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Includes: README explaining purpose / scope / temporary-location framing / format decision, CONTRIBUTING.md with proposed workflow + per-class semver versioning policy + validation commands, format/equipment-class.schema.json defining the shape of a class template (classId, version, displayName, applicability, signals, alarms, optional stateModel), format/tag-definition.schema.json defining the shape of a single canonical signal (name, dataType, category, unit, isArray, accessLevel, writeIdempotent, isHistorized, scaling), format/uns-subtree.schema.json defining the shape of a per-site UNS subtree (enterprise + site + areas + lines), classes/fanuc-cnc.json as the worked pilot class with 16 signals + 3 alarms + suggested state-derivation notes (per OtOpcUa corrections doc D1), uns/example-warsaw-west.json as a worked UNS subtree example, docs/overview.md (what / why / lifecycle / what's NOT in this repo), docs/format-decisions.md (8 numbered decisions covering JSON Schema choice per corrections D2, per-class semver, additive-only minor bumps, _default placeholder reservation, signal-name vs UNS-segment regex distinction, stateModel-as-informational, no per-equipment overrides at this layer, applicability.drivers as OtOpcUa driver enumeration), docs/consumer-integration.md (how OtOpcUa / Redpanda / dbt each integrate). $id URLs in the JSON schemas resolve at the actual current path so validators don't 404. Top-level README adds a row to the Component Detail Files table pointing to schemas/. Corrections doc B2 (schemas-repo dependencies) marked partially RESOLVED with the seed location and a list of what still needs the plan team or cross-team owner to decide (owner team naming, dedicated repo migration, format-decision ratification, FANUC CNC pilot confirmation, CI gate setup, Redpanda + dbt consumer integration plumbing). Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
57 lines
4.2 KiB
Markdown
57 lines
4.2 KiB
Markdown
# Format Decisions
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Why the schemas repo looks the way it does. Each decision is open for the schemas-repo owner team to revisit.
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## D1 — JSON Schema (Draft 2020-12) as the authoring format
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**Alternatives considered**: Protobuf (`.proto`), YAML, custom DSL.
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**Choice**: JSON Schema.
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**Why**:
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- Idiomatic for .NET 10 (System.Text.Json + JsonSchema.Net) — OtOpcUa reads templates with no extra dependencies
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- Idiomatic for CI tooling — every CI runner can `jq` and validate JSON Schema without extra toolchain (`ajv`, `jsonschema`, etc.)
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- Best authoring experience: text format, mergeable in git, structured diffing, IDE autocomplete via the `$schema` reference
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- Validation at multiple layers: operator-visible Admin UI errors in OtOpcUa, schemas-repo CI gates, downstream consumer runtime validation
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- Protobuf is better for *wire* serialization (size, speed, generated code) but worse for *authoring* (binary, requires `.proto` compiler, poor merge story in git)
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- Where wire-format efficiency matters (Redpanda events), we code-generate Protobuf from the JSON Schema source. One-way derivation is simpler than bidirectional sync.
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## D2 — Per-class versioning, semver
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**Alternatives considered**: whole-repo versioning, no versioning.
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**Choice**: each class file has its own `version` field (semver); the repo also tags overall releases.
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**Why**:
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- Different classes evolve at different rates (FANUC CNC may stabilize while Modbus PLC catalog grows)
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- Consumers can pin per-class for fine-grained compatibility (e.g. `fanuc-cnc@0.1.0` + `modbus-plc@0.3.2`)
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- Repo-level tags exist to bundle a known-good combination for consumers that want one anchor
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## D3 — Strict additive policy on minor bumps
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**Why**: removes ambiguity. If I see `class@1.3.0`, I know its signal set is a strict superset of `class@1.0.0` (and `class@1.x.y` for any earlier x.y). Breaking changes only happen at major-version boundaries.
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## D4 — `_default` reserved as placeholder for unused UNS levels
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Imported from `lmxopcua/docs/v2/plan.md` decision #108.
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**Why**: some sites have no Area-level distinction (single-building sites). Rather than letting the UNS path have inconsistent depth across sites, we mandate 5 levels always with `_default` as the placeholder. Downstream consumers can rely on path depth.
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## D5 — Tag names use PascalCase or snake_case (class's choice), NOT UNS-segment regex
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**Why**: UNS path segments (Enterprise/Site/Area/Line/Equipment) are infrastructure-level identifiers — they go on the wire of every browse, every URI, every dashboard filter. The regex (`^[a-z0-9-]{1,32}$`) reflects that constraint.
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Signal names (level 6) are vocabulary-level identifiers — they live inside an equipment node. Keeping them in PascalCase or snake_case (e.g. `RunState`, `actual_feedrate`) is more readable for operators looking at OPC UA browse output, and matches OPC UA SDK conventions which expect identifier-style names rather than URL-safe slugs.
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## D6 — `stateModel` is informational, not authoritative
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**Why**: state derivation lives at Layer 3 (System Platform / Ignition). Placing the derivation rules in the schemas repo would create dual sources of truth (and the schemas-repo version would inevitably drift). Instead, the class template lists which states the class supports + an informational note about what the rough mapping looks like; Layer 3 owns the actual derivation logic.
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## D7 — No per-equipment overrides at this layer
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**Why**: per-equipment config (which specific CNC has which program, etc.) is OtOpcUa's central config DB concern. Mixing per-instance config with per-class definitions in this repo would muddy the separation and cause the repo to grow with deployment-specific data instead of staying small + reusable.
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## D8 — `applicability.drivers` lists OtOpcUa drivers explicitly
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**Why**: the schemas repo is OT-side-focused. The OtOpcUa driver enumeration is the closest thing to a canonical "how do you get raw data from this equipment" vocabulary that exists across the org. If a future class is populated by a non-OtOpcUa source, the field becomes optional or extends. For now, listing OtOpcUa driver IDs makes the consumer-side validation (per `lmxopcua/docs/v2/plan.md` decision #111 — driver type ↔ namespace kind) trivial.
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