root/galaxy-central/tools/data_source/echo.xml

<?xml version="1.0"?>

<tool name="Echo" id="echo1">

        <description>
                echoes parameters  
        </description>
        
        <command interpreter="python">echo.py $input $database $output </command>

        <inputs>
                <param format="tabular" name="input" type="data" label="Input stuff"/>
        <param type="select" name="database" label="Database">
            <option value="alignseq.loc">Human (hg18)</option>
            <option value="faseq.loc">Fly (dm3)</option>
        </param>
        </inputs>

        <outputs>
                <data format="input" name="output" label="Blat on ${database.value_label}" />
        </outputs>

</tool>