Please download the following files containing simple knowledge bases about a family:

• CLIPS file: family_en.clp.zip
• Prolog file: family_en.pl
• Manual for CLIPS: Basic Programming Guide, version online

Both files have corresponding content:

• The same facts.
• The same relationships defined on the facts.

In addition, files contain a single rule defining the child relation.

After downloading the files, they have to be loaded into corresponding Knowledge Bases (KB):

• CLIPS:

   (load family_en.clp) 

  If everything was loaded correctly, you should a feedback similar to:

  Defining deffacts: initial-facts
  Defining defrule: child +j
  TRUE 

  The TRUE is the most important part of this feedback. If FALSE appears, it means that loading failed.

• Prolog:

   [family]. 

  The succesful loading should display something similar to:

  % family compiled 0.01 sec, 9,232 bytes
  true. 

  Notice the true again.

To view the contents of the KB, enter:

• CLIPS:

  (reset)
  (facts) 

  • How many facts are in the KB?
• Prolog:

  listing. 

CLIPS uses the forward-chaining. The inference is implemented as a loop, that checks what rules can be executed based on the current state of the KB. Then the found rules are executed and the cycle repeats. The loop ends when it fails to find a rule to execute. The input of the forward-chaining algorithm is the set of facts in the knowledge base.

• To check what rules are ready to be run, type

   (agenda) 

  • What rules are ready to run?
  • What facts trigger these rules?
  • How to explain the result?
• To run the inference process, type

   (run) 

  • What is the output?
  • How many facts are in the database?
  • What facts were added?
  • Have you expected the result?

In Prolog we use backward-chaining and the process is inverted. The input of this algorithm is target — fact that we want to infer. We may say that this a goal-oriented approach. Let's ask:

• What women are included in the knowledge base:

   woman(X). 

  With the ; key, we can continue to list all the possible answers of the inference. If you want to interrupt, press „enter”.

• What pairs of type (mom, child) are included in the KB:

   mother(Mom, Child). 

• What children does Dariusz have?

   father(dariusz, Child). 

• What are the names of all the fathers:

   father(Father, _). 

• What sons does Dariusz have:

   father(dariusz, Son), man(Son). 

Both files contain a rule defines who/what is a child.

• How to interpret these rules?
• Do they use the same notion of a child?

CLIPS failed to start this rule (previous point). In Prolog, we can query using this rule:

child(X, Y).

• Run the above query and …
• describe what happened?
• Has the situation been analogous to that in CLIPS?
• Does the rule in CLIPS failed because of the same reason?

In order to run the child rule, we have to define:

• In CLIPS: a rule that adds a parent to the knowledge base (changing the knowledge base will trigger the next inference cycle):

  (defrule parent
   (or (mother ?x ?y) (father ?x ?y))
  =>
   (assert (parent ?x ?y))
  )

• In Prolog: a rule defining a relationship (child, parent):

  parent(X, Y) :-
    father(X, Y).
  parent(X, Y) :-
    mother(X, Y). 

  It is worth noting that in the case of Prolog, we define two rules. One can assume that there is a conjuction (OR) between these two rules.

• Repeat steps:
  • CLIPS: 1. and 3. (start with executing (clear) to clear the fact base)
  • Prolog: 1 and 4.
• How many facts are there in the CLIPS database?
• What are the active rules in CLIPS?
• Why is the child rule inactive?

We can try now to supplement the current KB with new rules, that define other relationships:

• Both tools can answer who is the child of which parent. How to extend the rules base of both tools with the help of the child concept so that they can tell who is the son and who is the daughter?
  • Define the appropriate rules.
  • Start the inference to check if the defined rule is correct.
  • You can also try to simply display the facts in CLIPS.

• The knowledge base can also be supplemented by a rule defining marriage. With existing facts and rules, you can define that two people are married if:
  • are different sex,
  • have a common child.
• This rule will cause the inference to omit the childless couples. In order to define the proper notion of marriage, KB would have to be supplemented with additional facts (what facts?)

Knowing that the concepts brother is defined as follow:

• CLIPS:

  (defrule brother
   (siblings ?x ?y)
   (man ?x)
  =>
   (assert (brother ?x ?y))
  )

• Prolog:

  brother(X, Y) :-
    siblings(X, Y),
    man(X).

Define two additional rules:

• „siblings(X, Y)” — two different people with a common parent
• „sister(X,Y)”