Fundamental question about ADTs

Hi all Recently I've been reading /Code Complete/ by Steve McConnell, and in it he recommends the use of ADTs, or Abstract Data Types, which I have been thinking about implementing in a major project I am currently embarking on. Basically the question that I have for the list is this: If I have a relatively simple class, for example Photo, then why does McConnell recommend that I do this: <?php $caption = $instanceOfPhotoClass->getCaption(); //do something with $caption $instanceOfPhotoClass->setCaption($caption); ?> Rather than this: <?php $caption = $instanceOfPhotoClass->caption; // do something with $caption $instanceOfPhotoClass->caption = $caption; ?> I'm just looking for some alternative explanations to what McConnell offers in the book. I can understand that the first example allows me to "know" when an attribute has been modified... but it annoys me that I have code like this: class Photo { private $caption; [...] public function setCaption($newCaption) { $this->caption = $newCaption; } } It just seems so pointless...... Thanks in advance for any comments. Jasper