# 2.2.3 Connecting On-chain and Off-chain Data

The CreDA protocol performs in-depth mining using data from all public chains. Through the W3C standard compliant DID protocol, the CreDA Credit Oracle establishes the modeling for participants’ public historic cross-chain data by constructing an oracle network and a trusted computing element network. In this way, the oracle provides comprehensive and dynamic credit ratings for users through decentralized technology. The decentralized oracle node network enables off-chain credit calculation with the results fed into smart contracts on-chain through oracles.

When a smart contract on the blockchain needs to obtain specific data, it will send a data request (‘contract request’). CreDA's Credit Oracle will register the data request as an "event" and send the data request to the corresponding nodes, starting the validation bidding process among the different nodes. The oracle will select a certain number of appropriate oracle nodes to complete the task. The nodes selected by the credit oracle will obtain all the data and provide a result after verifying and aggregating this data.

![Credit Oracle Technology Milestones](https://1888623400-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FIkBpl0Jl7LkylvgjTcLr%2Fuploads%2FhlwfYIHnu8wsPd9Lj2PN%2FPicture3.png?alt=media\&token=32e8367b-7471-4a45-9be4-e8433233dd10)


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