OO extensions compatibility between v4 and v5

Hi, I'm new to the lists so I hope my questions havent been asked and answered before. I did search the archives and couldnt find anything though. I am also very new to php extensions in general so please forgive any stupidity on my part. I am about to embark on writing an extension between PHP and a system called EMC Centera which is a massive low-cost data storage technology and have a few questions: 1. I am considering extending the standard file operations in PHP to accept a Centera URI [e.g. open('centera://etc_etc_etc')] and was wondering if this would be an onerous task seeing as the file system in question is quite unlike other file systems out there. I'm only hoping it will be trivial as the file operations already support things like http:// which are very different too. 2. If I wrote the extension using PHP4 OO syntax would it be compatible to PHP5 OO syntax as I noticed a few differences. eg:

      php4:    $obj->set("flagx", 1);
      php5:    $obj->flagx = 1;

Thanks, Chad.