Comp763: Modern Computer Games

Using Constraint Logic Programmingto Analyze the Chronology in a William Faulkner Story

Jennifer Burg Sheau-Dong Lang

Irwin Chiu HauComputer ScienceMcGill University

Winter 2004

Comp763: Modern Computer Games

Overview

Introduction “A Rose to Emily” by William Faulkner Constraint Logic Programming The Constraint Satisfaction Algorithm and

Conflict Sets Useful Extensions Conclusion

Comp763: Modern Computer Games

Introduction

Narratives• In movies:

» Essential component– Every movie

• In games:» Interesting component

– Some games

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Introduction

A good story• Quality

» The storyline

» Character Development

» Plot twist

» Logical

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Introduction

A good story may have• Flaws

• Conflicts

Human beings are• Sensitive to these issues

• Good in spotting conflicts

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Introduction

Movies / Novels• Conflicts could

» Lead us to confusion

» Ruin the storyline

Games• Conflicts could cause serious problems

» Hinder game completion

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Introduction

Dealing with conflicts• Detecting

• Removing

Comp763: Modern Computer Games

Overview

Introduction “A Rose to Emily” by William Faulkner Constraint Logic Programming The Constraint Satisfaction Algorithm and

Conflict Sets Useful Extensions Conclusion

Comp763: Modern Computer Games

A Rose For Emily

Novel• Written by William Faulkner

• Originally published on April 30, 1930

The story• Not told in chronological order

• Broken into countless pieces

• Very difficult to understand

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A Rose For Emily

The challenge• English literature courses

» Story Analysis– Developing a list of the descriptive details associated with Emily

· Her appearance

· Surroundings

– Reconstructing a chronological list of events

• This paper» Analysis

– Events sorting

– Conflicts detection

Comp763: Modern Computer Games

Overview

Introduction “A Rose to Emily” by William Faulkner Constraint Logic Programming The Constraint Satisfaction Algorithm and

Conflict Sets Useful Extensions Conclusion

Comp763: Modern Computer Games

Constraint Logic Programming

In this paper, CLP is applied to analyze the chronology of “A Rose for Emily”

What is CLP?• Family of programming languages that allow

» Declarative problem statements

» Expression of constraints in specialized domains

Comp763: Modern Computer Games

Constraint Logic Programming

CLP language allows a programmer to • Express a problem declaratively rather than

procedurally» Augmented with expression of constraints

– Integers, rational numbers and Boolean values

– Equations and inequalities

• Find a solution» Solving the system of constraints

– Resolution-based inference

– Constraint satisfaction

Comp763: Modern Computer Games

Constraint Logic Programming

CLP is used to solve problems• Circuit design

• Resource allocation

• Discrete optimization applications

• Analyze the Chronology in a William Faulkner Story

• Detecting conflicts in computer games

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CLP(R) Applied to Time Elements

Analyze the Chronology in a William Faulkner Story

···

Table 1 Variables and Their Meaning

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CLP(R) Applied to Time Elements

Table 2 Constraints and Their Meaning

···

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Overview

Introduction “A Rose to Emily” by William Faulkner Constraint Logic Programming The Constraint Satisfaction Algorithm and

Conflict Sets Useful Extensions Conclusion

Comp763: Modern Computer Games

The Constraint Satisfaction Algorithm

CLP program can be divided into two components• An inference engine

» Binding of variables

• A constraint solver» Each inequality constraint: a1x1 + … + anxn ≤ b

» System of constraints

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Prolog

PROgramming in LOGic A declarative language

• Knowledge Base» Facts

• Inference» Rules

• Query

In this paper, CLP(R) is implemented in Prolog

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Conflict Sets

The system• Satisfiable

• Not satisfiable

Not satisfiable => There are conflicts• Conflict sets

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The Conflict in "A Rose for Emily"

B ≥ E D – E ≥ 8 E = B

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Removing the Conflict

The conflict uncovered by the CLP(R)• Minimal conflict

To resolve the conflict• Removing any conflicting constraint

In this example (A Rose For Emily)• We choose to remove E = B

• And the solver finds 5 solutions

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A solution for “A Rose for Emily”

Comp763: Modern Computer Games

Overview

Introduction “A Rose to Emily” by William Faulkner Constraint Logic Programming The Constraint Satisfaction Algorithm and

Conflict Sets Useful Extensions Conclusion

Comp763: Modern Computer Games

Useful Extensions

CLP(R) • Useful for chronological sorting of events

» In stories where events are related out-of-order.

How is it related to games?• Adventure games have

» Events

» Puzzles

• CLP(R) can be applied to games

Comp763: Modern Computer Games

Useful Extensions

Providing an graphical interface• define points in time,

• indicate which points are before which others

• give dates where dates are known

• ask for a sort

• receive a list of conflicting constraints

Comp763: Modern Computer Games

Overview

Introduction “A Rose to Emily” by William Faulkner Constraint Logic Programming The Constraint Satisfaction Algorithm and

Conflict Sets Useful Extensions Conclusion

Comp763: Modern Computer Games

Conclusion

Novels / Movies• A story should not have any conflicts

Games • Puzzles and story should not have any conflicts

CLP(R) is a powerful tool• Can be used to analyze a story

» Sort events

» Detect conflicts

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Questions?

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