diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..f11d5ae
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1,4 @@
+build/
+*.user
+.cache/
+compile_commands.json
diff --git a/CMakeLists.txt b/CMakeLists.txt
new file mode 100644
index 0000000..014c8a1
--- /dev/null
+++ b/CMakeLists.txt
@@ -0,0 +1,14 @@
+cmake_minimum_required(VERSION 3.22)
+project(PipeDiagram VERSION 0.1 LANGUAGES CXX)
+
+set(CMAKE_CXX_STANDARD 20)
+set(CMAKE_CXX_STANDARD_REQUIRED ON)
+set(CMAKE_AUTOMOC ON)
+set(CMAKE_AUTORCC ON)
+
+find_package(Qt6 REQUIRED COMPONENTS Core Gui Widgets Svg Test)
+
+add_subdirectory(src)
+
+enable_testing()
+add_subdirectory(tests)
diff --git a/README.md b/README.md
new file mode 100644
index 0000000..651aeac
--- /dev/null
+++ b/README.md
@@ -0,0 +1,21 @@
+# PipeDiagram — Pipeline Network Diagram Editor
+
+Qt 6 editor for drawing pipeline networks (water, power, …): SVG nodes with typed
+ports, grid-aligned orthogonal connectors with arc jump-overs, grouped editable
+properties, styleable edges, and a mock flow simulation with animated flow.
+
+## Build
+
+```bash
+cmake -S . -B build -G Ninja
+cmake --build build
+./build/src/pipediagram
+```
+
+## Test
+
+```bash
+ctest --test-dir build --output-on-failure
+```
+
+See `docs/plan/plan.md` for architecture and the feature checklist.
diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
new file mode 100644
index 0000000..b8c2e75
--- /dev/null
+++ b/src/CMakeLists.txt
@@ -0,0 +1,11 @@
+# Core: document model, routing, solver — no Widgets dependency, headless-testable.
+add_library(diagcore STATIC
+    core/Types.h
+    core/Types.cpp
+    core/TypeRegistry.h
+    core/TypeRegistry.cpp
+    core/NetworkModel.h
+    core/NetworkModel.cpp
+)
+target_include_directories(diagcore PUBLIC ${CMAKE_CURRENT_SOURCE_DIR})
+target_link_libraries(diagcore PUBLIC Qt6::Core Qt6::Gui)
diff --git a/src/core/NetworkModel.cpp b/src/core/NetworkModel.cpp
new file mode 100644
index 0000000..d0446e0
--- /dev/null
+++ b/src/core/NetworkModel.cpp
@@ -0,0 +1,252 @@
+#include "NetworkModel.h"
+
+namespace diag {
+
+NetworkModel::NetworkModel(TypeRegistry* registry, QObject* parent)
+    : QObject(parent), m_registry(registry ? registry : &TypeRegistry::instance())
+{
+}
+
+QUuid NetworkModel::addNode(const QString& typeId, QPointF pos, QUuid id)
+{
+    const NodeType* type = m_registry->nodeType(typeId);
+    if (!type)
+        return {};
+    Node n;
+    n.id = id.isNull() ? QUuid::createUuid() : id;
+    n.typeId = typeId;
+    n.pos = pos;
+    m_nodes.insert(n.id, n);
+    m_nodeOrder.append(n.id);
+    emit nodeAdded(n.id);
+    return n.id;
+}
+
+void NetworkModel::removeNode(QUuid id)
+{
+    if (!m_nodes.contains(id))
+        return;
+    const QList<QUuid> attached = edgesOfNode(id);
+    for (QUuid e : attached)
+        removeEdge(e);
+    m_nodes.remove(id);
+    m_nodeOrder.removeOne(id);
+    emit nodeRemoved(id);
+}
+
+void NetworkModel::moveNode(QUuid id, QPointF pos)
+{
+    auto it = m_nodes.find(id);
+    if (it == m_nodes.end() || it->pos == pos)
+        return;
+    it->pos = pos;
+    emit nodeMoved(id);
+}
+
+const Node* NetworkModel::node(QUuid id) const
+{
+    auto it = m_nodes.constFind(id);
+    return it == m_nodes.constEnd() ? nullptr : &it.value();
+}
+
+QList<QUuid> NetworkModel::nodeIds() const
+{
+    return m_nodeOrder;
+}
+
+const NodeType* NetworkModel::nodeTypeOf(QUuid id) const
+{
+    const Node* n = node(id);
+    return n ? m_registry->nodeType(n->typeId) : nullptr;
+}
+
+bool NetworkModel::canConnect(QUuid nodeA, const QString& portA, QUuid nodeB,
+                              const QString& portB, QString* reason) const
+{
+    auto fail = [reason](const QString& why) {
+        if (reason)
+            *reason = why;
+        return false;
+    };
+
+    const NodeType* typeA = nodeTypeOf(nodeA);
+    const NodeType* typeB = nodeTypeOf(nodeB);
+    if (!typeA || !typeB)
+        return fail(tr("Unknown node"));
+    const PortSpec* pa = typeA->port(portA);
+    const PortSpec* pb = typeB->port(portB);
+    if (!pa || !pb)
+        return fail(tr("Unknown port"));
+    if (nodeA == nodeB && portA == portB)
+        return fail(tr("Cannot connect a port to itself"));
+    if (pa->relation != pb->relation)
+        return fail(tr("Incompatible port relations (%1 vs %2)").arg(pa->relation, pb->relation));
+    if (pa->direction == PortDirection::In && pb->direction == PortDirection::In)
+        return fail(tr("Cannot connect two inputs"));
+    if (pa->direction == PortDirection::Out && pb->direction == PortDirection::Out)
+        return fail(tr("Cannot connect two outputs"));
+    if (pa->maxConnections > 0 && connectionCount(nodeA, portA) >= pa->maxConnections)
+        return fail(tr("Port %1 is already occupied").arg(portA));
+    if (pb->maxConnections > 0 && connectionCount(nodeB, portB) >= pb->maxConnections)
+        return fail(tr("Port %1 is already occupied").arg(portB));
+    for (const auto& e : m_edges) {
+        const bool same = (e.fromNode == nodeA && e.fromPort == portA && e.toNode == nodeB
+                           && e.toPort == portB)
+            || (e.fromNode == nodeB && e.fromPort == portB && e.toNode == nodeA
+                && e.toPort == portA);
+        if (same)
+            return fail(tr("Ports are already connected"));
+    }
+    return true;
+}
+
+QUuid NetworkModel::addEdge(QUuid fromNode, const QString& fromPort, QUuid toNode,
+                            const QString& toPort, QUuid id)
+{
+    if (!canConnect(fromNode, fromPort, toNode, toPort))
+        return {};
+    const NodeType* typeA = nodeTypeOf(fromNode);
+    const PortSpec* pa = typeA->port(fromPort);
+    const PortSpec* pb = nodeTypeOf(toNode)->port(toPort);
+
+    Edge e;
+    e.id = id.isNull() ? QUuid::createUuid() : id;
+    // Normalize direction so the edge always leaves an Out port when one is present.
+    if (pa->direction == PortDirection::In || pb->direction == PortDirection::Out) {
+        e.fromNode = toNode;
+        e.fromPort = toPort;
+        e.toNode = fromNode;
+        e.toPort = fromPort;
+    } else {
+        e.fromNode = fromNode;
+        e.fromPort = fromPort;
+        e.toNode = toNode;
+        e.toPort = toPort;
+    }
+    e.relation = pa->relation;
+    m_edges.insert(e.id, e);
+    m_edgeOrder.append(e.id);
+    emit edgeAdded(e.id);
+    return e.id;
+}
+
+void NetworkModel::removeEdge(QUuid id)
+{
+    if (!m_edges.remove(id))
+        return;
+    m_edgeOrder.removeOne(id);
+    emit edgeRemoved(id);
+}
+
+const Edge* NetworkModel::edge(QUuid id) const
+{
+    auto it = m_edges.constFind(id);
+    return it == m_edges.constEnd() ? nullptr : &it.value();
+}
+
+QList<QUuid> NetworkModel::edgeIds() const
+{
+    return m_edgeOrder;
+}
+
+QList<QUuid> NetworkModel::edgesOfNode(QUuid nodeId) const
+{
+    QList<QUuid> out;
+    for (QUuid id : m_edgeOrder) {
+        const Edge& e = m_edges[id];
+        if (e.fromNode == nodeId || e.toNode == nodeId)
+            out.append(id);
+    }
+    return out;
+}
+
+int NetworkModel::connectionCount(QUuid nodeId, const QString& portId) const
+{
+    int count = 0;
+    for (const auto& e : m_edges) {
+        if (e.fromNode == nodeId && e.fromPort == portId)
+            ++count;
+        if (e.toNode == nodeId && e.toPort == portId)
+            ++count;
+    }
+    return count;
+}
+
+QVariant NetworkModel::defaultFor(const QList<PropertySpec>& specs, const QString& key)
+{
+    for (const auto& s : specs)
+        if (s.id == key)
+            return s.defaultValue;
+    return {};
+}
+
+void NetworkModel::setNodeProperty(QUuid id, const QString& key, const QVariant& value)
+{
+    auto it = m_nodes.find(id);
+    if (it == m_nodes.end() || it->props.value(key) == value)
+        return;
+    it->props.insert(key, value);
+    emit nodeChanged(id);
+}
+
+QVariant NetworkModel::nodeProperty(QUuid id, const QString& key) const
+{
+    const Node* n = node(id);
+    if (!n)
+        return {};
+    if (n->props.contains(key))
+        return n->props.value(key);
+    return defaultFor(m_registry->nodeProperties(n->typeId), key);
+}
+
+void NetworkModel::setEdgeProperty(QUuid id, const QString& key, const QVariant& value)
+{
+    auto it = m_edges.find(id);
+    if (it == m_edges.end() || it->props.value(key) == value)
+        return;
+    it->props.insert(key, value);
+    emit edgeChanged(id);
+}
+
+QVariant NetworkModel::edgeProperty(QUuid id, const QString& key) const
+{
+    const Edge* e = edge(id);
+    if (!e)
+        return {};
+    if (e->props.contains(key))
+        return e->props.value(key);
+    return defaultFor(m_registry->edgeProperties(e->relation), key);
+}
+
+void NetworkModel::setEdgeFlow(QUuid id, double rate)
+{
+    auto it = m_edges.find(id);
+    if (it == m_edges.end() || qFuzzyCompare(it->flowRate + 1.0, rate + 1.0))
+        return;
+    it->flowRate = rate;
+    emit flowChanged(id);
+}
+
+QPointF NetworkModel::portScenePos(QUuid nodeId, const QString& portId) const
+{
+    const Node* n = node(nodeId);
+    const NodeType* t = nodeTypeOf(nodeId);
+    if (!n || !t)
+        return {};
+    const PortSpec* p = t->port(portId);
+    if (!p)
+        return n->pos;
+    return n->pos
+        + QPointF(p->pos.x() * t->size.width(), p->pos.y() * t->size.height());
+}
+
+void NetworkModel::clear()
+{
+    m_nodes.clear();
+    m_edges.clear();
+    m_nodeOrder.clear();
+    m_edgeOrder.clear();
+    emit modelReset();
+}
+
+}  // namespace diag
diff --git a/src/core/NetworkModel.h b/src/core/NetworkModel.h
new file mode 100644
index 0000000..c4b2e66
--- /dev/null
+++ b/src/core/NetworkModel.h
@@ -0,0 +1,75 @@
+#pragma once
+
+#include "TypeRegistry.h"
+#include "Types.h"
+
+#include <QHash>
+#include <QObject>
+
+namespace diag {
+
+// The document model: nodes placed on the canvas and edges connecting their
+// ports. All edits are signalled so views stay in sync. Pure Qt Core/Gui —
+// usable headless in tests.
+class NetworkModel : public QObject {
+    Q_OBJECT
+public:
+    explicit NetworkModel(TypeRegistry* registry = nullptr, QObject* parent = nullptr);
+
+    TypeRegistry* registry() const { return m_registry; }
+
+    // --- nodes ---
+    QUuid addNode(const QString& typeId, QPointF pos, QUuid id = {});
+    void removeNode(QUuid id);  // cascades to attached edges
+    void moveNode(QUuid id, QPointF pos);
+    const Node* node(QUuid id) const;
+    QList<QUuid> nodeIds() const;
+    const NodeType* nodeTypeOf(QUuid id) const;
+
+    // --- edges ---
+    bool canConnect(QUuid nodeA, const QString& portA, QUuid nodeB, const QString& portB,
+                    QString* reason = nullptr) const;
+    QUuid addEdge(QUuid fromNode, const QString& fromPort, QUuid toNode, const QString& toPort,
+                  QUuid id = {});
+    void removeEdge(QUuid id);
+    const Edge* edge(QUuid id) const;
+    QList<QUuid> edgeIds() const;
+    QList<QUuid> edgesOfNode(QUuid nodeId) const;
+    int connectionCount(QUuid nodeId, const QString& portId) const;
+
+    // --- properties (values fall back to the spec default when unset) ---
+    void setNodeProperty(QUuid id, const QString& key, const QVariant& value);
+    QVariant nodeProperty(QUuid id, const QString& key) const;
+    void setEdgeProperty(QUuid id, const QString& key, const QVariant& value);
+    QVariant edgeProperty(QUuid id, const QString& key) const;
+
+    // Solver results (does not go through the undo stack).
+    void setEdgeFlow(QUuid id, double rate);
+
+    // Scene position of a port (node pos + relative port pos * size).
+    QPointF portScenePos(QUuid nodeId, const QString& portId) const;
+
+    void clear();
+
+signals:
+    void nodeAdded(QUuid id);
+    void nodeRemoved(QUuid id);
+    void nodeMoved(QUuid id);
+    void nodeChanged(QUuid id);
+    void edgeAdded(QUuid id);
+    void edgeRemoved(QUuid id);
+    void edgeChanged(QUuid id);
+    void flowChanged(QUuid id);
+    void modelReset();
+
+private:
+    static QVariant defaultFor(const QList<PropertySpec>& specs, const QString& key);
+
+    TypeRegistry* m_registry;
+    QHash<QUuid, Node> m_nodes;
+    QHash<QUuid, Edge> m_edges;
+    QList<QUuid> m_nodeOrder;  // stable iteration/serialization order
+    QList<QUuid> m_edgeOrder;
+};
+
+}  // namespace diag
diff --git a/src/core/TypeRegistry.cpp b/src/core/TypeRegistry.cpp
new file mode 100644
index 0000000..4e2eff2
--- /dev/null
+++ b/src/core/TypeRegistry.cpp
@@ -0,0 +1,338 @@
+#include "TypeRegistry.h"
+
+#include <QFile>
+#include <QJsonArray>
+#include <QJsonDocument>
+
+namespace diag {
+
+TypeRegistry::TypeRegistry() = default;
+
+TypeRegistry& TypeRegistry::instance()
+{
+    static TypeRegistry reg;
+    return reg;
+}
+
+void TypeRegistry::clear()
+{
+    m_relations.clear();
+    m_nodeTypes.clear();
+    m_catalogues.clear();
+    m_edgeProps.clear();
+}
+
+void TypeRegistry::addRelation(const Relation& r)
+{
+    m_relations.append(r);
+}
+
+void TypeRegistry::addNodeType(const NodeType& t)
+{
+    m_nodeTypes.append(t);
+}
+
+void TypeRegistry::addCatalogue(const Catalogue& c)
+{
+    m_catalogues.append(c);
+}
+
+void TypeRegistry::setEdgeProperties(const QString& relationId, const QList<PropertySpec>& specs)
+{
+    m_edgeProps.insert(relationId, specs);
+}
+
+const Relation* TypeRegistry::relation(const QString& id) const
+{
+    for (const auto& r : m_relations)
+        if (r.id == id)
+            return &r;
+    return nullptr;
+}
+
+QList<Relation> TypeRegistry::relations() const
+{
+    return m_relations;
+}
+
+const NodeType* TypeRegistry::nodeType(const QString& id) const
+{
+    for (const auto& t : m_nodeTypes)
+        if (t.id == id)
+            return &t;
+    return nullptr;
+}
+
+QList<const NodeType*> TypeRegistry::nodeTypes() const
+{
+    QList<const NodeType*> out;
+    out.reserve(m_nodeTypes.size());
+    for (const auto& t : m_nodeTypes)
+        out.append(&t);
+    return out;
+}
+
+QStringList TypeRegistry::nodeGroups() const
+{
+    QStringList groups;
+    for (const auto& t : m_nodeTypes)
+        if (!groups.contains(t.group))
+            groups.append(t.group);
+    return groups;
+}
+
+const Catalogue* TypeRegistry::catalogue(const QString& id) const
+{
+    for (const auto& c : m_catalogues)
+        if (c.id == id)
+            return &c;
+    return nullptr;
+}
+
+QList<const Catalogue*> TypeRegistry::catalogues() const
+{
+    QList<const Catalogue*> out;
+    out.reserve(m_catalogues.size());
+    for (const auto& c : m_catalogues)
+        out.append(&c);
+    return out;
+}
+
+QList<PropertySpec> TypeRegistry::commonNodeProperties()
+{
+    PropertySpec title;
+    title.id = QStringLiteral("title");
+    title.name = QStringLiteral("Title");
+    title.group = QStringLiteral("General");
+    title.type = PropertyType::String;
+    title.defaultValue = QString();
+
+    PropertySpec labelColor;
+    labelColor.id = QStringLiteral("labelColor");
+    labelColor.name = QStringLiteral("Label color");
+    labelColor.group = QStringLiteral("Presentation");
+    labelColor.type = PropertyType::Color;
+    labelColor.defaultValue = QString();  // empty = theme default
+
+    PropertySpec tags;
+    tags.id = QStringLiteral("tags");
+    tags.name = QStringLiteral("Tags");
+    tags.group = QStringLiteral("General");
+    tags.type = PropertyType::ValueList;
+    tags.defaultValue = QStringList();
+
+    return {title, tags, labelColor};
+}
+
+QList<PropertySpec> TypeRegistry::commonEdgeProperties()
+{
+    QList<PropertySpec> out;
+
+    PropertySpec title;
+    title.id = QStringLiteral("title");
+    title.name = QStringLiteral("Title");
+    title.group = QStringLiteral("General");
+    title.type = PropertyType::String;
+    title.defaultValue = QString();
+    out << title;
+
+    PropertySpec lineStyle;
+    lineStyle.id = QStringLiteral("lineStyle");
+    lineStyle.name = QStringLiteral("Line style");
+    lineStyle.group = QStringLiteral("Presentation");
+    lineStyle.type = PropertyType::Enum;
+    lineStyle.enumValues = {QStringLiteral("Solid"), QStringLiteral("Dashed"),
+                            QStringLiteral("Dotted"), QStringLiteral("DashDot")};
+    lineStyle.defaultValue = QStringLiteral("Solid");
+    out << lineStyle;
+
+    PropertySpec width;
+    width.id = QStringLiteral("lineWidth");
+    width.name = QStringLiteral("Line width");
+    width.group = QStringLiteral("Presentation");
+    width.type = PropertyType::Float;
+    width.defaultValue = 2.0;
+    width.min = 0.5;
+    width.max = 10.0;
+    out << width;
+
+    PropertySpec color;
+    color.id = QStringLiteral("color");
+    color.name = QStringLiteral("Color");
+    color.group = QStringLiteral("Presentation");
+    color.type = PropertyType::Color;
+    color.defaultValue = QString();  // empty = relation color
+    out << color;
+
+    const QStringList decorations = {QStringLiteral("None"), QStringLiteral("Arrow"),
+                                     QStringLiteral("Circle"), QStringLiteral("Diamond"),
+                                     QStringLiteral("Bar")};
+
+    PropertySpec head;
+    head.id = QStringLiteral("headDecoration");
+    head.name = QStringLiteral("Head decoration");
+    head.group = QStringLiteral("Presentation");
+    head.type = PropertyType::Enum;
+    head.enumValues = decorations;
+    head.defaultValue = QStringLiteral("Arrow");
+    out << head;
+
+    PropertySpec tail;
+    tail.id = QStringLiteral("tailDecoration");
+    tail.name = QStringLiteral("Tail decoration");
+    tail.group = QStringLiteral("Presentation");
+    tail.type = PropertyType::Enum;
+    tail.enumValues = decorations;
+    tail.defaultValue = QStringLiteral("None");
+    out << tail;
+
+    return out;
+}
+
+QList<PropertySpec> TypeRegistry::nodeProperties(const QString& typeId) const
+{
+    QList<PropertySpec> out = commonNodeProperties();
+    if (const NodeType* t = nodeType(typeId))
+        out.append(t->properties);
+    return out;
+}
+
+QList<PropertySpec> TypeRegistry::edgeProperties(const QString& relationId) const
+{
+    QList<PropertySpec> out = commonEdgeProperties();
+    out.append(m_edgeProps.value(relationId));
+    return out;
+}
+
+PropertySpec propertySpecFromJson(const QJsonObject& o)
+{
+    PropertySpec s;
+    s.id = o.value(QLatin1String("id")).toString();
+    s.name = o.value(QLatin1String("name")).toString(s.id);
+    s.group = o.value(QLatin1String("group")).toString(QStringLiteral("General"));
+    s.type = propertyTypeFromString(o.value(QLatin1String("type")).toString());
+    s.unit = o.value(QLatin1String("unit")).toString();
+    s.catalogueId = o.value(QLatin1String("catalogue")).toString();
+    s.min = o.value(QLatin1String("min")).toDouble();
+    s.max = o.value(QLatin1String("max")).toDouble();
+    s.readOnly = o.value(QLatin1String("readOnly")).toBool();
+    for (const auto& v : o.value(QLatin1String("values")).toArray())
+        s.enumValues.append(v.toString());
+    const QJsonValue def = o.value(QLatin1String("default"));
+    switch (s.type) {
+    case PropertyType::Int:
+        s.defaultValue = def.toInt();
+        break;
+    case PropertyType::Float:
+        s.defaultValue = def.toDouble();
+        break;
+    case PropertyType::CatalogueItems:
+    case PropertyType::ValueList: {
+        QStringList list;
+        for (const auto& v : def.toArray())
+            list.append(v.toString());
+        s.defaultValue = list;
+        break;
+    }
+    default:
+        s.defaultValue = def.toString();
+        break;
+    }
+    return s;
+}
+
+static QPointF pointFromJson(const QJsonValue& v, QPointF fallback = {})
+{
+    const QJsonArray a = v.toArray();
+    if (a.size() == 2)
+        return {a.at(0).toDouble(), a.at(1).toDouble()};
+    return fallback;
+}
+
+bool TypeRegistry::loadFromJson(const QByteArray& jsonData, QString* error)
+{
+    QJsonParseError perr;
+    const QJsonDocument doc = QJsonDocument::fromJson(jsonData, &perr);
+    if (doc.isNull()) {
+        if (error)
+            *error = perr.errorString();
+        return false;
+    }
+    clear();
+    const QJsonObject root = doc.object();
+
+    for (const auto& rv : root.value(QLatin1String("relations")).toArray()) {
+        const QJsonObject o = rv.toObject();
+        Relation r;
+        r.id = o.value(QLatin1String("id")).toString();
+        r.name = o.value(QLatin1String("name")).toString(r.id);
+        r.color = QColor(o.value(QLatin1String("color")).toString());
+        r.darkColor = QColor(o.value(QLatin1String("darkColor")).toString(
+            o.value(QLatin1String("color")).toString()));
+        addRelation(r);
+    }
+
+    for (const auto& cv : root.value(QLatin1String("catalogues")).toArray()) {
+        const QJsonObject o = cv.toObject();
+        Catalogue c;
+        c.id = o.value(QLatin1String("id")).toString();
+        c.name = o.value(QLatin1String("name")).toString(c.id);
+        for (const auto& iv : o.value(QLatin1String("items")).toArray()) {
+            const QJsonObject io = iv.toObject();
+            CatalogueItem item;
+            item.id = io.value(QLatin1String("id")).toString();
+            item.name = io.value(QLatin1String("name")).toString(item.id);
+            item.attributes = io.value(QLatin1String("attributes")).toObject().toVariantMap();
+            c.items.append(item);
+        }
+        addCatalogue(c);
+    }
+
+    const QJsonObject edgeProps = root.value(QLatin1String("edgeProperties")).toObject();
+    for (auto it = edgeProps.begin(); it != edgeProps.end(); ++it) {
+        QList<PropertySpec> specs;
+        for (const auto& pv : it.value().toArray())
+            specs.append(propertySpecFromJson(pv.toObject()));
+        setEdgeProperties(it.key(), specs);
+    }
+
+    for (const auto& tv : root.value(QLatin1String("nodeTypes")).toArray()) {
+        const QJsonObject o = tv.toObject();
+        NodeType t;
+        t.id = o.value(QLatin1String("id")).toString();
+        t.name = o.value(QLatin1String("name")).toString(t.id);
+        t.group = o.value(QLatin1String("group")).toString(QStringLiteral("Misc"));
+        t.svgPath = o.value(QLatin1String("svg")).toString();
+        const QPointF sz = pointFromJson(o.value(QLatin1String("size")), {60, 60});
+        t.size = QSizeF(sz.x(), sz.y());
+        for (const auto& pv : o.value(QLatin1String("ports")).toArray()) {
+            const QJsonObject po = pv.toObject();
+            PortSpec p;
+            p.id = po.value(QLatin1String("id")).toString();
+            p.relation = po.value(QLatin1String("relation")).toString();
+            p.direction = portDirectionFromString(po.value(QLatin1String("direction")).toString());
+            p.pos = pointFromJson(po.value(QLatin1String("pos")), {0.5, 0.5});
+            p.side = sideFromString(po.value(QLatin1String("side")).toString());
+            p.maxConnections = po.value(QLatin1String("maxConnections")).toInt(1);
+            t.ports.append(p);
+        }
+        for (const auto& pv : o.value(QLatin1String("properties")).toArray())
+            t.properties.append(propertySpecFromJson(pv.toObject()));
+        addNodeType(t);
+    }
+
+    return true;
+}
+
+bool TypeRegistry::loadFromFile(const QString& path, QString* error)
+{
+    QFile f(path);
+    if (!f.open(QIODevice::ReadOnly)) {
+        if (error)
+            *error = f.errorString();
+        return false;
+    }
+    return loadFromJson(f.readAll(), error);
+}
+
+}  // namespace diag
diff --git a/src/core/TypeRegistry.h b/src/core/TypeRegistry.h
new file mode 100644
index 0000000..5eb46c5
--- /dev/null
+++ b/src/core/TypeRegistry.h
@@ -0,0 +1,55 @@
+#pragma once
+
+#include "Types.h"
+
+#include <QHash>
+#include <QJsonObject>
+
+namespace diag {
+
+// Holds relation, node-type, catalogue and edge-property definitions.
+// Definitions are data-driven: loaded from a JSON config (see
+// resources/config/nodetypes.json). Common presentation/general property
+// specs for nodes and edges are built in.
+class TypeRegistry {
+public:
+    TypeRegistry();
+
+    static TypeRegistry& instance();
+
+    bool loadFromJson(const QByteArray& jsonData, QString* error = nullptr);
+    bool loadFromFile(const QString& path, QString* error = nullptr);
+    void clear();
+
+    void addRelation(const Relation& r);
+    void addNodeType(const NodeType& t);
+    void addCatalogue(const Catalogue& c);
+    void setEdgeProperties(const QString& relationId, const QList<PropertySpec>& specs);
+
+    const Relation* relation(const QString& id) const;
+    QList<Relation> relations() const;
+
+    const NodeType* nodeType(const QString& id) const;
+    QList<const NodeType*> nodeTypes() const;
+    QStringList nodeGroups() const;  // in definition order
+
+    const Catalogue* catalogue(const QString& id) const;
+    QList<const Catalogue*> catalogues() const;
+
+    // Full spec list: common specs + type/relation specific ones.
+    QList<PropertySpec> nodeProperties(const QString& typeId) const;
+    QList<PropertySpec> edgeProperties(const QString& relationId) const;
+
+    static QList<PropertySpec> commonNodeProperties();
+    static QList<PropertySpec> commonEdgeProperties();
+
+private:
+    QList<Relation> m_relations;
+    QList<NodeType> m_nodeTypes;
+    QList<Catalogue> m_catalogues;
+    QHash<QString, QList<PropertySpec>> m_edgeProps;  // by relation id
+};
+
+PropertySpec propertySpecFromJson(const QJsonObject& o);
+
+}  // namespace diag
diff --git a/src/core/Types.cpp b/src/core/Types.cpp
new file mode 100644
index 0000000..691af14
--- /dev/null
+++ b/src/core/Types.cpp
@@ -0,0 +1,107 @@
+#include "Types.h"
+
+namespace diag {
+
+const PortSpec* NodeType::port(const QString& portId) const
+{
+    for (const auto& p : ports)
+        if (p.id == portId)
+            return &p;
+    return nullptr;
+}
+
+const CatalogueItem* Catalogue::item(const QString& itemId) const
+{
+    for (const auto& i : items)
+        if (i.id == itemId)
+            return &i;
+    return nullptr;
+}
+
+QPointF sideVector(Side s)
+{
+    switch (s) {
+    case Side::Left: return {-1, 0};
+    case Side::Right: return {1, 0};
+    case Side::Top: return {0, -1};
+    case Side::Bottom: return {0, 1};
+    }
+    return {1, 0};
+}
+
+QString portDirectionToString(PortDirection d)
+{
+    switch (d) {
+    case PortDirection::In: return QStringLiteral("in");
+    case PortDirection::Out: return QStringLiteral("out");
+    case PortDirection::InOut: return QStringLiteral("inout");
+    }
+    return QStringLiteral("inout");
+}
+
+PortDirection portDirectionFromString(const QString& s)
+{
+    if (s == QLatin1String("in"))
+        return PortDirection::In;
+    if (s == QLatin1String("out"))
+        return PortDirection::Out;
+    return PortDirection::InOut;
+}
+
+QString sideToString(Side s)
+{
+    switch (s) {
+    case Side::Left: return QStringLiteral("left");
+    case Side::Right: return QStringLiteral("right");
+    case Side::Top: return QStringLiteral("top");
+    case Side::Bottom: return QStringLiteral("bottom");
+    }
+    return QStringLiteral("left");
+}
+
+Side sideFromString(const QString& s)
+{
+    if (s == QLatin1String("right"))
+        return Side::Right;
+    if (s == QLatin1String("top"))
+        return Side::Top;
+    if (s == QLatin1String("bottom"))
+        return Side::Bottom;
+    return Side::Left;
+}
+
+QString propertyTypeToString(PropertyType t)
+{
+    switch (t) {
+    case PropertyType::String: return QStringLiteral("string");
+    case PropertyType::Int: return QStringLiteral("int");
+    case PropertyType::Float: return QStringLiteral("float");
+    case PropertyType::Enum: return QStringLiteral("enum");
+    case PropertyType::CatalogueItem: return QStringLiteral("catalogueItem");
+    case PropertyType::CatalogueItems: return QStringLiteral("catalogueItems");
+    case PropertyType::Color: return QStringLiteral("color");
+    case PropertyType::ValueList: return QStringLiteral("valueList");
+    }
+    return QStringLiteral("string");
+}
+
+PropertyType propertyTypeFromString(const QString& s)
+{
+    if (s == QLatin1String("int"))
+        return PropertyType::Int;
+    if (s == QLatin1String("float"))
+        return PropertyType::Float;
+    if (s == QLatin1String("enum"))
+        return PropertyType::Enum;
+    if (s == QLatin1String("catalogueItem"))
+        return PropertyType::CatalogueItem;
+    if (s == QLatin1String("catalogueItems"))
+        return PropertyType::CatalogueItems;
+    if (s == QLatin1String("color"))
+        return PropertyType::Color;
+    if (s == QLatin1String("valueList"))
+        return PropertyType::ValueList;
+    return PropertyType::String;
+}
+
+}  // namespace diag
diff --git a/src/core/Types.h b/src/core/Types.h
new file mode 100644
index 0000000..326a5d3
--- /dev/null
+++ b/src/core/Types.h
@@ -0,0 +1,118 @@
+#pragma once
+
+#include <QColor>
+#include <QList>
+#include <QPointF>
+#include <QSizeF>
+#include <QString>
+#include <QStringList>
+#include <QUuid>
+#include <QVariant>
+#include <QVariantMap>
+
+namespace diag {
+
+// Which side of the node rectangle a port sits on; defines the exit
+// direction of the first routed segment.
+enum class Side { Left, Right, Top, Bottom };
+
+enum class PortDirection { In, Out, InOut };
+
+// A connection domain (water, power, ...). Edges may only join ports of the
+// same relation. Colors are per color scheme.
+struct Relation {
+    QString id;
+    QString name;
+    QColor color;      // light scheme
+    QColor darkColor;  // dark / high-contrast schemes
+};
+
+struct PortSpec {
+    QString id;
+    QString relation;
+    PortDirection direction = PortDirection::InOut;
+    QPointF pos;              // relative [0..1] within the node rect
+    Side side = Side::Left;
+    int maxConnections = 1;   // 0 = unlimited
+};
+
+enum class PropertyType {
+    String,
+    Int,
+    Float,
+    Enum,
+    CatalogueItem,   // value: item id (QString)
+    CatalogueItems,  // value: item ids (QStringList)
+    Color,           // value: "#rrggbb" string; empty = automatic
+    ValueList,       // value: QStringList of free-form values
+};
+
+struct PropertySpec {
+    QString id;
+    QString name;
+    QString group;    // "General", "Presentation", "Physics", ...
+    PropertyType type = PropertyType::String;
+    QVariant defaultValue;
+    QString unit;
+    QStringList enumValues;
+    QString catalogueId;
+    double min = 0.0;
+    double max = 0.0;  // min == max means unbounded
+    bool readOnly = false;
+};
+
+struct NodeType {
+    QString id;
+    QString name;
+    QString group;    // palette group
+    QString svgPath;  // resource path of the vector image
+    QSizeF size{60, 60};
+    QList<PortSpec> ports;
+    QList<PropertySpec> properties;  // in addition to common node properties
+
+    const PortSpec* port(const QString& portId) const;
+};
+
+struct CatalogueItem {
+    QString id;
+    QString name;
+    QVariantMap attributes;  // e.g. {"diameter": 50, "material": "steel"}
+};
+
+struct Catalogue {
+    QString id;
+    QString name;
+    QList<CatalogueItem> items;
+
+    const CatalogueItem* item(const QString& itemId) const;
+};
+
+struct Node {
+    QUuid id;
+    QString typeId;
+    QPointF pos;  // scene coordinates of the node rect's top-left corner
+    QVariantMap props;
+};
+
+struct Edge {
+    QUuid id;
+    QUuid fromNode;
+    QString fromPort;
+    QUuid toNode;
+    QString toPort;
+    QString relation;
+    QVariantMap props;
+    double flowRate = 0.0;  // solver result; positive flows from -> to
+};
+
+// Unit vector pointing away from the node for a given side.
+QPointF sideVector(Side s);
+
+QString portDirectionToString(PortDirection d);
+PortDirection portDirectionFromString(const QString& s);
+QString sideToString(Side s);
+Side sideFromString(const QString& s);
+QString propertyTypeToString(PropertyType t);
+PropertyType propertyTypeFromString(const QString& s);
+
+}  // namespace diag
diff --git a/tests/CMakeLists.txt b/tests/CMakeLists.txt
new file mode 100644
index 0000000..449baa0
--- /dev/null
+++ b/tests/CMakeLists.txt
@@ -0,0 +1,10 @@
+# Test targets are added per module; all run offscreen via ctest.
+function(diag_add_test NAME)
+    add_executable(${NAME} ${NAME}.cpp)
+    target_link_libraries(${NAME} PRIVATE ${ARGN} Qt6::Test)
+    add_test(NAME ${NAME} COMMAND ${NAME})
+    set_tests_properties(${NAME} PROPERTIES ENVIRONMENT "QT_QPA_PLATFORM=offscreen")
+endfunction()
+
+diag_add_test(tst_model diagcore)
+diag_add_test(tst_properties diagcore)
diff --git a/tests/TestFixtures.h b/tests/TestFixtures.h
new file mode 100644
index 0000000..8497a26
--- /dev/null
+++ b/tests/TestFixtures.h
@@ -0,0 +1,135 @@
+#pragma once
+
+// Shared in-code registry fixture: a minimal water + power schema mirroring
+// the shape of the shipped JSON config, without resource dependencies.
+
+#include "core/TypeRegistry.h"
+
+namespace fixtures {
+
+inline diag::PropertySpec floatSpec(const QString& id, const QString& name, const QString& group,
+                                    double def, const QString& unit = {})
+{
+    diag::PropertySpec s;
+    s.id = id;
+    s.name = name;
+    s.group = group;
+    s.type = diag::PropertyType::Float;
+    s.defaultValue = def;
+    s.unit = unit;
+    return s;
+}
+
+inline diag::PortSpec port(const QString& id, const QString& relation, diag::PortDirection dir,
+                           QPointF pos, diag::Side side, int maxConnections = 1)
+{
+    diag::PortSpec p;
+    p.id = id;
+    p.relation = relation;
+    p.direction = dir;
+    p.pos = pos;
+    p.side = side;
+    p.maxConnections = maxConnections;
+    return p;
+}
+
+inline void fillRegistry(diag::TypeRegistry& reg)
+{
+    using namespace diag;
+    reg.clear();
+
+    reg.addRelation({QStringLiteral("water"), QStringLiteral("Water"), QColor("#1c78c0"),
+                     QColor("#4aa3e8")});
+    reg.addRelation({QStringLiteral("power"), QStringLiteral("Power"), QColor("#d99000"),
+                     QColor("#f0b429")});
+
+    Catalogue pipes;
+    pipes.id = QStringLiteral("pipe_series");
+    pipes.name = QStringLiteral("Pipe series");
+    pipes.items = {{QStringLiteral("dn50"), QStringLiteral("DN50 Steel"),
+                    {{QStringLiteral("diameter"), 50}}},
+                   {QStringLiteral("dn100"), QStringLiteral("DN100 Steel"),
+                    {{QStringLiteral("diameter"), 100}}}};
+    reg.addCatalogue(pipes);
+
+    QList<PropertySpec> waterEdge;
+    waterEdge << floatSpec(QStringLiteral("length"), QStringLiteral("Length"),
+                           QStringLiteral("Physics"), 10.0, QStringLiteral("m"));
+    waterEdge << floatSpec(QStringLiteral("diameter"), QStringLiteral("Diameter"),
+                           QStringLiteral("Physics"), 100.0, QStringLiteral("mm"));
+    PropertySpec flowType;
+    flowType.id = QStringLiteral("flowType");
+    flowType.name = QStringLiteral("Flow type");
+    flowType.group = QStringLiteral("Physics");
+    flowType.type = PropertyType::Enum;
+    flowType.enumValues = {QStringLiteral("Laminar"), QStringLiteral("Turbulent")};
+    flowType.defaultValue = QStringLiteral("Laminar");
+    waterEdge << flowType;
+    PropertySpec series;
+    series.id = QStringLiteral("series");
+    series.name = QStringLiteral("Pipe series");
+    series.group = QStringLiteral("Physics");
+    series.type = PropertyType::CatalogueItem;
+    series.catalogueId = QStringLiteral("pipe_series");
+    waterEdge << series;
+    reg.setEdgeProperties(QStringLiteral("water"), waterEdge);
+
+    NodeType source;
+    source.id = QStringLiteral("source");
+    source.name = QStringLiteral("Source");
+    source.group = QStringLiteral("Water");
+    source.size = {60, 60};
+    source.ports = {port(QStringLiteral("out"), QStringLiteral("water"), PortDirection::Out,
+                         {1.0, 0.5}, Side::Right, 0)};
+    source.properties = {floatSpec(QStringLiteral("supply"), QStringLiteral("Supply"),
+                                   QStringLiteral("Physics"), 10.0, QStringLiteral("m³/h"))};
+    reg.addNodeType(source);
+
+    NodeType pump;
+    pump.id = QStringLiteral("pump");
+    pump.name = QStringLiteral("Pump");
+    pump.group = QStringLiteral("Water");
+    pump.size = {60, 60};
+    pump.ports = {port(QStringLiteral("in"), QStringLiteral("water"), PortDirection::In,
+                       {0.0, 0.5}, Side::Left),
+                  port(QStringLiteral("out"), QStringLiteral("water"), PortDirection::Out,
+                       {1.0, 0.5}, Side::Right)};
+    reg.addNodeType(pump);
+
+    NodeType junction;
+    junction.id = QStringLiteral("junction");
+    junction.name = QStringLiteral("Junction");
+    junction.group = QStringLiteral("Water");
+    junction.size = {40, 40};
+    junction.ports = {port(QStringLiteral("w"), QStringLiteral("water"), PortDirection::InOut,
+                           {0.0, 0.5}, Side::Left, 0),
+                      port(QStringLiteral("e"), QStringLiteral("water"), PortDirection::InOut,
+                           {1.0, 0.5}, Side::Right, 0),
+                      port(QStringLiteral("n"), QStringLiteral("water"), PortDirection::InOut,
+                           {0.5, 0.0}, Side::Top, 0),
+                      port(QStringLiteral("s"), QStringLiteral("water"), PortDirection::InOut,
+                           {0.5, 1.0}, Side::Bottom, 0)};
+    reg.addNodeType(junction);
+
+    NodeType consumer;
+    consumer.id = QStringLiteral("consumer");
+    consumer.name = QStringLiteral("Consumer");
+    consumer.group = QStringLiteral("Water");
+    consumer.size = {60, 60};
+    consumer.ports = {port(QStringLiteral("in"), QStringLiteral("water"), PortDirection::In,
+                           {0.0, 0.5}, Side::Left)};
+    consumer.properties = {floatSpec(QStringLiteral("demand"), QStringLiteral("Demand"),
+                                     QStringLiteral("Physics"), 10.0, QStringLiteral("m³/h"))};
+    reg.addNodeType(consumer);
+
+    NodeType generator;
+    generator.id = QStringLiteral("generator");
+    generator.name = QStringLiteral("Generator");
+    generator.group = QStringLiteral("Power");
+    generator.size = {60, 60};
+    generator.ports = {port(QStringLiteral("out"), QStringLiteral("power"), PortDirection::Out,
+                            {1.0, 0.5}, Side::Right, 0)};
+    reg.addNodeType(generator);
+}
+
+}  // namespace fixtures
diff --git a/tests/tst_model.cpp b/tests/tst_model.cpp
new file mode 100644
index 0000000..9d14480
--- /dev/null
+++ b/tests/tst_model.cpp
@@ -0,0 +1,145 @@
+#include "TestFixtures.h"
+#include "core/NetworkModel.h"
+
+#include <QSignalSpy>
+#include <QTest>
+
+using namespace diag;
+
+class TestModel : public QObject {
+    Q_OBJECT
+private slots:
+    void init()
+    {
+        fixtures::fillRegistry(m_reg);
+        delete m_model;
+        m_model = new NetworkModel(&m_reg, this);
+    }
+
+    void addNode_unknownTypeFails()
+    {
+        QVERIFY(m_model->addNode(QStringLiteral("nope"), {0, 0}).isNull());
+        QCOMPARE(m_model->nodeIds().size(), 0);
+    }
+
+    void addNode_emitsAndStores()
+    {
+        QSignalSpy spy(m_model, &NetworkModel::nodeAdded);
+        const QUuid id = m_model->addNode(QStringLiteral("pump"), {100, 40});
+        QVERIFY(!id.isNull());
+        QCOMPARE(spy.count(), 1);
+        QCOMPARE(m_model->node(id)->pos, QPointF(100, 40));
+        QCOMPARE(m_model->nodeTypeOf(id)->id, QStringLiteral("pump"));
+    }
+
+    void connect_validOutToIn()
+    {
+        const QUuid src = m_model->addNode(QStringLiteral("source"), {0, 0});
+        const QUuid pump = m_model->addNode(QStringLiteral("pump"), {200, 0});
+        QVERIFY(m_model->canConnect(src, "out", pump, "in"));
+        const QUuid e = m_model->addEdge(src, "out", pump, "in");
+        QVERIFY(!e.isNull());
+        QCOMPARE(m_model->edge(e)->relation, QStringLiteral("water"));
+    }
+
+    void connect_directionNormalized()
+    {
+        // Dragging from the In port must still produce an Out->In edge.
+        const QUuid src = m_model->addNode(QStringLiteral("source"), {0, 0});
+        const QUuid pump = m_model->addNode(QStringLiteral("pump"), {200, 0});
+        const QUuid e = m_model->addEdge(pump, "in", src, "out");
+        QVERIFY(!e.isNull());
+        QCOMPARE(m_model->edge(e)->fromNode, src);
+        QCOMPARE(m_model->edge(e)->toNode, pump);
+    }
+
+    void connect_relationMismatchFails()
+    {
+        const QUuid gen = m_model->addNode(QStringLiteral("generator"), {0, 0});
+        const QUuid pump = m_model->addNode(QStringLiteral("pump"), {200, 0});
+        QString reason;
+        QVERIFY(!m_model->canConnect(gen, "out", pump, "in", &reason));
+        QVERIFY(reason.contains(QStringLiteral("relation")));
+        QVERIFY(m_model->addEdge(gen, "out", pump, "in").isNull());
+    }
+
+    void connect_twoInputsFails()
+    {
+        const QUuid a = m_model->addNode(QStringLiteral("pump"), {0, 0});
+        const QUuid b = m_model->addNode(QStringLiteral("consumer"), {200, 0});
+        QVERIFY(!m_model->canConnect(a, "in", b, "in"));
+    }
+
+    void connect_selfPortFails()
+    {
+        const QUuid j = m_model->addNode(QStringLiteral("junction"), {0, 0});
+        QVERIFY(!m_model->canConnect(j, "w", j, "w"));
+        // Different ports on the same node are allowed.
+        QVERIFY(m_model->canConnect(j, "w", j, "e"));
+    }
+
+    void connect_occupiedPortFails()
+    {
+        const QUuid src = m_model->addNode(QStringLiteral("source"), {0, 0});
+        const QUuid p1 = m_model->addNode(QStringLiteral("pump"), {200, 0});
+        const QUuid p2 = m_model->addNode(QStringLiteral("pump"), {200, 100});
+        QVERIFY(!m_model->addEdge(src, "out", p1, "in").isNull());
+        QString reason;
+        QVERIFY(!m_model->canConnect(p2, "out", p1, "in", &reason));
+        QVERIFY(reason.contains(QStringLiteral("occupied")));
+        // Source "out" is unlimited (maxConnections = 0).
+        QVERIFY(m_model->canConnect(src, "out", p2, "in"));
+    }
+
+    void connect_duplicateEdgeFails()
+    {
+        const QUuid src = m_model->addNode(QStringLiteral("source"), {0, 0});
+        const QUuid j = m_model->addNode(QStringLiteral("junction"), {200, 0});
+        QVERIFY(!m_model->addEdge(src, "out", j, "w").isNull());
+        QVERIFY(!m_model->canConnect(src, "out", j, "w"));
+        QVERIFY(!m_model->canConnect(j, "w", src, "out"));
+    }
+
+    void junction_allowsManyConnections()
+    {
+        const QUuid j = m_model->addNode(QStringLiteral("junction"), {0, 0});
+        const QUuid src = m_model->addNode(QStringLiteral("source"), {-200, 0});
+        const QUuid c1 = m_model->addNode(QStringLiteral("consumer"), {200, -100});
+        const QUuid c2 = m_model->addNode(QStringLiteral("consumer"), {200, 100});
+        QVERIFY(!m_model->addEdge(src, "out", j, "w").isNull());
+        QVERIFY(!m_model->addEdge(j, "e", c1, "in").isNull());
+        QVERIFY(!m_model->addEdge(j, "e", c2, "in").isNull());
+        QCOMPARE(m_model->connectionCount(j, "e"), 2);
+    }
+
+    void removeNode_cascadesEdges()
+    {
+        const QUuid src = m_model->addNode(QStringLiteral("source"), {0, 0});
+        const QUuid pump = m_model->addNode(QStringLiteral("pump"), {200, 0});
+        const QUuid c = m_model->addNode(QStringLiteral("consumer"), {400, 0});
+        m_model->addEdge(src, "out", pump, "in");
+        m_model->addEdge(pump, "out", c, "in");
+        QSignalSpy edgeSpy(m_model, &NetworkModel::edgeRemoved);
+        m_model->removeNode(pump);
+        QCOMPARE(edgeSpy.count(), 2);
+        QCOMPARE(m_model->edgeIds().size(), 0);
+        QCOMPARE(m_model->nodeIds().size(), 2);
+    }
+
+    void moveNode_emitsAndUpdatesPortPos()
+    {
+        const QUuid pump = m_model->addNode(QStringLiteral("pump"), {0, 0});
+        QSignalSpy spy(m_model, &NetworkModel::nodeMoved);
+        m_model->moveNode(pump, {100, 100});
+        QCOMPARE(spy.count(), 1);
+        // Port "out" is at relative (1.0, 0.5) of a 60x60 node.
+        QCOMPARE(m_model->portScenePos(pump, "out"), QPointF(160, 130));
+    }
+
+private:
+    TypeRegistry m_reg;
+    NetworkModel* m_model = nullptr;
+};
+
+QTEST_GUILESS_MAIN(TestModel)
+#include "tst_model.moc"
diff --git a/tests/tst_properties.cpp b/tests/tst_properties.cpp
new file mode 100644
index 0000000..2f5dff4
--- /dev/null
+++ b/tests/tst_properties.cpp
@@ -0,0 +1,134 @@
+#include "TestFixtures.h"
+#include "core/NetworkModel.h"
+
+#include <QJsonDocument>
+#include <QJsonObject>
+#include <QSignalSpy>
+#include <QTest>
+
+using namespace diag;
+
+class TestProperties : public QObject {
+    Q_OBJECT
+private slots:
+    void init()
+    {
+        fixtures::fillRegistry(m_reg);
+        delete m_model;
+        m_model = new NetworkModel(&m_reg, this);
+    }
+
+    void nodeProperty_fallsBackToDefault()
+    {
+        const QUuid src = m_model->addNode(QStringLiteral("source"), {0, 0});
+        QCOMPARE(m_model->nodeProperty(src, "supply").toDouble(), 10.0);
+        QCOMPARE(m_model->nodeProperty(src, "title").toString(), QString());
+        m_model->setNodeProperty(src, "supply", 42.5);
+        QCOMPARE(m_model->nodeProperty(src, "supply").toDouble(), 42.5);
+    }
+
+    void edgeProperty_commonAndRelationSpecs()
+    {
+        const QUuid src = m_model->addNode(QStringLiteral("source"), {0, 0});
+        const QUuid pump = m_model->addNode(QStringLiteral("pump"), {200, 0});
+        const QUuid e = m_model->addEdge(src, "out", pump, "in");
+
+        const auto specs = m_reg.edgeProperties(QStringLiteral("water"));
+        QStringList ids;
+        for (const auto& s : specs)
+            ids << s.id;
+        // Common presentation specs plus water physics specs.
+        for (const char* expected : {"title", "lineStyle", "lineWidth", "color",
+                                     "headDecoration", "tailDecoration", "length", "diameter",
+                                     "flowType", "series"})
+            QVERIFY2(ids.contains(QLatin1String(expected)), expected);
+
+        QCOMPARE(m_model->edgeProperty(e, "lineStyle").toString(), QStringLiteral("Solid"));
+        QCOMPARE(m_model->edgeProperty(e, "diameter").toDouble(), 100.0);
+        QCOMPARE(m_model->edgeProperty(e, "flowType").toString(), QStringLiteral("Laminar"));
+    }
+
+    void propertyGroups_present()
+    {
+        const auto specs = m_reg.edgeProperties(QStringLiteral("water"));
+        QStringList groups;
+        for (const auto& s : specs)
+            if (!groups.contains(s.group))
+                groups << s.group;
+        QVERIFY(groups.contains(QStringLiteral("General")));
+        QVERIFY(groups.contains(QStringLiteral("Presentation")));
+        QVERIFY(groups.contains(QStringLiteral("Physics")));
+    }
+
+    void allPropertyTypes_storeAndRead()
+    {
+        const QUuid src = m_model->addNode(QStringLiteral("source"), {0, 0});
+        const QUuid pump = m_model->addNode(QStringLiteral("pump"), {200, 0});
+        const QUuid e = m_model->addEdge(src, "out", pump, "in");
+
+        m_model->setNodeProperty(src, "title", QStringLiteral("Main intake"));   // String
+        m_model->setNodeProperty(src, "tags", QStringList{"district-1", "hp"});  // ValueList
+        m_model->setNodeProperty(src, "labelColor", QStringLiteral("#ff8800"));  // Color
+        m_model->setEdgeProperty(e, "length", 125.5);                            // Float
+        m_model->setEdgeProperty(e, "flowType", QStringLiteral("Turbulent"));    // Enum
+        m_model->setEdgeProperty(e, "series", QStringLiteral("dn50"));           // CatalogueItem
+
+        QCOMPARE(m_model->nodeProperty(src, "title").toString(), QStringLiteral("Main intake"));
+        QCOMPARE(m_model->nodeProperty(src, "tags").toStringList(),
+                 (QStringList{"district-1", "hp"}));
+        QCOMPARE(m_model->nodeProperty(src, "labelColor").toString(), QStringLiteral("#ff8800"));
+        QCOMPARE(m_model->edgeProperty(e, "length").toDouble(), 125.5);
+        QCOMPARE(m_model->edgeProperty(e, "flowType").toString(), QStringLiteral("Turbulent"));
+        QCOMPARE(m_model->edgeProperty(e, "series").toString(), QStringLiteral("dn50"));
+    }
+
+    void catalogue_lookup()
+    {
+        const Catalogue* c = m_reg.catalogue(QStringLiteral("pipe_series"));
+        QVERIFY(c);
+        QCOMPARE(c->items.size(), 2);
+        const CatalogueItem* dn50 = c->item(QStringLiteral("dn50"));
+        QVERIFY(dn50);
+        QCOMPARE(dn50->attributes.value(QStringLiteral("diameter")).toInt(), 50);
+        QVERIFY(!c->item(QStringLiteral("missing")));
+    }
+
+    void propertySpec_parsesFromJson()
+    {
+        const auto doc = QJsonDocument::fromJson(R"({
+            "id": "materials", "name": "Materials", "group": "Physics",
+            "type": "catalogueItems", "catalogue": "pipe_series",
+            "default": ["dn50"], "readOnly": false
+        })");
+        const PropertySpec s = propertySpecFromJson(doc.object());
+        QCOMPARE(s.type, PropertyType::CatalogueItems);
+        QCOMPARE(s.catalogueId, QStringLiteral("pipe_series"));
+        QCOMPARE(s.defaultValue.toStringList(), QStringList{"dn50"});
+
+        const auto doc2 = QJsonDocument::fromJson(R"({
+            "id": "mode", "type": "enum", "values": ["A", "B"], "default": "B",
+            "min": 1, "max": 5
+        })");
+        const PropertySpec s2 = propertySpecFromJson(doc2.object());
+        QCOMPARE(s2.enumValues, (QStringList{"A", "B"}));
+        QCOMPARE(s2.defaultValue.toString(), QStringLiteral("B"));
+        QCOMPARE(s2.min, 1.0);
+        QCOMPARE(s2.max, 5.0);
+    }
+
+    void propertyChange_emitsSignal()
+    {
+        const QUuid src = m_model->addNode(QStringLiteral("source"), {0, 0});
+        QSignalSpy spy(m_model, &NetworkModel::nodeChanged);
+        m_model->setNodeProperty(src, "title", QStringLiteral("A"));
+        m_model->setNodeProperty(src, "title", QStringLiteral("A"));  // no-op
+        QCOMPARE(spy.count(), 1);
+    }
+
+private:
+    TypeRegistry m_reg;
+    NetworkModel* m_model = nullptr;
+};
+
+QTEST_GUILESS_MAIN(TestProperties)
+#include "tst_properties.moc"