[2922d1]: doc / html / using_pyke / proving_goals.html Maximize Restore History

Download this file

proving_goals.html    236 lines (223 with data), 9.9 kB

  1
  2
  3
  4
  5
  6
  7
  8
  9
 10
 11
 12
 13
 14
 15
 16
 17
 18
 19
 20
 21
 22
 23
 24
 25
 26
 27
 28
 29
 30
 31
 32
 33
 34
 35
 36
 37
 38
 39
 40
 41
 42
 43
 44
 45
 46
 47
 48
 49
 50
 51
 52
 53
 54
 55
 56
 57
 58
 59
 60
 61
 62
 63
 64
 65
 66
 67
 68
 69
 70
 71
 72
 73
 74
 75
 76
 77
 78
 79
 80
 81
 82
 83
 84
 85
 86
 87
 88
 89
 90
 91
 92
 93
 94
 95
 96
 97
 98
 99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" lang="en" xml:lang="en">
<head>
<title>Proving Goals</title>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<link rel="stylesheet" href="../stylesheets/pyke.css" type="text/css" />
</head>
<body>
<table id="page-table">
<thead class="head">
<tr id="header1"><th id="header" colspan="3">
&nbsp;
</th></tr>
<tr id="header2">
<th id="crumb-left"></th>
<th id="crumb-line">
<div id="nav">
<ul>
<li><a href="../index.html">Home</a></li>
<li>&gt;</li>
<li><a href="index.html">Using Pyke</a></li>
<li>&gt;</li>
<li>Proving Goals</li>
</ul>
</div>
</th>
<th id="crumb-right"></th>
</tr>
</thead>
<tbody id="body">
<tr id="body-tr">
<td id="left-nav">
<div id="left-nav-div">
<div class="title-nav"><a href="../index.html">Home</a></div><div class="nav-branch">
<div class="normal-nav"><a href="../about_pyke/index.html">About Pyke</a></div>
<div class="normal-nav"><a href="../logic_programming/index.html">Logic Programming</a></div>
<div class="normal-nav"><a href="../knowledge_bases/index.html">Knowledge Bases</a></div>
<div class="normal-nav"><a href="../pyke_syntax/index.html">Pyke Syntax</a></div>
<div class="title-nav"><a href="index.html">Using Pyke</a></div><div class="nav-branch">
<div class="normal-nav"><a href="creating_engine.html">Creating an Engine</a></div>
<div class="normal-nav"><a href="adding_facts.html">Asserting Facts</a></div>
<div class="normal-nav"><a href="proving_goals.html">Proving Goals</a></div>
<div class="normal-nav"><a href="other_functions.html">Other functions</a></div>
</div>
<div class="normal-nav"><a href="../examples.html">Examples</a></div>
<div class="normal-nav"><a href="../PyCon2008-paper.html">PyCon 2008 Paper</a></div>
</div>
</div>
<div id="icons">
<div id="project-page">
<a href="http://sourceforge.net/projects/pyke/">Pyke Project Page</a>
</div>
Please Make a Donation:<br />
<a href="http://sourceforge.net/donate/index.php?group_id=207724">
<img src="http://images.sourceforge.net/images/project-support.jpg"
width="88" height="32" border="0"
alt="Support This Project" /> </a> <br /><br />
Hosted by: <br />
<a href="http://sourceforge.net/projects/pyke">
<img src="http://sflogo.sourceforge.net/sflogo.php?group_id=207724&amp;type=14"
width="150" height="40"
alt="Get Python Knowledge Engine (PyKE) at SourceForge.net. Fast, secure and Free Open Source software downloads" /></a>
</div>
</td>
<td id="main-td">
<div id="main">
<a name="startcontent" id="startcontent"></a>
<div class="document" id="proving-goals">
<h1 class="title">Proving Goals</h1>
<!-- 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')
>>> from pyke import knowledge_engine
>>> my_engine = knowledge_engine.engine(__file__)
>>> my_engine.add_universal_fact('family', 'son_of', ('bruce', 'thomas'))
>>> my_engine.add_universal_fact('family', 'son_of', ('david', 'bruce'))
>>> my_engine.activate('bc_related0') -->
<p>Though Pyke has the capability to return multiple answers to a single goal,
often you just want the first answer:</p>
<dl class="docutils">
<dt><em>some_engine</em>.prove_1_goal(goal, **args)</dt>
<dd><p class="first"><tt class="docutils literal">goal</tt> is a Pyke goal (as a string). This may include <a class="reference external" href="../logic_programming/pattern_matching/pattern_variables.html">pattern
variables</a> (which start with a '$').</p>
<pre class="doctest-block">
&gt;&gt;&gt; my_engine.prove_1_goal('bc_related0.father_son(thomas, david, $depth)')
({'depth': ('grand',)}, None)
</pre>
<p class="last">Returns the first proof found as a 2-tuple: a dict of bindings for the
pattern variables, and a <a class="reference external" href="../logic_programming/plans.html">plan</a>. The plan is <tt class="docutils literal">None</tt> if no plan was
generated; otherwise, it is a Python function as described <a class="reference external" href="other_functions.html#running-and-pickling-plans">here</a>.</p>
</dd>
</dl>
<blockquote>
<p>Args must be specified as keyword arguments and are set as the value of
the corresponding pattern variable.</p>
<pre class="doctest-block">
&gt;&gt;&gt; vars, plan = \
... my_engine.prove_1_goal('bc_related0.father_son($father, $son, $depth)',
... father='thomas',
... son='david')
&gt;&gt;&gt; sorted(vars.items(), key=lambda item: item[0])
[('depth', ('grand',)), ('father', 'thomas'), ('son', 'david')]
</pre>
<p>Prove_1_goal raises <tt class="docutils literal">pyke.knowledge_engine.CanNotProve</tt> if no proof is
found:</p>
<pre class="doctest-block">
&gt;&gt;&gt; my_engine.prove_1_goal('bc_related0.father_son(thomas, bogus, $depth)')
Traceback (most recent call last):
...
pyke.knowledge_engine.CanNotProve: Can not prove bc_related0.father_son(thomas, bogus, $depth)
</pre>
</blockquote>
<dl class="docutils">
<dt><em>some_engine</em>.prove_goal(goal, **args)</dt>
<dd><p class="first">This returns a context manager for a generator yielding 2-tuples, as
above. Unlike <tt class="docutils literal">prove_1_goal</tt> it does not raise an exception if no
proof is found:</p>
<pre class="doctest-block">
&gt;&gt;&gt; from __future__ import with_statement
</pre>
<pre class="doctest-block">
&gt;&gt;&gt; with my_engine.prove_goal(
... 'bc_related0.father_son(thomas, $son, $depth)') as gen:
... for vars, plan in gen:
... print(vars['son'], vars['depth'])
bruce ()
david ('grand',)
</pre>
<p>Like <tt class="docutils literal">prove_1_goal</tt>, above, <a class="reference external" href="../logic_programming/pattern_matching/pattern_variables.html">pattern variables</a> in the <a class="reference external" href="../logic_programming/rules/backward_chaining.html">goal</a> may be
specified with keyword arguments:</p>
<pre class="last doctest-block">
&gt;&gt;&gt; with my_engine.prove_goal(
... 'bc_related0.father_son($father, $son, $depth)',
... father='thomas') as gen:
... for vars, plan in gen:
... print(vars['son'], vars['depth'])
bruce ()
david ('grand',)
</pre>
</dd>
</dl>
<div class="section" id="compiling-goals-at-program-startup">
<h2>Compiling Goals at Program Startup</h2>
<p>Similar to Python's regular expression library, <tt class="docutils literal">re</tt>, you may compile your
goal statements once at program startup:</p>
<blockquote>
<pre class="doctest-block">
&gt;&gt;&gt; from pyke import goal
</pre>
<pre class="doctest-block">
&gt;&gt;&gt; my_goal = goal.compile('bc_related0.father_son($father, $son, $depth)')
</pre>
</blockquote>
<p>Then use <tt class="docutils literal">my_goal.prove_1</tt> and <tt class="docutils literal">my_goal.prove</tt> as many times as you'd
like:</p>
<blockquote>
<pre class="doctest-block">
&gt;&gt;&gt; vars, plan = my_goal.prove_1(my_engine, father='thomas', son='david')
&gt;&gt;&gt; sorted(vars.items(), key=lambda item: item[0])
[('depth', ('grand',)), ('father', 'thomas'), ('son', 'david')]
</pre>
<pre class="doctest-block">
&gt;&gt;&gt; with my_goal.prove(my_engine, father='thomas') as gen:
... for vars, plan in gen:
... print(vars['son'], vars['depth'])
bruce ()
david ('grand',)
</pre>
</blockquote>
<!-- ADD_LINKS MARKER -->
</div>
</div>
<!-- <div id="return-to-top">
<a href="#">Return to Top</a>
</div>
-->
</div>
</td>
<td id="right-nav">
<div id="right-nav-div">
<h3>More:</h3>
<div class="right-item"><a href="creating_engine.html">Creating an Inference Engine Object</a><p>How to create a Pyke <em>inference engine</em> object.</p>
</div>
<div class="right-item"><a href="adding_facts.html">Asserting New Facts</a><p>How to dynamically assert new <em>facts</em> from your Python program.</p>
</div>
<div class="right-item"><a href="proving_goals.html">Proving Goals</a><p>Using Pyke's API to prove goals from your Python program.</p>
</div>
<div class="right-item"><a href="other_functions.html">Other Functions</a><p>Other miscellaneous functions available that you might be interested
in, such as tracing rules and smart error tracebacks that show lines
from your .krb files.</p>
</div>
</div>
</td>
</tr>
</tbody>
<tfoot id="foot">
<tr id="foot2">
<td id="copyright" colspan="3">
Copyright &copy; 2007-2009 Bruce Frederiksen
</td>
</tr>
</tfoot>
</table>
<div id="last-modified">
Page last modified
Wed, Mar 10 2010.
</div>
<script type="text/javascript">
var gaJsHost = (("https:" == document.location.protocol) ?
"https://ssl." : "http://www.");
document.write(unescape("%3Cscript src='" + gaJsHost +
"google-analytics.com/ga.js' type='text/javascript'%3E%3C/script%3E"));
</script>
<script type="text/javascript">
try {
var pageTracker = _gat._getTracker("UA-6310805-1");
pageTracker._trackPageview();
} catch(err) {}
</script>
</body>
</html>