def extract_metadata
      raise ArgumentError, "MIME type unspecified or not configured" if schema.blank?
      fn = "extract_#{schema.downcase}_metadata"
      raise ArgumentError, "Unsupported metadata standard: #{schema}" unless respond_to?(fn.to_sym)
      send(fn, metadata_xml)
    end
def extract_metadata
      raise ArgumentError, "MIME type unspecified or not configured" if schema.blank?
      fn = "extract_#{schema.downcase}_metadata"
      raise ArgumentError, "Unsupported metadata standard: #{schema}" unless respond_to?(fn.to_sym)
      send(fn, metadata_xml)
    end
Extracts properties from the constitutent external metadata file
 @example
   extract_iso19139_metadata
   extract_fgdc_metadata
   extract_mods_metadata
 @return [Hash]