text: Title: How to calculate relevance/score for a query asked by the user against the trained document on a scale of 0-1
  Body: **Question**
  How to calculate relevance/score for a query asked by the user against the trained documents ?
  
  **Additional context**
  @abhishekraok  @DmitryKey 
  
   
   As relevance/score for the results obtained against the documents is very important to be known , so that user is aware of the confidence level of the retrieved documents .
  
  Could you please let us know how is this calculated?
  
  - If this is incorporated in this code base where is it?
  - How do we do it for a BERT model ?( is it using dot product calculation? )
  