# Address Space

Address-space construction is a two-layer system. The **driver-facing layer** is the streaming builder: a driver implements `ITagDiscovery.DiscoverAsync` (`src/Core/ZB.MOM.WW.OtOpcUa.Core.Abstractions/ITagDiscovery.cs`) and emits `Folder` / `Variable` / `AddProperty` calls into an `IAddressSpaceBuilder` as it walks its backend — no buffering of the whole tree. `GenericDriverNodeManager` (`src/Core/ZB.MOM.WW.OtOpcUa.Core/OpcUa/GenericDriverNodeManager.cs`) wraps that builder to capture alarm-condition sinks and routes alarm events from the driver to them. The **SDK materialization layer** turns the resulting node descriptions into live OPC UA nodes: `OpcUaPublishActor` drives the write-only `IOpcUaAddressSpaceSink`, whose production binding `SdkAddressSpaceSink` (`src/Server/ZB.MOM.WW.OtOpcUa.OpcUaServer/SdkAddressSpaceSink.cs`) forwards to `OtOpcUaNodeManager` (`src/Server/ZB.MOM.WW.OtOpcUa.OpcUaServer/OtOpcUaNodeManager.cs`), a `CustomNodeManager2` subclass that owns the `FolderState` / `BaseDataVariableState` instances. The same code path serves Galaxy object hierarchies, Modbus PLC registers, AB CIP tags, TwinCAT symbols, FOCAS CNC parameters, and OPC UA Client aggregations — Galaxy is one driver of seven, not the driver.

## Root folder

`OtOpcUaNodeManager.CreateAddressSpace` creates a single shared root `FolderState` (`NodeId = OtOpcUa`, `BrowseName = OtOpcUa`, `EventNotifier = None`) under the standard OPC UA `Objects` folder, wired with an `Organizes` reference. Every driver's folders and variables hang beneath this one root; the server is published under a single `ApplicationUri = urn:OtOpcUa` (the `OpcUaApplicationHostOptions.ApplicationUri` default) and all nodes live in the server's single custom namespace, not a per-driver `urn:OtOpcUa:{DriverInstanceId}`. The UNS Area → Line → Equipment folder skeleton under the root is materialised by `Phase7Applier.MaterialiseHierarchy` (`src/Server/ZB.MOM.WW.OtOpcUa.OpcUaServer/Phase7Applier.cs`); SystemPlatform (Galaxy) tags are materialised by `Phase7Applier.MaterialiseGalaxyTags`.

## IAddressSpaceBuilder surface

`IAddressSpaceBuilder` (`src/Core/ZB.MOM.WW.OtOpcUa.Core.Abstractions/IAddressSpaceBuilder.cs`) offers three calls:

- `Folder(browseName, displayName)` — creates a child `FolderState` and returns a child builder scoped to it.
- `Variable(browseName, displayName, DriverAttributeInfo attributeInfo)` — creates a `BaseDataVariableState` and returns an `IVariableHandle` the driver keeps for alarm wiring.
- `AddProperty(browseName, DriverDataType, value)` — attaches a `PropertyState` for static metadata (e.g. equipment identification fields).

Drivers drive ordering. Typical pattern: root → folder per equipment → variables per tag. `GenericDriverNodeManager.BuildAddressSpaceAsync` calls `DiscoverAsync` once on startup and once per rediscovery cycle, tearing down the previous alarm subscription and clearing its sink registry before each re-walk so a redeploy doesn't double-fire alarm events.

## DriverAttributeInfo → OPC UA variable

Each variable carries a `DriverAttributeInfo` (`src/Core/ZB.MOM.WW.OtOpcUa.Core.Abstractions/DriverAttributeInfo.cs`):

| Field | Role |
|---|---|
| `FullName` | driver-side full reference used as the lookup key for Read/Write/Subscribe; also seeds the variable's string `NodeId` |
| `DriverDataType` | resolved to a built-in `DataTypeIds.*` NodeId at materialization time — `OtOpcUaNodeManager.ResolveBuiltInDataType` maps the data-type name string; each driver first maps its native type into `DriverDataType` (e.g. Galaxy via `Browse/DataTypeMap.Map`) |
| `IsArray` / `ArrayDim` | declared 1-D-array length carried as metadata; the Galaxy discoverer sets `ArrayDim` only when the gateway reports a positive dimension |
| `SecurityClass` | write-authorization tier (`SecurityClassification`); enforced server-side by the `NodePermissions` ACL evaluator (`TriePermissionEvaluator`) mapping each `OpcUaOperation` to a required permission bit. The Galaxy driver also caches it per full reference (`_securityByFullRef`) to answer `GetSecurityClassification` |
| `IsHistorized` | marks the attribute as feeding historian / HistoryRead |
| `IsAlarm` | drives the `MarkAsAlarmCondition` pass (see below) |
| `WriteIdempotent` | when true the attribute's writes are safe to replay, so the capability invoker may apply Polly retry; defaults false so pulses / acks / counters aren't auto-retried |
| `Source` | `NodeSourceKind` discriminator (`Driver` / `Virtual` / `ScriptedAlarm`) that decides which subsystem dispatches the node's Read/Write/Subscribe |

The variable is created with `StatusCode = BadWaitingForInitialData` and a null value until the first Read or `ISubscribable.OnDataChange` push lands. Note the production SDK sink (`OtOpcUaNodeManager.EnsureVariable`) currently materialises every variable as `ValueRank = Scalar`, read-only `AccessLevel`, and `Historizing = false` — the `IsArray`/`IsHistorized` intent lives in `DriverAttributeInfo` but is not yet projected onto the SDK node.

## CapturingBuilder + alarm sink registration

`GenericDriverNodeManager.BuildAddressSpaceAsync` wraps the supplied builder in a `CapturingBuilder` before calling `DiscoverAsync`. The wrapper observes every `Variable()` call: when a returned `IVariableHandle.MarkAsAlarmCondition(AlarmConditionInfo)` fires, the sink is registered in the manager's `_alarmSinks` dictionary keyed by the variable's `FullReference`. Subsequent `IAlarmSource.OnAlarmEvent` pushes are routed to the matching sink by `SourceNodeId`. This keeps the alarm-wiring protocol declarative — drivers just flag `DriverAttributeInfo.IsAlarm = true` and the materialization of the OPC UA `AlarmConditionState` node is handled by the server layer. See `docs/AlarmTracking.md`.

## NodeId scheme

All nodes share the server's single custom namespace (`NamespaceIndex`); NodeIds are string identifiers, not numeric. The string values come from the source rows / driver references — there is no per-driver namespace prefix:

| Node type | NodeId (string identifier) | Example |
|---|---|---|
| Shared root | `OtOpcUa` | `OtOpcUa` |
| UNS Area / Line / Equipment folder | the Config-DB `UnsAreaId` / `UnsLineId` / `EquipmentId` | `EQ_Press_07` |
| Galaxy tag variable | the MXAccess reference (`Phase7Applier` uses `GalaxyTagPlan.MxAccessRef`) | `DelmiaReceiver_001.DownloadPath` |
| Equipment tag variable | the driver full reference from `DriverAttributeInfo.FullName` | driver-specific |

For Galaxy the variable `FullName` is the `tag_name.AttributeName` MXAccess reference; AB CIP uses `tag.Name` or `tag.Name.member` for UDT members; the shape is the driver's choice. Browse-path resolution (OPC UA `TranslateBrowsePathsToNodeIds`) is the canonical way clients map a browse path to one of these flat NodeIds.

## Per-driver hierarchy examples

- **Galaxy**: `GalaxyDriver.DiscoverAsync` delegates to `GalaxyDiscoverer` (`src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.Galaxy/Browse/GalaxyDiscoverer.cs`), which walks the hierarchy from `IGalaxyHierarchySource` — one folder per Galaxy object (browse name = `contained_name`, falling back to `tag_name`), one variable per dynamic attribute (full reference = `tag_name.AttributeName`). It copies the gateway-supplied `IsAlarm` flag through to `DriverAttributeInfo` and, for alarm-bearing attributes, calls `MarkAsAlarmCondition` with the five sub-attribute refs built by `AlarmRefBuilder`.
- **Modbus**: streams one folder per device, one variable per register range from `ModbusDriverOptions`. No alarm surface.
- **AB CIP**: `AbCipDriver.DiscoverAsync` emits an `AbCip` root, then a folder per configured device. Pre-declared tags become variables under the device folder; UDT (`Structure`) tags fan out into a sub-folder with one variable per member; when controller browse is enabled, `IAbCipTagEnumerator` adds discovered tags under a `Discovered/` sub-folder. (`AbCipTemplateCache` caches UDT layouts for the libplctag enumerator.)
- **OPC UA Client**: re-exposes a remote server's address space — `OpcUaClientDriver.DiscoverAsync` browses the upstream from `BrowseRoot` into a `Remote` folder (pass 1), then batch-reads DataType/AccessLevel/ValueRank/Historizing per variable before registering them (pass 2).

See `docs/v2/driver-specs.md` for the per-driver discovery contracts.

## Rediscovery

Drivers that implement `IRediscoverable` fire `OnRediscoveryNeeded` when their backend signals a change. Galaxy's `DeployWatcher` raises it when the observed `time_of_last_deploy` advances; TwinCAT raises it on the ADS symbol-version-changed signal (`DeviceSymbolVersionInvalid`, error 1809). Core re-runs `DiscoverAsync` and diffs — see `docs/IncrementalSync.md`. Drivers that don't implement `IRediscoverable` (Modbus, S7, OPC UA Client) only change their address space when a new generation is published from the Config DB.

## Key source files

- `src/Core/ZB.MOM.WW.OtOpcUa.Core/OpcUa/GenericDriverNodeManager.cs` — orchestration + `CapturingBuilder`
- `src/Server/ZB.MOM.WW.OtOpcUa.OpcUaServer/OtOpcUaNodeManager.cs`, `src/Server/ZB.MOM.WW.OtOpcUa.OpcUaServer/SdkAddressSpaceSink.cs` — OPC UA materialization (write-only sink fed by the actor system)
- `src/Server/ZB.MOM.WW.OtOpcUa.OpcUaServer/Phase7Applier.cs` — materialises the UNS folder hierarchy + Galaxy tags into the sink
- `src/Core/ZB.MOM.WW.OtOpcUa.Core/OpcUa/EquipmentNodeWalker.cs` — walks Config-DB Equipment-namespace rows into the builder
- `src/Core/ZB.MOM.WW.OtOpcUa.Core.Abstractions/IAddressSpaceBuilder.cs` — builder contract
- `src/Core/ZB.MOM.WW.OtOpcUa.Core.Abstractions/ITagDiscovery.cs` — driver discovery capability
- `src/Core/ZB.MOM.WW.OtOpcUa.Core.Abstractions/DriverAttributeInfo.cs` — per-attribute descriptor