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ITEC 380

ITEC 380. Organization of programming languages Lecture 8 – Prolog. Review. Prolog What are its 2 major components?. Objectives. Prolog Basic principles Examples Example programs. Declarative Programming.

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ITEC 380

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  1. ITEC 380 Organization of programming languages Lecture 8 – Prolog

  2. Review • Prolog • What are its 2 major components?

  3. Objectives • Prolog • Basic principles • Examples • Example programs

  4. DeclarativeProgramming • Instead of focusing on how to accomplish a particular task, focus on what to accomplish • Declare the intent and let the tool do the rest • Limits what is possible • Specific language that is limited compared to say C • Leaves little room for traditional optimization • Do you know of any declarative languages?

  5. Example • SQL • Insert knowledge where mind = attentive • Declare what should happen, not how • B-trees? • Recursive descent algorithms? SELECT * FROM Book WHERE price > 100.00 ORDER BY title;

  6. Prolog • Declarative statements in prolog • Facts that are true • Rules that are made up of groups of facts • Variables that hold a specific value • Goal • Ask what the value of an expression is • True / False / Numeric

  7. Facts • A true statement • Syntax • Factname(identifier that is mapped to factname) • Factname(ident1, ident2) Means that ident1 is the Factname of ident2 • Example male(Bob) female(Jill) parent(Jill, Bill) parent(Bob, Bill)

  8. But wait • Have to store up a “knowledge base” before you can make queries • Declares a set of facts • Can be used to make queries later on • Difference of what should be done versus how to go about it

  9. Loading • Once you have saved your knowledge base you can load it into prolog • Needs to have a .pl extension • Synatx • [filename]. %Note the . is the prolog equivalent to a ; • Do not use the .pl extension • Once you have done that you can use it

  10. Example • View a simple knowledge base • Load it • Make queries about it male(bob). female(jill). parent(jill,bill). parent(bob, bill). father(TheDad, TheChild) :- parent(TheDad,TheChild), male(TheDad). mother(TheMom, TheChild) :- parent(TheMom,TheChild), female(TheMom).

  11. User I/O • Need to get input to truly exercise the system • Expanding the knowledge base • write(‘Data\nNewLine\nData’) • read(Variable) • Method • Have a rule that uses read, then combine with a , and then use the new variable in the facts

  12. Expanded • Making our previous knowledge base have I/O male(bob). female(jill). parent(jill,bill). parent(bob, bill). father(TheDad, TheChild) :- parent(TheDad,TheChild), male(TheDad). mother(TheMom, TheChild) :- parent(TheMom,TheChild), female(TheMom). iTester :- write('Type the mother\'s name\n'), read(Mom), write('Type the child\'s name\n'), read(Child), mother(Mom, Child).

  13. Issue • Test out someone not in the DB • Use lower case variables, then upper case • Why? • Run the test manually… • Variable case matters! • Lower case = constants • Upper case = variables • Anonymous variables • Use _

  14. Prolog power • An example of declarative logic and inference • The game of clue • What are you declaring in clue? • What are you trying to find out? • How does this relate to RL relevance?

  15. The miracle of trace • See exactly what is happening during evaluation • Turn on with trace. • See what happens when you load a file? • What happens when you call a function?

  16. Numbers • Working with constants • True/false 8 is 6+2. • Setting a value X is 4. • Setting up formulas • formula(x,y) :- Y=X*2. • Note formulas must be placed in knowledge base! • Test with 1) 3,A then 3,a then 3,4 • Why did it get the results it did?

  17. More capabilities • Can do relational queries • A is 7, A>5. • Note: , means and ; means or • What are the implications of using the ; above? • Can also use Rule1 -> Rule2 to only execute Rule2 if Rule1 is true • Trivia: What does the, mean in prolog • How could we prompt the user for their salary and print out what the percentage they pay in tax is (30%)?

  18. Next week • More in-depth with prolog • Lists • Recursion

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