In reality, deleting facts is generally not something one wants to do as it's considered a "non-logical" operation. However, you can use retract/1 if you really need to:

AI-NeuralNet-Simple-0.03 $ aiprolog 


Welcome to AI::Prolog v 0.732
Copyright (c) 2005, Curtis "Ovid" Poe.
AI::Prolog comes with ABSOLUTELY NO WARRANTY.  This library is free so
+ftware;
you can redistribute it and/or modify it under the same terms as Perl 
+itself.

Type '?' for help.

?- help('retract/1') 

retract/1

    Remove facts from the database. You cannot remove rules. This may
    change in the future. See assert(X).

     retract(loves(ovid,java)).

help(retract/1) 

Yes
?-

[download]

You can also just type "help" at the aiprolog prompt to see a list of all built-in predicates you can get help for:

?- help.

Help is available for the following builtins:

!/0          assert/1     call/1       consult/1    div/2    
eq/2         fail/0       ge/2         gt/2         halt/1   
if/3         is/2         le/2         listing/0    listing/1
lt/2         minus/2      mod/2        mult/2       ne/2     
nl/0         not/1        notrace/0    once/1       or/2     
plus/2       pow/2        print/1      println/1    retract/1
trace/0      true/0       var/1        write/1      writeln/1

help 

Yes
?-

[download]

If you really want to get a decent grounding in Prolog, see Amzi's "Adventure in Prolog". It's a free online book which lets guides through building four different Prolog applications. It's quite cool. Most of the basics work in AI::Prolog, but it could still use a lot of work/patches.

Cheers,
Ovid

New address of my CGI Course.

In reply to Re^3: Query database in Prolog by Ovid
in thread Query database in Prolog by zby

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.