   +-------+ 
   | user  | 
   |       | 
   +-------+ 
       |     
       v     
  +-------+  
  |client |  
  |       |  
  +-------+  
    ^     |  
    |     |  
  HTTP    |  
    |     |  
    v     v  
+-----------+
|Web Server |
|           |
+-----------+
   |      |  
queries   |  
   |      |  
   v      v  
+-----------+
|PostgreSQL |
|           |
+-----------+
