Architecture

Here is the architecture showing the interaction between Parallel Finance parachain and Relaychain, other parachains, and Non-Polkadot blockchain.

For communication between parachain and parachain, between parachain and relaychain, `XCM` is the way to do this. Here is a detailed introduction to XCM.

Cross-Consensus Message Format (XCM) · Polkadot Wiki

As to communication between parachain and Non-Polkadot blockchain. the way is through Bridge, a bridge will include multi relayers to make it decentralized. it's still being implemented.