How can PHP developers differentiate between aggregation and composition in UML diagrams?

PHP developers can differentiate between aggregation and composition in UML diagrams by understanding the relationship between the classes involved. Aggregation represents a "has-a" relationship where one class owns or contains another class, but the contained class can exist independently. Composition, on the other hand, represents a stronger relationship where one class is a part of another class and cannot exist without it.

class Engine {
    // Engine class implementation
}

class Car {
    private $engine;

    // Aggregation relationship
    public function setEngine(Engine $engine) {
        $this->engine = $engine;
    }
}

class Wheel {
    // Wheel class implementation
}

class Vehicle {
    private $wheels;

    // Composition relationship
    public function __construct() {
        $this->wheels = [];
        for ($i = 0; $i < 4; $i++) {
            $this->wheels[] = new Wheel();
        }
    }
}