System Overview
BandChain is a high-performance public blockchain that allows anyone to make a request for APIs and services available on the traditional web. It is built on top of the Cosmos SDK, and utilizes Tendermint's Byzantine Fault Tolerance consensus algorithm to reach immediate finality. This finality is specifically reached upon getting confirmations from a sufficient number of block validators.
BandChain's network consists of a number of network participants, each owning BAND tokens. These participants can be broken down into two groups; validators and delegators. We will be focusing on validators in this section.
Validators are responsible for performing two main functions on the network. First, they are responsible for proposing and committing new blocks in the blockchain. They participate in the block consensus protocol by broadcasting votes which contain cryptographic signatures signed by each validator's private key. This is similar to most other Cosmos-based delegated proof-of-stake blockchains.
Each validator will have a certain amount of BAND tokens bonded to them. The source of these tokens can either be their own holdings, or the tokens delegated to them by other token owners. In most cases, there will be a large number of parties with tokens staked to them. In that case, the top 100 validator candidates with the most token staked to them will become BandChain’s validators.
The role the validators described above is similar to those of validators on many other Cosmos-based blockchains. In addition, most transactions supported by BandChain (asset transfer, staking, slashing, etc.) are also derived from Cosmos-SDK. What makes BandChain unique, and the origin of the validators' second duty, is the chain's capability to natively support external data query.
Blockchain networks are historically deterministic by nature. This means that the current state of a blockchain is entirely and strictly determined by previous transactions and events that occurred on the chain. This limits the possible use cases of decentralized applications built on those networks. BandChain aims to fix this limitation. With our data oracle, anyone can make a request for APIs and services available on the traditional web, all while not having to rely on a centralized party. This allows dApps to leverage existing data on the internet without compromising on security.
Before any data requests can be made, two conditions must be met:
- The oracle script that describes the data request must also have been published
- The data sources related to the aforementioned oracle script must be published to BandChain
Data sources are the most fundamental unit of the oracle system. It describes the procedure to retrieve raw data points from a primary source and the fee associated with a query made to that source.
On BandChain, anyone can submit and register a data source into the system. To publish a data source, one must send a MsgCreateDataSource message to the chain. Once deployed, a data source can be referenced by a unique int64 identifier assigned to it. If the data source owner wants to edit the source's details once it has been published, they can use that unique identifier as a reference key.
An oracle script is an executable program that encodes (1) the set of raw data requests to the sources it needs and (2) the way to aggregate raw data reports into the final result. These sources can be the data sources published on the network, as well as other oracle scripts. This composability makes oracle scripts very similar to smart contracts. See the terminology section for more information on oracle scripts, including its features and limitations.
A data request to Band's oracle begins when an external party requests data from the oracle by broadcasting MsgRequestData. The contents of the message includes the oracle script the requester wants to invoke and other query and security parameters.
Once the data transaction is confirmed on BandChain, the requested oracle script will begin its execution. The script's execution process can be split into two phases.
First, the oracle script's preparation function will emit the set of raw data requests necessary to continue the script's execution.The chain's validators, who are chosen at random (TODO: LINK TO DECENTRALIZED VALIDATOR SAMPLING SECTION) for security reasons, will then inspect the raw data requests and execute the associated data sources' procedures as instructed by the request. Each validator that successfully retrieved the data will then submit a raw data report to BandChain, containing the results they got from each of the data sources, by broadcasting MsgReportData. Once a sufficient number of validators, specified in the data request’s security parameters, have reported the their results, BandChain will begin executing the oracle script’s second phase.
This second phase begins by aggregating all of the validators' reports into a final singular result. This final result is then permanently stored in BandChain's application state. Once stored, the result becomes available on the chain's state tree and can be sent to other blockchains through Inter-Blockchain Communication (TODO: LINK TO IBC SECTION).
When the final result is successfully stored, an oracle data proof is also produced. This proof is a Merkle proof that shows the existence of the final result of the data request as well as other related information (oracle script hash, the parameters, the time of execution, etc) on BandChain. This proof can then be used by smart contracts on other blockchain to verify the existence of the data as well as to decode and retrieve the result stored. Both of these can be done by interacting with our lite client.