To answer the question about the names...PHP is just coming into being object oriented. Yes, PHP4 had some OOP aspects to it but was never really an object oriented language. So, now that there is a need for OOP terms they are being borrowed from other languages and depending on their background, different people are using different terms. So yes, an instance variable is a data member which is also a property.

Maybe this will help clears things up a little. I use the terms instance variables and and instance methods because they belong to a single instance of an object. There are also static members and static methods which belong to every instance of an object.

I agree with you about introducing OOP with PHP4. I don't see why you would ever want to do that. Definitely go with PHP5. As far as a book recommendation, I personally like the Wrox books. They are very easy to understand and follow. Beginning PHP5 may be a good one. It may cover some stuff you already know but it will explain it in an object oriented method.

If it is OOP in general that you need help understanding here is how it was explained to me.

Object oriented code relies on us defining classes in our code. A class is pretty much just functions and variables that are separated into logical groups. Say we have two things we are working with, cookies and cars. A car has an engine (a variable) and we can start that engine (a function). A cookie has chocolate chips (a variable) and we can eat it (a function). We wouldn’t try to eat our engine so there is no need for our cookies to know about the engine.

Speaking of cookies, we don’t define an object in our code. What we actually do is define the properties of our object and what it will do. This was explained to me as being a cookie cutter. All of our objects will be cut from this class but will actually each be its own “instance”.

Let’s try writing a class for our car. First we need to describe what a car is. A car has an engine, a transmission, a certain number of doors, a color, and a number of miles it has been driven.
<?php class Car { public $engine; public $transmission; public $doors; public $color; public $mileage; } ?>
Now we have variables that describe our car. Notice that our car has no engine, transmission, etc. We need to create an instance of our car in order to set these properties. We do this using the “new” keyword.

@<?php
class Car {
...
}

$myCar = new Car();
$myCar->color = ‘Red’;
echo “My car is “.$myCar->color.”<br/>”;

$yourCar = new Car();
$yourCar->color = ‘Black’;
echo “Your car is “.$yourCar->color;
?>@

So we have created two separate instances of car, $myCar and $yourCar, and have set the color property for each. They are both cars but they have their own distinct properties.

Actually these are all instance members. A static member would be preceded with the static keyword. Say we wanted all our cars to be Hondas. We could add a static field “Make”.
@
<?php
class Car { public $engine; ... public static $make = ‘Honda’;

public make() { return Car::$make; } } ?> @

Now if we go back and modify our first code we can add the following.

@
...
echo “Your car is “.$yourCar->color;

echo ‘My car is a ‘.$myCar->make().’<br/>’;
echo ‘Your car is a ‘.$yourCar->make().’<br/>’;
Car::$make = ‘Cheverolet’;
echo ‘My car is now a ‘.$myCar->make().’<br/>’;
echo ‘Your car is now a’.$yourCar->make().’<br/>’;
@

Notice that both cars are “Cheverolet” even though we only change the value of make for $myCar. This is because make is static. Static means that the same variable is used across all instances of Car. Also, static fields are accessed differently than instance fields. Rather than -> they are accessed with :: and they are also accessed directly from the class rather than the instance. This is why we have created a function called make() which returns the value of the static field.

Once you have got this down you will also need to take a look at the other modifiers. There is public, private, static, and const. These apply to functions/methods as well.