Every data tool has an intermediate representation, whether it admits to one or not. It is the thing a model becomes after parsing and before execution, and it quietly decides what the tool can do.
dbt's IR is templated text, which is why ref() is a string and why a macro can produce SQL no analyser can reason about. An earlier iteration of Interlace effectively had a pandas DataFrame as its IR — every model boundary ran an eager .execute() and fed the result back in — which cost us laziness, dialect portability and any hope of semantic change detection, all at once.
Three properties, one root cause. That is what an IR does: it sets the ceiling.
So the current design committed to one sentence:
The canonical IR is a sqlglot AST + Arrow schema. The canonical wire format is an Arrow RecordBatchReader. Materialisation happens exactly once, at the sink, as a single native SQL statement executed inside the owning engine.
