<?php
class DataHelper
{
    private $dbh = null;
    private $dsn = "some default connex string";

    public __construct($myDsn = '') {
        if (!is_empty($myDsn)) {
            $this->dsn = $myDsn;
        }
    }

    public connect() {
        if (is_null($this->dbh)) {
            $this->dbh = DB::connect($this->dsn);
        }

        if (PEAR::isError($this->dbh)) {
            throw new Exception($this->dbh->getMessage());
        }
    }

    public query($queryString, array $params = array())
    {
        // code
    }
}