Architecture

UnitFlow is organized in layers with strict downward dependencies. This matches the contributor guidelines in the main repository.

Layer	Package	Role
Dimension algebra	unitflow.core	Base dimensions, exponent vectors
Exact scale	unitflow.core	Rational coefficients, explicit π
Unit semantics	unitflow.core	Immutable units, composition
Quantity core	unitflow.core	Arithmetic, conversion, equality
Display	unitflow.core	Human-readable formatting
Definition system	unitflow.define	define_unit, namespaces, registries, prefixes
Catalogs	unitflow.catalogs	Curated SI and mechanical packs
Expressions	unitflow.expr	Symbols, trees, constraints, compile helpers
Serialization	unitflow.serialization	Structural JSON-safe payloads
Backends	unitflow.backends	Optional NumPy integration

Dependency rules

• core does not depend on NumPy or expression-only layers.

• expr may depend on Quantity, Unit, and Dimension.

• catalogs depend on the semantic core, not on backends.

• backends depend on core, not the reverse.

Changing dependency direction requires an explicit design discussion. See the full policy in the repository CONTRIBUTING.md.