I think you could have a look at this https://datahubproject.io/docs/metadata-modeling/extending-the-metadata-model

Thanks for the suggestions. Now I understand that I don't need to create a new entity. Rather, I want to extend a already existing entity with a new metadata aspect. For example, I want to add a new aspect name "purpose" for "datasets". I want to create purpose for both tables and columns of the datasets. But, I am confused here where should I create the new aspect and on which entity file to add it. The documentation also doesn't give proper guidance about the directory structure. Would you kindly provide me some suggestions here?

maybe you dont need to create an aspect? just use the data property field?