The L0 Token Standard is a common interface for L0 Cells, which are used to connect each state channel or L1 to the global DAG L0 as well as each other; forming the HyperGraph network as a whole. This allows developers of state channels and other systems to integrate using the same API and deployment process. The motivation here is to provide a common layer for currency operations that can be understood and validated by many separate networks extending the core protocol.
As each L1 composing the network may be extending the core L0 operations in it’s own way, it is desirable to have a common interface for shared logic related to currency operations. For those, a common shared executor layer surrounding operations related to currency validation can be used and extended in order for currency transactions across networks to be validated by unique networks. As the L1 may offer functionality more complicated than a conventional currency operation, the L0 token standard offers a way to restrict the operations to those that can be easily shared across the L0 by defining an appropriate interface.
Following a pattern similar to the erc-20 standard, the L0 interface is a trait that can be defined for the L0 Cell that contains required methods for accessing state channel ledger data and publishing final ledger state data to other L0 cells. However it differs in that it contains the datatypes and order of operations for state updates inside of its Cell. These are it's Algebra and Coalgebra which construct a type-safe program to be executed within the Cell functor by it's Hylomorphism. The external api is contained within the actual p2p server.
An example Cell implementation following the standard is shown in the DAG L0 which contain the required data types and state update logic. The required methods are shown in the L0 API. Note this is in alpha state and will be expanded such that the required Algebra/Coalgebras will be added to custom Cell logic at instantiation.
Integrating existing L1 protocols
Existing L1 protocols can integrate with others by deploying an L0 Cell that implements the L0 standard interface. By integrate we mean that their ledgers can share meta-state for use cases such as swaps (DAG L0), cross validation of each other's data or creating graphs of reactive execution logic. Deployment of this L0 cell can be on the same or different machines as your L1 node. They subscribe to L1 ledger data and publish converged state data called "Snapshots" to their L1 as well as other L0s of state channels that have integrated their data somewhere within their consensus pipeline. Integration also required deploying a state channel definition to each other's ACI.
Deploying to the global $DAG L0
As above, a state channel definition must be deployed to the DAG L0 ACI (Application Chain Interface). This interface follows the convention typically established by ABIs (application binary interfaces,) but in the context of partially shared executor validation contexts specific to microservices. In order to provide the security required for an open network to register untrusted state channel definitions in real time, validation functions are currently limited to hash based validation on ledger states of numeric type.