title: Source Vs PTransform
body: <p>I am new to the project, and I am trying to create a connector between Dataflow and a database.</p>
  
  <p>The documentation clearly states that I should use a Source and a Sink but I see a lot of people using directly a PTransform associated with a PInput or a PDone.</p>
  
  <p>The source/sink API is in experimental (which explaines all the examples with the PTransform), but seems more easy to integrate it with a custom runner (ie: spark for example).</p>
  
  <p>If I refer to the code, the two methods are used. I cannot see any use case where it will be more interesting to use the PTransform API.</p>
  
  <p>Is the Source/Sink API is supposed to remplace the PTranform API?</p>
  
  <p>Did I miss something that clearly differentiate the two methods?</p>
  
  <p>Is the Source/Sink API stable enough to be considered the good way to code inputs and outputs?</p>
  
  <p>Thank for you advice!</p>