# Potential order book designs on Miden
There are three models we have discussed during our call. The models differ by the degree of self-custody and speed for the user.

## Orders as notes - fully non-custodial

Fully non-custodial, as both the maker and taker execute and prove transactions locally. Takes ~2s each due to blocktime. Order price updates or cancellation can be ms.

| Action | Time | Comment |
| -------- | -------- | -------- |
| Create order | 2s | On-chain |
| Take order | 2s | On-chain (next block) |
| Order price update* | <10 ms | Revealing parts of the note script |
| Order canceling** | <10 ms | Non-revealing pre-image |

'* One note can contain many order each with its own price. These prices can be revealed one after another in real time.
'** Note consumption can require a secret that market maker holds - market makers need to be constantly online then. Cancellation means not sending out the secret anymore.

A potential design can be found [here](https://github.com/0xPolygonMiden/examples/discussions/138).

## Orders as notes using ephemeral notes - semi-custodial
Semi-custodial, since state gets committed every 2 seconds. The "in-flight' state of the order book (i.e., the last ~2 seconds of activity) is controlled by the operator. Ephemeral notes don't need to be on-chain. Operator proves on behalf of user. He knows the future state and users can act on trusted off-chain state. First note of a chain must still be on-chain.


| Action | Time | Comment |
| -------- | -------- | -------- |
| Create order | 2s | On-chain |
| Take order* | 500 ms | Off-chain |
| Order price update | <10 ms | Off-chain |
| Order canceling | <10 ms | Off-chain |

'* Taking requires a transaction to be executed against taker account. Operator executes. Time depends on the machine and final design.

## Orders as balances in a Miden account
Semi-custodial. Each Miden account can act as its own Validium or zkRollup. Assets are locked as balances in the account. A single state change in the order book account can update multiple balances, allowing many users to be served simultaneously.


| Action | Time | Comment |
| -------- | -------- | -------- |
| Initial deposit | 2s | Blocktime |
| Create order | 100 ms | Signature check |
| Take order | 100 ms | Signature check |
| Order price update | 100 ms | Signature check |
| Order canceling | 100 ms | Signature check |