[MNG-8537] Keep Maven Namespace the same

api/maven-api-model/src/main/mdo/maven.mdo

@@ -45,7 +45,7 @@
 -->
 <model xmlns="http://codehaus-plexus.github.io/MODELLO/2.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
   xsi:schemaLocation="http://codehaus-plexus.github.io/MODELLO/2.0.0 https://codehaus-plexus.github.io/modello/xsd/modello-2.0.0.xsd"
-  xml.namespace="http://maven.apache.org/POM/${version}"
+  xml.namespace="http://maven.apache.org/POM/4.0.0"
   xml.schemaLocation="https://maven.apache.org/xsd/maven-${version}.xsd">
   <id>maven</id>
   <name>Maven</name>

compat/maven-model-builder/src/main/resources/org/apache/maven/model/pom-4.1.0.xml

@@ -20,9 +20,9 @@ under the License.
 -->
 
 <!-- START SNIPPET: superpom -->
-<project xmlns="http://maven.apache.org/POM/4.1.0"
+<project xmlns="http://maven.apache.org/POM/4.0.0"
          xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
-         xsi:schemaLocation="http://maven.apache.org/POM/4.1.0 https://maven.apache.org/xsd/maven-4.1.0.xsd">
+         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.1.0.xsd">
   <modelVersion>4.1.0</modelVersion>
 
   <properties>

compat/maven-model-builder/src/main/resources/org/apache/maven/model/pom-4.2.0.xml

@@ -20,9 +20,9 @@ under the License.
 -->
 
 <!-- START SNIPPET: superpom -->
-<project xmlns="http://maven.apache.org/POM/4.2.0"
+<project xmlns="http://maven.apache.org/POM/4.0.0"
          xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
-         xsi:schemaLocation="http://maven.apache.org/POM/4.2.0 https://maven.apache.org/xsd/maven-4.2.0.xsd">
+         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.2.0.xsd">
   <modelVersion>4.2.0</modelVersion>
 
   <properties>

impl/maven-cli/src/main/java/org/apache/maven/cling/invoker/mvnup/goals/ModelUpgradeStrategy.java

@@ -28,6 +28,7 @@
 import eu.maveniverse.domtrip.Editor;
 import eu.maveniverse.domtrip.Element;
 import eu.maveniverse.domtrip.maven.MavenPomElements;
+import eu.maveniverse.domtrip.maven.MavenPomElements.Namespaces;
 import org.apache.maven.api.Lifecycle;
 import org.apache.maven.api.cli.mvnup.UpgradeOptions;
 import org.apache.maven.api.di.Named;
@@ -49,13 +50,11 @@
 import static eu.maveniverse.domtrip.maven.MavenPomElements.Elements.SUBPROJECTS;
 import static eu.maveniverse.domtrip.maven.MavenPomElements.ModelVersions.MODEL_VERSION_4_0_0;
 import static eu.maveniverse.domtrip.maven.MavenPomElements.ModelVersions.MODEL_VERSION_4_1_0;
-import static eu.maveniverse.domtrip.maven.MavenPomElements.Namespaces.MAVEN_4_0_0_NAMESPACE;
-import static eu.maveniverse.domtrip.maven.MavenPomElements.Namespaces.MAVEN_4_1_0_NAMESPACE;
 import static org.apache.maven.cling.invoker.mvnup.goals.ModelVersionUtils.getSchemaLocationForModelVersion;
 
 /**
  * Strategy for upgrading Maven model versions (e.g., 4.0.0 → 4.1.0).
- * Handles namespace updates, schema location changes, and element conversions.
+ * Handles schema location changes and element conversions.
  */
 @Named
 @Singleton
@@ -181,7 +180,7 @@ private void upgradeNamespaceAndSchemaLocation(Editor editor, UpgradeContext con
         }
 
         // Update namespace based on target model version
-        String targetNamespace = getNamespaceForModelVersion(targetModelVersion);
+        String targetNamespace = Namespaces.MAVEN_4_0_0_NAMESPACE;
 
         // Use element's attribute method to set the namespace declaration
         // This modifies the element in place and marks it as modified
@@ -264,19 +263,6 @@ private String determineTargetModelVersion(UpgradeContext context) {
         }
     }
 
-    /**
-     * Gets the namespace URI for a model version.
-     */
-    private String getNamespaceForModelVersion(String modelVersion) {
-        if (MavenPomElements.ModelVersions.MODEL_VERSION_4_2_0.equals(modelVersion)) {
-            return MavenPomElements.Namespaces.MAVEN_4_2_0_NAMESPACE;
-        } else if (MODEL_VERSION_4_1_0.equals(modelVersion)) {
-            return MAVEN_4_1_0_NAMESPACE;
-        } else {
-            return MAVEN_4_0_0_NAMESPACE;
-        }
-    }
-
     /**
      * Upgrades deprecated Maven 3 phase names to Maven 4 equivalents.
      * This replaces pre-/post- phases with before:/after: phases.

impl/maven-cli/src/main/java/org/apache/maven/cling/invoker/mvnup/goals/ModelVersionUtils.java

@@ -26,12 +26,6 @@
 import static eu.maveniverse.domtrip.maven.MavenPomElements.ModelVersions.MODEL_VERSION_4_0_0;
 import static eu.maveniverse.domtrip.maven.MavenPomElements.ModelVersions.MODEL_VERSION_4_1_0;
 import static eu.maveniverse.domtrip.maven.MavenPomElements.ModelVersions.MODEL_VERSION_4_2_0;
-import static eu.maveniverse.domtrip.maven.MavenPomElements.Namespaces.MAVEN_4_0_0_NAMESPACE;
-import static eu.maveniverse.domtrip.maven.MavenPomElements.Namespaces.MAVEN_4_1_0_NAMESPACE;
-import static eu.maveniverse.domtrip.maven.MavenPomElements.Namespaces.MAVEN_4_2_0_NAMESPACE;
-import static eu.maveniverse.domtrip.maven.MavenPomElements.SchemaLocations.MAVEN_4_0_0_SCHEMA_LOCATION;
-import static eu.maveniverse.domtrip.maven.MavenPomElements.SchemaLocations.MAVEN_4_1_0_SCHEMA_LOCATION;
-import static eu.maveniverse.domtrip.maven.MavenPomElements.SchemaLocations.MAVEN_4_2_0_SCHEMA_LOCATION;
 
 /**
  * Utility class for handling Maven model version operations during upgrades.
@@ -47,7 +41,7 @@ private ModelVersionUtils() {
 
     /**
      * Detects the model version from a POM document.
-     * Uses both the modelVersion element and namespace URI for detection.
+     * Uses the modelVersion element for detection.
      *
      * @param pomDocument the POM document (domtrip Document)
      * @return the detected model version
@@ -68,16 +62,6 @@ public static String detectModelVersion(Document pomDocument) {
             }
         }
 
-        // Fallback to namespace URI detection
-        String namespaceUri = root.namespaceDeclaration(null);
-        if (MAVEN_4_2_0_NAMESPACE.equals(namespaceUri)) {
-            return MODEL_VERSION_4_2_0;
-        } else if (MAVEN_4_1_0_NAMESPACE.equals(namespaceUri)) {
-            return MODEL_VERSION_4_1_0;
-        } else if (MAVEN_4_0_0_NAMESPACE.equals(namespaceUri)) {
-            return MODEL_VERSION_4_0_0;
-        }
-
         // Default fallback
         return MODEL_VERSION_4_0_0;
     }
@@ -239,20 +223,20 @@ public static boolean removeModelVersion(Document document) {
     }
 
     /**
-     * Gets the schema location for a model version.
+     * Gets the xsi:schemaLocation attribute value for a model version.
      *
      * @param modelVersion the model version
      * @return the schema location
      */
     public static String getSchemaLocationForModelVersion(String modelVersion) {
         if (MODEL_VERSION_4_2_0.equals(modelVersion)) {
-            return MAVEN_4_2_0_SCHEMA_LOCATION;
+            return "http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.2.0.xsd";
         } else if (MODEL_VERSION_4_1_0.equals(modelVersion)) {
-            return MAVEN_4_1_0_SCHEMA_LOCATION;
+            return "http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.1.0.xsd";
         } else if (isNewerThan410(modelVersion)) {
             // For versions newer than 4.1.0 but not specifically 4.2.0, use 4.2.0 schema
-            return MAVEN_4_2_0_SCHEMA_LOCATION;
+            return "http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.2.0.xsd";
         }
-        return MAVEN_4_0_0_SCHEMA_LOCATION;
+        return "http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd";
     }
 }

impl/maven-cli/src/main/java/org/apache/maven/cling/invoker/mvnup/goals/UpgradeConstants.java

@@ -0,0 +1,234 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+package org.apache.maven.cling.invoker.mvnup.goals;
+
+/**
+ * Constants used throughout the Maven upgrade tools.
+ * Organized into logical groups for better maintainability.
+ */
+public final class UpgradeConstants {
+
+    private UpgradeConstants() {
+        // Utility class
+    }
+
+    /**
+     * Maven model version constants.
+     */
+    public static final class ModelVersions {
+        /** Maven 4.0.0 model version */
+        public static final String MODEL_VERSION_4_0_0 = "4.0.0";
+
+        /** Maven 4.1.0 model version */
+        public static final String MODEL_VERSION_4_1_0 = "4.1.0";
+
+        private ModelVersions() {
+            // Utility class
+        }
+    }
+
+    /**
+     * Common XML element names used in Maven POMs.
+     */
+    public static final class XmlElements {
+        // Core POM elements
+        public static final String MODEL_VERSION = "modelVersion";
+        public static final String GROUP_ID = "groupId";
+        public static final String ARTIFACT_ID = "artifactId";
+        public static final String VERSION = "version";
+        public static final String PARENT = "parent";
+        public static final String RELATIVE_PATH = "relativePath";
+        public static final String PACKAGING = "packaging";
+        public static final String NAME = "name";
+        public static final String DESCRIPTION = "description";
+        public static final String URL = "url";
+
+        // Build elements
+        public static final String BUILD = "build";
+        public static final String PLUGINS = "plugins";
+        public static final String PLUGIN = "plugin";
+        public static final String PLUGIN_MANAGEMENT = "pluginManagement";
+        public static final String DEFAULT_GOAL = "defaultGoal";
+        public static final String DIRECTORY = "directory";
+        public static final String FINAL_NAME = "finalName";
+        public static final String SOURCE_DIRECTORY = "sourceDirectory";
+        public static final String SCRIPT_SOURCE_DIRECTORY = "scriptSourceDirectory";
+        public static final String TEST_SOURCE_DIRECTORY = "testSourceDirectory";
+        public static final String OUTPUT_DIRECTORY = "outputDirectory";
+        public static final String TEST_OUTPUT_DIRECTORY = "testOutputDirectory";
+        public static final String EXTENSIONS = "extensions";
+        public static final String EXECUTIONS = "executions";
+        public static final String GOALS = "goals";
+        public static final String INHERITED = "inherited";
+        public static final String CONFIGURATION = "configuration";
+
+        // Module elements
+        public static final String MODULES = "modules";
+        public static final String MODULE = "module";
+        public static final String SUBPROJECTS = "subprojects";
+        public static final String SUBPROJECT = "subproject";
+
+        // Dependency elements
+        public static final String DEPENDENCIES = "dependencies";
+        public static final String DEPENDENCY = "dependency";
+        public static final String DEPENDENCY_MANAGEMENT = "dependencyManagement";
+        public static final String CLASSIFIER = "classifier";
+        public static final String TYPE = "type";
+        public static final String SCOPE = "scope";
+        public static final String SYSTEM_PATH = "systemPath";
+        public static final String OPTIONAL = "optional";
+        public static final String EXCLUSIONS = "exclusions";
+
+        // Profile elements
+        public static final String PROFILES = "profiles";
+        public static final String PROFILE = "profile";
+
+        // Project information elements
+        public static final String PROPERTIES = "properties";
+        public static final String INCEPTION_YEAR = "inceptionYear";
+        public static final String ORGANIZATION = "organization";
+        public static final String LICENSES = "licenses";
+        public static final String DEVELOPERS = "developers";
+        public static final String CONTRIBUTORS = "contributors";
+        public static final String MAILING_LISTS = "mailingLists";
+        public static final String PREREQUISITES = "prerequisites";
+        public static final String SCM = "scm";
+        public static final String ISSUE_MANAGEMENT = "issueManagement";
+        public static final String CI_MANAGEMENT = "ciManagement";
+        public static final String DISTRIBUTION_MANAGEMENT = "distributionManagement";
+        public static final String REPOSITORIES = "repositories";
+        public static final String PLUGIN_REPOSITORIES = "pluginRepositories";
+        public static final String REPOSITORY = "repository";
+        public static final String PLUGIN_REPOSITORY = "pluginRepository";
+        public static final String REPORTING = "reporting";
+
+        private XmlElements() {
+            // Utility class
+        }
+    }
+
+    /**
+     * Common indentation patterns for XML formatting.
+     */
+    public static final class Indentation {
+        public static final String TWO_SPACES = "  ";
+        public static final String FOUR_SPACES = "    ";
+        public static final String TAB = "\t";
+        public static final String DEFAULT = TWO_SPACES;
+
+        private Indentation() {
+            // Utility class
+        }
+    }
+
+    /**
+     * Common Maven plugin constants.
+     */
+    public static final class Plugins {
+        /** Default Maven plugin groupId */
+        public static final String DEFAULT_MAVEN_PLUGIN_GROUP_ID = "org.apache.maven.plugins";
+
+        /** Maven plugin artifact prefix */
+        public static final String MAVEN_PLUGIN_PREFIX = "maven-";
+
+        /** Standard reason for Maven 4 compatibility upgrades */
+        public static final String MAVEN_4_COMPATIBILITY_REASON = "Maven 4 compatibility";
+
+        private Plugins() {
+            // Utility class
+        }
+    }
+
+    /**
+     * Common file and directory names.
+     */
+    public static final class Files {
+        /** Standard Maven POM file name */
+        public static final String POM_XML = "pom.xml";
+
+        /** Maven configuration directory (alternative name) */
+        public static final String MVN_DIRECTORY = ".mvn";
+
+        /** Default parent POM relative path */
+        public static final String DEFAULT_PARENT_RELATIVE_PATH = "../pom.xml";
+
+        private Files() {
+            // Utility class
+        }
+    }
+
+    /**
+     * Maven namespace constants.
+     */
+    public static final class Namespaces {
+        /** Maven namespace URI */
+        public static final String MAVEN_4_0_0_NAMESPACE = "http://maven.apache.org/POM/4.0.0";
+
+        /** Maven namespace URI */
+        public static final String MAVEN_4_1_0_NAMESPACE = "http://maven.apache.org/POM/4.0.0";
+
+        private Namespaces() {
+            // Utility class
+        }
+    }
+
+    /**
+     * Schema location constants.
+     */
+    public static final class SchemaLocations {
+        /** Schema location for 4.0.0 models */
+        public static final String MAVEN_4_0_0_SCHEMA_LOCATION =
+                Namespaces.MAVEN_4_0_0_NAMESPACE + " https://maven.apache.org/xsd/maven-4.0.0.xsd";
+
+        /** Schema location for 4.1.0 models */
+        public static final String MAVEN_4_1_0_SCHEMA_LOCATION =
+                Namespaces.MAVEN_4_1_0_NAMESPACE + " https://maven.apache.org/xsd/maven-4.1.0.xsd";
+
+        private SchemaLocations() {
+            // Utility class
+        }
+    }
+
+    /**
+     * XML attribute constants.
+     */
+    public static final class XmlAttributes {
+        /** Schema location attribute name */
+        public static final String SCHEMA_LOCATION = "schemaLocation";
+
+        /** XSI namespace prefix */
+        public static final String XSI_NAMESPACE_PREFIX = "xsi";
+
+        /** XSI namespace URI */
+        public static final String XSI_NAMESPACE_URI = "http://www.w3.org/2001/XMLSchema-instance";
+
+        // Combine attributes
+        public static final String COMBINE_CHILDREN = "combine.children";
+        public static final String COMBINE_SELF = "combine.self";
+
+        // Combine attribute values
+        public static final String COMBINE_OVERRIDE = "override";
+        public static final String COMBINE_MERGE = "merge";
+        public static final String COMBINE_APPEND = "append";
+
+        private XmlAttributes() {
+            // Utility class
+        }
+    }
+}