public TdlClass AddClass(string identifier)
{
if (identifier == "")
{
return(null);
}
TdlClass tdlClass = new TdlClass(identifier, this);
_Classes.Add(tdlClass);
ClassIdentifierLookup.Add(identifier, tdlClass);
ClassLookup.Add(tdlClass.ObjectId, tdlClass);
Root.AddClass(tdlClass);
return(tdlClass);
}