DLL equivalent for php

hi, i'm quite new to php and postgresql, and here's my question. i've previously worked in nt4 with sqlserver 7.0 and vbasic and asp pages. using these i was able to write .dll files in vb that would handle a particular database. then a package linked to the dll file would be created on the server, and then inside my asp pages i could just say set myitem1 = server.createobject("MyObj.Item1") where MyObj is the name of the package on the server referring to the dll file and Item1 is just some class in the dll. then myitem1 could use the member functions and methods of the Item1 class to manipulate the database from inside the asp pages. My question is, is there something equivalent to this in php and postgresqp, what is is and how does it work?? thanks very much, sasha