Once we decide which chain we want our smart contracts to live on, we need a way to pull data from that chain. This is where the indexing and querying layer comes in.

What do we mean by indexing and querying? To build dapps that use data from the blockchain, we need a reliable, developer-friendly way to get that data. Reading data directly from a blockchain is a complex process, we should use dedicated, already-existing tools.

If we use a tool like Infura, for example, we are provided with a REST endpoint that we can use to run data queries on the blockchain. If we want to monitor the chain for certain activities, like NFT purchases, we can do this by using another one of these tools. There are both centralized and decentralized methods of querying and posting blockchain data.