Knowledge & Uncertainty in AI

Knowledge-Based Agents

A knowledge-based system (KBS) uses artificial intelligence techniques to store, manipulate, and reason with knowledge. The knowledge is typically represented in the form of rules or facts, enabling the system to draw conclusions or make decisions.

Example of class KnowledgeBase:


<?php

namespace app\classes\knowledgebase;

class KnowledgeBase {
    private array $facts = [];

    public function tell(string $sentence): void {
        $this->facts[] = $sentence;
    }

    public function ask(string $query): ?string {
        foreach ($this->facts as $fact) {
            if ($this->matches($query, $fact)) {
                return $fact;
            }
        }
        return null;
    }

    private function matches(string $query, string $fact): bool {
        return str_contains($fact, $query);
    }

    public function getFacts(): array {
        return $this->facts;
    }
}

Example of class KBAgent:


<?php

namespace app\classes\knowledgebase;

class KBAgent {
    private int $t = 0;

    public function __construct(
        private KnowledgeBase $kb = new KnowledgeBase()
    ) {}

    public function makePerceptSentence(array $percept, int $t): string {
        return "At time {$t}, perceived: " . json_encode($percept);
    }

    public function makeActionQuery(int $t): string {
        return "action_at_time_{$t}";
    }

    public function makeActionSentence(array $action, int $t): string {
        return "At time {$t}, performed action: " . json_encode($action);
    }

    private function printStep(int $stepNumber, string $title, string $content, $eol = "\n"): void {
        echo <<<OUTPUT
        Step {$stepNumber}: {$title}
        --------------------
        {$content}
        {$eol}
        OUTPUT;
    }

    private function printInitialState(int $timeStep, array $percept): void {
        $content = <<<CONTENT
        Time step: {$timeStep}
        Percept received: {$this->jsonEncode($percept)}
        CONTENT;

        $this->printStep(1, 'Initial State', $content);
    }

    private function printPerceptSentence(string $sentence): void {
        $this->printStep(2, 'Percept Sentence Created', $sentence);
    }

    private function printActionGenerated(array $action): void {
        $this->printStep(3, 'Action Generated', 'Action: ' . $this->jsonEncode($action));
    }

    private function printFinalState(int $nextTimeStep, string $actionSentence): void {
        $content = <<<CONTENT
        Time step incremented to: {$nextTimeStep}
        Action recorded in KB: {$actionSentence}
        CONTENT;

        $this->printStep(4, 'Final Knowledge Base State', $content, eol: '');
    }

    private function jsonEncode(array $data): string {
        return json_encode($data, JSON_THROW_ON_ERROR);
    }

    public function process(array $percept): array {
        // Step 1: Show initial state
        $this->printInitialState($this->t, $percept);

        // Tell KB about the percept
        $perceptSentence = $this->makePerceptSentence($percept, $this->t);
        $this->kb->tell($perceptSentence);

        // Step 2: Show percept sentence
        $this->printPerceptSentence($perceptSentence);

        // Ask KB what action to take and use default if none found
        $action = $this->kb->ask($this->makeActionQuery($this->t))
            ?? $this->defaultAction($percept);

        // Step 3: Show action
        $this->printActionGenerated($action);

        // Tell KB about the action taken
        $actionSentence = $this->makeActionSentence($action, $this->t);
        $this->kb->tell($actionSentence);

        // Step 4: Show final state
        $this->printFinalState($this->t + 1, $actionSentence);

        // Increment time step
        $this->t++;

        return $action;
    }

    private function defaultAction(array $percept): array {
        return [
            'type' => 'default_action',
            'percept' => $percept
        ];
    }
}