isset empty or ...?

[email protected] (John Taylor-Johnston) Sun, 31 Mar 2013 00:53:08 -0400

Newsgroups	php.general
Message-ID	<[email protected]>

I'm using

if($mydata->DPRresponselocationaddress1 != "")

is this the same as

if (!isset($mydata->DPRresponselocationaddress))
http://php.net/manual/en/function.isset.php

or

if (!empty($mydata->DPRresponselocationaddress))
http://php.net/manual/en/function.empty.php

or is there another function I have not learned yet? I don't really get 
the difference between isset and empty.

John