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NewsClip(TM) News Filtering Language

Turn Usenet into the network you want it to be.

Usenet is an information explosion. If you're on it, you know the problem is not finding stuff to read, it's finding the *right* stuff to read in a vast sea of information. Sometimes it's like looking for a needle in a haystack.

To help, we developed NewsClip, a programming language that lets you control what you will and will not read. Other tools only let you control what's presented to you through newsgroup selection and the elimination of messages that match certain pattern strings. What's worse, they use up your time doing it.

With NewsClip, you can control what is shown to you as finely as you desire, with all the tools of a powerful programming language at your disposal. The programs you write are compiled, so they filter your news the way you want it, quickly -- often without any noticeable delay.

Your NewsClip programs accept, reject or weight articles based on C-like expressions you write to describe what you want or don't want to see. For example, you might reject all articles in "rec.humor" that are cross-posted to "talk.bizarre," unless they are posted by a user at your own site with:

	reject if is rec.humor && is talk.bizarre &&
			domain(from) != my_domain;
What you can do is limitless.

Your compiled programs can work in several ways. With a few small alterations to your newsreader (patches are provided for the RN reader), your program will filter news as you read it, usually with no delay. You simply see the articles you wish to see. The modified RN reader can also send commands to the filter program to interactively control filtering.

You can also arrange to filter news in the background, or at night. Your filter program will read your news subscription file, scan all unread articles, and pre-mark undesired articles as read, so you never see them. This works with any system that uses a .newsrc file.

NewsClip programs can also filter a list of article filenames, such as a list of articles to be fed to another system. This way you can fine tune the feeding of articles to other systems as precisely as you desire. You can also arrange to feed other sites by creating a newsrc for the destination site, so that you don't need the "sys" file.

An important thing to remember is that with NewsClip, you are not limited to describing what you don't want to see, as is the case with RN KILL files. You can also request what you want to see, and eliminate all the rest. Or you can combine the two, or vary the rules from group to group or message to message.

Here are some of the things you can do:

  • Eliminate or request followup trees. You can kill off or follow a topic or subtopic based on the subject or the "Message-id:" and "References:" lines.
  • Control cross-posting. You can request to only see articles cross-posted to multiple groups, or reject or accept articles based on what groups they are cross-posted to. You can even reject any article cross-posted to too many groups.
  • Eliminate a user, group of users or even a site. You can arrange not only to not see the postings of certain users, but also to not even see the followups to those postings. You can thus eliminate unwanted users or classes of postings from *your* net -- you'll never even know they're there.
  • Keyword match articles based on the presence of patterns in header items or various sections of the article text. You can ask to see articles that mention "unix" but don't mention "ms-dos."
  • Accept your own articles and give priority to followups to your own articles.
  • Accept articles posted only to a local distribution, even if they're in a netwide group. As shown above, you can arrange to accept articles from people on your own site, even if you might not normally see them.
  • Reject articles with signatures that are too long, or which contain too much included text.
  • Accept only original (non-followup) articles and followups to those articles that you have explicitly decided to track. (It's like having a Usenet 1/10th the volume of the current one.)
In other words, with NewsClip, you can turn Usenet into the network you want it to be. Anything that a computer program can figure out about an article can be used to decide whether you will see the article or not.

How NewsClip Works

The NewsClip compiler translates your filter program into a C program. This C program is compiled by your local C compiler and linked with the NewsClip library. That library processes articles and handles the interface to news readers and the real world.

The goal of your program is to decide whether to accept or reject an article. This can be done piece by piece (reject if this, accept if that) or it can be done by giving a score to the article based on conditional expressions. You can add points to articles with things you like, and take them away from articles with things you don't like. At the end, if the score is still positive, you see the article.

	if( lines > 200 )
		adjust 200-lines;
The language is C-like, but has data types that represent the kind of things found in articles and article headers. Perhaps most important is the "database" type, which is really an integer array that you can index with string values. You use databases to keep track of users, message-ids, patterns, subjects and other key items you might look for in articles.

Your NewsClip program can update databases on its own. If an article comes in that you really hate, you can automatically put its message-id in a database that marks messages you don't want to see followups of. To you, it's as if the message was never posted.

	if( from in badusers ) {
    		badmessages[message_id] = true;
Databases can be stored on disk, and a special feature allows you to "expire" database records that have not been accessed in a while.

Your filter program can run in parallel with a newsreader like RN. We have developed a general protocol that any newsreader can use to talk to a filter program. This includes the ability to send commands to the filter program, such as "kill all articles with this subject."

To examine an article, you mainly work with the header. There are predefined external variables for all the major headers, or you can custom-declare your own:

	header string array keys : "keywords", ",";
(This gets you an array variable called "keys" whose elements will be the comma-delimited keywords from the "Keywords:" header line.)

You can define your own procedures and functions in the NewsClip language, or even import C functions from the C libraries or your own C programs.

	extern int strlen( string );
NewsClip contains a special "distribution" feature that lets you check the distribution of an article and estimate how many machines it will go to. You can thus accept or reject articles based on their audience as well as their newsgroup.

You can split up articles into various regions when doing pattern matching in the body. The signature, main text, non-included text and whole body are all regions that you can examine independently.

reject if line_count(signature) > 20
	|| newtext has "ron.*reagan";

How to Get NewsClip

NewsClip runs on most Unix systems, including Xenix/286. It requires a C compiler and a standard news directory structure. It can also be used in conjunction with "RRN."

NewsClip is a product of Looking Glass Software Limited, marketed by ClariNet Communications Corp. It is available free to most ClariNews subscribers. ClariNews provides electronic publications, including live newswire news, computer industry news and other electronic services. The newswire can be filtered well by NewsClip programs.

NewsClip is also available free for non-commercial use to non-subscribers. You can get Newsclip via ftp.

Sample Program

/* Sample NEWSCLIP program that shows what you can do */
/* This program is far more complex than a typical system, which
   would usually be quite short. */

/* Please folks, this is not the newsclip program that I use, and I
   don't advocate all the different filtering things here.  I am
   just using them as examples of how to do certain things net people
   have suggested they wanted done. */

	/* You can include pre-defined header lines */
	extern userid From;			/* the From: line */
	extern newsgroup array newsgroups;	/* the Newsgroups: line */
	extern int distribution_level;		/* max distr of article */
	extern string array references;		/* parent articles */
	extern string Subject;			/* subject line */
	extern int followup;			/* is it a followup? */
	extern int lines;			/* header variable */
	/* or define your own header lines */
	header string mess_id : "message-id";
	/* declare variables */
	int counter;
	/* some databases I will look things up in */
	database badmessages;			/* message-ids I don't want
						to see followsup to */
	database hated_users;			/* users I don't want to
						   see articles from */
	database my_articles;			/* message-ids that I
						want to see ALL followups to */
	/* declare external C functions from the Newsclip library or your
	   own C libraries */
	extern int strlen( string );

	/* you can define procedures and functions */

nice_group( newsgroup n )
	extern string left( string, int );
	/* you like all sci newsgroups and rec.humor.funny */
	return n == #rec.humor.funny || left(n,1) == "sci";

INIT() {
	extern procedure set_include_prefix(string);
	/* this code gets run when the program starts */
	set_include_prefix( "[:>]" );
	hated_users = read_database( "~./hatedusers" );
	my_articles = read_database( "~./myarticles" );

	/* This gets called when we begin to scan a new newsgroup */
	/* read in the database of bad message-ids for this group */
	badmessages = read_database( "~./kill/~n/killdb" );

	/* this gets called to end the newsgroup */
	extern datetime time_now;

	/* write out the bad message database, delete all entries that
	  are older than one month */
	write_database( badmessages, "~./kill/~n/killdb", time_now - month );
	free_database( badmessages );

	/* here is the main part.  The code that is executed for every
	   article to accept or reject it */

	newsgroup n;
	extern string domain( string );
	extern string right( string, int );
	extern int dlevel( newsgroup );
	extern string my_domain;
	extern string my_mail_address;

	/* show me everything written by people at my own site */
	if( domain(From) == my_domain ) {
		/* Note my own articles in a database of good ones */
		if( From == my_mail_address )
			my_articles[mess_id] = true;
	 else if( domain(From) == "hated.domain.com" )
		reject;		/* never show me anything from THAT site */
	/* also show me anything posted only for citywide distribution */
	accept if distribution_level <= dlevel(#city);

	reject if count(newsgroups) > 6;	/* I hate crossposting */

	/* See if it's a followup to one of MY messages */
	accept if References in my_articles;

	/* See if any of the messages this is a followup of are in
	   our database of bad messages.  If so, reject it */

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