eclipse-syson · pcdavid · Apr 10, 2026
diff --git a/CHANGELOG.adoc b/CHANGELOG.adoc
@@ -90,6 +90,8 @@ Also use that same tool in the `interconnection` compartment.
 - https://github.com/eclipse-syson/syson/issues/2166[#2166] [diagrams] Reorganize tools to create `ExhibitStateUsage` graphical nodes, to ends up with two tools, one for parallel, one for non-parallel.
 Both tools optionally allow selecting an existing `StateUsage` to exhibit.
 - https://github.com/eclipse-syson/syson/issues/2179[#2179] [diagrams] Improve selection dialog by regrouping all standard libraries candidates under a "Libraries" category.
+- https://github.com/eclipse-syson/syson/issues/2116[#2116] [explorer] In the _Explorer_ view, the items corresponding to the internals of `Expression` elements (syntax tree) are now hidden by default.
+Disabling the _Hide expression internals_ filter in the _Explorer_ view allows to display them if needed.
 
 === New features
 

diff --git a/.../test/java/org/eclipse/syson/application/controller/explorer/view/SysONExplorerTests.java b/.../test/java/org/eclipse/syson/application/controller/explorer/view/SysONExplorerTests.java
@@ -47,6 +47,7 @@
 import org.eclipse.syson.application.controller.explorer.testers.TreeItemContextMenuTester;
 import org.eclipse.syson.application.controller.explorer.testers.TreePathTester;
 import org.eclipse.syson.application.data.ActionTransitionUsagesProjectData;
+import org.eclipse.syson.application.data.ExpressionSamplesProjectData;
 import org.eclipse.syson.application.data.GeneralViewEmptyTestProjectData;
 import org.eclipse.syson.application.data.ProjectWithLibraryDependencyContainingCommentAndLibraryPackageTestProjectData;
 import org.eclipse.syson.application.data.ProjectWithLibraryDependencyContainingLibraryPackageTestProjectData;
@@ -871,4 +872,128 @@ public void sysONExplorerTreeExpressionLabelTest() {
                 .thenCancel()
                 .verify(Duration.ofSeconds(10));
     }
+
+    @DisplayName("GIVEN the SysON Explorer, WHEN displaying an Expression item, THEN its internal details are hidden by default")
+    @GivenSysONServer({ ExpressionSamplesProjectData.SCRIPT_PATH })
+    @Test
+    public void sysONExplorerHidesExpressionInternalsByDefault() {
+        List<String> defaultFilters = this.explorerDefaultFiltersSearchService.findTreeDefaultFilterIds(ExpressionSamplesProjectData.EDITING_CONTEXT_ID, this.sysONExplorerTreeDescriptionId);
+
+        var expandedItemIds = List.of(
+                ExpressionSamplesProjectData.SemanticIds.EXPRESSIONS_DOCUMENT_ID,
+                ExpressionSamplesProjectData.SemanticIds.EXPRESSIONS_PACKAGE_ID,
+                ExpressionSamplesProjectData.SemanticIds.TANK_ID,
+                ExpressionSamplesProjectData.SemanticIds.TANK_MAX_VOLUME_ATTRIBUTE_ID,
+                ExpressionSamplesProjectData.SemanticIds.TANK_MAX_VOLUME_ATTRIBUTE_VALUE_ID,
+                ExpressionSamplesProjectData.SemanticIds.TANK_PRESSURE_LIMIT_CONSTRAINT_ID,
+                ExpressionSamplesProjectData.SemanticIds.TANK_PRESSURE_LIMIT_CONSTRAINT_VALUE_ID);
+
+        var explorerRepresentationId = this.representationIdBuilder.buildExplorerRepresentationId(this.sysONExplorerTreeDescriptionId, expandedItemIds, defaultFilters);
+        var input = new ExplorerEventInput(UUID.randomUUID(), ExpressionSamplesProjectData.EDITING_CONTEXT_ID, explorerRepresentationId);
+        var flux = this.explorerEventSubscriptionRunner.run(input).flux();
+        TestTransaction.flagForCommit();
+        TestTransaction.end();
+
+        var treeId = new AtomicReference<String>();
+        Consumer<Object> initialTreeContentConsumer = assertRefreshedTreeThat(tree -> {
+            assertThat(tree).isNotNull();
+            treeId.set(tree.getId());
+            assertThat(tree.getChildren()).hasSize(2);
+            var documentItem = tree.getChildren().get(0);
+            assertThat(documentItem.getChildren()).hasSize(1);
+            assertThat(documentItem.getLabel().toString()).isEqualTo("expressions.sysml");
+            var packageItem = documentItem.getChildren().get(0);
+            assertThat(packageItem.getLabel().toString()).isEqualTo("Expressions");
+
+            assertThat(packageItem.getChildren()).hasSize(7);
+
+            var tankItem = this.getChildByLabel(packageItem, "Tank");
+            assertThat(tankItem).isPresent();
+
+            var maxVolumeAttribute = this.getChildByLabel(tankItem.get(), "maxVolume");
+            assertThat(maxVolumeAttribute).isPresent();
+            assertThat(maxVolumeAttribute.get().getChildren()).hasSize(2);
+            var maxVolumeAttributeValueItem = maxVolumeAttribute.get().getChildren().get(0);
+            assertThat(maxVolumeAttributeValueItem.getLabel().toString()).isEqualTo("100.0 * minVolume");
+            assertThat(maxVolumeAttributeValueItem.getChildren()).isEmpty(); // Details filtered out by default
+
+            var pressureLimitAttribute = this.getChildByLabel(tankItem.get(), "pressureLimit");
+            assertThat(pressureLimitAttribute).isPresent();
+            assertThat(pressureLimitAttribute.get().getChildren()).hasSize(1);
+            var pressureLimitAttributeValueItem = pressureLimitAttribute.get().getChildren().get(0);
+            assertThat(pressureLimitAttributeValueItem.getLabel().toString()).isEqualTo("pressure <= maxPressure");
+            assertThat(pressureLimitAttributeValueItem.getChildren()).isEmpty(); // Details filtered out by default
+
+        });
+
+        StepVerifier.create(flux)
+                .consumeNextWith(initialTreeContentConsumer)
+                .thenCancel()
+                .verify(Duration.ofSeconds(10));
+    }
+
+    @DisplayName("GIVEN the SysON Explorer, WHEN displaying an Expression item, THEN its internal details can be revealed by disabling the corresponding filter")
+    @GivenSysONServer({ ExpressionSamplesProjectData.SCRIPT_PATH })
+    @Test
+    public void sysONExplorerExpressionInternalsCanBeRevealed() {
+        List<String> defaultFilters = this.explorerDefaultFiltersSearchService.findTreeDefaultFilterIds(ExpressionSamplesProjectData.EDITING_CONTEXT_ID, this.sysONExplorerTreeDescriptionId);
+        // Keep all defaults but HIDE_EXPRESSION_INTERNALS_ID
+        List<String> activeFilters = defaultFilters.stream().filter(filterId -> !SysONTreeFilterConstants.HIDE_EXPRESSION_INTERNALS_ID.equals(filterId)).toList();
+
+        var expandedItemIds = List.of(
+                ExpressionSamplesProjectData.SemanticIds.EXPRESSIONS_DOCUMENT_ID,
+                ExpressionSamplesProjectData.SemanticIds.EXPRESSIONS_PACKAGE_ID,
+                ExpressionSamplesProjectData.SemanticIds.TANK_ID,
+                ExpressionSamplesProjectData.SemanticIds.TANK_MAX_VOLUME_ATTRIBUTE_ID,
+                ExpressionSamplesProjectData.SemanticIds.TANK_MAX_VOLUME_ATTRIBUTE_VALUE_ID,
+                ExpressionSamplesProjectData.SemanticIds.TANK_PRESSURE_LIMIT_CONSTRAINT_ID,
+                ExpressionSamplesProjectData.SemanticIds.TANK_PRESSURE_LIMIT_CONSTRAINT_VALUE_ID);
+
+        var explorerRepresentationId = this.representationIdBuilder.buildExplorerRepresentationId(this.sysONExplorerTreeDescriptionId, expandedItemIds, activeFilters);
+        var input = new ExplorerEventInput(UUID.randomUUID(), ExpressionSamplesProjectData.EDITING_CONTEXT_ID, explorerRepresentationId);
+        var flux = this.explorerEventSubscriptionRunner.run(input).flux();
+        TestTransaction.flagForCommit();
+        TestTransaction.end();
+
+        var treeId = new AtomicReference<String>();
+        Consumer<Object> initialTreeContentConsumer = assertRefreshedTreeThat(tree -> {
+            assertThat(tree).isNotNull();
+            treeId.set(tree.getId());
+            assertThat(tree.getChildren()).hasSize(2);
+            var documentItem = tree.getChildren().get(0);
+            assertThat(documentItem.getChildren()).hasSize(1);
+            assertThat(documentItem.getLabel().toString()).isEqualTo("expressions.sysml");
+            var packageItem = documentItem.getChildren().get(0);
+            assertThat(packageItem.getLabel().toString()).isEqualTo("Expressions");
+
+            assertThat(packageItem.getChildren()).hasSize(7);
+
+            var tankItem = this.getChildByLabel(packageItem, "Tank");
+            assertThat(tankItem).isPresent();
+
+            var maxVolumeAttribute = this.getChildByLabel(tankItem.get(), "maxVolume");
+            assertThat(maxVolumeAttribute).isPresent();
+            assertThat(maxVolumeAttribute.get().getChildren()).hasSize(2);
+            var maxVolumeAttributeValueItem = maxVolumeAttribute.get().getChildren().get(0);
+            assertThat(maxVolumeAttributeValueItem.getLabel().toString()).isEqualTo("100.0 * minVolume");
+            assertThat(maxVolumeAttributeValueItem.getChildren()).hasSize(2); // Details visible
+
+            var pressureLimitAttribute = this.getChildByLabel(tankItem.get(), "pressureLimit");
+            assertThat(pressureLimitAttribute).isPresent();
+            assertThat(pressureLimitAttribute.get().getChildren()).hasSize(1);
+            var pressureLimitAttributeValueItem = pressureLimitAttribute.get().getChildren().get(0);
+            assertThat(pressureLimitAttributeValueItem.getLabel().toString()).isEqualTo("pressure <= maxPressure");
+            assertThat(pressureLimitAttributeValueItem.getChildren()).hasSize(2); // Details visible
+
+        });
+
+        StepVerifier.create(flux)
+                .consumeNextWith(initialTreeContentConsumer)
+                .thenCancel()
+                .verify(Duration.ofSeconds(10));
+    }
+
+    private Optional<TreeItem> getChildByLabel(TreeItem parent, String label) {
+        return parent.getChildren().stream().filter(child -> child.getLabel().toString().equals(label)).findFirst();
+    }
 }
diff --git a/...e/syson/application/controllers/explorer/view/ExplorerViewControllerIntegrationTests.java b/...e/syson/application/controllers/explorer/view/ExplorerViewControllerIntegrationTests.java
@@ -399,7 +399,8 @@ public void testSysONFiltersOnSysONExplorer() {
                 SysONTreeFilterConstants.HIDE_SYSML_STANDARD_LIBRARIES_TREE_FILTER_ID,
                 SysONTreeFilterConstants.HIDE_USER_LIBRARIES_TREE_FILTER_ID,
                 SysONTreeFilterConstants.HIDE_ROOT_NAMESPACES_ID,
-                SysONTreeFilterConstants.HIDE_EXPOSE_ELEMENTS_TREE_ITEM_FILTER_ID);
+                SysONTreeFilterConstants.HIDE_EXPOSE_ELEMENTS_TREE_ITEM_FILTER_ID,
+                SysONTreeFilterConstants.HIDE_EXPRESSION_INTERNALS_ID);
     }
 
     @DisplayName("GIVEN the Sirius Explorer View, WHEN querying the filters, THEN no syson filters are returned")

diff --git a/...cation/src/test/java/org/eclipse/syson/application/data/ExpressionSamplesProjectData.java b/...cation/src/test/java/org/eclipse/syson/application/data/ExpressionSamplesProjectData.java
@@ -0,0 +1,44 @@
+/*******************************************************************************
+ * Copyright (c) 2026 Obeo.
+ * This program and the accompanying materials
+ * are made available under the terms of the Eclipse Public License v2.0
+ * which accompanies this distribution, and is available at
+ * https://www.eclipse.org/legal/epl-2.0/
+ *
+ * SPDX-License-Identifier: EPL-2.0
+ *
+ * Contributors:
+ *     Obeo - initial API and implementation
+ *******************************************************************************/
+package org.eclipse.syson.application.data;
+
+/**
+ * Ids for project "Expression-Samples".
+ *
+ * @author pcdavid
+ */
+public class ExpressionSamplesProjectData {
+    public static final String EDITING_CONTEXT_ID = "aac82b89-8d53-4b16-91b4-deccc180ba62";
+
+    public static final String SCRIPT_PATH = "/scripts/database-content/ExpressionSamples.sql";
+
+    /**
+     * Ids of the semantic elements.
+     */
+    public static final class SemanticIds {
+        public static final String EXPRESSIONS_DOCUMENT_ID = "ef3e6929-0415-4295-b42f-64bed8bd4f55";
+
+        public static final String EXPRESSIONS_PACKAGE_ID = "baf5ea6a-7861-4b92-8be2-3fe7a2ebc415";
+
+        public static final String TANK_ID = "2bde22f7-a834-4afa-84bf-1bae1bb434d8";
+
+        public static final String TANK_MAX_VOLUME_ATTRIBUTE_ID = "d9926727-7378-4177-a940-2fb6c1c89dce";
+
+        public static final String TANK_MAX_VOLUME_ATTRIBUTE_VALUE_ID = "a9216e54-f44c-4b1f-b262-13650324d325";
+
+        public static final String TANK_PRESSURE_LIMIT_CONSTRAINT_ID = "7d42ee06-3c27-4eaa-9438-344fc789906a";
+
+        public static final String TANK_PRESSURE_LIMIT_CONSTRAINT_VALUE_ID = "faa3b115-5b07-4ecf-9147-0d58ceffaf9c";
+
+    }
+}
diff --git a/...ation/syson-application/src/test/resources/scripts/database-content/ExpressionSamples.sql b/...ation/syson-application/src/test/resources/scripts/database-content/ExpressionSamples.sql
diff --git a/...rc/main/java/org/eclipse/syson/sysml/metamodel/services/MetamodelQueryElementService.java b/...rc/main/java/org/eclipse/syson/sysml/metamodel/services/MetamodelQueryElementService.java
@@ -19,6 +19,7 @@
 import java.util.function.Predicate;
 
 import org.eclipse.syson.sysml.ActorMembership;
+import org.eclipse.syson.sysml.BooleanExpression;
 import org.eclipse.syson.sysml.Connector;
 import org.eclipse.syson.sysml.Element;
 import org.eclipse.syson.sysml.Expression;
@@ -80,16 +81,41 @@ public boolean isStakeholder(Element element) {
     }
 
     /**
-     * Check if a given {@code element} is an {@link Expression} definition. We can not simply rely on whether the
-     * element is an instance of {@link Expression} as many types in SysMLv2 inherit from this type without being
-     * themselves an actual expressions.
+     * Check if a given {@link Element element} is an {@link Expression expression} definition. We can not simply rely
+     * on whether the element is an instance of {@link Expression expression} as many types in SysMLv2 inherit from this
+     * type without being themselves an actual expressions.
      *
      * @param element
      *            the element to test.
      * @return true if the element is an actual expression definition.
      */
     public boolean isExpressionDefinition(Element element) {
-        return element instanceof Expression && !(element instanceof Usage);
+        return element instanceof Expression && !(element instanceof Usage) && !(element instanceof BooleanExpression);
+    }
+
+    /**
+     * Check is a given {@link Element element} is a top-level {@link Expression expression}. In most cases, end-users
+     * are only interested with these and not the internal elements which are technically also expressions but represent
+     * parts of the overall expression.
+     *
+     * @param element
+     *            the element to test.
+     * @return true if the element is a top-level expression definition.
+     */
+    public boolean isTopLevelExpression(Element element) {
+        boolean result = false;
+        if (this.isExpressionDefinition(element)) {
+            result = true;
+            var ancestor = element.getOwner();
+            while (ancestor != null) {
+                if (this.isExpressionDefinition(ancestor)) {
+                    result = false;
+                    break;
+                }
+                ancestor = ancestor.getOwner();
+            }
+        }
+        return result;
     }
 
     /**

diff --git a/...se/syson/tree/explorer/filters/HideExpressionInternalsTreeItemAlteredContentProvider.java b/...se/syson/tree/explorer/filters/HideExpressionInternalsTreeItemAlteredContentProvider.java
@@ -0,0 +1,47 @@
+/*******************************************************************************
+ * Copyright (c) 2026 Obeo.
+ * This program and the accompanying materials
+ * are made available under the terms of the Eclipse Public License v2.0
+ * which accompanies this distribution, and is available at
+ * https://www.eclipse.org/legal/epl-2.0/
+ *
+ * SPDX-License-Identifier: EPL-2.0
+ *
+ * Contributors:
+ *     Obeo - initial API and implementation
+ *******************************************************************************/
+package org.eclipse.syson.tree.explorer.filters;
+
+import java.util.List;
+import java.util.Objects;
+
+import org.eclipse.sirius.components.representations.VariableManager;
+import org.eclipse.sirius.web.application.views.explorer.services.api.IExplorerTreeItemAlteredContentProvider;
+import org.eclipse.syson.tree.explorer.services.api.ISysONExplorerFilterService;
+import org.springframework.stereotype.Service;
+
+/**
+ * An implementation of {@link IExplorerTreeItemAlteredContentProvider} allowing to hide internal elements of
+ * expressions from Explorer tree.
+ *
+ * @author pcdavid
+ */
+@Service
+public class HideExpressionInternalsTreeItemAlteredContentProvider implements IExplorerTreeItemAlteredContentProvider {
+
+    private final ISysONExplorerFilterService filterService;
+
+    public HideExpressionInternalsTreeItemAlteredContentProvider(ISysONExplorerFilterService filterService) {
+        this.filterService = Objects.requireNonNull(filterService);
+    }
+
+    @Override
+    public boolean canHandle(Object object, List<String> activeFilterIds) {
+        return activeFilterIds.contains(SysONTreeFilterConstants.HIDE_EXPRESSION_INTERNALS_ID);
+    }
+
+    @Override
+    public List<Object> apply(List<Object> computedChildren, VariableManager variableManager) {
+        return this.filterService.hideExpressionInternals(computedChildren);
+    }
+}
diff --git a/...vices/src/main/java/org/eclipse/syson/tree/explorer/filters/SysONTreeFilterConstants.java b/...vices/src/main/java/org/eclipse/syson/tree/explorer/filters/SysONTreeFilterConstants.java
@@ -32,4 +32,6 @@ public class SysONTreeFilterConstants {
     public static final String HIDE_ROOT_NAMESPACES_ID = UUID.nameUUIDFromBytes("SysONTreeRootNamespacesFilter".getBytes()).toString();
 
     public static final String HIDE_EXPOSE_ELEMENTS_TREE_ITEM_FILTER_ID = UUID.nameUUIDFromBytes("SysONTreeExposeElementsFilter".getBytes()).toString();
+
+    public static final String HIDE_EXPRESSION_INTERNALS_ID = UUID.nameUUIDFromBytes("SysONTreeExpressionInternalsFilter".getBytes()).toString();
 }
diff --git a/...es/src/main/java/org/eclipse/syson/tree/explorer/services/SysONExplorerFilterService.java b/...es/src/main/java/org/eclipse/syson/tree/explorer/services/SysONExplorerFilterService.java
@@ -20,10 +20,12 @@
 import org.eclipse.sirius.components.core.api.IEditingContext;
 import org.eclipse.syson.services.UtilService;
 import org.eclipse.syson.services.api.ISysONResourceService;
+import org.eclipse.syson.sysml.Element;
 import org.eclipse.syson.sysml.Expose;
 import org.eclipse.syson.sysml.LibraryPackage;
 import org.eclipse.syson.sysml.Membership;
 import org.eclipse.syson.sysml.Namespace;
+import org.eclipse.syson.sysml.metamodel.services.MetamodelQueryElementService;
 import org.eclipse.syson.sysml.util.ElementUtil;
 import org.eclipse.syson.tree.explorer.filters.SysONTreeFilterConstants;
 import org.eclipse.syson.tree.explorer.services.api.ISysONExplorerFilterService;
@@ -41,8 +43,11 @@ public class SysONExplorerFilterService implements ISysONExplorerFilterService {
 
     private final ISysONResourceService sysONResourceService;
 
+    private final MetamodelQueryElementService metamodelQueryElementService;
+
     public SysONExplorerFilterService(final ISysONResourceService sysONResourceService) {
         this.sysONResourceService = Objects.requireNonNull(sysONResourceService);
+        this.metamodelQueryElementService = new MetamodelQueryElementService();
     }
 
     @Override
@@ -127,6 +132,17 @@ public List<Object> hideExposeElements(List<Object> elements) {
                 .toList();
     }
 
+    @Override
+    public List<Object> hideExpressionInternals(List<Object> elements) {
+        return elements.stream().filter(e -> {
+            boolean isExpressionInternalElement = false;
+            if (e instanceof Element element && !this.metamodelQueryElementService.isTopLevelExpression(element)) {
+                isExpressionInternalElement = element.getOwner() != null && this.metamodelQueryElementService.isTopLevelExpression(element.getOwner());
+            }
+            return !isExpressionInternalElement;
+        }).toList();
+    }
+
     @Override
     public List<Object> applyFilters(IEditingContext editingContext, List<?> elements, List<String> activeFilterIds) {
         List<Object> alteredElements = new ArrayList<>(elements);
@@ -148,6 +164,9 @@ public List<Object> applyFilters(IEditingContext editingContext, List<?> element
         if (activeFilterIds.contains(SysONTreeFilterConstants.HIDE_EXPOSE_ELEMENTS_TREE_ITEM_FILTER_ID)) {
             alteredElements = this.hideExposeElements(alteredElements);
         }
+        if (activeFilterIds.contains(SysONTreeFilterConstants.HIDE_EXPRESSION_INTERNALS_ID)) {
+            alteredElements = this.hideExpressionInternals(alteredElements);
+        }
         return alteredElements;
     }
 

diff --git a/...c/main/java/org/eclipse/syson/tree/explorer/services/api/ISysONExplorerFilterService.java b/...c/main/java/org/eclipse/syson/tree/explorer/services/api/ISysONExplorerFilterService.java
@@ -1,5 +1,5 @@
 /*******************************************************************************
- * Copyright (c) 2024, 2025 Obeo.
+ * Copyright (c) 2024, 2026 Obeo.
  * This program and the accompanying materials
  * are made available under the terms of the Eclipse Public License v2.0
  * which accompanies this distribution, and is available at
@@ -41,6 +41,8 @@ public interface ISysONExplorerFilterService {
 
     List<Object> hideExposeElements(List<Object> elements);
 
+    List<Object> hideExpressionInternals(List<Object> elements);
+
     List<Object> applyFilters(IEditingContext editingContext, List<?> elements, List<String> activeFilterIds);
 
 }