Introduction to CLIPS: An expert programming language

1
Introduction to CLIPS An expert programming
language

• CLIPS (C Language Integrated Production System)
  A programming language designed by NASA/Johnson
  Space Center with the specific purpose of
  providing high portability, low cost, and easy
  integration with external systems.
• was written using the C programming language

2
Introduction to CLIPS An expert programming
language

• Three basic components of CLIPS
• Fact list contains the data on which inferences
  are derived
• Knowledge base contains all the rules
• Inference engine controls overall execution

3
Introduction to CLIPS An expert programming
language

• 3 types of programming paradigms supported by
  CLIPS
• rule-based
• object-oriented
• Procedural
• We will primarily focus on CLIPS as a rule-
• based programming language in this class

4
Introduction to CLIPS An expert programming
language

• The inferencing and representation capabilities
  provided by CLIPS rule-based programming language
  is similar to, but more powerful than, OPS5.
• Syntactically, CLIPS rules closely resemble the
  rules of ART, ART-IM, Eclipse, and Cognate.
• CLIPS supports only forward chaining rules.

5
CLIPS Notation

• Symbols and characters Anything not enclosed by
  the character pairs lt gt, , or should be
  entered exactly as shown
• e.g. (example)
• This syntax description means that (example)
  should be entered as shown. The character (
  should be entered first, followed by e, x,
  a, etc

6
CLIPS Notation

• Square brackets, , indicate that the contents
  of the brackets are optional.
• e.g. (example 1)
• Indicates that the 1 found within the brackets
  is optional. So the following would both be
  consistent with the syntax
• (example)
• OR
• (example 1)

7
CLIPS Notation

• The less than and greater than characters, lt gt,
  indicate that a replacement is to be made with a
  value of the type specified by the contents found
  within lt gt.
• e.g. ltintegergt
• indicates that a substitution should be made
  with an actual integer value
• (example ltintegergt) could be
• (example 1)
• (example 5)
• (example -20)
• it is important to note that spaces shown in
  the syntax description should be included in the
  entry.

8
CLIPS Notation

• Another notation is the following a
  description. This indicates that the description
  can be replaced with zero or more occurrences of
  the value specified. Spaces should be placed
  after each occurrence of a value.
• e.g. ltintegergt could be replaced with
• 1
• 1 2
• 1 2 3
• or with any number of integers, or with nothing
  at all

9
CLIPS Notation

• A description followed by a indicates that one
  or more of the values specified by the
  description should be used in placed of the
  syntax description.
• e.g. ltintegergt is equivalent to
• ltintegergt ltintegergt

10
CLIPS Notation

• A vertical bar, , indicates a choice among one
  or more of the items separated by the bars.
• e.g. all none some could be replaced with
  
• all
• none
• some

11
CLIPS Fields

• Tokens represent groups of characters that have
  special meaning to CLIPS as CLIPS reads
  characters from the keyboard or files, it groups
  them together into tokens. Some tokens such as
  left and right parentheses consist of only 1
  character.
• Fields a group of tokens.
• 7 types of fields (also called the CLIPS
  primitive data types)
• Float
• Integer
• Symbol
• String
• External address
• Instance name
• Instance address

12
CLIPS Notation

• Numeric fields numbers.
• two types
• integers any number consisting of an optional
  sign followed by only digits is stored as an
  integer.
• e.g.
• 1
• 3
• -1
• 65
• floats all other numbers
• e.g.
• 1.5
• 1.0
• 0.7
• 9e1
• 3.5e10

13
CLIPS Fields

• Three parts of numeric fields
• sign either or -
• value contains one or more digits with a single
  optional decimal point contained with the digits.
  
• exponent consists of the letter e or E followed
  by an optional or - followed by one or more
  digits.

14
CLIPS Symbols

• symbol a field that starts with a printable
  ASCII character and is followed by zero or more
  characters.
• The end of a symbol is reached when a delimiter
  is encountered.
• Symbols cannot contain delimiters (with the
  exception of lt which may be the first character
  in a symbol).
• The ? and ? sequence cannot be placed at the
  beginning of a symbol since these are used to
  denote variables.
• A sequence of characters which doesnt follow the
  numeric format is treated as a symbol.

15
CLIPS Delimiters

• delimiter includes any nonprintable ASCII
  character e.g. spaces, tabs, carriage returns,
  line feeds, the , ( , ) , , , , , and lt
  characters.

16
CLIPS An example

• examples of valid symbols
• Space-Station
• February
• fire
• activate_sprinkler_system
• notify-fire-department
• !?
• 345B
• note underscore _ and hyphen - characters
  should be used to tie symbols together to make
  them a single field.

17
CLIPS additional information

• case sensitivity CLIPS will preserve the
  uppercase and lowercase letters it finds in
  tokens.
• e.g.
• case-sensitive
• Case-sensitive
• CASE-SENSITIVE

18
CLIPS strings

• strings
• must begin and end with double quotes . The
  quotes are part of the fields there can be zero
  or more characters of any kind between the double
  quotes including characters normally used by
  CLIPS as delimiters.
• e.g.
• activate the sprinkler system
• Shut down electrical junction 387.
• !7
• John Q. Madison
• spaces normally act as delimiters to separate
  fields (such as characters) and other tokens.
  Additional spaces used between tokens are
  discarded. Spaces included in the string are
  preserved.
• e.g. all of these are distinct strings
• spaces
• spaces
• spaces
• spaces
• note if surrounding double quotes were
  removed, CLIPS would consider
  each of the lines to contain the same word since
  spaces other than those used
  as delimiters would be ignored.

19
CLIPS double quotes

• It is not possible to directly place a double
  quote within a string
• e.g. three-tokens
• this would be interpreted by CLIPS as 3 separate
  tokens since double quotes act as delimiters. It
  would read it as
• three-tokens
• to correct this use the backslash \ operator
  
• e.g.
• \ single-token\ will be interpreted by CLIPS
  as
• single-token
• the backslash character may be placed within a
  string by using two backslashes in succession
• e.g.
• \\single-token\\ will be interpreted by CLIPS
  as
• \single-token\

20
CLIPS other types of fields

• external addresses represent the address of an
  external data structure returned by a
  user-defined function (a function written in a
  language such as C or Ada and linked with CLIPS
  to add additional functionality) its not
  possible to create this type of data in the basic
  unmodified version of CLIPS.
• instance addresses like external addresses, can
  only be obtained as the return value from a
  function fields used in conjunction with COOL.
  
• instance names symbols enclosed within left and
  right square brackets e.g. pump-1 fields used
  in conjunction with COOL.

21
CLIPS multifield value

• multifield value a series of zero or more fields
  contained together are usually created by
  calling a function or when specifying initial
  values for facts.
• e.g. a zero length multifield is ( )
• e.g. a multifield containing the symbols this
  and that is (this that)

22
CLIPS Entering CLIPS

• Entering issue appropriate run command for the
  machine the CLIPS prompt will appear
• CLIPSgt
• at this point, commands are entered directly into
• CLIPS. This is called the top level.

23
CLIPS Exiting CLIPS

• Exiting the normal mode for exiting CLIPS is
  with the exit command.
• e.g. (exit)
• The parentheses around exit is a command to be
  executed and not just the symbol exit. The
  symbol exit without enclosing parentheses has
  quite a different meaning than (exit).

24
CLIPS a sample session

• sample session of entering CLIPS, evaluating a
  constant field value, evaluating a function, and
  then exiting using the exit command
• Agt CLIPS press enter
• CLIPS (v6.0 05/12/93)
• CLIPSgt exit press enter because this
  exit is not enclosed in parentheses, CLIPS
  interprets is as input, not a command
• exit
• CLIPSgt ( 3 4) press enter
• 7
• CLIPSgt (exit) press enter interprets it as a
  command and exits
• Agt exits CLIPS

25
CLIPS Facts

• fact a chunk of information in CLIPS they
  consist of a relation name (a symbolic field)
  followed by zero or more slots (also symbolic
  fields) and their associated values.
• e.g. of a fact
• (person (name John Q. Public)
• (age 23)
• (eye-color blue)
• (hair-color black))
• the symbol person is the facts relation name and
  the fact contains 4 slots name, age, eye-color,
  hair-color. The values of the slots are John Q.
  Public, 23, blue, black the order in which slots
  are specified are irrelevant.
• the following fact is treated by CLIPS identical
  to the one above
• (person (hair-color black)
• (name John Q. Public)
• (eye-color blue)
• (age 23)

26
CLIPS Deftemplate Construct

• before facts can be created, CLIPS has to know
  the list of valid slots for a given relation
  name.
• deftemplate construct groups of facts which
  share the same relation name and contain common
  information analogous to a record structure.
• constructs form the core of a CLIPS program by
  adding the programmers knowledge to the CLIPS
  environment and are different from functions and
  commands.

27
CLIPS another example of syntax

• general format of a deftemplate
• e.g.
• (deftemplate ltrelation-namegt ltoptional-commentgt
• ltslot-definitiongt)
• the syntax description ltslot-definitiongt is
  defined as
• (slot ltslot-namegt) (multislot ltslot-namegt)
• using this syntax, person fact could be
• (deftemplate person an example
• deftemplate (slot name)
• (slot age)
• (slot eye-color)
• (slot hair-color))

28
CLIPS Multifield slots

• single-field slots slots of a fact that have
  been specified with the slot keyword in their
  corresponding deftemplate are allowed to contain
  only one value
• multifield slots slots that are allowed to
  contain zero or more values
• the name slot of the person deftemplate stores
  the persons name as a single string value the
  fact that was viewed before is illegal as a
  single-field slot, but is legal if name is a
  multifield slot.

29
CLIPS Ordered facts

• deftemplate facts facts with a relation name
  that has a corresponding deftemplate.
• ordered facts facts with relation name that
  does not have a corresponding deftemplate they
  have a single implied multifield slot which is
  used to store all values following the relation
  name. Whenever CLIPS encounters an ordered fact,
  it automatically creates an implied deftemplate
  for that fact (as opposed to an explicit
  deftemplate created using the deftemplate
  construct) since an ordered fact has only one
  slot, the slot name isnt required when defining
  a fact.
• a list of numbers could be represented with the
  following fact
• (number-list 7 9 3 4 20)
• This is equivalent to defining the deftemplate
• (deftemplate number-list (multislot values))
• and then defining the fact as follows
• (number-list (values 7 9 3 4 20))

30
CLIPS Ordered facts (continued)

• deftemplates should be used whenever possible
  because the slot names make the facts more
  readable and easier to work with.
• 2 cases in which ordered facts are useful
• Facts consisting of just a relation name are
  useful as flags and look identical regardless of
  whether a deftemplate has been defined.
• e.g. (all-orders-processed)
• could be used as a flag to indicate when all
  orders have been processed.
• For facts containing a single slot, the slot name
  is usually synonymous with the relation name.
• (time 845)
• (food-groups meat dairy bread
  fruits-and-vegetables)
• are just as meaningful as
• (time (value 845))
• (food-groups (values meat dairy bread
  fruits-and-vegetables))

31
CLIPS Adding and removing facts

• the group of all facts known to CLIPS is stored
  in the fact list facts representing information
  can be added and removed from the fact list. New
  facts can be added to the fact list using the
  assert command.
• e.g. (assert ltfactgt)
• using the person deftemplate, add John Q. Public
  to the fact list
• CLIPSgt
• (deftemplate person
• (slot name)
• (slot age)
• (slot eye-color)
• (slot hair-color)) press enter
• CLIPSgt
• (assert (person (name John Q. Public)
• (age 23)
• (eye-color blue)
• (hair-color black)) ) press enter
• ltFact-0gt
• CLIPSgt

32
CLIPS adding and removing facts (continued)

• facts command can be used to display the facts in
  the fact list.
• e.g.
• CLIPSgt (facts) press enter
• f-0 (person (name John Q. Public)
  (age 23)
• (eye-color blue) (hair-color black))
• For a total of 1 fact.
• CLIPSgt
• the term f-0 is the fact identifier assigned to
  the fact by CLIPS. Every fact is assigned a fact
  identifier starting with the letter f and
  followed by an integer called the fact
  index.
• Normally, CLIPS doesnt accept duplicate entries
  of a fact therefore, attempting to place a
  second John Q. Public fact with identical slot
  values will have no result.

33
CLIPS viewing a portion of the fact list

• to view a portion of the fact list, do
• (facts ltstartgt ltendgt ltmaximumgt)
• where ltstartgt, ltendgt, and ltmaximumgt are
  positive integers. If no arguments are specified,
  all facts are displayed.
• if the ltstartgt argument is specified, all facts
  with fact indexes greater than or equal to
  ltstartgt are displayed.
• if ltstartgt and ltendgt are specified, all facts
  with fact indexes greater than or equal to
  ltstartgt and less than or equal to ltendgt are
  displayed.
• if ltmaximumgt is specified along with ltstartgt and
  ltendgt, no more than ltmaximumgt facts will be
  displayed.

34
CLIPS Removing facts

• retraction removing facts from fact list is
  done with the retract command.
• e.g. (retract ltfact-indexgt)
• fact indices of one or more facts to be retraced
  are included as the arguments of the retract
  command.
• a single retract command can be used to retract
  multiple facts at once
• (retract 0 1)
• To remove John Q. Public from the fact list
• (retract 0)
• attempting to retract a nonexistent fact will
  produce the following error message (where
  PRNTUTIL1 is a key for finding the error
  message in CLIPS Reference Manual.
• PRNTUTIL1 Unable to find fact ltfact-identifiergt

35
CLIPS Modifying and duplicating facts

• modify command slot values of deftemplate facts
  can be modified using the modify command.
• (modify ltfact-indexgt ltslot-modifiergt)
• where ltslot-modifiergt is
• (ltslot-namegt ltslot-valuegt)
• to modify John Q. Public, do
• CLIPSgt (modify 0 (age 24)) press enter
• ltFact-2gt
• CLIPSgt (facts) press enter
• f-2 (person (name John Q. Public) (age
  24)
• (eye-color blue)
  (hair-color black))
• For a total of 1 fact.
• CLIPSgt

36
CLIPS duplicate command

• duplicate command works the same as the modify
  command with the exception that it does not
  retract the original fact.
• to add another name but keep the same field
  values, do
• CLIPSgt (duplicate 2 (name Jack S. Public))
  press enter
• ltFact-3gt
• CLIPSgt (facts) press enter
• f-2 (person (name John Q. Public)
• (age 24)
• (eye-color blue) (hair-color black))
• f-3 (person (name Jack S. Public)
  (age 24)
• (age 24)
• (eye-color blue) (hair-color black))
• For a total of 2 facts.
• CLIPSgt
• note modify and duplicate commands can not be
  used with ordered facts.

37
CLIPS The watch command

• watch command useful for debugging programs.
• (watch ltwatch-itemgt)
• where ltwatch-itemgt is one of the symbols
  facts, rules, activations, statistics,
  compilations, or all.
• a. watch can be used to watch more than one
  feature of CLIPS execution.
• b. all can be used to enable all of the
  watch features.
• The effects of a watch command may be turned off
  by using the corresponding unwatch command.
• (unwatch ltwatch-itemgt)

38
CLIPS watch command (continued)

• note CLIPS will automatically print a message
  indicating that an update has been made to the
  fact list whenever facts are asserted or
  retracted.
• e.g.
• CLIPSgt (FACTS 3 3) press enter
• f-3 (person (name Jack S. Public)
  (age 24)
• (eye-color blue) (hair-color
  black))
• For a total of 1 fact.
• CLIPSgt (watch facts) press enter
• CLIPSgt (modify 3 (age 25) press enter
• ? f-3 (person (name Jack S. Public) (age 24)
• (eye-color blue)
• (hair-color black))
• ?f-4 (person (name Jack S.
  Public) (age 25)
• (eye-color blue)
• (hair-color black))
• ltFact-4gt
• CLIPSgt
• The ? indicates that the fact is being
  retracted.
• The ? indicates that the fact is being
  asserted.

39
CLIPS Deffacts Construct

• deffacts construct groups of facts which
  represent initial knowledge the following
  deffacts statement provides initial information
  about people we have already learned about
• (deffacts people some people we know
• (person (name John Q. Public) (age 24)
• (eye-color blue) (hair-color
  black))
• (person (name John Q. Public) (age 24)
• (eye-color blue) (hair-color
  black))
• the general format of a deffacts is
• (deffacts ltdeffacts namegt ltoptional commentgt
• ltfactsgt)

40
CLIPS reset command

• reset command removes all facts from the fact
  list and then asserts the facts from existing
  deffacts statement.
• e.g. (reset)
• assuming that the people deffacts had been
  entered, the following shows how the reset
  command adds facts to the list
• CLIPSgt (unwatch facts) press enter
• CLIPSgt (facts) press enter
• f-0 (initial-fact)
• f-1 (person (name John Q. Public)
  (age 24)
• (eye-color blue) (hair-color black))
• f-2 (name Jack S. Public) (age 24)
• (eye-color blue) (hair-color black))
• For a total of 3 facts.
• CLIPSgt
• note the output shows the facts from the
  deffacts statement and a new fact generated by
  the reset command called initial-fact.

41
CLIPS reset command (continued)

• Upon start-up, CLIPS automatically defines the
  following two constructs
• (deftemplate initial-fact)
• (deffacts initial-fact (initial-fact))
• Even if you havent identified any deffacts
  statements, a reset will assert the fact
  (initial-fact).
• The fact identifier of the initial fact is
  always f-0.

42
CLIPS Final Note

• Any additional information concerning CLIPS or to
  download CLIPS version 6.21 go to website
• http//www.ghg.net/clips/CLIPS.html