Hello, @yingzhang
Disease and symptoms are going together in CDM - we rely on the data and mostly don’t do a differential diagnosis. Some symptoms, however, can be transformed into observations if you find suitable concept_ids.
Also, if conditions and symptoms come from different sources, you may be interested in different types for these records. Just a week ago we had a vocabulary release for consolidated Type Concepts and new Condition Statuses. You can find useful links and check the vocabulary release here: Important vocabulary release: Type Concept and Condition Status