tcl dom get attributes as a list

<Testcases>
<Testcase tc_name="tc1">
  <Parameters>
    <Input_Arguments>tc1_arg1</Input_Arguments>                 
    <Input_Arguments>tc2_arg2</Input_Arguments>
  </Parameters>  
</Testcase>
<Testcase tc_name="tc2">
  <Parameters>
    <Input_Arguments>tc2_arg1</Input_Arguments>
    <Input_Arguments>tc2_arg2</Input_Arguments>
  </Parameters>  
</Testcase>
</Testcases>

Above is my xml, I want to use tdom to first read in all "tc_name" attributes as a tcl list. Then use each tc_name in the list to locate corresponding parameters. Please tell me how to do that, thanks!

Your headline says tcl dom but your question says tdom and it's tagged as tdom so I'll go for a majority decision and give a tdom answer - they are different packages!

First you need to parse the raw xml with

# Assumes that xmlText holds your raw XML
dom parse $xmlText doc

Now get a list of the tc_name nodes

set nodes [$doc selectNodes {Testcases/Testcase[@tc_name]}

Now cycle around those nodes accessing the Parameter nodes

foreach node $nodes {
    set params [$node selectNodes Parameters]
    foreach param $params {
        # Do some stuff
    }
}

Don't forget to get rid of the document once you've finished with it. (Note that this will happen automatically when the proc exits if you're doing it inside a proc.)

$doc delete

I'm not completely sure what it is you want to do finally, so here's a bit of code to output each argument, with its tc_name, one per line:

dom parse {<Testcases>
             <Testcase tc_name="tc1">
               <Parameters>
                 <Input_Arguments>tc1_arg1</Input_Arguments>                 
                 <Input_Arguments>tc2_arg2</Input_Arguments>
               </Parameters>  
             </Testcase>
             <Testcase tc_name="tc2">
               <Parameters>
                 <Input_Arguments>tc2_arg1</Input_Arguments>
                 <Input_Arguments>tc2_arg2</Input_Arguments>
               </Parameters>  
             </Testcase>
           </Testcases>
        } doc
foreach testcase [$doc selectNodes Testcases/Testcase] {
    set name [$testcase getAttribute tc_name]
    foreach arg [$testcase selectNodes Parameters/Input_Arguments] {
        foreach child [$arg childNodes] {
            puts stdout $name\ [$child nodeValue]
        }
    }
}
$doc delete;          # Tidy away the parsed document

I hope this gives enough pointers to things for you to be able to complete your task