|Date: ||Wed, 11 Jun 2003 18:12:55 -0600|
|Reply-To: ||Jack Hamilton <JackHamilton@FIRSTHEALTH.COM>|
|Sender: ||"SAS(r) Discussion" <SAS-L@LISTSERV.UGA.EDU>|
|From: ||Jack Hamilton <JackHamilton@FIRSTHEALTH.COM>|
|Content-Type: ||text/plain; charset=us-ascii|
In private email, a regular contributor here asked me about newsgroups,
which have been mentioned on SAS-L but not explained. I decided to send
an expanded version of my explanation to the list as well.
In short, a newsgroup is similar to a bulletin board or AOL forum.
People (usually called "posters") submit (or "post") messages, and other
people can read and respond to them. Messages are organized so that
similar messages are presented together.
This sounds like a mailing list, and indeed newsgroups and mailing
lists often serve the same purposes. The main differences between the
two are how messages are distributed and how messages are read.
A mailing list, such as SAS-L, runs everything through a single server
(you can also think of it as a single point of failure). If I want to
send a message to everyone on SAS-L, I just mail it to
firstname.lastname@example.org, and it gets distributed to a centrally
maintained list of subscribers. (SAS-L is a peered mailing list,
meaning that there are actually several servers, but that doesn't change
the workings in any essential way.)
With a newsgroup, there's no central point of control and no single
list of subscribers. Every site that carries news (a much smaller
number than the number of sites carrying mail) has software called a
news server. If I post a message to comp.soft-sys.sas, which is the
mirrored version of SAS-L, my news server assigns it a unique ID number,
which usually contains the host name and some pseudo-random characters.
Suppose the ID is 12345.newsguy.com. Later in the day, my news server
will connect to neighboring news servers with which it has agreed to
share news. It will ask each server in turn "Do you have message
12345.newsguy.com?" If the answer is no, it will send my message to
that server. When that server, in turn, connects to its neighbors, the
process will be repeated, and eventually my message will reach every
server in the world that carries comp.soft-sys.sas.
In the old days, this process might take a long time - maybe a week to
get to Europe, and much longer to get to remote parts of the globe (the
connections were originally done over dial-up lines at night). Now it's
very fast -- major news servers are constantly connecting to each other
over high-speed internet lines.
To read and post news, you use a news reader. Common news readers are
Netscape Messenger, Forte Agent (what I use at home), and Microsoft
Outlook. On Unix systems, many people use trn or xrn. Just how you
select newsgroups, read messages, and post varies between readers. The
reading process is somewhat similar to the distribution process -- your
news reader keeps track of the articles it's read, and when you connect
to the news server it uses that list to figure out which messages are
new and should be displayed. 
By the way, there's another kind of newsgroup that does have a central
point of control. Moderated newsgroups, often used for controversial
subjects, require postings to have moderator approval before being
distributed. When you post to a moderated newsgroup, the message is
mailed to the moderator, who approves it and injects it into the news
stream from his or her own machine.
There's a bidirectional mail-to-news gateway between SAS-L and
comp.soft-sys.sas. In theory, everything which appears in one will
eventually appear in the other. For various obscure reasons, this
occasionally breaks down, but one good feature of the gateway is that it
lets us read and post via email, but use the newsgroup search features
You can read, search, and post newsgroup messages through the web using
Google Groups -- click on the Groups tab on the main page. I don't use
that interface for reading, because it's too hard to keep track of what
I've already read, but I do use it for searching, and occasionally for
posting. For some people, doing everything through the web is more
There are more than 40,000 newsgroups.
 This is an oversimplification. For one thing, the news reader and
news server use a short, locally assigned message number rather than a
message ID, to save space and make processing easier.
Manager, Technical Development
Metrics Department, First Health
West Sacramento, California USA