All these were written by great sages. When one sage writes something great then how his creation is being categorized among them? Means, if he writes something then after completion, how is it decided that his newly creation will be considered as Veda, Purana, Upanishad, smritis etc.,? Who decides whether new creation will fall in which category? And also what's the difference between all these categories.
They all (Puruna, upanishads etc) provides the knowledge then why these knowledge is being categorized and on what basis?
Note: There might be more categories also available but I remember only these for now.