 11 21:08 2006 data.tar.gz

The file data.tar.gz is a simple tar file of the files of the package, with the right user name
and protections, based at /.

    % cat debian-binary 
    2.0

    % ls -lR control
    control:
    total 756
    -rw-r--r--  1 dan academic    357 Oct 11 21:03 control
    -rw-r--r--  1 dan academic 765066 Oct 11 21:03 md5sums

    % cat control/control
    Package: macaulay2-0.9.91
    Version: i686-Linux-usr-2
    Section: alien
    Priority: extra
    Architecture: all
    Depends: libc6 (>= 2.3.4-1), libgcc1 (>= 1:4.0.2)
    Installed-Size: 45652
    Maintainer: root <root@ytterbium.math.uiuc.edu>
    Description: Converted Slackware tgz package
     Converted Slackware tgz package
     .
     (Converted from a tgz package by alien version 8.64.)

    % head -3 control/md5sums 
    2dcea6f20f8510c260961b488ac3704f  usr/share/doc/macaulay2-0.9.91/copyright
    9bdb9840293f1678182fee9c720dc562  usr/share/doc/macaulay2-0.9.91/changelog.Debian.gz
    a8a4c861d958f437bcb7ea7a8a050273  usr/share/doc/Macaulay2/Core/LAYOUT.gz
