No, you didn't get me. setElementParent puts an element as parent of other. setElementData sets a data on an element. Both "values" will disappear when the main element is destroyed.
Example:
local ped1 = createPed( ... );
local ped2 = createPed( ... );
setElementParent( ped1, ped2 ); -- sets 'ped2' as parent of 'ped1'
destroyElement( ped1 ); -- now ped2 is destroyed because it's a parent ( or child, whatever you want to call it ) of 'ped1'
--
local ped3 = createPed( ... );
setElementData( ped3, "isNormalPed", true );
if ( getElementData( ped3, "isNormalPed" ) ) then
outputChatBox( "Ped is a civillian!", ... );
end