First we take up the structure of an email address.
Net nodes corresponding to internet machines have IP addresses.
whose Syntax is:
where d's are decimal numbers.
Human internet addresses have the Syntax:
Fully Qualified Domain Name
where FDQN has the form:
A Domain is the name of the broadest internet subdivision.
Standard existing top level domains:
.com Commercial Oroganizations
.edu Educational and Academic organizations
.int Special international organizations
.mil Networks & orgs under Milnet run by US dept. of defense
.gov US government: Whitehouse, Senate,
Treasury dept., IRS, NASA, Library of Congress,
.net Organizational networks of Internet, info & serv centers
[Some Inet services are under .com]
Backbone, regional and commercial networks:
AlterNet, ANSnet, BARRnet, CERFnet, NEARnet, PSInet,
Gov type nets: ESnet, NSFnet, NSFnet
National Services Center
.org Reasearch and no for profit organizations
NB local nonprofit networks in the us and other countries use a
different terminating field in the FQDN:
.us United States
.uk United Kingdom
.us United States
Full Country Code List
Outside us, the penultimate field "ac" is equivalent to the "edu"
terminator in .us, while a penultimate field "co" is equivalent to
the "com" terminator in us.
Human Internet Addresses are looked up and converted to the
internally used IP addresses at selected computers that maintain
conversion tables. These are often referred to as "name servers".
Your Internet server (the machine) keeps a list of several of
these name servers that it can use, in case any one of these is
in heavy use and times out or happens to be down. Your server
may also maintain a relatively small cache of most often needed
conversions so that it does not have to interrogate a name server
While within an email address, every thing to the left of the
separator symbol '@' is case insensitive, what appears to the
right, may or may not be be case sensitive. Write it as you
see it in a From field to be safe.
Now, secondly consider the URL syntax:
this has the general form
[method]://[IP address/[Full path name]
[method]://[FQDN]/[Full path name]
[method] is a variable that can be filled with names
of specific methods of access, exaples of which
These method desigbations are case insensitive.
The [IP address] is as explained in the case of email addresses
above; the same can be said for [FQDN]. Remember the FQDN is
case insensitive. There is a quirk in many FQDNs: it is often
said that the prefix "www" or "WWW" is unnecessary. In some
cases it is and in others not. If it is specified, use it.
I can be a signal to a remote site regarding the selection of
a particular access method, namely the http method which has a
physical entrance or port.
The Surprisre comes, especial for the mind dulled MSrobots
and unix impaired internet users, when the full pathname part
of the URL contains UC and LC letters. Unlike most of the crap
that comes from MS, unix systems are and always have been
case sensitive. A file or directory "FOO" is absolutely
distinct from a similarly named "foo" or "Foo". If you
see case distinctions in the pathname part of a URL, use them.
All the real internet servers run some brand of unix; increasingly
the brand is Linux.
Prefixes and Suffixes in full path names.
1) DOS and its MS spawn like WINCRAP only allow one
suffix (one "." in a name ane 3 characters in the
extension (that which lies to the right of the dot).
2) Unix systems have no such restrictions.
3) The proper extension for an HTML file is ".html"
a locution that is impossible on DOS and WINCRAP
systems. If you see the extension ".htm", it is
probably not a mistake, merely an indication that
the file resides on an inferior and less than unix
4) Other possibile extensions for WWW accessible files
are ".txt" (no hypertext), ".shtml", "gif", ".aps",
".jpeg" and others, or even no extention which is
actually an undeclared ".txt" file.
5) On unix systems, the "~" (tilde) symbol has a special
significance that comes from a shorthand of the C shell
(csh). "~jerk", in the full pathname refers in csh
to the home directory of the user "jerk", where ever it
may be in the hierarchical dile system.
On the net, the expression "~jerk" refers to the
subdirectory "public_html" of the users home directory.
If a net surfer specifies a directory such as
One of two things can happen depending on whether user
"bread" has put a file called "index.html" or "index.htm"
in the directory "~bread/public_html/". If the index
file is there, that is what will be accessed, if it is
not there, the contents of the directory will be displayed
as a menu.
Other than these few rules and their exceptions, the URL structure
and syntax is remarkably simple and clear. As an old math professor
once put it: why it's so simple, even a kindergarten child could do it.
There are more strange things that can follow the full path name
stucture which involve machine transfers, and database queries.
Check back for when I feel like writing about and parsing that
mumbo jumbo into understandable English.
Have fun -
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Created: April 29, 1998
Last Updated: May 28, 2000