c# PML.NET NET CONTROL

I have a question.

I Want to use variable like below

DbExpression expr1 = DbExpression.Parse("NAMN");
DbExpression expr2 = DbExpression.Parse($"CATREF OF ({expr1})");

because i want TO USE LIKE THIS

SPCO > CATREF >  PTSE > PTAX > GET PBORE(PARAM 1) AS VAR1 > FIND PBORE(PARAM 1) IN SCOM > RESULT

DbExpression expr2 = DbExpression.Parse("RESULT");

HELP ME....

BELOW IS FULL? CODE

[PMLNetCallable()]
public Hashtable Getelements(string root)

{

Hashtable elementsTable = new Hashtable();

DbElement element = DbElement.GetElement(root);

TypeFilter filt = new TypeFilter();
filt = new TypeFilter(Aveva.Core.Database.DbElementTypeInstance.SPCOMPONENT);
DBElementCollection collection;
collection = new DBElementCollection(element, filt);
int index = 0;

foreach (DbElement ele in collection)
{
DbExpression expr1 = DbExpression.Parse("NAMN");
DbExpression expr2 = DbExpression.Parse($"CATREF OF ({expr1})");

string NAME = ele.EvaluateAsString(expr1);
string CATA = ele.EvaluateAsString(expr2);