.. $Id: index.txt 4dca5ad0f397 2010-03-10 mtnyogi $
.. 
.. Copyright © 2007-2010 Bruce Frederiksen
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restindex
    crumb: Using Pyke
    page-description:
        How your Python program calls Pyke.
    /description
    section-pages: , creating_engine, adding_facts, proving_goals, other_functions
    format: rest
    encoding: utf8
    output-encoding: utf8
    include: yes
    initialheaderlevel: 2
/restindex

uservalues
    filedate: $Id: index.txt 4dca5ad0f397 2010-03-10 mtnyogi $
/uservalues

==========
Using Pyke
==========

This describes how to call Pyke from your Python program.

Getting Started
===============

.. this code is hidden and will set __file__ to the doc/examples directory.
   >>> import os
   >>> __file__ = \
   ...   os.path.join(os.path.dirname(os.path.dirname(os.getcwd())),
   ...                'examples')

The simplest use of Pyke involves three steps:

`Create an engine`_ object.

    >>> from pyke import knowledge_engine

    >>> my_engine = knowledge_engine.engine(__file__)

    This step compiles the Pyke source files, if out of date, and loads the
    `knowledge bases`_.

    There are three kinds of Pyke source files:

    #.  `.kfb files`_ define `fact bases`_, which are compiled into .fbc pickle
        files.
    #.  `.krb files`_ define `rule bases`_, which are compiled into 1 to 3 .py
        Python source files.
    #.  `.kqb files`_ define `question bases`_, which are compiled into .qbc
        pickle files.

    See `Creating an Inference Engine`_ to control where the compiled files
    are written, load knowledge bases from multiple directories, distribute
    your application without your knowledge base files, or distribute using
    egg files.

Activate `rule bases`_.

    >>> my_engine.activate('bc_related')

    You may activate one rule base for each `rule base category`_.  Simply
    pass multiple arguments to ``activate``.

    .. note::

       Even if you only have one rule base, you must still activate it.

    This is when the `forward-chaining rules`_ are run.

Prove_ goal_.

    >>> my_engine.prove_1_goal('bc_related.father_son(bruce, $son, ())')
    ({'son': 'david'}, None)

    The goal might be met by simply matching an already known fact_, or
    through the use of `backward-chaining rules`_.

    Then if you want to prove another goal, you can just repeat the last step.
    In this case, the `forward-chaining rules`_ are only run once and all goals
    operate against the same set of known facts.

    >>> my_engine.prove_1_goal('bc_related.father_son(thomas, $grandson, (grand))')
    ({'grandson': 'david'}, None)

    See `Proving Goals`_ to pass different arguments into goals, compile the
    goal statements once in advance, and to retrieve multiple answers for a
    goal.

Dynamically Asserting Facts
===========================

To dynamically assert_ facts_ within your Python program, a new step is
added:

    Create the engine object:

    >>> my_engine = knowledge_engine.engine(__file__)

Assert_ facts_.

>>> my_engine.assert_('family2', 'son_of', ('spike_the_dog', 'david'))

These facts must be asserted prior to activating the rule bases so that they
are available to the `forward-chaining rules`_.  This example shows asserting
case specific facts that are deleted before running the next case (as shown
in the next section, below).  But you can also assert universal facts that
apply to all cases.  See `Asserting New Facts`_ for more information.

    After asserting your facts, activate your rule bases and prove your goal
    as before:

    >>> my_engine.activate('bc_related')
    >>> my_engine.prove_1_goal('bc_related.father_son(bruce, $grandson, (grand))')
    ({'grandson': 'spike_the_dog'}, None)

Using Different Facts for Different Cases
=========================================

But if you want to prove goals against different sets of facts or using
different rule bases, you need to reset_ the Pyke engine:

    Only need this once:

    >>> my_engine = knowledge_engine.engine(__file__)

    First case, as before:

    >>> my_engine.assert_('family2', 'son_of', ('spike_the_dog', 'david'))
    >>> my_engine.activate('bc_related')
    >>> my_engine.prove_1_goal('bc_related.father_son(bruce, $grandson, (grand))')
    ({'grandson': 'spike_the_dog'}, None)

Reset the Pyke engine.

>>> my_engine.reset()

This erases all of the case specific facts that you asserted in step 2, as
well as all of the facts asserted by the `forward-chaining rules`_.

It also deactivates all of the `rule bases`_, so you'll need to call
activate again after asserting your facts.

    Second case:

    >>> my_engine.assert_('family2', 'son_of', ('felix_the_cat', 'david'))
    >>> my_engine.activate('bc_related')
    >>> my_engine.prove_1_goal('bc_related.father_son(bruce, $grandson, (grand))')
    ({'grandson': 'felix_the_cat'}, None)

