feat(mtconnect): serve DATA_SET/TABLE as compact JSON strings; park EVENT enumerations (#650)

Parser captures Entry/Cell content; the observation index merges /sample deltas
into the /current baseline (resetTriggered replaces, removed deletes, UNAVAILABLE
drops). Fixture gains a TABLE item and periodic DATA_SET/TABLE churn.

Claude-Session: https://claude.ai/code/session_01Ef2ozxS7QPanGT8uoATbTe

docs/drivers/MTConnect.md

@@ -103,8 +103,8 @@ request/response handshake — is a different mechanism and remains deferred; se
 | `TIME_SERIES` arrays (#627) | **Supported** as variable-length `double[]` (Float64 tags only) | [TIME_SERIES arrays](#time_series-arrays-627) |
 | One Agent client per driver, one `/raw` Device (#628) | **Enforced** (`MTConnectMultipleDevices` deploy error); multi-device Agents use several driver instances | [Known limitations](#known-limitations) |
 | Write-back (`IWritable`) | **Supported, off by default** (`Write.Enabled` + Agent `AllowPut`) | [Write-back](#write-back--observation-injection-off-by-default) |
-| EVENT controlled vocabularies as OPC UA enumerations | **Not supported** (stay String); not scheduled | See [Deferred](#deferred-not-in-this-build) |
+| EVENT controlled vocabularies as OPC UA enumerations | **Parked / won't fix** (stay String) - see rationale | [EVENT enumerations](#event-enumerations-650-parked--wont-fix) |
-| `DATA_SET` / `TABLE` representations | **Not supported** - read as `BadNotSupported` | [Quality mapping](#quality-mapping) |
+| `DATA_SET` / `TABLE` representations (#650) | **Supported** as a String carrying compact JSON | [DATA_SET / TABLE](#data_set--table-650) |
 | MTConnect Interfaces, SHDR ingest | Not built | [Deferred](#deferred-not-in-this-build) |
 
 **`IReadable.ReadAsync` is never called by the running server.** The
@@ -245,7 +245,7 @@ Other status codes an observation can surface:
 | `BadTypeMismatch` (`0x80740000`) | The Agent's text isn't a value of the tag's coerced type at all |
 | `BadOutOfRange` (`0x803C0000`) | The Agent reported a number the coerced type can't represent |
 | `BadDecodingError` (`0x80070000`) | A `TIME_SERIES` vector whose element count disagrees with the observation's own `sampleCount` (or the tag's fixed `ArrayDim`) — see [TIME_SERIES](#time_series-arrays-627) |
-| `BadNotSupported` (`0x803D0000`) | A shape this build doesn't materialize — a structured `DATA_SET`/`TABLE` observation (decided: stays unsupported, #627), or an array tag declared as anything other than Float64 |
+| `BadNotSupported` (`0x803D0000`) | A shape this build doesn't materialize — a `DATA_SET`/`TABLE` observation whose children are not `<Entry>` elements (a well-formed one is served as JSON since #650), or an array tag declared as anything other than Float64 |
 | `BadWaitingForInitialData` | Tag is authored but the Agent hasn't reported it yet |
 | `BadNodeIdUnknown` | DataItem id is neither authored nor ever observed |
 
@@ -272,8 +272,29 @@ in the Tag modal's array section).
 but the OPC UA node has no description/property slot through `DriverAttributeInfo`,
 and a sibling property node would need a new address-space mechanism. Decision:
 document it — the rate is a property of the Agent's DataItem (`sampleRate` in
-`/probe`), read it there. **`DATA_SET` / `TABLE` stay `BadNotSupported`** (decision, #627): they are
+`/probe`), read it there.
-key/value maps with no scalar or array OPC UA shape that preserves the keys.
+
+### DATA_SET / TABLE (#650)
+
+`DATA_SET` and `TABLE` observations carry their content in `<Entry key="…">` children (a `TABLE` entry holds
+`<Cell key="…">` children). They are served as a **String carrying compact, deterministic JSON** (OPC UA type
+String, never an array or structure - no new node shape, history/ACL/alarm paths unchanged; discovery and
+type inference already type these items String):
+
+- `DATA_SET` -> `{"offsetX":1.25,"toolNumber":7}`; `TABLE` -> `{"G54":{"X":1.0,"Y":2},"G55":{"X":3}}`.
+- Keys are ordinal-sorted at every level, no whitespace - the same content always serialises to the same
+  bytes, so value-dedup works. Values that are *strict JSON numbers* are emitted as numbers with their original
+  token (lossless: `1.0` stays `1.0`); anything else (`007`, `+5`, `on`) is a string.
+- **Merge semantics follow MTConnect 2.x.** A `/current` document states the *whole* set and **replaces** it;
+  a `/sample` chunk carries *deltas* that **merge** by key (a `TABLE` row is replaced as a unit by a later entry
+  for the same row key). An observation with `resetTriggered` replaces the accumulated set, and a
+  `resetTriggered` observation with no entries is the empty set `{}`. Several observations of one item in one
+  document fold in document order. The accumulated set is dropped on an Agent restart (`instanceId` change).
+- `removed="true"` deletes the key (or row): it is **absent** from the JSON, never `null`.
+- `UNAVAILABLE` is `BadNoCommunication` as for any observation, and also drops the accumulated set, so a
+  later delta cannot resurrect pre-outage entries.
+- An observation whose children are not `<Entry>` elements stays `BadNotSupported`. Writes to these items stay
+  refused (`WriteAsync` excludes them).
 
 ### Subscribe — the `/sample` pump
 
@@ -483,9 +504,13 @@ and records a state only when an alarm handler was attached to receive it. Conse
   unchanged triggers no re-subscribe, and needs none — the server-side carry-over covers it.
 - An alarm-only driver (no value tags) still runs the `/sample` pump.
 
-**EVENT controlled vocabularies as OPC UA enumerations — not built (parked, low priority).** EVENT values (`Execution`,
+### EVENT enumerations (#650): parked / won't fix
-`ControllerMode`, …) stay Strings carrying the Agent's own word; an enumeration would need a per-type
+
-vocabulary table that vendors extend freely.
+EVENT values (`Execution`, `ControllerMode`, …) stay Strings carrying the Agent's own word. Modelling them as
+OPC UA enumerations was considered and **declined**: the vocabulary is vendor-extensible, so it needs a per-type
+table plus an unknown-value fallback, a per-type enum node shape through discovery and raw-tag type inference,
+and it would break every consumer that reads these items as String (ScadaBridge) for little gain. Reopen only
+with an opt-in, tag-level `enumValues` design.
 
 ## Known limitations
 
@@ -563,9 +588,8 @@ for anything beyond values-and-conditions.
    pin the parsing rule itself.
 5. **A CONDITION alarm shows one condition per DataItem** — the most severe active `nativeCode`, not one
    Part 9 condition per code (see [CONDITION alarms](#condition-alarms-626)).
-6. **Structured `DATA_SET`/`TABLE` observations surface as
+6. **`DATA_SET`/`TABLE` observations are JSON Strings** (#650, see
-   `BadNotSupported`**, not an approximation — see the Quality mapping table.
+   [DATA_SET / TABLE](#data_set--table-650)); `TIME_SERIES` is served as `double[]` (#627, see
-   `TIME_SERIES` is served as `double[]` (#627, see
    [TIME_SERIES arrays](#time_series-arrays-627)); the sample rate is not
    surfaced on the node.
 
@@ -585,9 +609,8 @@ for anything beyond values-and-conditions.
 - **P1.5 fast-follow** (design
   [§9](../plans/2026-07-15-mtconnect-driver-design.md#9-phasing--effort)): CONDITION → native Part 9
   alarms **shipped** (#626, see [CONDITION alarms](#condition-alarms-626)); EVENT
-  controlled-vocabulary values → OPC UA enumerations is **not built** (EVENTs stay Strings), and
+  controlled-vocabulary values → OPC UA enumerations is **parked / won't fix** (EVENTs stay Strings, #650);
-  structured `DATA_SET`/`TABLE` observations stay `BadNotSupported`; both are tracked as a low-priority
+  `DATA_SET`/`TABLE` are served as JSON Strings (#650).
-  follow-up, not part of P1.5.
 - **P2 (on demand): SHDR adapter ingest.** A `SourceMode: "Agent" | "Shdr"`
   switch that opens the raw pipe-delimited SHDR TCP socket directly. Loses
   auto-discovery (no device model without an Agent in front, so

src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.MTConnect/MTConnectDriver.cs

@@ -747,7 +747,7 @@ public sealed partial class MTConnectDriver
             // Built from the SAME authored tags as the shared index, so the authored-vs-unknown
             // distinction and every coercion behave identically — it is a snapshot, not a variant.
             var snapshot = new MTConnectObservationIndex(binding.IndexTags);
-            snapshot.Apply(current);
+            snapshot.Apply(current, baseline: true);
 
             var results = new DataValueSnapshot[fullReferences.Count];
             for (var i = 0; i < results.Length; i++)
@@ -2337,7 +2337,7 @@ public sealed partial class MTConnectDriver
     private void ApplyAndFanOut(MTConnectStreamsResult document, bool baseline = false)
     {
         var index = ObservationIndex;
-        index.Apply(document);
+        index.Apply(document, baseline);
 
         // #626: CONDITION observations also feed the alarm path, which keeps its own multi-condition state
         // (a /sample Normal for one nativeCode is not a return to normal while another code is active).
@@ -2801,7 +2801,7 @@ public sealed partial class MTConnectDriver
             }
 
             var index = new MTConnectObservationIndex(binding.IndexTags);
-            index.Apply(current);
+            index.Apply(current, baseline: true);
             Volatile.Write(ref _index, index);
 
             // #626: the CONDITION tracker is per-session state like the index. Nothing is RAISED here — the

src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.MTConnect/MTConnectDtos.cs

@@ -167,6 +167,17 @@ public sealed record MTConnectStreamsResult(
 ///     observation. Carried for the parser contract; not yet surfaced on the served node (see
 ///     docs/drivers/MTConnect.md). <c>null</c> when absent.
 /// </param>
+/// <param name="Entries">
+///     The parsed <c>&lt;Entry key="…"&gt;</c> children of a <c>DATA_SET</c> / <c>TABLE</c> observation (#650), in
+///     document order, or <c>null</c> when the observation had none. A <c>TABLE</c> entry carries
+///     <see cref="MTConnectDataSetEntry.Cells"/>. The observation index folds these into a JSON String — see
+///     <see cref="MTConnectObservationIndex"/>. <see cref="IsStructured"/> stays <c>true</c> beside them: it is the
+///     wire-shape fact, this is the content.
+/// </param>
+/// <param name="ResetTriggered">
+///     <c>true</c> when the observation carried a non-empty <c>resetTriggered</c> attribute — the Agent's statement that
+///     the set was reset, so this observation <b>replaces</b> the accumulated set rather than merging into it.
+/// </param>
 /// <param name="Condition">
 ///     The CONDITION-only detail (#626) — set exactly when the observation came from a
 ///     <c>&lt;Condition&gt;</c> container, <c>null</c> for every Sample/Event. Its presence is what marks an
@@ -179,7 +190,25 @@ public sealed record MTConnectObservation(
     bool IsStructured = false,
     int? SampleCount = null,
     double? SampleRate = null,
-    MTConnectConditionDetail? Condition = null);
+    MTConnectConditionDetail? Condition = null,
+    IReadOnlyList<MTConnectDataSetEntry>? Entries = null,
+    bool ResetTriggered = false);
+
+/// <summary>One <c>&lt;Cell key="…"&gt;</c> of a <c>TABLE</c> row (#650).</summary>
+public sealed record MTConnectDataSetCell(string Key, string Value);
+
+/// <summary>
+///     One <c>&lt;Entry key="…"&gt;</c> of a <c>DATA_SET</c> / <c>TABLE</c> observation (#650).
+/// </summary>
+/// <param name="Key">The entry's <c>key</c> attribute, verbatim.</param>
+/// <param name="Value">A <c>DATA_SET</c> entry's trimmed text; <c>null</c> for a <c>TABLE</c> row or a removed entry.</param>
+/// <param name="Removed"><c>true</c> when the entry carried <c>removed="true"</c>: the key is deleted from the set.</param>
+/// <param name="Cells">A <c>TABLE</c> row's cells in document order; <c>null</c> for a <c>DATA_SET</c> entry.</param>
+public sealed record MTConnectDataSetEntry(
+    string Key,
+    string? Value,
+    bool Removed,
+    IReadOnlyList<MTConnectDataSetCell>? Cells = null);
 
 /// <summary>
 ///     What an MTConnect CONDITION observation says beyond its state word (#626). Every field is the

src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.MTConnect/MTConnectObservationIndex.cs

@@ -1,6 +1,9 @@
 using System.Collections.Concurrent;
 using System.Collections.Frozen;
 using System.Globalization;
+using System.Text.Encodings.Web;
+using System.Text.Json;
+using System.Text.RegularExpressions;
 using ZB.MOM.WW.OtOpcUa.Core.Abstractions;
 
 namespace ZB.MOM.WW.OtOpcUa.Driver.MTConnect;
@@ -50,7 +53,7 @@ namespace ZB.MOM.WW.OtOpcUa.Driver.MTConnect;
 ///     <para>
 ///         <b>Shapes this build does not represent</b> are coded <c>BadNotSupported</c> with a null
 ///         value rather than approximated: a non-Float64 array tag and a <c>DATA_SET</c> / <c>TABLE</c>
-///         observation (a Float64 <c>TIME_SERIES</c> vector is served as <c>double[]</c>, #627). The latter carries its
+///         observation whose children are not <c>&lt;Entry&gt;</c> elements (a Float64 <c>TIME_SERIES</c> vector is served as <c>double[]</c>, #627). The latter carries its
 ///         real content in <c>&lt;Entry key=…&gt;</c> child elements, which reach a text-valued
 ///         observation concatenated with the keys discarded — a two-entry set reads as the single
 ///         token <c>"12"</c> — and because the type inference correctly demotes those
@@ -111,6 +114,18 @@ internal sealed class MTConnectObservationIndex
         }.ToFrozenDictionary(StringComparer.OrdinalIgnoreCase);
 
     private readonly ConcurrentDictionary<string, DataValueSnapshot> _snapshots = new(StringComparer.Ordinal);
+
+    // #650: the accumulated DATA_SET / TABLE content per dataItemId. A /sample chunk carries only the entries
+    // that changed, so the served JSON is the merge of the baseline and every delta since. Row value is the
+    // entry's text (DATA_SET) or its cell map (TABLE). Only the single pump (or a one-shot snapshot) calls
+    // Apply, but the lock keeps a concurrent one-shot read-through from corrupting a shared index.
+    private readonly Dictionary<string, SortedDictionary<string, SetEntry>> _sets = new(StringComparer.Ordinal);
+    private readonly object _setsLock = new();
+
+    private sealed record SetEntry(string? Value, SortedDictionary<string, string>? Cells);
+
+    private static readonly Regex JsonNumber = new(
+        @"^-?(0|[1-9][0-9]*)(\.[0-9]+)?([eE][+-]?[0-9]+)?$", RegexOptions.Compiled | RegexOptions.CultureInvariant);
     private readonly FrozenDictionary<string, MTConnectTagDefinition> _tags;
     private readonly TimeProvider _timeProvider;
 
@@ -159,7 +174,11 @@ internal sealed class MTConnectObservationIndex
     /// <param name="result">The parsed streams document. An observation-free result is a legal
     /// keep-alive and leaves the index untouched.</param>
     /// <exception cref="ArgumentNullException"><paramref name="result"/> is <c>null</c>.</exception>
-    public void Apply(MTConnectStreamsResult result)
+    /// <param name="baseline">
+    ///     <c>true</c> for a <c>/current</c> document, which states the <b>whole</b> DATA_SET / TABLE and so replaces
+    ///     the accumulated set; <c>false</c> (default) for a <c>/sample</c> chunk, whose entries are deltas merged into it.
+    /// </param>
+    public void Apply(MTConnectStreamsResult result, bool baseline = false)
     {
         ArgumentNullException.ThrowIfNull(result);
 
@@ -170,9 +189,12 @@ internal sealed class MTConnectObservationIndex
         // — writing every observation and merging snapshots in place — would need a read-modify-write
         // per key and could expose a half-merged state to a concurrent reader.
         var resolved = new Dictionary<string, MTConnectObservation>(StringComparer.Ordinal);
-        foreach (var observation in result.Observations)
+        var seenSets = new HashSet<string>(StringComparer.Ordinal);
+        foreach (var raw in result.Observations)
         {
-            if (observation is null || string.IsNullOrWhiteSpace(observation.DataItemId)) continue;
+            if (raw is null || string.IsNullOrWhiteSpace(raw.DataItemId)) continue;
+
+            var observation = FoldDataSet(raw, baseline, seenSets);
 
             resolved[observation.DataItemId] =
                 resolved.TryGetValue(observation.DataItemId, out var incumbent)
@@ -217,7 +239,130 @@ internal sealed class MTConnectObservationIndex
     ///     <c>instanceId</c> changes, every value the index holds describes a device model that no
     ///     longer exists, and serving it would be worse than serving nothing.
     /// </summary>
-    public void Clear() => _snapshots.Clear();
+    public void Clear()
+    {
+        _snapshots.Clear();
+        lock (_setsLock) _sets.Clear();
+    }
+
+    /// <summary>
+    ///     DATA_SET / TABLE (#650). Folds an observation's <c>&lt;Entry&gt;</c> children into the accumulated set for
+    ///     its dataItemId and returns a plain String observation carrying the merged JSON; any other observation is
+    ///     returned untouched, except that an <c>UNAVAILABLE</c> one drops the accumulated set (a later delta must not
+    ///     resurrect pre-outage entries).
+    ///     <para>
+    ///         Semantics (MTConnect 2.x): a <c>/current</c> document (<paramref name="baseline"/>) or an observation
+    ///         with <c>resetTriggered</c> <b>replaces</b> the set; otherwise entries merge by key. <c>removed="true"</c>
+    ///         deletes the key (the key is absent from the JSON, never <c>null</c>). A TABLE row is replaced as a unit
+    ///         by a later entry for the same row key; a removed row key disappears. Several observations of one item in
+    ///         a single document fold in document order — only the first replaces on a baseline.
+    ///     </para>
+    /// </summary>
+    private MTConnectObservation FoldDataSet(MTConnectObservation observation, bool baseline, HashSet<string> seenSets)
+    {
+        var id = observation.DataItemId;
+
+        if (observation.Entries is not { Count: > 0 } entries)
+        {
+            if (observation.ResetTriggered && !observation.IsStructured)
+            {
+                // resetTriggered with no entries: an empty set, which is a legitimate value rather than an absence.
+                lock (_setsLock) _sets[id] = new SortedDictionary<string, SetEntry>(StringComparer.Ordinal);
+                seenSets.Add(id);
+                return observation with { Value = "{}", ResetTriggered = false };
+            }
+
+            if (string.IsNullOrWhiteSpace(observation.Value) ||
+                string.Equals(observation.Value, UnavailableSentinel, StringComparison.Ordinal))
+            {
+                lock (_setsLock) _sets.Remove(id);
+            }
+
+            return observation;
+        }
+
+        string json;
+        lock (_setsLock)
+        {
+            var first = seenSets.Add(id);
+            if (!_sets.TryGetValue(id, out var set) || observation.ResetTriggered || (baseline && first))
+            {
+                set = new SortedDictionary<string, SetEntry>(StringComparer.Ordinal);
+                _sets[id] = set;
+            }
+
+            foreach (var entry in entries)
+            {
+                if (entry.Removed)
+                {
+                    set.Remove(entry.Key);
+                }
+                else if (entry.Cells is not null)
+                {
+                    var cells = new SortedDictionary<string, string>(StringComparer.Ordinal);
+                    foreach (var cell in entry.Cells) cells[cell.Key] = cell.Value;
+                    set[entry.Key] = new SetEntry(null, cells);
+                }
+                else
+                {
+                    set[entry.Key] = new SetEntry(entry.Value ?? string.Empty, null);
+                }
+            }
+
+            json = RenderSet(set);
+        }
+
+        return observation with { Value = json, IsStructured = false, Entries = null, ResetTriggered = false };
+    }
+
+    /// <summary>
+    ///     Compact, deterministic JSON: keys ordinal-sorted, no whitespace. Values that are strict JSON numbers are
+    ///     emitted as numbers with their original token (lossless — <c>007</c> and <c>+5</c> stay strings); everything
+    ///     else is a string.
+    /// </summary>
+    private static string RenderSet(SortedDictionary<string, SetEntry> set)
+    {
+        using var stream = new MemoryStream();
+        using (var w = new Utf8JsonWriter(stream, new JsonWriterOptions { Encoder = JavaScriptEncoder.UnsafeRelaxedJsonEscaping }))
+        {
+            w.WriteStartObject();
+            foreach (var (key, entry) in set)
+            {
+                w.WritePropertyName(key);
+                if (entry.Cells is null)
+                {
+                    WriteScalar(w, entry.Value ?? string.Empty);
+                    continue;
+                }
+
+                w.WriteStartObject();
+                foreach (var (cellKey, cellValue) in entry.Cells)
+                {
+                    w.WritePropertyName(cellKey);
+                    WriteScalar(w, cellValue);
+                }
+
+                w.WriteEndObject();
+            }
+
+            w.WriteEndObject();
+        }
+
+        return System.Text.Encoding.UTF8.GetString(stream.ToArray());
+    }
+
+    private static void WriteScalar(Utf8JsonWriter w, string text)
+    {
+        if (JsonNumber.IsMatch(text) &&
+            double.TryParse(text, NumberStyles.Float, CultureInfo.InvariantCulture, out var d) && double.IsFinite(d))
+        {
+            w.WriteRawValue(text);
+        }
+        else
+        {
+            w.WriteStringValue(text);
+        }
+    }
 
     private DateTime Now => _timeProvider.GetUtcNow().UtcDateTime;
 

src/Drivers/ZB.MOM.WW.OtOpcUa.Driver.MTConnect/MTConnectStreamsParser.cs

@@ -363,11 +363,13 @@ internal static class MTConnectStreamsParser
     ///     <c>null</c> when there is none. Text found anywhere below an observation belongs to it —
     ///     that is what <c>XElement.Value</c> meant.
     /// </param>
+    /// <param name="entryCollector">The enclosing observation's DATA_SET / TABLE entry list (#650), or <c>null</c> outside one.</param>
     private static void ReadElement(
         XmlReader reader,
         ContainerKind parent,
         List<MTConnectObservation> observations,
-        ValueSink? textSink)
+        ValueSink? textSink,
+        List<MTConnectDataSetEntry>? entryCollector = null)
     {
         var isObservation = parent != ContainerKind.None;
         var isCondition = parent == ContainerKind.Condition;
@@ -379,6 +381,8 @@ internal static class MTConnectStreamsParser
         string? conditionState = null;
         int? sampleCount = null;
         double? sampleRate = null;
+        var resetTriggered = false;
+        List<MTConnectDataSetEntry>? entries = null;
         (string? NativeCode, string? NativeSeverity, string? Qualifier, string? Type) conditionAttributes = default;
 
         if (isObservation)
@@ -405,6 +409,8 @@ internal static class MTConnectStreamsParser
             // against the declared sampleCount only when one parses).
             if (!isCondition)
             {
+                resetTriggered = !string.IsNullOrWhiteSpace(MTConnectXml.OptionalAttribute(reader, "resetTriggered"));
+                entries = [];
                 sampleCount = int.TryParse(
                     MTConnectXml.OptionalAttribute(reader, "sampleCount"),
                     NumberStyles.Integer,
@@ -431,7 +437,7 @@ internal static class MTConnectStreamsParser
         // enclosing observation's sink: a condition is never nested inside a text-valued observation.
         var sink = isObservation ? new ValueSink() : textSink;
 
-        var hasElements = !reader.IsEmptyElement && ReadChildren(reader, kind, observations, sink);
+        var hasElements = !reader.IsEmptyElement && ReadChildren(reader, kind, observations, sink, entries ?? entryCollector);
 
         if (!isObservation)
         {
@@ -475,7 +481,9 @@ internal static class MTConnectStreamsParser
             IsStructured: !isCondition && hasElements,
             SampleCount: sampleCount,
             SampleRate: sampleRate,
-            Condition: condition);
+            Condition: condition,
+            Entries: entries is { Count: > 0 } ? entries : null,
+            ResetTriggered: resetTriggered);
     }
 
     /// <summary>
@@ -486,7 +494,8 @@ internal static class MTConnectStreamsParser
         XmlReader reader,
         ContainerKind kind,
         List<MTConnectObservation> observations,
-        ValueSink? sink)
+        ValueSink? sink,
+        List<MTConnectDataSetEntry>? entries)
     {
         var hasElements = false;
 
@@ -496,7 +505,17 @@ internal static class MTConnectStreamsParser
             {
                 case XmlNodeType.Element:
                     hasElements = true;
-                    ReadElement(reader, kind, observations, sink);
+
+                    // #650: an <Entry> directly under a non-condition observation is DATA_SET / TABLE
+                    // content, captured structurally rather than as concatenated text.
+                    if (entries is not null && kind == ContainerKind.None && MTConnectXml.IsNamed(reader, "Entry"))
+                    {
+                        ReadEntry(reader, entries, sink);
+                    }
+                    else
+                    {
+                        ReadElement(reader, kind, observations, sink, entries);
+                    }
 
                     break;
 
@@ -520,6 +539,60 @@ internal static class MTConnectStreamsParser
         return hasElements;
     }
 
+    /// <summary>
+    ///     Consumes one <c>&lt;Entry&gt;</c> (and its <c>&lt;Cell&gt;</c> children, for a TABLE row), honouring the
+    ///     <see cref="ReadChildren"/> cursor contract: returns on the entry's end tag, or on the entry itself when empty.
+    ///     An entry with no <c>key</c> is dropped — it cannot be addressed.
+    /// </summary>
+    private static void ReadEntry(XmlReader reader, List<MTConnectDataSetEntry> entries, ValueSink? sink)
+    {
+        var key = MTConnectXml.OptionalAttribute(reader, "key");
+        var removed = string.Equals(MTConnectXml.OptionalAttribute(reader, "removed")?.Trim(), "true", StringComparison.OrdinalIgnoreCase);
+        var empty = reader.IsEmptyElement;
+        var text = new System.Text.StringBuilder();
+        List<MTConnectDataSetCell>? cells = null;
+
+        while (!empty && reader.Read())
+        {
+            if (reader.NodeType == XmlNodeType.EndElement) break;
+
+            if (reader.NodeType == XmlNodeType.Element && MTConnectXml.IsNamed(reader, "Cell"))
+            {
+                cells ??= [];
+                var cellKey = MTConnectXml.OptionalAttribute(reader, "key");
+                var cellText = new System.Text.StringBuilder();
+                if (!reader.IsEmptyElement)
+                {
+                    while (reader.Read() && reader.NodeType != XmlNodeType.EndElement)
+                    {
+                        if (reader.NodeType is XmlNodeType.Text or XmlNodeType.CDATA or XmlNodeType.SignificantWhitespace)
+                            { cellText.Append(reader.Value); sink?.Append(reader.Value); }
+                        else if (reader.NodeType == XmlNodeType.Element)
+                            reader.Skip();
+                    }
+                }
+
+                if (!string.IsNullOrEmpty(cellKey)) cells.Add(new MTConnectDataSetCell(cellKey, cellText.ToString().Trim()));
+            }
+            else if (reader.NodeType is XmlNodeType.Text or XmlNodeType.CDATA or XmlNodeType.SignificantWhitespace)
+            {
+                { text.Append(reader.Value); sink?.Append(reader.Value); }
+            }
+            else if (reader.NodeType == XmlNodeType.Element)
+            {
+                reader.Skip();
+            }
+        }
+
+        if (string.IsNullOrEmpty(key)) return;
+
+        entries.Add(removed
+            ? new MTConnectDataSetEntry(key, null, true)
+            : cells is not null
+                ? new MTConnectDataSetEntry(key, null, false, cells)
+                : new MTConnectDataSetEntry(key, text.ToString().Trim(), false));
+    }
+
     /// <summary>
     ///     A condition's state is its element name. <c>Unavailable</c> is normalized to the
     ///     <see cref="UnavailableSentinel"/> spelling so downstream quality mapping has exactly one

tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.MTConnect.IntegrationTests/Docker/Devices.xml

@@ -27,7 +27,8 @@
     EVENT, controlled vocabulary     -> String           fixture_execution, fixture_avail, fixture_mode
     EVENT, free text                 -> String           fixture_program, fixture_block (never fed),
                                                          fixture_writeback (never fed; write target)
-    EVENT, DATA_SET representation   -> String           fixture_varset
+    EVENT, DATA_SET representation   -> String           fixture_varset (JSON object, #650)
+    EVENT, TABLE representation      -> String           fixture_worktable (JSON object of objects, #650)
     CONDITION (any type)             -> String + IsAlarm fixture_x_travel, fixture_logic
 
   fixture_block is deliberately NEVER fed by the adapter, so the Agent reports it
@@ -113,8 +114,10 @@
                   legal value, and never fed by the adapter, so nothing races the assertion.
                 -->
                 <DataItem category="EVENT" id="fixture_writeback" name="Pwriteback" type="PROGRAM_COMMENT"/>
-                <!-- DATA_SET representation demotes to String even though the Agent sends key=value entries. -->
+                <!-- DATA_SET representation is served as a String carrying JSON (#650); the Agent sends key=value entries. -->
                 <DataItem category="EVENT" id="fixture_varset" name="Pvars" type="VARIABLE" representation="DATA_SET"/>
+                <!-- TABLE representation (#650): rows of cells, served as nested JSON. -->
+                <DataItem category="EVENT" id="fixture_worktable" name="Ptab" type="WORK_OFFSET" representation="TABLE"/>
                 <DataItem category="CONDITION" id="fixture_logic" name="Plogic" type="LOGIC_PROGRAM"/>
               </DataItems>
             </Path>

tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.MTConnect.IntegrationTests/Docker/README.md

@@ -83,7 +83,8 @@ observation correlation key is visible.
 | `fixture_linenumber` | `Pline` | EVENT | LINE_NUMBER | | Int64 |
 | `fixture_program` | `Pprogram` | EVENT | PROGRAM | | String |
 | `fixture_block` | `Pblock` | EVENT | BLOCK | | String — **never fed ⇒ UNAVAILABLE** |
-| `fixture_varset` | `Pvars` | EVENT | VARIABLE | DATA_SET | String (structured ⇒ BadNotSupported) |
+| `fixture_varset` | `Pvars` | EVENT | VARIABLE | DATA_SET | String — JSON object (#650); `toolNumber`/`offsetX`/`offsetZ` stable, `cycle` moves every ~5 s |
+| `fixture_worktable` | `Ptab` | EVENT | WORK_OFFSET | TABLE | String — JSON object of objects (#650); `G54`/`G55` stable, `G56` row moves every ~5 s |
 | `fixture_logic` | `Plogic` | CONDITION | LOGIC_PROGRAM | | String + IsAlarm |
 | `fixture_asset_changed` / `fixture_asset_removed` | — | EVENT | ASSET_CHANGED / ASSET_REMOVED | | String |
 

tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.MTConnect.IntegrationTests/Docker/adapter.py

@@ -89,9 +89,12 @@ class Feed:
             [
                 ("Favail", "AVAILABLE"),
                 ("Pprogram", "OTOPCUA-FIXTURE.NC"),
-                # DATA_SET representation: the Agent renders these as <Entry key=...> children,
+                # DATA_SET / TABLE representations: the Agent renders these as <Entry key=...>
-                # which is precisely the wire shape the driver demotes to String / BadNotSupported.
+                # children, which the driver serves as a JSON String (#650). The three Pvars keys
-                ("Pvars", "toolNumber=7 offsetX=1.25 offsetZ=-0.5"),
+                # are STABLE for the life of the fixture; the periodic feed only touches `cycle`
+                # (Pvars) and the G56 row (Ptab).
+                ("Pvars", "toolNumber=7 offsetX=1.25 offsetZ=-0.5 cycle=0"),
+                ("Ptab", "G54={X=1.0 Y=2.0} G55={X=3.0} G56={X=0 Z=0.5}"),
             ]
         )
         self.send_conditions()
@@ -142,6 +145,17 @@ class Feed:
                 [("Cmode", CONTROLLER_MODES[(self._ticks // 44) % len(CONTROLLER_MODES)])]
             )
 
+        # DATA_SET / TABLE churn (#650): every ~5 s change one key / one row so a live gate can
+        # observe a /sample delta merge. The other keys / rows never change.
+        if self._ticks % 20 == 0:
+            n = self._ticks // 20
+            self.send_observations(
+                [
+                    ("Pvars", f"cycle={n}"),
+                    ("Ptab", f"G56={{X={n} Z=0.5}}"),
+                ]
+            )
+
         # Re-assert conditions occasionally so a late-attaching driver still sees them.
         if self._ticks % 60 == 0:
             self.send_conditions()

tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.MTConnect.IntegrationTests/MTConnectAgentIntegrationTests.cs

@@ -448,6 +448,40 @@ public sealed class MTConnectAgentIntegrationTests(MTConnectAgentFixture agent)
         results.ShouldAllBe(r => r.Value == null);
     }
 
+    /// <summary>
+    ///     #650: the fixture's DATA_SET (<c>fixture_varset</c>) and TABLE (<c>fixture_worktable</c>) read as Good
+    ///     Strings carrying JSON. Only the keys the adapter never mutates are asserted exactly; the periodic
+    ///     <c>cycle</c> key / <c>G56</c> row are asserted present, because they move every ~5 s.
+    /// </summary>
+    [Fact(Timeout = TestTimeoutMs)]
+    public async Task Read_serves_data_set_and_table_as_json_strings()
+    {
+        SkipIfDown();
+
+        await using var live = await LiveDriverAsync(
+            [Tag("fixture_varset", DriverDataType.String), Tag("fixture_worktable", DriverDataType.String)]);
+
+        var results = await live.Driver.ReadAsync(["fixture_varset", "fixture_worktable"], Ct);
+
+        if (results.Any(r => r.StatusCode == BadNoCommunication))
+        {
+            Assert.Skip("The fixture's adapter is not feeding Pvars/Ptab (UNAVAILABLE). Is the adapter service running?");
+        }
+
+        results.ShouldAllBe(r => r.StatusCode == Good);
+
+        using var set = JsonDocument.Parse(results[0].Value.ShouldBeOfType<string>());
+        set.RootElement.GetProperty("toolNumber").GetInt32().ShouldBe(7);
+        set.RootElement.GetProperty("offsetX").GetDouble().ShouldBe(1.25);
+        set.RootElement.GetProperty("offsetZ").GetDouble().ShouldBe(-0.5);
+        set.RootElement.TryGetProperty("cycle", out _).ShouldBeTrue();
+
+        using var table = JsonDocument.Parse(results[1].Value.ShouldBeOfType<string>());
+        table.RootElement.GetProperty("G54").GetProperty("Y").GetDouble().ShouldBe(2.0);
+        table.RootElement.GetProperty("G55").GetProperty("X").GetDouble().ShouldBe(3.0);
+        table.RootElement.GetProperty("G56").GetProperty("Z").GetDouble().ShouldBe(0.5);
+    }
+
     // ---- subscriptions: the /sample long poll ----
 
     /// <summary>

tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.MTConnect.Tests/MTConnectDataSetTests.cs

@@ -0,0 +1,175 @@
+using Shouldly;
+using Xunit;
+using ZB.MOM.WW.OtOpcUa.Core.Abstractions;
+
+namespace ZB.MOM.WW.OtOpcUa.Driver.MTConnect.Tests;
+
+/// <summary>
+///     #650 — DATA_SET / TABLE observations are served as a String carrying compact, deterministic JSON.
+///     Pins the parse (entries, cells, removed, resetTriggered) and the index's merge semantics
+///     (/current replaces, /sample merges, UNAVAILABLE drops the accumulated set).
+/// </summary>
+public sealed class MTConnectDataSetTests
+{
+    private const uint Good = 0x00000000u;
+    private const uint BadNoCommunication = 0x80310000u;
+
+    private static string Doc(string events, string attrs = "") =>
+        $"""
+        <MTConnectStreams>
+          <Header instanceId="1" nextSequence="2" firstSequence="1"/>
+          <Streams><DeviceStream><ComponentStream><Events>{events}</Events></ComponentStream></DeviceStream></Streams>
+        </MTConnectStreams>
+        """;
+
+    private static string DataSet(string body, string attrs = "") =>
+        $"""<VariableDataSet dataItemId="ds" timestamp="2026-07-24T12:00:00Z"{attrs}>{body}</VariableDataSet>""";
+
+    private static string Table(string body, string attrs = "") =>
+        $"""<WorkOffsetTable dataItemId="tb" timestamp="2026-07-24T12:00:00Z"{attrs}>{body}</WorkOffsetTable>""";
+
+    private static MTConnectObservationIndex NewIndex() =>
+        new([new MTConnectTagDefinition("ds", DriverDataType.String), new MTConnectTagDefinition("tb", DriverDataType.String)]);
+
+    private static void Apply(MTConnectObservationIndex idx, string events, bool baseline = false) =>
+        idx.Apply(MTConnectStreamsParser.Parse(Doc(events)), baseline);
+
+    [Fact]
+    public void Parser_captures_entries_cells_removed_and_reset()
+    {
+        var result = MTConnectStreamsParser.Parse(Doc(
+            DataSet("""<Entry key="a">1</Entry><Entry key="b" removed="true"/>""", " resetTriggered=\"MANUAL\"") +
+            Table("""<Entry key="G54"><Cell key="X">1.5</Cell><Cell key="Y">2</Cell></Entry>""")));
+
+        var ds = result.Observations[0];
+        ds.ResetTriggered.ShouldBeTrue();
+        ds.Entries!.Count.ShouldBe(2);
+        ds.Entries[0].ShouldBe(new MTConnectDataSetEntry("a", "1", false));
+        ds.Entries[1].Removed.ShouldBeTrue();
+
+        var tb = result.Observations[1];
+        tb.Entries!.ShouldHaveSingleItem().Cells!.Select(c => (c.Key, c.Value))
+            .ShouldBe([("X", "1.5"), ("Y", "2")]);
+    }
+
+    [Fact]
+    public void Data_set_is_served_as_sorted_compact_json_with_numbers_and_strings()
+    {
+        var idx = NewIndex();
+        Apply(idx, DataSet("""<Entry key="toolNumber">7</Entry><Entry key="offsetX">1.25</Entry><Entry key="name">A &amp; "B"</Entry><Entry key="part">007</Entry>"""), baseline: true);
+
+        var snap = idx.Get("ds");
+        snap.StatusCode.ShouldBe(Good);
+        snap.Value.ShouldBe("""{"name":"A & \"B\"","offsetX":1.25,"part":"007","toolNumber":7}""");
+    }
+
+    [Fact]
+    public void Table_is_served_as_nested_json()
+    {
+        var idx = NewIndex();
+        Apply(idx, Table("""<Entry key="G55"><Cell key="X">3</Cell></Entry><Entry key="G54"><Cell key="Y">2</Cell><Cell key="X">1.0</Cell></Entry>"""), baseline: true);
+
+        idx.Get("tb").Value.ShouldBe("""{"G54":{"X":1.0,"Y":2},"G55":{"X":3}}""");
+    }
+
+    [Fact]
+    public void Sample_delta_merges_and_removed_entry_disappears()
+    {
+        var idx = NewIndex();
+        Apply(idx, DataSet("""<Entry key="a">1</Entry><Entry key="b">2</Entry>"""), baseline: true);
+
+        Apply(idx, DataSet("""<Entry key="b">3</Entry><Entry key="c">x</Entry>"""));
+        idx.Get("ds").Value.ShouldBe("""{"a":1,"b":3,"c":"x"}""");
+
+        Apply(idx, DataSet("""<Entry key="a" removed="true"/>"""));
+        idx.Get("ds").Value.ShouldBe("""{"b":3,"c":"x"}""");
+    }
+
+    [Fact]
+    public void Table_row_delta_replaces_the_row_and_removed_row_disappears()
+    {
+        var idx = NewIndex();
+        Apply(idx, Table("""<Entry key="G54"><Cell key="X">1</Cell><Cell key="Y">2</Cell></Entry><Entry key="G55"><Cell key="X">3</Cell></Entry>"""), baseline: true);
+
+        Apply(idx, Table("""<Entry key="G54"><Cell key="X">9</Cell></Entry><Entry key="G55" removed="true"/>"""));
+
+        idx.Get("tb").Value.ShouldBe("""{"G54":{"X":9}}""");
+    }
+
+    [Fact]
+    public void Current_baseline_replaces_rather_than_merges()
+    {
+        var idx = NewIndex();
+        Apply(idx, DataSet("""<Entry key="a">1</Entry><Entry key="b">2</Entry>"""), baseline: true);
+        Apply(idx, DataSet("""<Entry key="c">3</Entry>"""), baseline: true);
+
+        idx.Get("ds").Value.ShouldBe("""{"c":3}""");
+    }
+
+    [Fact]
+    public void ResetTriggered_replaces_the_accumulated_set_on_a_sample()
+    {
+        var idx = NewIndex();
+        Apply(idx, DataSet("""<Entry key="a">1</Entry>"""), baseline: true);
+        Apply(idx, DataSet("""<Entry key="z">9</Entry>""", " resetTriggered=\"MANUAL\""));
+
+        idx.Get("ds").Value.ShouldBe("""{"z":9}""");
+    }
+
+    [Fact]
+    public void ResetTriggered_with_no_entries_is_an_empty_set_not_an_absence()
+    {
+        var idx = NewIndex();
+        Apply(idx, DataSet("""<Entry key="a">1</Entry>"""), baseline: true);
+        Apply(idx, DataSet("", " resetTriggered=\"MANUAL\""));
+
+        var snap = idx.Get("ds");
+        snap.StatusCode.ShouldBe(Good);
+        snap.Value.ShouldBe("{}");
+    }
+
+    [Fact]
+    public void Unavailable_is_BadNoCommunication_and_drops_the_accumulated_set()
+    {
+        var idx = NewIndex();
+        Apply(idx, DataSet("""<Entry key="a">1</Entry>"""), baseline: true);
+
+        Apply(idx, DataSet("UNAVAILABLE"));
+        var snap = idx.Get("ds");
+        snap.StatusCode.ShouldBe(BadNoCommunication);
+        snap.Value.ShouldBeNull();
+
+        // A delta after the outage must not resurrect the pre-outage entry.
+        Apply(idx, DataSet("""<Entry key="b">2</Entry>"""));
+        idx.Get("ds").Value.ShouldBe("""{"b":2}""");
+    }
+
+    [Fact]
+    public void Several_observations_in_one_document_fold_in_order()
+    {
+        var idx = NewIndex();
+        Apply(idx, DataSet("""<Entry key="a">1</Entry>""") + DataSet("""<Entry key="b">2</Entry>"""), baseline: true);
+
+        idx.Get("ds").Value.ShouldBe("""{"a":1,"b":2}""");
+    }
+
+    [Fact]
+    public void Clear_forgets_the_accumulated_set()
+    {
+        var idx = NewIndex();
+        Apply(idx, DataSet("""<Entry key="a">1</Entry>"""), baseline: true);
+        idx.Clear();
+        Apply(idx, DataSet("""<Entry key="b">2</Entry>"""));
+
+        idx.Get("ds").Value.ShouldBe("""{"b":2}""");
+    }
+
+    [Fact]
+    public void Structured_content_that_is_not_entries_stays_BadNotSupported()
+    {
+        var idx = NewIndex();
+        Apply(idx, DataSet("<Other>1</Other>"), baseline: true);
+
+        idx.Get("ds").StatusCode.ShouldBe(0x803D0000u);
+    }
+}

tests/Drivers/ZB.MOM.WW.OtOpcUa.Driver.MTConnect.Tests/MTConnectObservationIndexTests.cs

@@ -589,11 +589,12 @@ public sealed class MTConnectObservationIndexTests
 
     /// <summary>
     ///     End-to-end through the real parser: the entry list that concatenates to the single token
-    ///     "12" is caught by the parser's structured flag and never surfaces as a Good value. This is
+    ///     "12" must never surface as that noise. Since #650 it is served as JSON carrying the keys
-    ///     the leg that would regress silently if the parser stopped setting the flag.
+    ///     (full semantics in <c>MTConnectDataSetTests</c>); the structured-without-entries shape above
+    ///     stays BadNotSupported.
     /// </summary>
     [Fact]
-    public void A_parsed_data_set_observation_never_surfaces_as_a_good_value()
+    public void A_parsed_data_set_observation_never_surfaces_as_concatenated_text()
     {
         const string xml = """
             <MTConnectStreams>
@@ -612,8 +613,8 @@ public sealed class MTConnectObservationIndexTests
 
         var snap = idx.Get("ds1");
 
-        snap.StatusCode.ShouldBe(BadNotSupported);
+        snap.StatusCode.ShouldBe(Good);
-        snap.Value.ShouldBeNull();
+        snap.Value.ShouldBe("""{"V1":1,"V2":2}""");
     }
 
     /// <summary>An ordinary text observation is not structured — the flag must not be over-applied.</summary>