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Cross-Consensus Message Format (XCM) is a messaging format and language used to communicate between consensus systems.
XCM is designed to provide a generalized and extensible set of instructions that can facilitate transaction completion across a variety of consensus systems, transaction formats, and transport protocols.
A Closer Look at XCM
One of Polkadot’s key features is interoperability between various parachains and other consensus-based systems. XCM is essentially a language that allows two blockchains to interact with each other and perform complex interchain interactions. However, XCM is not limited to the Polkadot network. The main function of XCM is to define a common format that allows different consensus systems to communicate with each other. XCM also does not define how messages are passed between the two consensus systems. Instead, it defines how the message should look and behave and includes instructions for the intended on-chain operation.
XCM messages are delivered to participating parachains via Cross Chain Message Passing (XCMP), which has four core design principles that it adheres to.
Asynchronous – XCM messages do not assume that the sender will block contention.
Absolute – XCM ensures that messages are conveyed and interpreted accurately. Once a message is sent, the sender can be confident that the message will be delivered and processed as the sender intended.
Asymmetric – XCM messages follow a 'fire and forget' paradigm. This means that the sender has no way of knowing whether the message was received. The results must be delivered separately from the sender, along with any additional messages back to the source.
Agnostic – XCM makes no assumptions about the nature of the consensus system. It can be used in any system where finality is reached through consensus.
How is XCM a groundbreaking leap forward in cross-chain technology?
XCM offers several improvements over previous and existing bridging solutions. Previous cross-chain technologies typically involved moving tokens between chains. XCM messages can carry any data, enabling functionality beyond token transfer and facilitating innovative services not supported by legacy networks. XCM messages are programmable, allowing for a high level of cross-chain interoperability never before seen in blockchain technology.
XCM is also very insecure and unreliable. Before the advent of XCM, blockchains had no way to communicate other than using bridges that relied on third parties, which led to a series of infamous hacks. Inter-parachain messages on Polkadot share the same security as the rest of the network. There is also no need to deposit your funds with a third-party custodian or centralized entity. XCM also works between smart contracts based on different virtual machines, connecting networks built on different consensus mechanisms.
One of the main goals of XCM is to improve communication between chains and make system parachains a reality. Let’s take Polkadot’s Relay Chain as an example. In addition to parachain management and shared security, relay chains handle user balances, assets, governance, auctions, and staking. In an ideal situation, relay chains should only be utilized for shared security. System parachains can help relieve the core responsibilities of relay chains by using standard formats such as XCM.
Format for Agreed Communication
XCM began as an approach to cross-chain communication. However, it has now evolved into a format for cross-consensus communication that can be performed between chains, smart contracts, palettes, bridges, and sharded enclaves such as SPREE. As mentioned earlier, XCM is a format for how to perform message transfer. This is similar to how RESTful services use REST as an architectural development style, with HTTP requests containing specific parameters to perform specific tasks.
Disclaimer: This article is provided for informational purposes only. It is not provided or intended to be used as legal, tax, investment, financial or other advice.
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