Transcript 17 Lecture CSC462 .pptx

Artificial Intelligence
Lecture No. 17
Dr. Asad Ali Safi
Assistant Professor,
Department of Computer Science,
COMSATS Institute of Information Technology (CIIT)
Islamabad, Pakistan.
Summary of Previous Lecture
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•
•
•
Types of inference engines
Forward chaining and backward chaining
Conflict resolution
Advantages/disadvantages of rule-based expert
systems
Today’s Lecture
• What is CLIPS?
• CLIPS difference
• Interacting with clips
CLIPS
• CLIPS is a public domain software tool for
building expert systems.
• The name is an acronym for "C Language
Integrated Production System."
• The first versions of CLIPS were developed
starting in 1985 at NASA-Johnson Space Center,
until the mid-1990s when the development
group's responsibilities ceased to focus on expert
system technology.
• The original name of the project was NASA's AI
Language (NAIL).
CLIPS
• Source
• Installation
• GUI
CLIPS
• CLIPS is a type of computer language designed
for writing applications called expert systems.
• CLIPS is called an expert system tool because
it is a complete environment for developing
expert systems which includes features such
as an integrated editor and a debugging tool.
What is CLIPS?
 CLIPS
is a multiparadigm programming language
that provides support for:


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Rule-based
Object-oriented
Procedural programming
 Syntactically,
Eclipse
 CLIPS/R2
 JESS

CLIPS resembles:
Other CLIPS Characteristics
 CLIPS
supports only forward-chaining rules.
 The OOP capabilities of CLIPS are referred to as
CLIPS Object-Oriented Language (COOL).
 The procedural language capabilities of CLIPS
are similar to languages such as:



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C
C++
Pascal
Lisp
Fact List
(contains data)
Knowledge
Base
(contains rules)
Inference
Engine
(controls execution)
Program
• A program written in CLIPS may consist of
rules, facts, and objects. The inference engine
decides which rules should be executed and
when.
• A rule-based expert system written in CLIPS is
a data-driven program
• Where the facts, and objects if desired, are
the data that stimulate execution via the
inference engine.
CLIPS difference
• This is one example of how CLIPS differs from
procedural languages such as Java, BASIC,
FORTRAN, and C.
• In procedural languages, execution can proceed
without data. That is, the statements are
sufficient in those languages to cause execution.
– For example, a statement such as PRINT 2 + 2 could be
immediately executed in BASIC. This is a complete
statement that does not require any additional data to
cause its execution.
– However, in CLIPS, data are required to cause the
execution of rules.
Interacting with clips
• CLIPS expert systems may be executed in
three ways:
– interactively using a simple, text-oriented,
command prompt interface;
– interactively using a window/menu/mouse
interface on certain machines;
– or as embedded expert systems in which the user
provides a main program and controls execution
of the expert system.
• The generic CLIPS interface is a simple, interactive,
text-oriented, command prompt interface for high
portability.
• The standard usage is to create or edit a knowledge
base using any standard text editor, save the
knowledge base as one or more text files, exit the
editor and execute CLIPS, then load the knowledge
base into CLIPS.
• The interface provides commands for viewing the
current state of the system, tracing execution, adding
or removing information, and clearing CLIPS.
Top Level Commands
• When the “CLIPS>” prompt is printed, a command may be
entered for evaluation. Commands may be function calls,
constructs, local or global variables, or constants.
• If a function call is entered, that function is evaluated and its
return value is printed.
• Function calls in CLIPS use a prefix notation—the operands to
a function always appear after the function name. Entering a
construct definition at the CLIPS prompt creates a new
construct of the appropriate type.
•
•
CLIPS> (+ 3 4)
7
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•
•
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CLIPS> (bind ?a 5)
5
CLIPS> (+ ?a 3)
8
CLIPS> (reset)
CLIPS> ?a
[EVALUATN1] Variable a is unbound
FALSE
CLIPS>
Data Types
• CLIPS provides eight primitive data types for
representing information. These types are float,
integer, symbol, string, external-address, factaddress, instance-name and instance-address.
• Numeric information can be represented using floats
and integers. Symbolic information can be
represented using symbols and strings. A number
consists only of digits (0-9), a decimal point (.), a sign
(+ or -), and, optionally, an (e) for exponential
notation with its corresponding sign.
•
• A number is either stored as a float or an integer.
Any number consisting of an optional sign
followed by only digits is stored as an integer
(represented internally by CLIPS as a C long
integer). All other numbers are stored as floats
(represented internally by CLIPS as a C doubleprecision float).
• Some examples of integers are
• 237 15 +12 -32
• Some examples of floats are
• 237e3 15.09 +12.0 -32.3e-7
Symbol
• A symbol in CLIPS is any sequence of characters that starts
with any printable ASCII character and is followed by zero or
more printable ASCII characters. When a delimiter is found,
the symbol is ended. The following characters act as
delimiters: any non-printable ASCII character (including
spaces, tabs, carriage returns, and line feeds), a double quote,
opening and closing parentheses “(” and “)”, an ampersand
“&”, a vertical bar “|”, a less than “<”, and a tilde “~”.
• A semicolon “;” starts a CLIPS comment and also acts as a
delimiter.
• Delimiters may not be included in symbols with the
exception of the “<“ character which may be the first
character in a symbol. In addition, a symbol may not begin
with either the “?” character or the “$?” sequence of
characters (although a symbol may contain these
characters). These characters are reserved for variables
• CLIPS is case sensitive (i.e. uppercase letters will match only
uppercase letters). Note that numbers are a special case of
symbols
• Some simple examples of symbols are
• foo Hello B76-HI bad_value
• 127A 456-93-039 @+=-% 2each
String
• A string is a set of characters that starts with a double
quote (") and is followed by zero or more printable
characters.
• A string ends with double quotes. Double quotes may be
embedded within a string by placing a backslash (\) in front
of the character.
• A backslash may be embedded by placing two consecutive
backslash characters in the string.
• Some examples are
– "foo" "a and b" "1 number" "a\"quote"
• Note that the string “abcd" is not the same as the symbol
abcd. They both contain the same characters, but are of
different types.
Fact
• A fact is a list of atomic values that are either
referenced positionally (ordered facts) or by
name (non-ordered or template facts).
• Facts are referred to by index or address;
• The printed format of a fact-address is:
• <Fact-XXX>
• where XXX is the fact-index.
Instance
• An instance is an object that is an instantiation or specific
example of a class. Objects in CLIPS are defined to be floats,
integers, symbols, strings, multifield values, externaladdresses, fact-addresses or instances of a user-defined class.
• A user-defined class is created using the defclass construct.
• An instance of a user-defined class is created with the makeinstance function, and such an instance can be referred to
uniquely by address or uniquely referred to by name.
• An instance-name is formed by enclosing a symbol within left
and right brackets. Thus, pure symbols may not be
surrounded by brackets.
• Some examples of instance-names are:
– [pump-1] [foo] [+++] [123-890]
• Note that the brackets are not part of the name of the
instance; they merely indicate that the enclosed symbol is
an instance-name.
• An instance-address can only be obtained by binding the
• return value of a function called instance-address or by
binding a variable to an instance matching an object
pattern on the LHS of a rule
• A reference to an instance of a user-defined class can either
be by name or address; instance-addresses should only be
used when speed is critical.
• Within CLIPS, the printed representation of an instanceaddress is <Instance-XXX>
• where XXX is the name of the instance.
Function
• A function in CLIPS is a piece of executable code
identified by a specific name which returns a
useful value or performs a useful side effect (such
as displaying information).
• There are several types of functions. User defined
functions and system defined functions
• System defined functions are those functions that
have been defined internally by the CLIPS
environment. User defined functions are
functions that have been defined externally of
the CLIPS environment.
• Function calls in CLIPS use a prefix notation – the arguments to a
function always appear after the function name.
• Function calls begin with a left parenthesis, followed by the name of
the function, then the arguments to the function follow (each
argument separated by one or more spaces).
• Arguments to a function can be primitive data types, variables, or
another function call. The function call is then closed with a right
parenthesis.
• Some examples of function calls using the addition (+) and
multiplication (*) functions are shown following.
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–
–
–
–
–
–
(+ 3 4 5)
(* 5 6.0 2)
(+ 3 (* 8 9) 4)
(* 8 (+ 3 (* 2 3 4) 9) (* 3 4))
CLIPS> (+ 2 3(- 10 5))
10
CLIPS> (+ 2 3(- 5 10))
0
CLIPS> (+ 2 3(- 5 15))
?
Facts
• Facts are one of the basic high-level forms for
representing information in a CLIPS system.
Each fact represents a piece of information
which has been placed in the current list of
facts, called the fact-list.
• Facts are the fundamental unit of data used by
rules
• Facts may be added to the fact-list (using the assert
command), removed from the fact-list (using the
retract command), modified (using the modify
command), or duplicated (using the duplicate
command) through explicit user interaction or as a
CLIPS program executes.
• The number of facts in the fact-list and the amount of
information that can be stored in a fact is limited only
by the amount of memory in the computer.
• If a fact is asserted into the fact-list that exactly
matches an already existing fact, the new assertion will
be ignored (however, this behavior can be changed,
• Some commands, such as the retract, modify, and
duplicate commands, require a fact to be
specified.
• A fact can be specified either by fact-index or
fact-address. Whenever a fact is added (or
modified) it is given a unique integer index called
a fact-index.
• Fact-indices start at zero and are incremented by
one for each new or changed fact. Whenever a
reset or clear command is given, the fact-indices
restart at zero.
• A fact may also be specified through the use of a
fact-address.
Summery of Today’s Lecture
• What is CLIPS?
• CLIPS difference
• Interacting with clips