the installer script is not firing magento?

Question

i have setup the resource like the following at config file,

<?xml version="1.0" encoding="UTF-8"?>
<config>
    <DigitalHorizons_Att>
        <version>0.1.0</version>
    </DigitalHorizons_Att>
    <frontend>
        <routers>
            <att>
                <use>standard</use>
                <args>
                    <module>DigitalHorizons_Att</module>
                    <frontName>att</frontName>
                </args>
            </att>
        </routers>
    </frontend>
    <global>
        <resources>
            <digitalhorizons_att_setup>
                <setup>
                    <module>DigitalHorizons_Att</module>
                    <class>DigitalHorizons_Att_Model_Resource_Setup</class>
                </setup>
            </digitalhorizons_att_setup>
        </resources>
    </global>
</config>

this is not fires the installer scripts at

local\DigitalHorizons\Att\sql\digitalhorizons_att_setup\install-0.1.0.php

when i delete DigitalHorizons_Att_Model_Resource_Setup class at app\code\local\DigitalHorizons\Att\Model\Resource\Setup.php

it says the following error,

Warning: include(DigitalHorizons\Att\Model\Resource\Setup.php): failed to open stream: No such file or directory in E:\wamp\www\sample\lib\Varien\Autoload.php on line 93

the following content is there is at the installer file,

<?php
   echo 'Running This Upgrade: '.get_class($this)."\n <br /> \n";
   die("Exit for now");
?>

Answer 1

change

local\DigitalHorizons\Att\sql\att_setup\install-0.1.0.php

to

local\DigitalHorizons\Att\sql\digitalhorizons_att_setup\inst‌​all-0.1.0.php

make sure your module version is same 0.1.0 in config.xml

<modules>
    <DigitalHorizons_Att>
        <version>0.1.0</version>
    </DigitalHorizons_Att>
</modules> 

and also check remove the entry of digitalhorizons_att_s‌​etup from core_resource table

Answer 2

you need to add following node in your config.xml update as follow

you have define connection and read and write nodes in config.xml

<?xml version="1.0" encoding="UTF-8"?>
<config>
<DigitalHorizons_Att>
    <version>0.1.0</version>
</DigitalHorizons_Att>
<frontend>
    <routers>
        <att>
            <use>standard</use>
            <args>
                <module>DigitalHorizons_Att</module>
                <frontName>att</frontName>
            </args>
        </att>
    </routers>
</frontend>
<global>
    <resources>
        <digitalhorizons_att_setup>
            <setup>
                <module>DigitalHorizons_Att</module>
                <class>DigitalHorizons_Att_Model_Resource_Setup</class>
            </setup>
            <connection>
                <use>core_setup</use>
            </connection>
        </digitalhorizons_att_setup>
        <digitalhorizons_att_write>   
            <connection>         
                <use>core_write</use>     
            </connection> 
        </digitalhorizons_att_write> 

        <digitalhorizons_att_read>     
            <connection>        
                <use>core_read</use>
            </connection>   
        </digitalhorizons_att_read>
    </resources>
</global>
</config>