1. AI/ES (Artificial Intelligence / Expert System) Visual Prolog: Part 2
2012. Fall.
SME., Pukyong Nat’l Univ.
Kim, Minsoo

2. Contents The IDE – In detail Fundamental Prolog
PIE: Prolog Inference Engine
Program Control in Prolog

3. The IDE – In detail Project Life Cycle Creation Building Browsing
properties of the project (dll/exe, gui/console, …)
Building
compiling & linking
Browsing
IDE provide information about project
Development
add/remove/edit project source files
Debugging
follow program execution and exploit its state

4. The IDE – In detail Open sample project ‘ch01p01’
‘Open Project’ or [Project/Open]

5. The IDE – In detail Project Tree
…/My Documents/Visual Prolog Projects/
ch01p01/TaskWindow/Toolbars
*.cl / *.i / *.pro / *.dlg / *.frm / *.win / *.mnu / *.ico
*.ctl / *.tb / *.cur / *.bmp / *.lib
#include directives: *.pack / *.ph
$(ProDir)  logical node

6. The IDE – In detail
Your ‘main’ program
Open ‘main.pro’ file

7. The IDE – In detail Add a package (folder)
‘ch01p01’  New In Existing Package

8. The IDE – In detail Add a form in the package
samplePackage  New In Existing Package

9. The IDE – In detail Edit ‘query’ From
Add controls  Edit Field, Push Button
Name (*_ctl), Text

10. The IDE – In detail Connect ‘query’ form to File/Open menu
TaskMenu.win  [File/Open] Uncheck Disabled
Change code  Save/Build/Execute

11. The IDE – In detail Add ‘ClickResponder’ to a Push Button
Open ‘query’ form  Click ‘Ask!’ Button
Properties/Events  ClickResponder

12. The IDE – In detail Change ‘AboutDialog’
AboutDialog.dlg  Properties/Events
CloseResponder  Edit/Save/Build/Execute!

13. The IDE – In detail Add ‘ClickResponder’ to a Push Button
AboutDialog.dlg  Click ‘OK’ Button
Properties/Events  ClickResponder

14. The IDE – In detail Save / Build / Execute
Try Query Form, About Dialog

15. Fundamental Prolog Prolog’s Formal System for Reasoning
predicate (relation)
describes the relation between some objects.
fact: ‘predicate(argument, … )’
describes a static relation between objects.
rule: ‘conclusion :- premise1, …, premiseN.’
general relations between (groups of) objects.
IF premise1, …, premiseN THEN conclusion.
John is the father of Bill  father(“Bill”, “John”)
Thomas lives in Groningen  lives_in(“Thomas”, “Groningen”)
John is married to Claire  is_married_to(“John”, “Claire”) …
grandFather(GrandChild, GrandFather) :-
father(GrandChild, Father), father(Father, GrandFather).

16. Fundamental Prolog In Prolog …
Facts and rules are called clauses.
A theory is a set of clauses.
Questions to the inference engine are goals.
Horn clauses  (fact + rule + goal clause)
Horn Clause Logic (Alfred Horn)
father(“Bill”, “John”).
father(“Pam”, “Bill”).
father(“Sue”, “Jim”).
grandFather(GrandChild, GrandFather) :-
father(GrandChild, Father), father(Father, GrandFather).
a theory with 3 facts and 1 rule.
Is Jim the father of Sue?
Is John the father of Sue?
Who is the father of Pam?
Is John the father of Ann?
Is John the grandfather of Pam?
Yes
No (there is no such fact)
Bill
No (we cannot state to ‘yes’)

17. Fundamental Prolog A Prolog program … Consists of a theory and a goal.
When a program starts it tries to find a solution to the goal in the theory.
Yes / No
No solution ~ Multiple solutions
father(“Bill”, “John”).
father(“Pam”, “Bill”).
father(“Sue”, “Jim”).
grandFather(GrandChild, GrandFather) :-
father(GrandChild, Father), father(Father, GrandFather).
a theory with 3 facts and 1 rule.
Is Jim the father of Sue?
Is John the father of Sue?
Who is the father of Pam?
Is John the father of Ann?
Is John the grandfather of Pam?
?- father(“Sue”, “Jim”).
?- father(“Sue”, “Jonh”).
?- father(“Pam”, X).
?- father(“Ann”, “John”).
?- grandFather(“Pam”, “John”).

18. PIE: Prolog Inference Engine
Running PIE Project
Classical Prolog interpreter
Horn Clause Logic
Install Examples
Run [Visual Prolog/Setup Examples]
Select [Help/Install Examples…]
Open PIE project
…/My Documents/Visual Prolog Examples/pie
Build / Execute
PIE Program
Dialog Window (for goals)
Program Window: [File/New]  “…/FILE0.PRO”
Place your theory (facts and rules)

19. PIE: Prolog Inference Engine
Enter your theory in the Program Window
[Engine/Reconsult]  load your theory to engine
[File/Save] to save your theory as a file.

20. PIE: Prolog Inference Engine
After [Engine/Reconsule]
Type a goal in the Dialog Window and <Enter>.
Start with lower case letter and end with period.

21. PIE: Prolog Inference Engine
Try following goals
Logical AND(,) / OR(;)
father(“Sue”, “Jim”).
father(“Sue”, “Jonh”).
father(“Pam”, X).
father(“Ann”, “John”).
grandFather(“Pam”, “John”).
father(X, Y).
father(“Sue”, “Jim”), father(“Bill”, “John”).
father(“Sue”, “Jim”); father(“Bill”, “John”).

22. PIE: Prolog Inference Engine
Extending the family theory
Add facts/rules  increase intellectual power
[Engine/Reconsult]  Try sibling(X, Y).

23. PIE: Prolog Inference Engine
Modify sibling & add fullBloodedSibling rule
Reconsult & Try again!

24. Program Control in Prolog
Rigid search for solving the goal
Pattern matching: left to right, top to bottom
?- father(“Sue”, “Jim”).
1. father(“Bill”, “Jonh”)  fail.
2. father(“Pam”, “Bill”)  fail.
3. father(“Sue”, “Jim”)  match  success!
4. Stop search even though there is a
father(“Jack”, “Bill”) predicate.
 Answer is Yes.

25. Program Control in Prolog
Match while breaking down the goal
Substitution(binding a variable), backtracking
?- grandFather(“Sue”, “Jim”).
1. grandFather(“Sue”, “Jim”) :-
father(“Sue”, Father), father(Father, “Jim”).
1-A Subgoal: ?- father(“Sue”, Father).
A.1. father(“Bill”, “John”)  fail.
A.2. father(“Pam”, “Bill”)  fail.
A.3. father(“Sue”, “Jim”)  Bind Father = “Jim”.
1-B. Subgoal: ?- father(“Jim”, “Jim”).
B.1. father(“Bill”, “John”)  fail.
B.2. father(“Pam”, “Bill”)  fail.
B.3. father(“Sue”, “Jim”)  fail.
B.4. father(“Jack”, “Bill”)  fail.
B.5. No more father predicate  no solution  backtrack!
A.4. father(“Jack”, “Bill”)  fail.
A.5. No more father predicate  no solution  backtrack!
2. No more grandFather rule  fail  No Solution.

26. Program Control in Prolog
Failing
No fact or rule that satisfy current goal  fail
Go back to backtrack point
Relentless search for solutions
Check all the possible predicates and search all the possible solutions.

27. Program Control in Prolog
Cut: !
Prevent backtracking
Used to prevent the search for more solutions
Once the engine pass the cut(!), it is impossible to backtrack to predicates that precede the cut.
There is no way back to an alternative!
Two main use of ‘cut’
Green cut: when you are sure that certain clauses will never give rise to meaningful solutions, it’s a waste of time and storage space to use them in looking for alternative solutions.
Red cut: when the logic of program demands the cut, to prevent consideration of alternative subgoals.

28. Program Control in Prolog
Green cut
Try this theory and search this goal.
And introduce a cut in the goal clause.

29. Program Control in Prolog
Red cut
Switch-case statement like control
Try this theory and search this goal.
r(X) :- X = 1, !, a, b, c.
r(X) :- X = 2, !, d.
r(X) :- X = 3, !, c, e.
r(_) :- write(“This is a catch-all clause”).

30. Program Control in Prolog
Recursion
A definition that is defined in terms of itself.
Recursion must make progress  divide & conquer!
Recursion must terminate  no infinite-loop!
Think of this recursive rule.
ancestor(Person, Ancestor) :- parent(Person, Ancestor).
ancestor(Person, Ancestor) :-
parent(Person, P1), parent(P1, Ancestor).
parent(Person, P1), parent(P1, P2), parent(P2, Ancestor).
...
ancestor(Person, Ancestor) :- parent(Person, Ancestor).
ancestor(Person, Ancestor) :-
parent(Person, P1), ancestor(P1, Ancestor).

31. Program Control in Prolog
Side Effects
A predicate can succeed or fail
Evaluated to be true of false.
Always failing predicate: ‘fail’
Always succeeding predicates: reading/writing
In Prolog predicates that … has side effects.
always succeed.
do more than simply evaluate to true or false.
Think of this goal clause
?- ancestor(“Pam”, AA), write(“Ancestor of Pam: ”, AA), nl().
?- ancestor(“Pam”, AA), write(“Ancestor of Pam: ”, AA), nl(), fail.