public void buildERD() throws MainException {
		
		Iterator<String> tableNamesItr = tableNames.iterator();
		
		while(tableNamesItr.hasNext()) {
			
			String tableName = (String) tableNamesItr.next();
			
			// if table name has not already been processed
			if (entityTypes.get(tableName) == null && relationshipTypes.get(tableName) == null) {
				constructNode(tableName);
			}
			
		}
		
	}