According to the Oxford English Dictionary, according to is the usage of the words according and to as a compound preposition. The definition of the adjective according is:
1. With to. Corresponding to something; agreeing, matching. Obs.*
5. As a compound preposition. according to: as stated or formulated by.
The word according itself means:
- Suitable, fitting, appropriate; in accordance with something previously stated.
So according to would mean: "in accordance with", "suitable to", "appropriate to", etc.
Based on and based upon do have similar meanings, there's a good question about it here.
Oxford English Dictionary describes base used as a figurative:
a. A fundamental principle, an underlying basis, a foundation
b. A ground for an action or attitude; an underlying reason or justification.
They don't mention the compound usages of based upon and based on, but the meaning can be inferred. Merriam Webster describes a definition of base for kids as:
— base on or base upon
: to make or form from a starting point < It's based on a true story. >
According to states that the following statement or idea is something someone or something would agree with or have conveyed themselves. Based upon states that the following idea, statement, or work is built off of something else.
Another way to look at: according to is attempting to paraphrase or quote someone or something, while based on or based upon is creating a separate idea, work, or statement that has been influenced by or has been structured from the original.