Let's look at the various strategies with which you can achieve one or more of the previous use cases. We will learn the strategies that we can implement in Quorum, but not all the ones that are available for public or other blockchains. We will also look at examples of how to implement these strategies.
The easiest way to achieve interoperability is to have a centralized third-party through which blockchains can talk to each other. Essentially, you need to trust the third-party.
However, centralized interoperability projects, such as Oraclize, have solved the trust problem. Oraclize enables your Ethereum smart contracts to communicate with the WWW; that is, it enables you to make REST API calls, fetch a Bitcoin account balance, check the file status in IPFS, and so on. Oraclize also provides a proof for smart contracts stating that the results have not been manipulated; therefore, Oraclize has tackled the trust issue...