class_docstr: A class like DatasetMetadata also holding `PCollection`s and an asset_map.
  
  `deferred_metadata` is a PCollection containing a single DatasetMetadata.
  `asset_map` is a Dictionary mapping asset keys to filenames.
code: def schema(self):
      return self.dataset_metadata.schema
  
file_path: transform/tensorflow_transform/beam/tft_beam_io/beam_metadata_io.py
imports: import json
  import os
  import apache_beam
  import tensorflow
  from tensorflow_transform import output_wrapper
  from tensorflow_transform.beam import common
  from tensorflow_transform.tf_metadata import metadata_io
  from tfx_bsl.types import tfx_namedtuple
label_desc: Use image node_id 1 for calling the BeamDatasetMetadata obj's underlying member method code with example usage: obj.schema() and returns: self