lorenzb/bellog

Tools for the four-valued logic programming language BelLog

BelLog

Tools for the four-valued logic programming language BelLog.

For details of the language see: http://dx.doi.org/10.3929/ethz-a-010045530

A policy interpreter is available at www.bellog.org

INSTALL

To use the BelLog interpreter you need to install:

• pexpect: http://pexpect.readthedocs.org/en/latest/
• XSB: http://xsb.sourceforge.net/

Configure the BelLog interpreter with the correct path to your XSB binary. Edit the file src/config and edit the line

'XSB_PATH' : 'path to xsb'

where you change path to xsb with the path to XSB.

BELLOG SYNTAX

A BelLog policy file is a file that contains one rule per line. The syntax of policy rules is given below:

<rule>      := <atom> :- <query>
<query>     := <value> | <atom> | !<query> | ~<query> | (<query> ^ ... ^ <query>) 
               | (<query> <binary op> <query>) | (<query> < <query> > <query>)
<binary-op> := -plus- | -times- | -<value>-> 
<atom>      := <pred>[(<arg>, ... , <arg>)][@arg]
<pred>      := [a-z][a-z|A-Z|0-9|_]*
<arg>       := <const> | <var>
<const>     := [a-z][a-z|A-Z|0-9|_|']*
<var>       := [A-Z][a-z|A-Z|0-9|_|']*
<value>     := true | false | bot | top

The ternary operator p < q > r is the standard if-then-else. The result of p < q > r is p if q evaluates to true, and otherwise it is r.

An example of a BelLog policy file is:

p(X) :- ( (q(X) -plus- r(X)) -top-> s(X) )
q(a) :- true
r(a) :- false
s(a) :- bot

USAGE

To run the BelLog interpreter type:

$ ./src/run.py -i bellog_file -q query

where bellog_file is a BelLog policy file and query is written using the syntax of query elements; see syntax above.

EXAMPLE

$ ./src/run.py -i examples/simple.blg -q "p(a)"