Expand description
Glossary
§Glossary
§XCM (Cross-Consensus Messaging)
A messaging format meant to communicate intentions between consensus systems. XCM could also refer to a single message.
§Instructions
XCMs are composed of a sequence of instructions. Each instruction aims to convey a particular intention. There are instructions for transferring and locking assets, handling fees, calling arbitrary blobs, and more.
§Consensus system
A system that can reach any kind of consensus. For example, relay chains, parachains, smart contracts. Most messaging between consensus systems has to be done asynchronously, for this, XCM is used. Between two smart contracts on the same parachain, however, communication can be done synchronously.
§Location
A way of addressing consensus systems. These could be relative or absolute.
§Junction
The different ways of descending down a Location hierarchy.
A junction can be a Parachain, an Account, or more.
§Asset
A way of identifying assets in the same or another consensus system, by using a
Location.
§Sovereign account
An account in a consensus system that is controlled by an account in another consensus system.
Runtimes use a converter between a Location and an account.
These converters implement the ConvertLocation trait.
§Teleport
A way of transferring assets between two consensus systems without the need of a third party. It consists of the sender system burning the asset that wants to be sent over and the recipient minting an equivalent amount of that asset. It requires a lot of trust between the two systems, since failure to mint or burn will reduce or increase the total issuance of the token.
§Reserve asset transfer
A way of transferring assets between two consensus systems that don’t trust each other, by using a third system they both trust, called the reserve. The real asset only exists on the reserve, both sender and recipient only deal with derivatives. It consists of the sender burning a certain amount of derivatives, telling the reserve to move real assets from its sovereign account to the destination’s sovereign account, and then telling the recipient to mint the right amount of derivatives. In practice, the reserve chain can also be one of the source or destination.
§XCVM
The virtual machine behind XCM. Every XCM is an XCVM programme. Holds state in registers.
An implementation of the virtual machine is the xcm-executor.
§Holding register
An XCVM register used to hold arbitrary Assets during the execution of an XCVM programme.
§Barrier
An XCM executor configuration item that works as a firewall for incoming XCMs. All XCMs have to pass the barrier to be executed, else they are dropped. It can be used for whitelisting only certain types or messages or messages from certain senders.
Lots of barrier definitions exist in xcm-builder.
§VMP (Vertical Message Passing)
Umbrella term for both UMP (Upward Message Passing) and DMP (Downward Message Passing).
The following diagram shows the uses of both protocols:
flowchart relay[Relaychain] --"DMP"--> paraA["Parachain(2000)"] relay --"DMP"--> paraB["Parachain(2001)"] paraA --"UMP"--> relay paraB --"UMP"--> relay
§UMP (Upward Message Passing)
Transport-layer protocol that allows parachains to send messages upwards to their relay chain.
§DMP (Downward Message Passing)
Transport-layer protocol that allows the relay chain to send messages downwards to one of their parachains.
§XCMP (Cross-Consensus Message Passing)
Transport-layer protocol that allows parachains to send messages between themselves, without going through the relay chain.
§HRMP (Horizontal Message Passing)
Transport-layer protocol that allows a parachain to send messages to a sibling parachain going through the relay chain. It’s a precursor to XCMP, also known as XCMP-lite. It uses a mixture of UMP and DMP.