SWI-Prolog 1

Focal point

• Knowledge base: A collection of Facts and Rules.
• Syntax
• Atoms
• Numbers
• Variables
• Complex terms

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Start SWI-Prolog in Windows

Prior Knowledge

• Prolog 這個名稱由 Program + logic 組成，常被應用於人工智慧與計算語言學的邏輯程式語言。
• swipl-win.exe: 執行 .pl 檔，讓使用者與 Prolog 互動的視窗程式。
• Prolog Programs 的主要架構: Facts, Rules, Queries.
  • Facts: Things that unconditionally true of some situation.
  • Rules: Things that conditionally true of the situation.
  • Queries: Users ask questions to use Prolog program.
• Prolog 和過去我們學的 C, Java, C# 等 Procedure-Oreinted Languages 不同。我們不需要一步步告訴 Prolog 要怎麼做，使用者只需要提問，Prolog 便會藉由 knowledge bases 來推論結果。
• Prolog query knowledge bases from top to bottom, trying to match the expression you asking.
  • 比對第一條 rule 不符合，便會往下比對下一條 rule。
  • 補充：使用 Prolog query from top to bottom 的特性來寫 rules，盡量避免寫 if..else.. (... :- .... -> ... ; ...)。
• After Prolog reports back to us, you could use semicolon ; (means or) to ask Prolog: are there any alternatives?
• Using Prolog symbol (like semicolon) is more efficient as Prolog only has to deal with one rule but hard to read for human.
• %: 註解符號。
• ,: Prolog symbol for "AND", means conjunction.
• ;: Prolog symbol for "OR" means disjunction.
• :-: It means "if", or "is implied by". A :- B. means A is true if B is true.
  • The part on the left-hand side of the :- is called the head of the rule, the part on the right-hand side is called the body.
  • A fact could be view as a rule with an empty body. Which is means the fact as a condition that do not any antecedent (前情) condition.
• Modus ponens (假說推論): Prolog 藉由 facts and rules 來推論結果的步驟。

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A Knowledge Base of Prolog

happy(Abby).
playsAirGuitar(Taylor).
listen2Music(Abby):- happy(Abby).
happy(Taylor):- playsAirGuitat(Taylor).
singing(Abby):- listen2Music(Abby).
singing(Taylor):- happy(Taylor).

• Facts: happy(Abby) and playsAirGuitar(Taylor).
• Rules: listen2Music(Abby) :- happy(Abby), happy(Taylor):- playsAirGuitar(Taylor), singing(Abby):- listen2Music(Abby), and singing(Taylor):- happy(Taylor).
• This knowledge base has six clouses and four predicates (happy, playsAirGuitar, listen2Music, singing).

Keywords

• Clouses: All of the facts and rules contained in a knowledge base.
• Predicates: The facts and rules consist knowledge base.

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Variable Modus Ponens

Knowledge Base

woman(mia).
loves(marsellus,mia).

Query

% 請告訴我 marsellus 愛哪個女生？
?- loves(marsellus,X), woman(X).

Return value

X = mia

• Prolog reports back the variable bindings to us if it could find out a bindings which satisfy all queries.
• Modus ponens:
  • Search loves(marsellus,X), woman(X)..
  • Find out loves(marsellus,mia)..
  • Binding mia with X.
  • Find out woman(mia)..
  • Both loves(marsellus,mia) and woman(mia). queries are matched.
  • Reports back the variables bindings X = mia.

Keywords

• Variable: A word beginning with an upper-case letter which is a placeholder for information.

Variable modus ponens 2

Knowledge Base

loves(vincent,mia).
loves(marsellus,mia).
loves(pumpkin,honey_bunny).
loves(honey_bunny,pumpkin).

jealous(X,Y):- loves(X,Z), loves(Y,Z).

Query

% 請告訴我 marsellus 會吃誰的醋？
?- jealous(marsellus,W).

Return value

W = vincent

• Modus ponens:
  • Searching jealous(marsellus,W)..
  • Find out jealous(X,Y):- loves(X,Z), loves(Y,Z)..
  • Binging marsellus with X.
  • Searching loves(marsellus,Z)..
  • Find out loves(marsellus,mia)..
  • Binding mia with Z.
  • Searching loves(Y,mia)..
  • Find out loves(vincent,mia)..
  • Binding vincent with Y.
  • jealous(marsellus,vincent). is true
  • Binding vincent with W.
  • Report back W = vincent.