def extract_metadata(id)
      return {} if metadata_files.blank?
      metadata_file = metadata_files.find { |f| f.id == id }
      metadata_file.extract_metadata if metadata_file
    end
def extract_metadata(id)
      return {} if metadata_files.blank?
      metadata_file = metadata_files.find { |f| f.id == id }
      metadata_file.extract_metadata if metadata_file
    end
Extracts properties from the constitutent external metadata file
 @return [Hash]