Writing some classes in php

Last friday I was kinda bored at work so I decided to renew my functions and write some classes, I started with the ones that I use most, and just wrote a class to conect, execute a sql query and return an array with the data using a firebird database, nothing really usefull, but makes my life easier.

class firebird{
 var $conexao_id;
 function firebird() {
   $bd = "localhost:/path/to/database.gdb";
   $usr = "SYSDBA";
   $snh = "masterkey";
   $charset ="ISO8859_1";
   # Conecta ao banco de dados
   $this->conexao_id = ibase_connect($bd, $usr, $snh, $charset) or die("Erro na conexão: ".ibase_errmsg());
   return $this->conexao_id;
 }

 function consulta($sql){
   if($sql != '') {
     $resultado = ibase_query($this->conexao_id, sprintf($sql)) or die(ibase_errmsg());
     while($item = ibase_fetch_assoc($resultado)){
       $items[] = $item;
     }
     $rows = count($items);
     if($rows > 0) {
       ibase_free_result($resultado);
       return $items;
     } else {
       return false;
     }
   } else {
     return false;
   }
 }
 function fechar() {
   ibase_close($this->$conexao_id);
 }
}

This is just the begging, I'm planning to convert all my functions to OOP and try to make them as much reusable as possible :)