# Data Type Mapping

Data-type mapping is driver-defined. Each driver translates its native attribute metadata into two driver-agnostic enums from `Core.Abstractions` — `DriverDataType` (`src/ZB.MOM.WW.OtOpcUa.Core.Abstractions/DriverDataType.cs`) and `SecurityClassification` (`src/ZB.MOM.WW.OtOpcUa.Core.Abstractions/SecurityClassification.cs`) — and populates the `DriverAttributeInfo` record it hands to `IAddressSpaceBuilder.Variable(...)`. Core doesn't interpret the native types; it trusts the driver's translation.

## DriverDataType → OPC UA built-in type

`DriverNodeManager.MapDataType` (`src/ZB.MOM.WW.OtOpcUa.Server/OpcUa/DriverNodeManager.cs`) is the single translation table for every driver:

| DriverDataType | OPC UA NodeId |
|---|---|
| `Boolean` | `DataTypeIds.Boolean` (i=1) |
| `Int32` | `DataTypeIds.Int32` (i=6) |
| `Float32` | `DataTypeIds.Float` (i=10) |
| `Float64` | `DataTypeIds.Double` (i=11) |
| `String` | `DataTypeIds.String` (i=12) |
| `DateTime` | `DataTypeIds.DateTime` (i=13) |
| anything else | `DataTypeIds.BaseDataType` |

The enum also carries `Int16 / Int64 / UInt16 / UInt32 / UInt64 / Reference` members for drivers that need them; the mapping table is extended as those types surface in actual drivers. `Reference` is the Galaxy-style attribute reference — it's encoded as an OPC UA `String` on the wire.

## Per-driver mappers

Each driver owns its native → `DriverDataType` translation:

- **Galaxy Proxy** — `GalaxyProxyDriver.MapDataType(int mxDataType)` and `MapSecurity(int mxSec)` (inline in `src/ZB.MOM.WW.OtOpcUa.Driver.Galaxy.Proxy/GalaxyProxyDriver.cs`). The Galaxy `mx_data_type` integer is sent across the Host↔Proxy pipe and mapped on the Proxy side. Galaxy's full classic 16-entry table (Boolean / Integer / Float / Double / String / Time / ElapsedTime / Reference / Enumeration / Custom / InternationalizedString) is preserved but compressed into the seven-entry `DriverDataType` enum — `ElapsedTime` → `Float64`, `InternationalizedString` → `String`, `Reference` → `Reference`, enumerations → `Int32`.
- **AB CIP** — `src/ZB.MOM.WW.OtOpcUa.Driver.AbCip/AbCipDataType.cs` maps CIP tag type codes.
- **Modbus** — `src/ZB.MOM.WW.OtOpcUa.Driver.Modbus/ModbusDriver.cs` maps register shapes (16-bit signed, 16-bit unsigned, 32-bit float, etc.) including the DirectLogic quirk table in `DirectLogicAddress.cs`.
- **S7 / AB Legacy / TwinCAT / FOCAS / OPC UA Client** — each has its own inline mapper or `*DataType.cs` file per the same pattern.

The driver's mapping is authoritative — when a field type is ambiguous (a `LREAL` that could be bit-reinterpreted, a BCD counter, a string of a particular encoding), the driver decides the exposed OPC UA shape.

## Array handling

`DriverAttributeInfo.IsArray = true` flips `ValueRank = OneDimension` on the generated `BaseDataVariableState`; scalars stay at `ValueRank.Scalar`. `DriverAttributeInfo.ArrayDim` carries the declared length. Writing element-by-element (OPC UA `IndexRange`) is a driver-level decision — see `docs/ReadWriteOperations.md`.

## SecurityClassification — metadata, not ACL

`SecurityClassification` is driver-reported metadata only. Drivers never enforce write permissions themselves — the classification flows into the Server project where `WriteAuthzPolicy.IsAllowed(classification, userRoles)` (`src/ZB.MOM.WW.OtOpcUa.Server/Security/WriteAuthzPolicy.cs`) gates the write against the session's LDAP-derived roles, and (Phase 6.2) the `AuthorizationGate` + permission trie apply on top. This is the "ACL at server layer" invariant recorded in `feedback_acl_at_server_layer.md`.

The classification values mirror the v1 Galaxy model so existing Galaxy galaxies keep their published semantics:

| SecurityClassification | Required role | Write-from-OPC-UA |
|---|---|---|
| `FreeAccess` | — | yes (even anonymous) |
| `Operate` | `WriteOperate` | yes |
| `Tune` | `WriteTune` | yes |
| `Configure` | `WriteConfigure` | yes |
| `SecuredWrite` | `WriteOperate` | yes |
| `VerifiedWrite` | `WriteConfigure` | yes |
| `ViewOnly` | — | no |

Drivers whose backend has no notion of classification (Modbus, most PLCs) default every tag to `FreeAccess` or `Operate`; drivers whose backend does carry the notion (Galaxy, OPC UA Client relaying `UserAccessLevel`) translate it directly.

## Historization

`DriverAttributeInfo.IsHistorized = true` flips `AccessLevel.HistoryRead` and `Historizing = true` on the variable. The driver must then implement `IHistoryProvider` for HistoryRead service calls to succeed; otherwise the node manager surfaces `BadHistoryOperationUnsupported` per request.

## Key source files

- `src/ZB.MOM.WW.OtOpcUa.Core.Abstractions/DriverDataType.cs` — driver-agnostic type enum
- `src/ZB.MOM.WW.OtOpcUa.Core.Abstractions/SecurityClassification.cs` — write-authz tier metadata
- `src/ZB.MOM.WW.OtOpcUa.Core.Abstractions/DriverAttributeInfo.cs` — per-attribute descriptor
- `src/ZB.MOM.WW.OtOpcUa.Server/OpcUa/DriverNodeManager.cs` — `MapDataType` translation
- `src/ZB.MOM.WW.OtOpcUa.Server/Security/WriteAuthzPolicy.cs` — classification-to-role policy
- Per-driver mappers in each `Driver.*` project