14 - CLIPS e JESS

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Programming a Knowledge Based Application
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Overview
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Rule-based Intelligent UI
 Inference Engine
Knowledge
 Base
 (Rules)
Working
Memory
 (Facts)
User Interface
 Agenda
“Intelligence”
(Knowledge-based system)
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Rule-based Intelligent UI
 Inference Engine
Knowledge
 Base
 (Rules)
Working
Memory
 (Facts)
User Interface
 Agenda
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Components 
of a Rule-Based System (1)
FACT BASE or fact list represents the initial state of the problem. This is the data from which inferences are derived.
RULE BASE or knowledge base (KB) contains a set of rules which can transform the problem state into a solution. It is the set of all rules.
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Components 
of a Rule-Based Language (2)
INFERENCE ENGINE controls overall execution. It matches the facts against the rules to see what rules are applicable. It works in a recognize-act cycle:
match the facts against the rules
choose which rules instantiation to fire
execute the actions associated with the rule
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CLIPS
C Language Integrated Production System
Public domain software
Supports:
Forward Chaining Rules based on Rete algorithm
Procedural Programming
Object-oriented programming (COOL)
Can be integrated with other C/C++ programs/applications
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JESS
Java Expert System Shell
Inspired by CLIPS => forward chaining rule system + Rete algorithm
Free demo version available (trial period of 30 days)
Can be integrated with other Java code
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Bakcground
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Production Rules
Production rules were developed for use in automata theory, formal grammars, programming language design & used for psychological modeling before they were used for expert systems.
Also called condition-action, or situation-action rules.
Encode associations between patterns of data given to the system & the actions the system should perform as a consequence.
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Canonical Systems
Production rules are grammar rules for manipulating strings of symbols.
Also called rewrite rules (they rewrite one string into another).
First developed by Post (1943), who studied the properties of rule systems based on productions & called his systems canonical systems.
He proved any system of mathematics or logic could be written as a type of production rule system. Minsky showed that any formal system can be realized as a canonical system.
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Example of a Canonical System
Let A be the alphabet {a, b, c} 
With axioms a, b, c, aa, bb, cc
Then these production rules will give all the possible palindromes (and only palindromes) based on the alphabet, starting from the above axioms.
(P1) $ -> a$a
(P2) $ -> b$b
(P3) $ -> c$c
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Example continued
To generate bacab
P1 is applied to the axiom c to get aca
Then we apply P2 to get bacab
Using a different order gives a different result.
If P2 is applied to c we get bcb
If P1 is applied after we get abcba
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Production Systems for Problem Solving
In KB systems production rules are used to manipulate symbol structures rather than strings of symbols.
The alphabet of canonical systems is replaced by
a vocabulary of symbols
and a grammar for forming symbol structures.
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Rule-Based Production Systems
A production system consists of
a rule set / knowledge base / production memory
a rule interpreter / inference engine
that decides when to apply which rules
a working memory
that holds the data, goal statements, & intermediate results that make up the current state of the problem. 
Rules have the general form
IF <pattern> THEN <action>
P1, …, Pm  Q1, …, Qn
Patterns are usually represented by OAV vectors.
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An OAV Table
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RULES
General form:	a 	 	 b
				IF … THEN …
		IF < antecedent, condition, LHS>
		THEN <consequent, action, RHS>
 Antecedent match against symbol structure
Consequent contains special operator(s) to manipulate those symbol structures
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Syntax of Rules
The vocabulary consists of 
a set N of names of objects in the domain
a set P of property names that give attributes to objects
a set V of values that the attributes can have.
Grammar is usually represented by OAV triples
OAV triple is (object, attribute, value) triples
Example: (whale, size, large)
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Forward & Backward Chaining
Production rules can be driven forward or backward.
We can chain forward from conditions that we know to be true towards problem states those conditions allow us to establish the goal; or
We can chain backward from a goal state towards the conditions necessary for establishing it.
Forward chaining is associated with ‘bottom-up’ reasoning from facts to goals.
Backward chaining is associated with ‘top-down’ reasoning from facts to goals.
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Forward 			Backward Chaining 			Chaining
facts
goal
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Palindrome Example
If we have the following grammar rules
(P1) $ -> a$a
(P2) $ -> b$b
(P3) $ -> c$c
They can be used to generate palindromes  forward chaining
apply P1, P1, P3, P2, to c > aca aacaa caacaac -
Or they can be used to recognize palindromes  backward chaining
bacab matches the RHS of P2 but acbcb will not be accepted by any RHS
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Forward Chaining
Fig. based on http://ai-depot.com/Tutorial/RuleBased-Methods.html
Determine 
possible 
rules to fire
Select 
rule to 
fire
Conflict
resolution
strategy
Exit
No rule found
Conflict set
Fire 
rule
Rule found
Exit if specified by the rule
Rule
base
Working
memory
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Chaining & CLIPS/JESS
CLIPS and JESS uses forward chaining.
 The LHS of rules are matched against working memory.
 Then the action described in the RHS of the rule, that fires after conflict resolution, is performed.
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Palindrom Example
To generate bacab
P1 is applied to the axiom c to get aca
Then we apply P2 to get bacab
Using a different order gives a different result.
If P2 is applied to c we get bcb
If P1 is applied after we get abcba
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Markov algorithm
A Markov algorithm (1954) is a string rewriting system that uses grammar-like rules to operate on strings of symbols. Markov algorithms have been shown to have sufficient power to be a general model of computation.
Important difference from canonical system: now the set of rules is ordered
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Palindrom example revisited
To generate bacab
P1 is applied to the axiom c to get aca
Then we apply P2 to get bacab
Using a different order gives a different result.
If P2 is applied to c we get bcb
If P1 is applied after we get abcba
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Making it more efficient
The Rete algorithm is an efficient pattern matching algorithm for implementing rule-based expert systems. 
The Rete algorithm was designed by Dr. Charles L. Forgy of Carnegie Mellon University in 1979.
Rete has become the basis for many popular expert systems, including OPS5, CLIPS, and JESS. 
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RETE algorithm
Creates a decision tree where each node corresponds to a pattern occurring at the left-hand side of a rule
Each node has a memory of facts that satisfy the pattern
Complete LHS as defined by a path from root to a leaf.
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Rete example
(http://aaaprod.gsfc.nasa.gov/teas/Jess/JessUMBC/sld010.htm)
x?
y?
x?
y?
z?
Pattern 
Network
Rules: IF x & y THEN p
 IF x & y & z THEN q
p
Join Network
8 nodes
q
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Rete example
(http://aaaprod.gsfc.nasa.gov/teas/Jess/JessUMBC/sld010.htm)
x?
y?
z?
Pattern 
Network
Rules: IF x & y THEN p
 IF x & y & z THEN q
p
Join Network
6 nodes
q
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Rete example
(http://aaaprod.gsfc.nasa.gov/teas/Jess/JessUMBC/sld010.htm)
x?
y?
z?
Pattern 
Network
Rules: IF x & y THEN p
 IF x & y & z THEN q
p
Join Network
5 nodes
q
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Matching Patterns
At each cycle the interpreter
looks to see which rules have conditions that can be satisfied.
If a condition has no variables it will only be satisfied by an identical expression in working memory.
If the condition contains variables then it will be satisfied if there is an expression in working memory with an attribute-value pair that matches it in a way that is consistent with the way other conditions in the same rule have already been matched.
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Example of matching
(whale (species Beluga) (tail_fin NO)(dorsal_fin NO))
Matches the pattern (with variables)
(whale (species ?name) (tail_fin ?flukes) (dorsal_fin ?fin)
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The Working Memory
Holds data in the form of OAV vectors.
These data are then used by the interpreter to activate the rules.
The presence or absence of data elements in the working memory will trigger rules by satisfying patterns on the LHS of rules.
Actions such as assert or modify the working memory.
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Conflict Resolution
Production systems have a decision-making step between pattern matching & rule firing.
All rules that have their conditions satisfied are put on the agenda in CLIPS.
The set of rules on the agenda is sometimes called the conflict set.
Conflict resolution selects which rule to fire from the agenda.
Packages like CLIPS provide more than one option for conflict resolution
Sensibility (quick response to changes in WM) and Stability (continuous reasoning).
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Conflict Resolution in CLIPS
First, CLIPS uses salience to sort the rules. Then it uses the other strategies to sort rules with equal salience.
CLIPS uses refraction, recency & specificity in the form of following 7 strategies:
The depth strategy
The breadth strategy
The simplicity strategy
The complexity strategy
The LEX strategy
The MEA strategy
It is possible also to set strategy to random
Syntax: (set-strategy <strategy>)
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Salience
Normally the agenda acts like a stack.
The most recent activation placed on the agenda is the first rule to fire.
Salience allows more important rules to stay at the top of the agenda regardless of when they were added. 
If you do not explicitly say, CLIPS will assume the rule has a salience of 0.
a positive salience gives more weight to a rule
a negative salience gives less weight to a rule
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Refractoriness
A rule should not be allowed to fire more than once for the same data.
Prevents loops
Used in CLIPS and JESS (need to (refresh) to bypass it)
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How to
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Example
Simplified description of some varieties of cultivated apples:
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Rules
The simple way – write standard if..then rules:
IF (color == red && size == large)
	THEN variety = Cortland
We will need: 4 rules (+ rule(s) for asking questions) => minimum 5 rules
BUT: can do it in 2 rules in CLIPS/JESS
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Define Template
(deftemplate apple
	(multislot variety (type SYMBOL) )
	(slot size (type SYMBOL))
	(slot color (type SYMBOL) (default red))
	)
Other useful slot type: NUMBER
JESS note: in JESS multislots don’t have type
		 CLIPS allow both SYMBOL and STRING types, 	 	 JESS – only STRING
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Assert Facts
(deffacts apple_varieties
(apple (variety Cortland) (size large) (color red))
(apple (variety Golden delicious) (size large) (color yellow))
(apple (variety Red Delicious) (size medium) (color red))
(apple (variety Granny Smith) (size large) (color green))
)
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Create Rules – Rule 1
(defrule ask-size
	(declare (salience 100)) ;NOTE: JESS don’t use salience
	(initial-fact)
=>
	(printout t “Please enter the apple characteristics :“  crlf)
	(printout t “- color (red, yellow, green) : “)
	(bind ?ans1 (read))
	(printout t crlf “-size (large or medium) : “)
	(bind ?ans2 (read))
	(assert (apple (variety users) (color ?ans1) (size ?ans2)))
)
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Create Rules – Rule 2
(defrule variety
	(declare (salience 10)) ;JESS NOTE – take this out
	(apple (variety users) (size ?s) (color ?c))
	(apple (variety ?v&:(neq ?v users))(size ?s) (color ?c))
=>
(printout t “You’ve got a “ ?v crlf)
(halt)
)
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Run CLIPS
Type the code in a file, save it (e.g. apples.clp)
start CLIPS (type clips or xclips in UNIX/LINUX)
do: File -> Load (in XCLIPS) or type 
	(load “apples.clp”)
when the file is loaded CLIPS will display:
	defining deftemplate apple
	defining deffacts apple_varieties
	defining defrule ask-size +j
	defining defrule variety +j+j
	TRUE
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Run CLIPS
Type (reset) to put your initial facts in the fact base
CLIPS>(run)
Please enter the apple characteristics:
	- color red, yellow, green: red
- size (large or medium) : large
You’ve got a Cortland
CLIPS> (exit)
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Run JESS
UNIX command line:
java –classpath jess.jar jess.Main
Or start an applet console.html
Jess> (batch apples.clp)
	TRUE
	Jess> (reset)
	TRUE
	Jess> (run)
Please enter the apple characteristics:
	- color red, yellow, green: red
- size (large or medium) : large
You’ve got a Cortland
2
Jess> (exit)
	
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CLIPS resources
Official CLIPS website (maintained by Gary Riley):
	http://www.ghg.net/clips/CLIPS.html 
CLIPS Documentation:
http://www.ghg.net/clips/download/documentation
Examples:
	http://www.ghg.net/clips/download/executables/examples/ 
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Integrating CLIPS into C/C++
Go to the source code
Replace CLIPS main with user-defined main (follow the instructions within the main)
#include “clips.h” in classes that will use it
Compile all with ANSI C++ compiler
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Resources 
for CLIPS C++ integration
CLIPS advanced programming guide
Anonymous ftp from hubble.jsc.nasa.gov directory pub/clips/Documents
DLL for CLIPS 5.1 for Windows at ftp.cs.cmu.edu directory pub/clips/incoming
Examples can be found also at http://ourworld.compuserve.com/homepages/marktoml/cppstuff.htm and http://www.monmouth.com/%7Ekm2580/dlhowto.htm 
	
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JESS resources
http://herzberg.ca.sandia.gov/jess/ 
Includes instructions and examples for embedding JESS into a Java program (http://herzberg.ca.sandia.gov/jess/docs/61/embedding.html ) and or creating Java GUI from JESS (see http://herzberg.ca.sandia.gov/jess/docs/61/jessgui.html)