title: Spark SQL encapsulation of data sources
body: <p>I have a Dataset where 98% (older than one day ) of its data would be in Parquet file and 2% (the current day - real time feed) of data would be in HBase, i always need to union them to get final data set for that particular table or entity.</p>
  
  <p>So i would like my clients use the data seamlessly like below in any language they use for accessing spark or via spark shell or any BI tools  </p>
  
  <pre><code>spark.read.format("my.datasource").load("entity1")
  </code></pre>
  
  <p>internally i will read entity1's data from parquet and hbase then union them and return it.</p>
  
  <p>I googled and got few examples on extending DatasourceV2, most of them says you need to develop reader, but here i do not need new reader, but need to make use the existing ones (parquet and HBase).</p>
  
  <p>as i am not introducing any new datasource as such, do i need to create new datasource?  or is there any higher level abstraction/hook available?</p>