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Special Forums News, Links, Events and Announcements Complex Event Processing RSS News Some footnotes to Luckham's "short history of CEP- part 3" Post 302270250 by Linux Bot on Saturday 20th of December 2008 11:20:04 AM
Old 12-20-2008
Some footnotes to Luckham's "short history of CEP- part 3"

2008-12-20T10:05:00.013+02:00
Image
David Luckham, who took upon himself to be survey the history of "complex event processing" has written a series of articles about the roots and developments the CEP area, while this is relatively young as discipline, it has roots in other disciplines, and people who worked separately from different perspectives, origin disciplines, and types of applications.

I recommend reading it. I'll make just some small comments for the recent third article :

(1). One of assertions in the article states:There were research groups within these companies engaged on similar projects to those in universities. Some of the groups ended up producing
prototype CEP products. In these cases, the decisions as to whether to let these
prototypes go forward to productization were haphazard, probably because they
were made by a management that didn't understand the technology or its
potential.

Well - one must realize that corporate executives have infinite amount of wisdom, otherwise they have not been corporate executives, and if a decision looks haphazard, it is only due to the mental limitations of us, simple mortals.

(2). Another assertion is: But the largest number came out of an active database background. This is the reason why many of the commercial languages for event processing are
extensions of SQL
More accurately -- some of the current products we see are indeed descendants of "active databases" which was based on ECA (event condition action) rules. Among the products which apply this approach we can find RuleCore and Aptsoft (now Websphere Business Events); the products which extended SQL came from different paradigm in the database community of "data streams management" according to which, the queries are constant and data is flows, instead of databases in which the data stands and queries flow. This has been later development which started with Jennifer Widom's Stream project; the two paradigms, though both came from the database community should not be mixed (although there are certain individuals who were involved in both).



Source...
 

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EXPIRE(8)						      System Manager's Manual							 EXPIRE(8)

NAME
expire - Usenet article and history expiration program SYNOPSIS
expire [ -d dir ] [ -f file ] [ -g file ] [ -h file ] [ -i ] [ -N ] [ -n ] [ -p ] [ -r reason ] [ -t ] [ -v level ] [ -w number ] [ -x ] [ -z file ] [ expire.ctl ] DESCRIPTION
Expire scans the history(5) text file <pathdb in inn.conf>/history and uses the information recorded in it to purge itself or old news articles. And if the article whose storage method has self expire functionality, the control file is ignored except ``/remember/'' line for that article by default. In this case, expire probes the article to see if it still exists. If it does not exist, expire purges the relevant entries. To disable this, use the ``-N'' flag. If ``groupbaseexpiry'' in inn.conf is true, expire always treats all stored arti- cles whose storage method have self expire functionality regardless of its actual method. In this case ``-e'', ``-k'', ``-N'', ``-p'', ``-q'', ``-w'' and ``-z'' flags are ignored. Note that expire never purges articles which do not match any entry. OPTIONS
-d If the ``-d'' flag is used, then the new history file and database is created in the specified directory, dir. This is useful when the filesystem does not have sufficient space to hold both the old and new history files. When this flag is used, expire leaves the server paused and creates a zero-length file named after the new history file, with an extension of ``.done'' to indicate that it has successfully completed the expiration. The calling script should install the new history file and un-pause the server. The ``-r'' flag should be used with this flag. -f To specify an alternate history file, use the ``-f'' flag. This flag is valid if ``-d'' flag is used together, and the output will be written to this file. The default without ``-f'' flag is ``history.'' -g If the ``-g'' flag is given, then a one-line summary equivalent to the output of ``-v 1'' and preceded by the current time, will be appended to the specified file. -h To specify an alternate input text history file, use the ``-h'' flag. Expire uses the old dbz(3) database to determine the size of the new one. If ``-d'' flag is not used together, and the output file name will be with an extension of ``.n.'' The default with- out ``-h'' flag is <pathdb in inn.conf>/history. -i To ignore the old database, use the ``-i'' flag. -N If the article whose storage method has self expire functionality, then the control file is ignored for that article by default. If the ``-N'' flag is used, expire still uses the control file in this case. -n If innd is not running, use the ``-n'' flag and expire will not send the ``pause'' or ``go'' commands. (For more details on the commands, see ctlinnd(8)). Note that expire only needs exclusive access for a very short time -- long enough to see if any new articles arrived since it first hit the end of the file, and to rename the new files to the working files. -p Expire makes its decisions on the time the article arrived, as found in the history file. This means articles are often kept a lit- tle longer than with other expiration programs that base their decisions on the article's posting date. To use the article's post- ing date, use the ``-p'' flag. -r Expire normally sends a ``pause'' command to the local innd(8) daemon when it needs exclusive access to the history file, using the string ``Expiring'' as the reason. To give a different reason, use the ``-r'' flag. The process ID will be appended to the reason. When expire is finished and the new history file is ready, it sends a ``go'' command. -t If the ``-t'' flag is used, then expire will generate a list of the tokens that should be removed on its standard output, and the new history file will be left in history.n, history.n.dir, history.n.index and history.n.hash. This flag be useful for debugging when used with the ``-n'' flags. Note that if the ``-f'' flag is used, then the name specified with that flag will be used instead of history. -v The ``-v'' flag is used to increase the verbosity of the program, generating messages to standard output. The level should be a number, where higher numbers result in more output. Level one will print totals of the various actions done (not valid if a new history file is not written), level two will print report on each individual file, while level five results in more than one line of output for every line processed. -w Use the ``-w'' flag to ``warp'' time so that expire thinks it is running at some time other then the current time. The value should be a signed floating point number of the number of days to use as the offset. -x If the ``-x'' flag is used, then expire will not create any new history files. This is most useful when combined with the ``-n'' and ``-t'' flags to see how different expiration policies would change the amount of disk space used. -z If the ``-z'' flag is used, then articles are not removed, but their names are appended to the specified file. See the description of delayrm in news.daily(8). If a filename is specified, it is taken as the control file and parsed according to the rules in expire.ctl(5). A single dash (``-'') may be used to read the file from standard input. If no file is specified, the file <pathetc in inn.conf>/expire.ctl is read. HISTORY
Written by Rich $alz <rsalz@uunet.uu.net> for InterNetNews. This is revision 1.19.2.1, dated 2000/08/17. SEE ALSO
ctlinnd(8), dbz(3), expire.ctl(5), history(5), inn.conf(5), innd(8), inndcomm(3). EXPIRE(8)
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