World is the Kernel of MUD. It is a specific pattern for writing on-chain applications that bundle together:
- Store: MUD’s on-chain database
- Systems: stateless logic contracts that read and write to Store tables.
- Permissionless creation of tables and systems from anyone on-chain.
- Access-control for tables and systems based on namespaces.
- Modules: on-chain scripts installing tables, systems, and hooks on the World.
When using the World kernel, all the state and logic of the application is centralized in a single contract — the World contract. The World takes care of mediating writes to the Store depending on who requests them, and routes function-calls to their respective systems which then read and write to the Store on the World.
In its role as a router and as a centralized storage for state, the World is similar to a Diamond or a Proxy. The main difference between these patterns and the World framework is that the World allows for permissionlessly registering new logic and tables (=state) on the World. This is in contrast with Diamond and Proxy that require an admin in order to permission adding and upgrading logic.
Given Worlds have storage access management for Store, they can relax that requirement and let anyone add new logic and new tables to the application without introducing security risks.
This makes it possible for multiple actors — that do not necessarily trust each other — to build on the same Store and allow for interoperability across their tables and systems.
Of course this could have been done across multiple contracts, just like DeFi contract A can transfer an ERC-20 balance of DeFi contract B if it has been approved. However, by centralizing the state under a single contract and enforcing a standardized access control mechanism, the World framework makes it possible to build much better tools and frontend libraries to know about the entire state of the World.