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Define Your Domain as a Schema

2026.02.28

Guides

Define Your Domain as a Schema

Why Schemas Matter

Without schemas, a "temperature" field in one document might be Celsius while another uses Fahrenheit. An "age" field might be a raw integer in one record and a date of birth in another. ZK proofs cannot work with ambiguous data — they need a normalized, typed attribute space where comparisons are well-defined.

Lemma schemas solve this by defining, per domain, exactly what raw data looks like, what normalized data looks like, and how to transform one into the other.

Defining a Schema

A schema has three parts:

  1. Raw type — the shape of the original document.
  2. Norm type — the normalized attribute space used for commitments and proofs.
  3. normalize function — the transformation from Raw to Norm.
import { define } from "@lemmaoracle/sdk";

type UserKycRaw = { age: number; country: string };
type UserKycNorm = { age_bucket: "adult" | "minor"; country: string };

const userKycSchema = define<UserKycRaw, UserKycNorm>({
  id: "user-kyc-v1",
  normalize: (raw) => ({
    age_bucket: raw.age >= 18 ? "adult" : "minor",
    country: raw.country,
  }),
});

The id is referenced throughout the system — in prepare, documents.register, circuit metadata, and attributes.query. It is the thread that ties raw data to proofs to query results.

Normalization Is the Key Design Decision

The normalize function determines the granularity of your verified attributes. Consider temperature:

  • normalize: (raw) => ({ temp_bucket: raw.temperature < 10 ? "cold" : raw.temperature < 25 ? "mild" : "hot" }) — three buckets, lossy but privacy-preserving.
  • normalize: (raw) => ({ temperature: raw.temperature }) — exact value, no bucketing, less privacy.

This is a domain-specific design decision. Lemma does not prescribe the right granularity — it gives you the tools to define it precisely and ensures that ZK proofs and commitments operate on the normalized space you chose.

Generators: Documenting Data Origins

A schema defines the attribute space. A generator defines how raw documents are produced — which script, which inputs, which external APIs.

The generator_id and its hash are included in ZK public inputs, so every verified attribute traces not just to a schema and circuit, but to the exact process that produced the original data.

Circuits Complete the Picture

A schema normalizes data. A generator produces data. A circuit proves predicates on normalized, committed data. Together, these three components form a complete, auditable chain:

Generator → Raw document → Schema → Normalized attributes → Commitments → Circuit → Proof

When a consumer queries verified attributes, the response includes all three IDs — schemaId, generatorId, and circuitId — so the full chain of reasoning is transparent.

Extensibility by Design

Schemas, generators, and circuits are registered via the same pattern: metadata goes to a server-side registry, artifacts (wasm, zkey) are stored on IPFS/HTTPS, and IDs are referenced by other APIs. Adding a new domain means registering a new schema, writing a normalize function, and optionally creating circuits and generators. No changes to the core protocol are needed.

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