[10000truths]

> The set-theory approach is hard to do, but promising. Each object that wants something has a small set of the things it wants. There's a big pool of such sets. There's also a big pool of the items you have, which changes constantly. It's easy to express what you need to fetch and which objects are now ready to go as set intersection and difference operations. But you need representations for big sparse sets which can do set operations fast. Probably B-trees, or something in that space.

Incremental updates to dynamic dependency graphs is a familiar problem for build tooling. I personally have used the taskflow C++ library (https://github.com/taskflow/taskflow) to great effect.

> Microsoft Research fooled around with this concept years ago in a different context. The idea was to have a database which supported pending SQL queries. The query would return new results when the database changed such that the results of the query changed. The goal was to to support that for millions of pending queries. Financial traders would love to have that. It's a very hard scaling problem. Don't know how that came out.

Incremental view maintenance is an active area of research. The likes of Noria and Materialize have done this with SQL, and the pg_ivm Postgres extension looks promising. Not sure if there is an equivalent implementation geared towards entity-component systems, though.