We use MongoDB as our Database.
Posts have a simple structure as following :
{
_id : 'ObjectID',
title : 'String',
slug : 'String',
author : 'ObjectID',
dateAdded : 'Date'
...
...
...
upvotes : 'Number',
tags : ['ObjectID'] //array of nodes
}
For the sake of simplicity, I have omitted many other properties. But the bottomline is that the schema is very simple and flexible. As MongoDB is a schema less DB, we can always add new properties very easily.