<?php

interface CatI
{
    public function walk();
    public function feed();
}

abstract class Cat implements CatI
{
    protected $paws = 4;

    public function walk()
    {
        echo "Walking";
    }

}

class Tiger extends Cat
{
    public $power = 100;

    public function feed() {}
}

$myTiger = new Tiger();
$myTiger->walk(); // walking