# Query Engine Glossary

This is a short glossary for the query-engine and IR discussion.

## Terms

- `IR`: Intermediate representation. A simpler form that sits between elaboration and execution.
- `lowering`: The step that converts elaborated Geolog code into the IR.
- `table`: A relational object in the IR. It describes stored data with columns and sometimes a primary key.
- `law`: A logical rule or constraint in the IR. It says what relationships must hold about the data.
- `law checking`: Testing whether the current data satisfies a law.
- `query engine`: The execution component that consumes the IR and answers queries. In a broader design it may also do law checking, chase steps, and
  fixpoint work.
- `backend`: A concrete execution target, such as an in-memory database, Postgres, or a Rust-native storage/query layer.
- `backend-neutral`: Not tied to one storage or execution technology. The IR should ideally be backend-neutral.
- `RelTable`: A table representing a relation or predicate.
- `FunTable`: A table representing something function-like, where input columns determine an output.
- `foreignKeys`: Generated laws saying that if one row exists, dependent rows must also exist.
- `total`: Generated laws saying that if the inputs to a function exist, an output row must exist too.
- `runtime IR`: A second execution-oriented representation above the lowered theory IR. It would hold changing state needed during execution.
- `runtime state`: Mutable or evolving execution data, such as current facts, branch identity, witness allocation, equality classes, or provenance.
- `fixpoint`: The point where running the rules produces no new facts or changes.
- `chase`: The general reasoning process that repeatedly checks laws and adds whatever is needed to satisfy them.
- `witness`: A fresh element introduced to satisfy an existential conclusion.
- `branch`: One possible world or execution path created by a disjunctive rule.
- `equality merging`: Collapsing two terms or elements when the theory says they must be equal.
- `provenance`: Information about where a fact came from or which rules produced it.
- `planning`: Choosing how to execute a query or check a law efficiently.
- `adapter`: A layer that maps shared IR execution concepts onto one specific backend.

## Short mental model

- the front end parses, elaborates, and lowers
- the IR is the contract
- the query engine consumes that contract
- the backend is where execution actually lands