Pear DB class not found

I have create a class called Database.php for interacting with MySql database using Pear Db class.

Database.php

<?php 
require_once('DB.php');
require_once('cException.php');

class DataBase
{

    private $dsn = 'mysql://root:xxxxxx@localhost/avatar';
    private $conn;


    //Constructor
    function __construct() 
    {
        global $conn;
        $this->conn = DB::connect($dsn);
        if(DB::isError($conn))
        {
            throw new DatabaseConnectionException();
        }
    }

    //destructor
    function __destruct() 
    {
       $this->conn->disconnect();
    }

    public function select($query)
    {
        $conn->setFetchMode(DB_FETCHMODE_ASSOC);
        $result = & $conn->query($query);

        if(DB::isError($result))
        {
            return new SelectCommandException($result->getMessage());
        }

        return $result;
    }

    static public function instance()
    {
        static $objDB;

        if(! isset($objDB))
        {
            $objDB = new DataBase();
        }

        return $objDB;
    }
?>

And I am calling this class from a sample file test.php

test.php

<?php

ini_set('display_errors', 1);
ini_set('log_errors', 1);
ini_set('error_log', dirname(__FILE__) . '/error_log.txt');
error_reporting(E_ALL);


    require_once 'Database.php';

    try 
    {
        $db = DataBase::instance();
    }
    catch (DatabaseConnectionException $ex1)
    {
        echo $ex1->toString();
    }

    try 
    {
        $sql = "Select * from register";
        $result = $db->select($sql);
        var_dump($result);
    }
    catch (SelectCommandException $ex2)
    {
        echo $ex2->toString();
    }
?>

When I run test.php I get the following error

Warning: require_once(/usr/share/pear/DB.php): failed to open stream: No such file or directory in /var/www/Avatar/Database.php on line 2 Fatal error: require_once(): Failed opening required '/usr/share/pear/DB.php' (include_path='.:/usr/share/php:/usr/share/pear') in /var/www/Avatar/Database.php on line 2

I don't know why I am getting this error. In phpinfo() it shows include_path .:/usr/share/php:/usr/share/pear .:/usr/share/php:/usr/share/pear

I am using php5 and I even tried installing php-pear package, still I get the same error. I don't understand what's wrong here. Can someone please point me in a right direction.

Note : I have not installed php5 using sudo apt-get install php5. I have downloaded php5 packages using Keryx application.

Looks you did not install DB package, try in command prompt, do