What is Yellow Paper?

Ethereum Yellow Paper is a specification document of Ethereum.

Many specifications are written in Yellow Paper rather than White Paper.

We can learn many features of Ethereum from it.

Transactional singleton machine with shared state

Blockchain concept is called a "transactional singleton machine with shared-state" in Yellow Paper.

(Quote from Abstract)
We can call this paradigm a transactional singleton machine with shared-state.

Cryptographically-secured transactions update "shared-state"(ex. address, balance, remaining currency amount, etc ) via P2P network.

The state is defined as "version of the world of Ethereum"

(Quote from Chapter2)
It is this final state which we accept as the canonical version" of the world of Ethereum.

The state includes account balance, nonce( transaction count of every account), storage hash(the hash value of storage data ), code hash (the hash value of smart contract code).

"

Ethereum implements this paradigm in a generalised manner

Ethereum is a generalized implementation of a transaction-based singleton machine.

Ethereum has distinct state per account. Participants of the P2P network update the state by broadcasting transaction.

The transaction can invoke the smart contract method on the blockchain.

The smart contract is a feature of Ethereum. It is written by programming language (solidity , vyper and more) and the compiled its code is recorded on the blockchain.

The smart contract enables us to define original variables. So Yellow Paper tells,

(Quote from Chapter2)
The state can include such information as account balances, reputations, trust arrangements, data pertaining to information of the physical world

We can handle many types of data with Ethereum.

"Key Goal" of Ethereum

(Quote from Chapter1)
one key goal is to facilitate transactions between consenting individuals who would otherwise have no means to trust one another.

It tells that realization of "Trustless transaction" is important.

(Quote from Chapter1)
By specifying a state-change system through a rich and unambiguous language, and furthermore architecting a system such that we can reasonably expect that an agreement will be thus enforced autonomously, we can provide a means to this end.

And it tells "rich and unambiguous language" is useful for realization of the goal state-change system.