# Data Type Mapping — Galaxy Repository to OPC UA

## Scalar Type Mapping

| mx_data_type | Galaxy Description | OPC UA DataType | OPC UA NodeId | Notes |
|--------------|--------------------|-----------------|---------------|-------|
| 1 | Boolean | Boolean | i=1 | Direct mapping |
| 2 | Integer (Int32) | Int32 | i=6 | Galaxy integers are 32-bit signed |
| 3 | Float (Single) | Float | i=10 | 32-bit IEEE 754 |
| 4 | Double | Double | i=11 | 64-bit IEEE 754 |
| 5 | String | String | i=12 | Unicode string |
| 6 | Time (DateTime) | DateTime | i=13 | Galaxy DateTime to OPC UA DateTime (100ns ticks since 1601-01-01) |
| 7 | ElapsedTime (TimeSpan) | Double | i=11 | No native OPC UA TimeSpan; map to Double representing seconds (or use Duration type alias, NodeId i=290) |
| 8 | (reference) | String | i=12 | Object reference; expose as string representation |
| 13 | (enumeration) | Int32 | i=6 | Enum backing value is integer |
| 14 | (custom) | String | i=12 | Fallback to string |
| 15 | InternationalizedString | LocalizedText | i=21 | OPC UA LocalizedText supports locale + text pairs |
| 16 | (custom) | String | i=12 | Fallback to string |

## OPC UA Built-in Type Reference

For context, the full set of OPC UA built-in types and their NodeIds:

| NodeId | Type | Description |
|--------|------|-------------|
| i=1 | Boolean | True/false |
| i=2 | SByte | Signed 8-bit integer |
| i=3 | Byte | Unsigned 8-bit integer |
| i=4 | Int16 | Signed 16-bit integer |
| i=5 | UInt16 | Unsigned 16-bit integer |
| i=6 | Int32 | Signed 32-bit integer |
| i=7 | UInt32 | Unsigned 32-bit integer |
| i=8 | Int64 | Signed 64-bit integer |
| i=9 | UInt64 | Unsigned 64-bit integer |
| i=10 | Float | 32-bit IEEE 754 |
| i=11 | Double | 64-bit IEEE 754 |
| i=12 | String | Unicode string |
| i=13 | DateTime | Date and time (100ns ticks since 1601-01-01) |
| i=14 | Guid | 128-bit globally unique identifier |
| i=15 | ByteString | Sequence of bytes |
| i=21 | LocalizedText | Locale + text pair |

## Array Handling

When `is_array = 1` in the attributes query, the OPC UA variable node must be configured as an array.

### ValueRank

Set on the OPC UA variable node to indicate scalar vs array:

| is_array | ValueRank | Meaning |
|----------|-----------|---------|
| 0 | -1 (Scalar) | Value is not an array |
| 1 | 1 (OneDimension) | Value is a one-dimensional array |

### ArrayDimensions

When `ValueRank = 1`, set the `ArrayDimensions` attribute to a single-element array containing the `array_dimension` value from the attributes query.

Example for `MESReceiver_001.MoveInPartNumbers` (`is_array=1`, `array_dimension=50`):
- DataType: String (i=12)
- ValueRank: 1
- ArrayDimensions: [50]

Example for `TestMachine_001.MachineID` (`is_array=0`):
- DataType: String (i=12)
- ValueRank: -1
- ArrayDimensions: (not set)

## Security Classification

Galaxy attributes have a `security_classification` column that controls the access level required for writes. The attributes query returns this value for each attribute.

| security_classification | Galaxy Level | OPC UA Access | Description |
|-------------------------|--------------|---------------|-------------|
| 0 | FreeAccess | ReadWrite | No security restrictions |
| 1 | Operate | ReadWrite | Normal operating level (default) |
| 2 | SecuredWrite | ReadOnly | Requires elevated write access |
| 3 | VerifiedWrite | ReadOnly | Requires verified/confirmed write access |
| 4 | Tune | ReadWrite | Tuning-level access |
| 5 | Configure | ReadWrite | Configuration-level access |
| 6 | ViewOnly | ReadOnly | Read-only, no writes permitted |

Most attributes default to `Operate` (1). Higher values indicate more restrictive write access. `ViewOnly` (6) attributes should be exposed as read-only in OPC UA (`AccessLevel = CurrentRead` only, no `CurrentWrite`).

## DateTime Conversion

Galaxy `Time` (mx_data_type=6) stores DateTime values. OPC UA DateTime is defined as the number of 100-nanosecond intervals since January 1, 1601 (UTC). Ensure the conversion accounts for:
- Timezone: Galaxy may store local time; OPC UA expects UTC
- Epoch difference: adjust if Galaxy uses a different epoch (e.g., Unix epoch 1970-01-01)

## ElapsedTime Handling

Galaxy `ElapsedTime` (mx_data_type=7) represents a duration/timespan. OPC UA has no native TimeSpan type. Options:
- **Double (i=11)**: Store as seconds (recommended for simplicity)
- **Duration (i=290)**: OPC UA type alias for Double, semantically represents milliseconds — use if the OPC UA SDK supports it
