Some music related PHP stuff

<?php

class Interval {
    protected static $intervals = array(
        "Perfect Unison"        => 0,
            "P1"                => 0,
        "Minor second"          => 1,
            "m2"                => 1,
            "S"                 => 1,
        "Major second"          => 2,
            "M2"                => 2,
            "T"                 => 2,
        "Minor third"           => 3,
            "m3"                => 3,
        "Major third"           => 4,
            "M3"                => 4,
        "Perfect fourth"        => 5,
            "P4"                => 5,
        "Diminished fifth"      => 6,
            "Augmented forth"   => 6,
        "Perfect fifth"         => 7,
            "P5"                => 7,
        "Minor sixth"           => 8,
            "m6"                => 8,
        "Major sixth"           => 9,
            "M6"                => 9,
        "Minor seventh"         => 10,
            "m7"                => 10,
        "Major seventh"         => 11,
            "M7"                => 11,
        "Perfect octave"        => 12,
            "P6"                => 12,
    );
    protected $size;
    public function __get($name) {
        switch ($name) {
            case "Size":
                return $this->size;
        }
    }
    public function __toString() {
        return array_search($this->size, self::$intervals) ?: $this->size.'S';
    }
    public function __construct($size) {
        if(is_string($size)) {
            $size = self::$intervals[$size];
        }
        $this->size = $size;
    }
}

class Note {
    const NotationRegex = '/^([CDFGA][#]?|[EB])(0|[1-9][0-9]*)$/i';
    protected static $classes = array(
        0   => 'C',
        1   => 'C#',
        2   => 'D',
        3   => 'D#',
        4   => 'E',
        5   => 'F',
        6   => 'F#',
        7   => 'G',
        8   => 'G#',
        9   => 'A',
        10  => 'A#',
        11  => 'B',
    );

    protected $uid;

    public function __get($name) {
        switch ($name) {
            case "ID":
                return $this->uid;
            case "Class":
                return self::$classes[$this->uid%12];
            case "Octave";
                return floor($this->uid/12);
            case "Name";
                return $this->Class.$this->Octave;
            default:
                throw new Exception("No such property: $name");
        }
    }

    public function __toString() {
        return $this->Class;
    }

    public function __construct($id) {
        if(is_int($id)) {
            $this->uid = $id;
            return;
        }
        //Assume it is a string...
        $this->uid = self::convertNotation($id);
    }

    public function interval($note) {
        return new Interval($note->ID - $this->uid);
    }

    public function note($interval) {
        return new Note($this->uid + $interval->Size);
    }

    protected static function convertNotation($notation) {
        preg_match(self::NotationRegex, $notation, &$matches);
        return array_search($matches[1], self::$classes) + $matches[2] * 12;
    }
}

class Scale {
}

$x = new Note("C2");
$y = new Note("F#2");

echo "ID:       $x->ID\n";
echo "Class:    $x\n";
echo "Octave:   $x->Octave\n";
echo "Name:     $x->Name\n";

echo $x->interval($y)."\n";

$i = new Interval("P5");
echo "Interval:\t$i\n";

$z = $x->note($i);
echo "Name:\t$z->Name\n";

?>