if(val instanceof ConnectionPoint){
// named process element output, look in tables
ConnectionPoint cp=(ConnectionPoint)val;
if(subs.containsKey(cp.getElementName())){
NamedSource src=subs.get(cp.getElementName());
Parameter param=src.outputsByName().get(cp.getConnectionName());
if(param==null)
throw new IllegalArgumentException(MessageFormat.format(
"Element {0} does not have output {1} in {2}", cp.getElementName(),
cp.getConnectionName(), cp.getLocationText()));
return new SourceStore(src, param.i);