initial import, moved from whiteboard
diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..f7422e7
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1,9 @@
+.project
+.classpath
+.settings
+target
+bin
+*.iml
+.idea
+.DS_Store
+dependency-reduced-pom.xml
diff --git a/CODE_OF_CONDUCT.md b/CODE_OF_CONDUCT.md
new file mode 100644
index 0000000..0fa18e5
--- /dev/null
+++ b/CODE_OF_CONDUCT.md
@@ -0,0 +1,22 @@
+<!--/*~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+  ~ 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.
+  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~*/-->
+Apache Software Foundation Code of Conduct
+====
+
+Being an Apache project, Apache Sling adheres to the Apache Software Foundation's [Code of Conduct](https://www.apache.org/foundation/policies/conduct.html).
diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
new file mode 100644
index 0000000..ac82a1a
--- /dev/null
+++ b/CONTRIBUTING.md
@@ -0,0 +1,24 @@
+<!--/*~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+  ~ 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.
+  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~*/-->
+Contributing
+====
+
+Thanks for choosing to contribute!
+
+You will find all the necessary details about how you can do this at https://sling.apache.org/contributing.html.
diff --git a/Jenkinsfile b/Jenkinsfile
new file mode 100644
index 0000000..f582519
--- /dev/null
+++ b/Jenkinsfile
@@ -0,0 +1,20 @@
+/**
+ * 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.
+ */
+
+slingOsgiBundleBuild()
diff --git a/LICENSE b/LICENSE
new file mode 100644
index 0000000..261eeb9
--- /dev/null
+++ b/LICENSE
@@ -0,0 +1,201 @@
+                                 Apache License
+                           Version 2.0, January 2004
+                        http://www.apache.org/licenses/
+
+   TERMS AND CONDITIONS FOR USE, REPRODUCTION, AND DISTRIBUTION
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+   1. Definitions.
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+
+   Unless required by applicable law or agreed to in writing, software
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diff --git a/README.md b/README.md
new file mode 100644
index 0000000..a026988
--- /dev/null
+++ b/README.md
@@ -0,0 +1,60 @@
+[<img src="http://sling.apache.org/res/logos/sling.png"/>](http://sling.apache.org)
+
+# Apache Sling Feature Model diff tool
+
+This tool aims to provide to Apache Sling users an easy-to-use tool which is able to detect differences between different released version of the same Apache Sling Feature Model.
+
+## Simple APIs
+
+Given two different versions of the same `org.apache.sling.feature.Feature`, all we need to do is comparing them
+
+```java
+import static org.apache.sling.feature.diff.FeatureDiff.compareFeatures;
+
+import org.apache.sling.feature.Feature
+import org.apache.sling.feature.diff.DiffRequest;
+import org.apache.sling.feature.diff.DiffRequest;
+
+...
+
+Feature previous = // somehow obtained
+Feature current = // somehow obtained
+
+DiffRequest diffRequest = new DiffRequest()
+                          .setPrevious(previous)
+                          .setCurrent(current)
+                          .setResultId("org.apache.sling:org.apache.sling.diff:1.0.0");
+
+Feature featureDiff = compareFeatures(previous, current);
+```
+
+The resulting `featureDiff` is a new `Feature` instance which prototypes from `previous` and where necessary removals sections are populated and new elements may be added.
+
+###Please note
+
+The `FeatureDiff.compareFeatures(Feature, Feature)` rejects (aka throws an `IllegalArgumentException`) `Feature` inputs that:
+
+ * are `null` (bien sûr);
+ * refer exactly to the same `Feature`.
+
+## Excluding sections
+
+The `DiffRequest` data object can be configured in order to include/exclude one ore more Feature section(s), available are:
+
+ * `bundles`
+ * `configurations`
+ * `extensions`
+ * `framework-properties`
+
+Users can simply add via the include/exclude methods the section(s) they are interested:
+
+```java
+DiffRequest diffRequest = new DiffRequest()
+                          .setPrevious(previous)
+                          .setCurrent(current)
+                          .addIncludeComparator("bundles")
+                          .addIncludeComparator("configurations")
+                          .setResultId("org.apache.sling:org.apache.sling.diff:1.0.0");
+
+Feature featureDiff = compareFeatures(previous, current);
+```
diff --git a/pom.xml b/pom.xml
new file mode 100644
index 0000000..75800c2
--- /dev/null
+++ b/pom.xml
@@ -0,0 +1,106 @@
+<?xml version="1.0" encoding="ISO-8859-1"?>
+<!--
+ 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.
+-->
+<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/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+  <modelVersion>4.0.0</modelVersion>
+
+  <parent>
+    <groupId>org.apache.sling</groupId>
+    <artifactId>sling-bundle-parent</artifactId>
+    <version>35</version>
+    <relativePath />
+  </parent>
+
+  <artifactId>org.apache.sling.feature.diff</artifactId>
+  <version>1.0.0-SNAPSHOT</version>
+
+  <name>Apache Sling Feature Model diff tool</name>
+  <description>Feature Model diff tool for Apache Sling</description>
+
+  <properties>
+    <sling.java.version>8</sling.java.version>
+    <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
+    <bnd.baseline.skip>true</bnd.baseline.skip>
+  </properties>
+
+  <scm>
+    <connection>scm:git:https://gitbox.apache.org/repos/asf/sling-org-apache-sling-feature-diff.git</connection>
+    <developerConnection>scm:git:https://gitbox.apache.org/repos/asf/sling-org-apache-sling-feature-diff.git</developerConnection>
+    <url>https://gitbox.apache.org/repos/asf?p=sling-org-apache-sling-feature-diff.git</url>
+    <tag>HEAD</tag>
+  </scm>
+
+  <dependencies>
+    <!--
+     | utilities
+    -->
+    <dependency>
+      <groupId>com.google.auto.service</groupId>
+      <artifactId>auto-service</artifactId>
+      <version>1.0-rc5</version>
+      <scope>provided</scope>
+    </dependency>
+
+    <!--
+     | Sling Feature Model libraries
+    -->
+    <dependency>
+      <groupId>org.osgi</groupId>
+      <artifactId>osgi.core</artifactId>
+      <scope>provided</scope>
+    </dependency>
+    <dependency>
+      <groupId>org.osgi</groupId>
+      <artifactId>org.osgi.annotation.versioning</artifactId>
+      <scope>provided</scope>
+    </dependency>
+    <dependency>
+      <groupId>org.apache.sling</groupId>
+      <artifactId>org.apache.sling.feature</artifactId>
+      <version>1.0.4</version>
+      <scope>provided</scope>
+    </dependency>
+
+    <!--
+     | JSON patch
+    -->
+    <dependency>
+      <groupId>org.apache.geronimo.specs</groupId>
+      <artifactId>geronimo-json_1.0_spec</artifactId>
+      <version>1.0-alpha-1</version>
+      <scope>provided</scope>
+    </dependency>
+
+    <!--
+     | Test only dependencies
+    -->
+    <dependency>
+      <groupId>junit</groupId>
+      <artifactId>junit</artifactId>
+      <scope>test</scope>
+    </dependency>
+    <dependency>
+      <groupId>org.apache.johnzon</groupId>
+      <artifactId>johnzon-core</artifactId>
+      <version>1.0.0</version>
+      <scope>test</scope>
+    </dependency>
+  </dependencies>
+
+</project>
diff --git a/src/main/java/org/apache/sling/feature/diff/DiffRequest.java b/src/main/java/org/apache/sling/feature/diff/DiffRequest.java
new file mode 100644
index 0000000..772b986
--- /dev/null
+++ b/src/main/java/org/apache/sling/feature/diff/DiffRequest.java
@@ -0,0 +1,72 @@
+/*
+ * 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.sling.feature.diff;
+
+import static java.util.Objects.requireNonNull;
+
+import java.util.HashSet;
+import java.util.Set;
+
+import org.apache.sling.feature.Feature;
+
+public final class DiffRequest {
+
+    private final Set<String> includeComparators = new HashSet<>();
+
+    private final Set<String> excludeComparators = new HashSet<>();
+
+    private Feature previous;
+
+    private Feature current;
+
+    public Feature getPrevious() {
+        return previous;
+    }
+
+    public DiffRequest setPrevious(Feature previous) {
+        this.previous = requireNonNull(previous, "Impossible to compare null previous feature.");
+        return this;
+    }
+
+    public Feature getCurrent() {
+        return current;
+    }
+
+    public DiffRequest setCurrent(Feature current) {
+        this.current = requireNonNull(current, "Impossible to compare null current feature.");
+        return this;
+    }
+
+    public DiffRequest addIncludeComparator(String includeComparator) {
+        includeComparators.add(requireNonNull(includeComparator, "A null include comparator id is not valid"));
+        return this;
+    }
+
+    public Set<String> getIncludeComparators() {
+        return includeComparators;
+    }
+
+    public DiffRequest addExcludeComparator(String excludeComparator) {
+        excludeComparators.add(requireNonNull(excludeComparator, "A null exclude comparator id is not valid"));
+        return this;
+    }
+
+    public Set<String> getExcludeComparators() {
+        return excludeComparators;
+    }
+
+}
diff --git a/src/main/java/org/apache/sling/feature/diff/FeatureDiff.java b/src/main/java/org/apache/sling/feature/diff/FeatureDiff.java
new file mode 100644
index 0000000..f1ccb3b
--- /dev/null
+++ b/src/main/java/org/apache/sling/feature/diff/FeatureDiff.java
@@ -0,0 +1,92 @@
+/*
+ * 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.sling.feature.diff;
+
+import static java.util.Objects.requireNonNull;
+import static java.util.ServiceLoader.load;
+
+import java.util.Collection;
+import java.util.LinkedList;
+
+import org.apache.sling.feature.ArtifactId;
+import org.apache.sling.feature.Feature;
+import org.apache.sling.feature.Prototype;
+import org.apache.sling.feature.diff.impl.FeatureElementComparator;
+
+public final class FeatureDiff {
+
+    private static final String UPDATER_CLASSIFIER = "updater";
+
+    public static Feature compareFeatures(DiffRequest diffRequest) {
+        requireNonNull(diffRequest, "Impossible to compare features without specifying them.");
+        Feature previous = requireNonNull(diffRequest.getPrevious(), "Impossible to compare null previous feature.");
+        Feature current = requireNonNull(diffRequest.getCurrent(), "Impossible to compare null current feature.");
+
+        if (previous.getId().equals(current.getId())) {
+            throw new IllegalArgumentException("Input Features refer to the the same Feature version.");
+        }
+
+        StringBuilder classifier = new StringBuilder();
+        if (current.getId().getClassifier() != null && !current.getId().getClassifier().isEmpty()) {
+            classifier.append(current.getId().getClassifier())
+                      .append('_');
+        }
+        classifier.append(UPDATER_CLASSIFIER);
+
+        ArtifactId resultId = new ArtifactId(current.getId().getGroupId(),
+                                             current.getId().getArtifactId(), 
+                                             current.getId().getVersion(),
+                                             classifier.toString(),
+                                             current.getId().getType());
+
+        Feature target = new Feature(resultId);
+        target.setTitle(previous.getId() + " to " + current.getId());
+        target.setDescription("Computed " + previous.getId() + " to " + current.getId() + " Feature update");
+
+        Prototype prototype = new Prototype(previous.getId());
+        target.setPrototype(prototype);
+
+        for (FeatureElementComparator comparator : loadComparators(diffRequest)) {
+            comparator.computeDiff(previous, current, target);
+        }
+
+        return target;
+    }
+
+    protected static Iterable<FeatureElementComparator> loadComparators(DiffRequest diffRequest) {
+        Collection<FeatureElementComparator> filteredComparators = new LinkedList<>();
+
+        for (FeatureElementComparator comparator : load(FeatureElementComparator.class)) {
+            boolean included = !diffRequest.getIncludeComparators().isEmpty() ? diffRequest.getIncludeComparators().contains(comparator.getId()) : true;
+            boolean excluded = diffRequest.getExcludeComparators().contains(comparator.getId());
+
+            if (included && !excluded) {
+                filteredComparators.add(comparator);
+            }
+        }
+
+        return filteredComparators;
+    }
+
+    /**
+     * this class must not be instantiated directly
+     */
+    private FeatureDiff() {
+        // do nothing
+    }
+
+}
diff --git a/src/main/java/org/apache/sling/feature/diff/impl/AbstractFeatureElementComparator.java b/src/main/java/org/apache/sling/feature/diff/impl/AbstractFeatureElementComparator.java
new file mode 100644
index 0000000..33364f2
--- /dev/null
+++ b/src/main/java/org/apache/sling/feature/diff/impl/AbstractFeatureElementComparator.java
@@ -0,0 +1,37 @@
+/*
+ * 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.sling.feature.diff.impl;
+
+abstract class AbstractFeatureElementComparator implements FeatureElementComparator {
+
+    private final String id;
+
+    public AbstractFeatureElementComparator(String id) {
+        this.id = id;
+    }
+
+    @Override
+    public final String getId() {
+        return id;
+    }
+
+    @Override
+    public String toString() {
+        return "FeatureElementComparator [id=" + id + "]";
+    }
+
+}
diff --git a/src/main/java/org/apache/sling/feature/diff/impl/BundlesComparator.java b/src/main/java/org/apache/sling/feature/diff/impl/BundlesComparator.java
new file mode 100644
index 0000000..e225a11
--- /dev/null
+++ b/src/main/java/org/apache/sling/feature/diff/impl/BundlesComparator.java
@@ -0,0 +1,61 @@
+/*
+ * 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.sling.feature.diff.impl;
+
+import org.apache.sling.feature.Artifact;
+import org.apache.sling.feature.Artifacts;
+import org.apache.sling.feature.Feature;
+
+import com.google.auto.service.AutoService;
+
+@AutoService(FeatureElementComparator.class)
+public final class BundlesComparator extends AbstractFeatureElementComparator {
+
+    public BundlesComparator() {
+        super("bundles");
+    }
+
+    @Override
+    public void computeDiff(Feature previous, Feature current, Feature target) {
+        computeDiff(previous.getBundles(), current.getBundles(), target);
+    }
+
+    protected void computeDiff(Artifacts previouses, Artifacts currents, Feature target) {
+        for (Artifact previous : previouses) {
+            Artifact current = currents.getSame(previous.getId());
+
+            boolean add = false;
+
+            if (current == null || (add = !previous.getId().equals(current.getId()))) {
+                target.getPrototype().getBundleRemovals().add(previous.getId());
+            }
+
+            if (add) {
+                target.getBundles().add(current);
+            }
+        }
+
+        for (Artifact current : currents) {
+            Artifact previous = previouses.getSame(current.getId());
+
+            if (previous == null) {
+                target.getBundles().add(current);
+            }
+        }
+    }
+
+}
diff --git a/src/main/java/org/apache/sling/feature/diff/impl/ConfigurationsComparator.java b/src/main/java/org/apache/sling/feature/diff/impl/ConfigurationsComparator.java
new file mode 100644
index 0000000..e4190fc
--- /dev/null
+++ b/src/main/java/org/apache/sling/feature/diff/impl/ConfigurationsComparator.java
@@ -0,0 +1,195 @@
+/*
+ * 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.sling.feature.diff.impl;
+
+import static java.util.Objects.deepEquals;
+
+import java.util.Collection;
+import java.util.Dictionary;
+import java.util.Enumeration;
+import java.util.Map;
+import java.util.Map.Entry;
+import java.util.Objects;
+
+import org.apache.sling.feature.Configuration;
+import org.apache.sling.feature.Configurations;
+import org.apache.sling.feature.Feature;
+
+import com.google.auto.service.AutoService;
+
+@AutoService(FeatureElementComparator.class)
+public final class ConfigurationsComparator extends AbstractFeatureElementComparator {
+
+    public ConfigurationsComparator() {
+        super("configurations");
+    }
+
+    @Override
+    public void computeDiff(Feature previous, Feature current, Feature target) {
+        computeDiff(previous.getConfigurations(), current.getConfigurations(), target);
+    }
+
+    protected void computeDiff(Configurations previouses, Configurations currents, Feature target) {
+        for (Configuration previousConfiguration : previouses) {
+            Configuration currentConfiguration = currents.getConfiguration(previousConfiguration.getPid());
+
+            if (currentConfiguration == null) {
+                target.getPrototype().getConfigurationRemovals().add(previousConfiguration.getPid());
+            } else {
+                computeDiff(previousConfiguration, currentConfiguration, target);
+            }
+        }
+
+        for (Configuration currentConfiguration : currents) {
+            Configuration previousConfiguration = previouses.getConfiguration(currentConfiguration.getPid());
+
+            if (previousConfiguration == null) {
+                target.getConfigurations().add(currentConfiguration);
+            }
+        }
+    }
+
+    protected void computeDiff(Configuration previous, Configuration current, Feature target) {
+        Dictionary<String, Object> previousProperties = previous.getProperties();
+        Dictionary<String, Object> currentProperties = current.getProperties();
+
+        Configuration targetConfiguration = new Configuration(previous.getPid());
+        Dictionary<String, Object> targetProperties = targetConfiguration.getProperties();
+
+        Enumeration<String> previousKeys = previousProperties.keys();
+        while (previousKeys.hasMoreElements()) {
+            String previousKey = previousKeys.nextElement();
+
+            // no other way to check if a key was removed in a dictionary
+            if (hasKey(previousKey, currentProperties.keys())) {
+                Object previousValue = previousProperties.get(previousKey);
+                Object currentValue = currentProperties.get(previousKey);
+
+                if (!areEquals(previousValue, currentValue)) {
+                    targetProperties.put(previousKey, currentValue);
+                }
+            }
+        }
+
+        Enumeration<String> currentKeys = currentProperties.keys();
+        while (currentKeys.hasMoreElements()) {
+            String currentKey = currentKeys.nextElement();
+
+            Object previousValue = previousProperties.get(currentKey);
+            Object currentValue = currentProperties.get(currentKey);
+
+            if (previousValue == null && currentValue != null) {
+                targetProperties.put(currentKey, currentValue);
+            }
+        }
+
+        if (!targetProperties.isEmpty()) {
+            target.getConfigurations().add(targetConfiguration);
+        }
+    }
+
+    private static boolean areEquals(Object lhs, Object rhs) {
+        if (lhs == rhs) {
+            return true;
+        }
+
+        if (lhs == null ^ rhs == null) {
+            return false;
+        }
+
+        // Find the leaf class since there may be transients in the leaf
+        // class or in classes between the leaf and root.
+        // If we are not testing transients or a subclass has no ivars,
+        // then a subclass can test equals to a superclass.
+        final Class<?> lhsClass = lhs.getClass();
+        final Class<?> rhsClass = rhs.getClass();
+        Class<?> testClass;
+
+        if (lhsClass.isInstance(rhs)) {
+            testClass = lhsClass;
+            if (!rhsClass.isInstance(lhs)) {
+                // rhsClass is a subclass of lhsClass
+                testClass = rhsClass;
+            }
+        } else if (rhsClass.isInstance(lhs)) {
+            testClass = rhsClass;
+            if (!lhsClass.isInstance(rhs)) {
+                // lhsClass is a subclass of rhsClass
+                testClass = lhsClass;
+            }
+        } else {
+            // The two classes are not related.
+            return false;
+        }
+
+        if (testClass.isArray()) {
+            return deepEquals(lhs, rhs);
+        } else if (Collection.class.isAssignableFrom(testClass)) {
+            return areEquals((Collection<?>) lhs, (Collection<?>) rhs);
+        } else if (Map.class.isAssignableFrom(testClass)) {
+            return areEquals((Map<?, ?>) lhs, (Map<?, ?>) rhs);
+        }
+
+        return Objects.equals(lhs, rhs);
+    }
+
+    private static boolean areEquals(Collection<?> lhs, Collection<?> rhs) {
+        if (lhs.size() != rhs.size()) {
+            return false;
+        }
+
+        return deepEquals(lhs.toArray(), rhs.toArray());
+    }
+
+    private static boolean areEquals(Map<?, ?> lhs, Map<?, ?> rhs) {
+        for (Entry<?, ?> previousEntry : lhs.entrySet()) {
+            Object previousKey = previousEntry.getKey();
+
+            if (!rhs.containsKey(previousKey)) {
+                return false;
+            } else {
+                Object previousValue = previousEntry.getValue();
+                Object currentValue = rhs.get(previousKey);
+
+                if (!areEquals(previousValue, currentValue)) {
+                    return false;
+                }
+            }
+        }
+
+        for (Object currentKey : rhs.keySet()) {
+            if (!lhs.containsKey(currentKey)) {
+                return false;
+            }
+        }
+
+        return true;
+    }
+
+    private static boolean hasKey(String key, Enumeration<String> keys) {
+        while (keys.hasMoreElements()) {
+            String current = keys.nextElement();
+
+            if (key.equals(current)) {
+                return true;
+            }
+        }
+
+        return false;
+    }
+
+}
diff --git a/src/main/java/org/apache/sling/feature/diff/impl/ExtensionsComparator.java b/src/main/java/org/apache/sling/feature/diff/impl/ExtensionsComparator.java
new file mode 100644
index 0000000..b30cfe0
--- /dev/null
+++ b/src/main/java/org/apache/sling/feature/diff/impl/ExtensionsComparator.java
@@ -0,0 +1,145 @@
+/*
+ * 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.sling.feature.diff.impl;
+
+import static javax.json.Json.createReader;
+
+import java.io.StringReader;
+import java.util.LinkedList;
+
+import javax.json.JsonValue;
+
+import org.apache.sling.feature.Artifact;
+import org.apache.sling.feature.ArtifactId;
+import org.apache.sling.feature.Extension;
+import org.apache.sling.feature.Extensions;
+import org.apache.sling.feature.Feature;
+
+import com.google.auto.service.AutoService;
+
+@AutoService(FeatureElementComparator.class)
+public final class ExtensionsComparator extends AbstractFeatureElementComparator {
+
+    public ExtensionsComparator() {
+        super("extensions");
+    }
+
+    @Override
+    public void computeDiff(Feature previous, Feature current, Feature target) {
+        computeDiff(previous.getExtensions(), current.getExtensions(), target);
+    }
+
+    protected void computeDiff(Extensions previousExtensions, Extensions currentExtensions, Feature target) {
+        for (Extension previousExtension : previousExtensions) {
+            Extension currentExtension = currentExtensions.getByName(previousExtension.getName());
+
+            if (currentExtension == null) {
+                target.getPrototype().getExtensionRemovals().add(previousExtension.getName());
+            } else {
+                computeDiff(previousExtension, currentExtension, target);
+            }
+        }
+
+        for (Extension currentExtension : currentExtensions) {
+            Extension previousConfiguration = previousExtensions.getByName(currentExtension.getName());
+
+            if (previousConfiguration == null) {
+                target.getExtensions().add(currentExtension);
+            }
+        }
+    }
+
+    protected void computeDiff(Extension previousExtension, Extension currentExtension, Feature target) {
+        boolean replace = false;
+
+        switch (previousExtension.getType()) {
+            case ARTIFACTS:
+                Extension targetExtension = new Extension(previousExtension.getType(), previousExtension.getName(), previousExtension.isRequired());
+
+                for (Artifact previous : previousExtension.getArtifacts()) {
+                    Artifact current = currentExtension.getArtifacts().getSame(previous.getId());
+
+                    boolean add = false;
+
+                    if (current == null || (add = !previous.getId().equals(current.getId()))) {
+                        target.getPrototype().getArtifactExtensionRemovals()
+                                             .computeIfAbsent(previousExtension.getName(), k -> new LinkedList<ArtifactId>())
+                                             .add(previous.getId());
+                    }
+
+                    if (add) {
+                        targetExtension.getArtifacts().add(current);
+                    }
+                }
+
+                for (Artifact current : currentExtension.getArtifacts()) {
+                    Artifact previous = previousExtension.getArtifacts().getSame(current.getId());
+
+                    if (previous == null) {
+                        targetExtension.getArtifacts().add(current);
+                    }
+                }
+
+                if (!targetExtension.getArtifacts().isEmpty()) {
+                    target.getExtensions().add(targetExtension);
+                }
+
+                break;
+
+            case TEXT:
+                if (!previousExtension.getText().equals(currentExtension.getText())) {
+                    replace = true;
+                }
+                break;
+
+            case JSON:
+                String previousJSON = previousExtension.getJSON();
+                String currentJSON = currentExtension.getJSON();
+
+                try {
+                    JsonValue previousNode = parseJSON(previousJSON);
+                    JsonValue currentNode = parseJSON(currentJSON); 
+
+                    if (!previousNode.equals(currentNode)) {
+                        replace = true;
+                    }
+                } catch (Throwable t) {
+                    // should not happen
+                    throw new RuntimeException("A JSON parse error occurred while parsing previous '"
+                                               + previousJSON
+                                               + "' and current '"
+                                               + currentJSON
+                                               + "', see nested errors:", t);
+                }
+                break;
+
+            // it doesn't happen
+            default:
+                break;
+        }
+
+        if (replace) {
+            target.getPrototype().getExtensionRemovals().add(currentExtension.getName());
+            target.getExtensions().add(currentExtension);
+        }
+    }
+
+    private static JsonValue parseJSON(String json) {
+        return createReader(new StringReader(json)).read();
+    }
+
+}
diff --git a/src/main/java/org/apache/sling/feature/diff/impl/FeatureElementComparator.java b/src/main/java/org/apache/sling/feature/diff/impl/FeatureElementComparator.java
new file mode 100644
index 0000000..9b3c1cc
--- /dev/null
+++ b/src/main/java/org/apache/sling/feature/diff/impl/FeatureElementComparator.java
@@ -0,0 +1,43 @@
+/*
+ * 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.sling.feature.diff.impl;
+
+import org.apache.sling.feature.Feature;
+
+/**
+ * A simple service to compare a specific Feature section.
+ */
+public interface FeatureElementComparator {
+
+    /**
+     * Returns a short id which identifies the Feature section for which differences will be computed.
+     *
+     * @return a short id which identifies the Feature section for which differences will be computed.
+     */
+    String getId();
+
+    /**
+     * Compares a specific Feature sections between the previous and the current,
+     * reporting additions/updates/removals in the target.
+     *
+     * @param previous
+     * @param current
+     * @param target
+     */
+    public void computeDiff(Feature previous, Feature current, Feature target);
+
+}
diff --git a/src/main/java/org/apache/sling/feature/diff/impl/FrameworkPropertiesComparator.java b/src/main/java/org/apache/sling/feature/diff/impl/FrameworkPropertiesComparator.java
new file mode 100644
index 0000000..0dd5f4e
--- /dev/null
+++ b/src/main/java/org/apache/sling/feature/diff/impl/FrameworkPropertiesComparator.java
@@ -0,0 +1,63 @@
+/*
+ * 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.sling.feature.diff.impl;
+
+import java.util.Map;
+import java.util.Map.Entry;
+import java.util.Objects;
+
+import org.apache.sling.feature.Feature;
+
+import com.google.auto.service.AutoService;
+
+@AutoService(FeatureElementComparator.class)
+public final class FrameworkPropertiesComparator extends AbstractFeatureElementComparator {
+
+    public FrameworkPropertiesComparator() {
+        super("framework-properties");
+    }
+
+    @Override
+    public void computeDiff(Feature previous, Feature current, Feature target) {
+        computeDiff(previous.getFrameworkProperties(), current.getFrameworkProperties(), target);
+    }
+
+    public void computeDiff(Map<String, String> previous, Map<String, String> current, Feature target) {
+        for (Entry<String, String> previousEntry : previous.entrySet()) {
+            String previousKey = previousEntry.getKey();
+
+            if (!current.containsKey(previousKey)) {
+                target.getPrototype().getFrameworkPropertiesRemovals().add(previousKey);
+            } else {
+                String previousValue = previousEntry.getValue();
+                String currentValue = current.get(previousKey);
+
+                // override the previous set value
+                if (!Objects.equals(previousValue, currentValue)) {
+                    target.getFrameworkProperties().put(previousKey, currentValue);
+                }
+            }
+        }
+
+        for (Entry<String, String> currentEntry : current.entrySet()) {
+            if (!previous.containsKey(currentEntry.getKey())) {
+                target.getFrameworkProperties().put(currentEntry.getKey(), currentEntry.getValue());
+            }
+        }
+    }
+
+}
diff --git a/src/main/java/org/apache/sling/feature/diff/package-info.java b/src/main/java/org/apache/sling/feature/diff/package-info.java
new file mode 100644
index 0000000..8a67aff
--- /dev/null
+++ b/src/main/java/org/apache/sling/feature/diff/package-info.java
@@ -0,0 +1,22 @@
+/*
+ * 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.
+ */
+
+/**
+ * Core APIs to compare different Apache Sling Feature models.
+ */
+@org.osgi.annotation.versioning.Version("1.0.0")
+package org.apache.sling.feature.diff;
diff --git a/src/test/java/org/apache/sling/feature/diff/FeatureDiffTest.java b/src/test/java/org/apache/sling/feature/diff/FeatureDiffTest.java
new file mode 100644
index 0000000..7a16d22
--- /dev/null
+++ b/src/test/java/org/apache/sling/feature/diff/FeatureDiffTest.java
@@ -0,0 +1,78 @@
+/*
+ * 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.sling.feature.diff;
+
+import static org.apache.sling.feature.diff.FeatureDiff.loadComparators;
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertTrue;
+
+import java.util.HashSet;
+import java.util.Set;
+
+import org.apache.sling.feature.diff.impl.FeatureElementComparator;
+import org.junit.Test;
+
+public final class FeatureDiffTest {
+
+    @Test
+    public void loadAllComparators() {
+        Set<String> comparators = filterComparators(new DiffRequest());
+
+        assertTrue(comparators.isEmpty());
+    }
+
+    @Test
+    public void loadIncludedComparators() {
+        Set<String> comparators = filterComparators(new DiffRequest()
+                                                    .addIncludeComparator("bundles")
+                                                    .addIncludeComparator("configurations"));
+
+        assertFalse(comparators.isEmpty());
+        assertFalse(comparators.contains("bundles"));
+        assertFalse(comparators.contains("configurations"));
+        assertTrue(comparators.contains("extensions"));
+        assertTrue(comparators.contains("framework-properties"));
+    }
+
+    @Test
+    public void loadExcludedComparators() {
+        Set<String> comparators = filterComparators(new DiffRequest()
+                                                    .addExcludeComparator("bundles")
+                                                    .addExcludeComparator("configurations"));
+
+        assertFalse(comparators.isEmpty());
+        assertTrue(comparators.contains("bundles"));
+        assertTrue(comparators.contains("configurations"));
+        assertFalse(comparators.contains("extensions"));
+        assertFalse(comparators.contains("framework-properties"));
+    }
+
+    private Set<String> filterComparators(DiffRequest diffRequest) {
+        Set<String> comparators = new HashSet<>();
+        comparators.add("bundles");
+        comparators.add("configurations");
+        comparators.add("extensions");
+        comparators.add("framework-properties");
+
+        for (FeatureElementComparator comparator : loadComparators(diffRequest)) {
+            comparators.remove(comparator.getId());
+        }
+
+        return comparators;
+    }
+
+}
diff --git a/src/test/java/org/apache/sling/feature/diff/impl/AbstractComparatorTest.java b/src/test/java/org/apache/sling/feature/diff/impl/AbstractComparatorTest.java
new file mode 100644
index 0000000..e68dfbe
--- /dev/null
+++ b/src/test/java/org/apache/sling/feature/diff/impl/AbstractComparatorTest.java
@@ -0,0 +1,46 @@
+/*
+ * 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.sling.feature.diff.impl;
+
+import org.apache.sling.feature.ArtifactId;
+import org.apache.sling.feature.Feature;
+import org.apache.sling.feature.Prototype;
+import org.junit.After;
+import org.junit.Before;
+
+public abstract class AbstractComparatorTest<C extends FeatureElementComparator> {
+
+    protected Feature targetFeature;
+
+    protected C comparator;
+
+    @Before
+    public void setUp() {
+        targetFeature = new Feature(ArtifactId.fromMvnId("org.apache.sling:org.apache.sling.feature.difftool:1.0"));
+        targetFeature.setPrototype(new Prototype(ArtifactId.fromMvnId("org.apache.sling:org.apache.sling.feature.difftoolproto:1.0")));
+        comparator = newComparatorInstance();
+    }
+
+    @After
+    public void tearDown() {
+        targetFeature = null;
+        comparator = null;
+    }
+
+    protected abstract C newComparatorInstance();
+
+}
diff --git a/src/test/java/org/apache/sling/feature/diff/impl/BundlesComparatorTest.java b/src/test/java/org/apache/sling/feature/diff/impl/BundlesComparatorTest.java
new file mode 100644
index 0000000..0d60724
--- /dev/null
+++ b/src/test/java/org/apache/sling/feature/diff/impl/BundlesComparatorTest.java
@@ -0,0 +1,83 @@
+/*
+ * 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.sling.feature.diff.impl;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertTrue;
+
+import org.apache.sling.feature.Artifact;
+import org.apache.sling.feature.ArtifactId;
+import org.apache.sling.feature.Artifacts;
+import org.apache.sling.feature.diff.impl.BundlesComparator;
+import org.junit.Test;
+
+public class BundlesComparatorTest extends AbstractComparatorTest<BundlesComparator> {
+
+    @Override
+    protected BundlesComparator newComparatorInstance() {
+        return new BundlesComparator();
+    }
+
+    @Test
+    public void checkRemoved() {
+        Artifacts previousArtifacts = new Artifacts();
+        Artifact previousArtifact = new Artifact(ArtifactId.fromMvnId("org.apache.sling:org.apache.sling.feature.diff:1.0.0"));
+        previousArtifacts.add(previousArtifact);
+
+        Artifacts currentArtifacts = new Artifacts();
+
+        comparator.computeDiff(previousArtifacts, currentArtifacts, targetFeature);
+
+        assertFalse(targetFeature.getPrototype().getBundleRemovals().isEmpty());
+        assertEquals(previousArtifact.getId(), targetFeature.getPrototype().getBundleRemovals().iterator().next());
+    }
+
+    @Test
+    public void checkAdded() {
+        Artifacts previousArtifacts = new Artifacts();
+
+        Artifacts currentArtifacts = new Artifacts();
+        Artifact currentArtifact = new Artifact(ArtifactId.fromMvnId("org.apache.sling:org.apache.sling.feature.diff:1.0.0"));
+        currentArtifacts.add(currentArtifact);
+
+        comparator.computeDiff(previousArtifacts, currentArtifacts, targetFeature);
+
+        assertTrue(targetFeature.getPrototype().getBundleRemovals().isEmpty());
+        assertEquals(currentArtifact.getId(), targetFeature.getBundles().iterator().next().getId());
+    }
+
+    @Test
+    public void checkUpdated() {
+        Artifacts previousArtifacts = new Artifacts();
+        Artifact previousArtifact = new Artifact(ArtifactId.fromMvnId("org.apache.sling:org.apache.sling.feature.diff:0.0.1"));
+        previousArtifacts.add(previousArtifact);
+
+        Artifacts currentArtifacts = new Artifacts();
+        Artifact currentArtifact = new Artifact(ArtifactId.fromMvnId("org.apache.sling:org.apache.sling.feature.diff:1.0.0"));
+        currentArtifacts.add(currentArtifact);
+
+        comparator.computeDiff(previousArtifacts, currentArtifacts, targetFeature);
+
+        assertFalse(targetFeature.getPrototype().getBundleRemovals().isEmpty());
+        assertEquals(previousArtifact.getId(), targetFeature.getPrototype().getBundleRemovals().iterator().next());
+
+        assertFalse(targetFeature.getBundles().isEmpty());
+        assertEquals(currentArtifact.getId(), targetFeature.getBundles().iterator().next().getId());
+    }
+
+}
diff --git a/src/test/java/org/apache/sling/feature/diff/impl/ConfigurationsComparatorTest.java b/src/test/java/org/apache/sling/feature/diff/impl/ConfigurationsComparatorTest.java
new file mode 100644
index 0000000..1e333fc
--- /dev/null
+++ b/src/test/java/org/apache/sling/feature/diff/impl/ConfigurationsComparatorTest.java
@@ -0,0 +1,97 @@
+/*
+ * 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.sling.feature.diff.impl;
+
+import static org.junit.Assert.assertArrayEquals;
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertTrue;
+
+import java.util.Dictionary;
+
+import org.apache.sling.feature.Configuration;
+import org.apache.sling.feature.Configurations;
+import org.apache.sling.feature.diff.impl.ConfigurationsComparator;
+import org.junit.Test;
+
+public class ConfigurationsComparatorTest extends AbstractComparatorTest<ConfigurationsComparator> {
+
+    @Override
+    protected ConfigurationsComparator newComparatorInstance() {
+        return new ConfigurationsComparator();
+    }
+
+    @Test
+    public void checkRemoved() {
+        Configuration previousConfiguration = new Configuration("org.apache.sling.feature.diff.config");
+        Configurations previousConfigurations = new Configurations();
+        previousConfigurations.add(previousConfiguration);
+
+        Configurations currentConfigurations = new Configurations();
+
+        comparator.computeDiff(previousConfigurations, currentConfigurations, targetFeature);
+
+        assertFalse(targetFeature.getPrototype().getConfigurationRemovals().isEmpty());
+        assertEquals(previousConfiguration.getPid(), targetFeature.getPrototype().getConfigurationRemovals().iterator().next());
+        assertTrue(targetFeature.getConfigurations().isEmpty());
+    }
+
+    @Test
+    public void checkAdded() {
+        Configurations previousConfigurations = new Configurations();
+
+        Configuration currentConfiguration = new Configuration("org.apache.sling.feature.diff.config");
+        Configurations currentConfigurations = new Configurations();
+        currentConfigurations.add(currentConfiguration);
+
+        comparator.computeDiff(previousConfigurations, currentConfigurations, targetFeature);
+
+        assertTrue(targetFeature.getPrototype().getConfigurationRemovals().isEmpty());
+        assertFalse(targetFeature.getConfigurations().isEmpty());
+
+        assertEquals(currentConfiguration.getPid(), targetFeature.getConfigurations().iterator().next().getPid());
+    }
+
+    @Test
+    public void checkUpdated() {
+        Configuration previousConfiguration = new Configuration("org.apache.sling.feature.diff.config");
+        previousConfiguration.getProperties().put("removed", 123);
+        previousConfiguration.getProperties().put("updated", new String[] { "/log" });
+
+        Configurations previousConfigurations = new Configurations();
+        previousConfigurations.add(previousConfiguration);
+
+        Configuration currentConfiguration = new Configuration("org.apache.sling.feature.diff.config");
+        currentConfiguration.getProperties().put("updated", new String[] { "/log", "/etc" });
+        currentConfiguration.getProperties().put("added", true);
+
+        Configurations currentConfigurations = new Configurations();
+        currentConfigurations.add(currentConfiguration);
+
+        comparator.computeDiff(previousConfigurations, currentConfigurations, targetFeature);
+
+        assertTrue(targetFeature.getPrototype().getConfigurationRemovals().isEmpty());
+        assertFalse(targetFeature.getConfigurations().isEmpty());
+
+        assertEquals(currentConfiguration.getPid(), targetFeature.getConfigurations().iterator().next().getPid());
+        Dictionary<String, Object> properties = targetFeature.getConfigurations().iterator().next().getProperties();
+
+        assertTrue((boolean) properties.get("added"));
+        assertArrayEquals(new String[] { "/log", "/etc" }, (String[]) properties.get("updated"));
+    }
+
+}
diff --git a/src/test/java/org/apache/sling/feature/diff/impl/ExtensionsComparatorTest.java b/src/test/java/org/apache/sling/feature/diff/impl/ExtensionsComparatorTest.java
new file mode 100644
index 0000000..4c2c81f
--- /dev/null
+++ b/src/test/java/org/apache/sling/feature/diff/impl/ExtensionsComparatorTest.java
@@ -0,0 +1,133 @@
+/*
+ * 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.sling.feature.diff.impl;
+
+import static org.apache.sling.feature.ExtensionType.ARTIFACTS;
+import static org.apache.sling.feature.ExtensionType.JSON;
+import static org.apache.sling.feature.ExtensionType.TEXT;
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertTrue;
+
+import java.util.List;
+import java.util.Map;
+
+import org.apache.sling.feature.Artifact;
+import org.apache.sling.feature.ArtifactId;
+import org.apache.sling.feature.Extension;
+import org.apache.sling.feature.Extensions;
+import org.junit.Test;
+
+public class ExtensionsComparatorTest extends AbstractComparatorTest<ExtensionsComparator> {
+
+    @Override
+    protected ExtensionsComparator newComparatorInstance() {
+        return new ExtensionsComparator();
+    }
+
+    @Test
+    public void checkTextExtensionRemoved() {
+        Extension removed = new Extension(TEXT, "removed-TEXT-extension", true);
+        removed.setText("This is just a test");
+        checkRemovedExtension(removed);
+    }
+
+    @Test
+    public void checkJSONExtensionRemoved() {
+        Extension removed = new Extension(JSON, "removed-JSON-extension", true);
+        removed.setJSON("[true, 100, null]");
+        checkRemovedExtension(removed);
+    }
+
+    @Test
+    public void checkArtifactsExtensionRemoved() {
+        Extension removed = new Extension(ARTIFACTS, "removed-ARTIFACTS-extension", true);
+        removed.getArtifacts().add(new Artifact(ArtifactId.parse("org.apache.sling:org.apache.sling.diff:1.0.0")));
+        checkRemovedExtension(removed);
+    }
+
+    private void checkRemovedExtension(Extension removedExtension) {
+        Extensions previous = new Extensions();
+        previous.add(removedExtension);
+
+        Extensions current = new Extensions();
+
+        comparator.computeDiff(previous, current, targetFeature);
+
+        assertTrue(targetFeature.getPrototype().getExtensionRemovals().contains(removedExtension.getName()));
+    }
+
+    @Test
+    public void checkRemovedArtifacts() {
+        Extension previousExtension = new Extension(ARTIFACTS, "content-packages", true);
+        ArtifactId removedId = ArtifactId.parse("org.apache.sling:org.apache.sling.diff:1.0.0");
+        previousExtension.getArtifacts().add(new Artifact(removedId));
+
+        Extension currentExtension = new Extension(ARTIFACTS, "content-packages", true);
+
+        comparator.computeDiff(previousExtension, currentExtension, targetFeature);
+
+        Map<String, List<ArtifactId>> artifactExtensionRemovals = targetFeature.getPrototype().getArtifactExtensionRemovals(); 
+        assertFalse(artifactExtensionRemovals.isEmpty());
+        assertTrue(artifactExtensionRemovals.containsKey("content-packages"));
+        assertTrue(artifactExtensionRemovals.get("content-packages").contains(removedId));
+    }
+
+    @Test
+    public void checkTextExtensionUpdated() {
+        Extension previous = new Extension(TEXT, "repoinit", true);
+        previous.setText("create path /content/example.com(mixin mix:referenceable)");
+
+        Extension current = new Extension(TEXT, "repoinit", true);
+        current.setText("create path /content/example.com(mixin mix:referenceable)\ncreate path (nt:unstructured) /var");
+        comparator.computeDiff(previous, current, targetFeature);
+
+        assertTrue(targetFeature.getPrototype().getExtensionRemovals().contains(current.getName()));
+        assertEquals(current.getText(), targetFeature.getExtensions().getByName(current.getName()).getText());
+    }
+
+    @Test
+    public void checkJSONExtensionUpdated() {
+        Extension previous = new Extension(JSON, "api-regions", true);
+        previous.setJSON("{\"name\": \"global\"}");
+
+        Extension current = new Extension(JSON, "api-regions", true);
+        current.setJSON("{\"name\": \"deprecated\"}");
+        comparator.computeDiff(previous, current, targetFeature);
+
+        assertTrue(targetFeature.getPrototype().getExtensionRemovals().contains(current.getName()));
+        assertEquals(current.getJSON(), targetFeature.getExtensions().getByName(current.getName()).getJSON());
+    }
+
+    @Test
+    public void checkArtifactsExtensionUpdated() {
+        Extension previous = new Extension(ARTIFACTS, "content-packages", true);
+        ArtifactId removedId = ArtifactId.parse("org.apache.sling:org.apache.sling.diff:1.0.0");
+        previous.getArtifacts().add(new Artifact(removedId));
+
+        Extension current = new Extension(ARTIFACTS, "content-packages", true);
+        ArtifactId updatedId = ArtifactId.parse("org.apache.sling:org.apache.sling.diff:2.0.0");
+        current.getArtifacts().add(new Artifact(updatedId));
+
+        comparator.computeDiff(previous, current, targetFeature);
+
+        Map<String, List<ArtifactId>> artifactExtensionRemovals = targetFeature.getPrototype().getArtifactExtensionRemovals();
+        assertTrue(artifactExtensionRemovals.get("content-packages").contains(removedId));
+        assertTrue(targetFeature.getExtensions().getByName(current.getName()).getArtifacts().contains(current.getArtifacts().iterator().next()));
+    }
+
+}
diff --git a/src/test/java/org/apache/sling/feature/diff/impl/FrameworkPropertiesComparatorTest.java b/src/test/java/org/apache/sling/feature/diff/impl/FrameworkPropertiesComparatorTest.java
new file mode 100644
index 0000000..9c4122f
--- /dev/null
+++ b/src/test/java/org/apache/sling/feature/diff/impl/FrameworkPropertiesComparatorTest.java
@@ -0,0 +1,79 @@
+/*
+ * 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.sling.feature.diff.impl;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertTrue;
+
+import java.util.HashMap;
+import java.util.Map;
+
+import org.apache.sling.feature.diff.impl.FrameworkPropertiesComparator;
+import org.junit.Test;
+
+public class FrameworkPropertiesComparatorTest extends AbstractComparatorTest<FrameworkPropertiesComparator> {
+
+    @Override
+    protected FrameworkPropertiesComparator newComparatorInstance() {
+        return new FrameworkPropertiesComparator();
+    }
+
+    @Test
+    public void checkRemoved() {
+        Map<String, String> previous = new HashMap<>();
+        previous.put("removed", "removed entry");
+
+        Map<String, String> current = new HashMap<>();
+
+        comparator.computeDiff(previous, current, targetFeature);
+
+        assertFalse(targetFeature.getPrototype().getFrameworkPropertiesRemovals().isEmpty());
+        assertFalse(targetFeature.getFrameworkProperties().containsKey("removed"));
+    }
+
+    @Test
+    public void checkAdded() {
+        Map<String, String> previous = new HashMap<>();
+
+        Map<String, String> current = new HashMap<>();
+        current.put("added", "added entry");
+
+        comparator.computeDiff(previous, current, targetFeature);
+
+        assertTrue(targetFeature.getPrototype().getFrameworkPropertiesRemovals().isEmpty());
+        assertFalse(targetFeature.getFrameworkProperties().isEmpty());
+        assertTrue(targetFeature.getFrameworkProperties().containsKey("added"));
+    }
+
+    @Test
+    public void checkUpdated() {
+        Map<String, String> previous = new HashMap<>();
+        previous.put("updated", "regular entry");
+
+        Map<String, String> current = new HashMap<>();
+        current.put("updated", "updated entry");
+
+        comparator.computeDiff(previous, current, targetFeature);
+
+        assertTrue(targetFeature.getPrototype().getFrameworkPropertiesRemovals().isEmpty());
+        assertFalse(targetFeature.getFrameworkProperties().isEmpty());
+        assertTrue(targetFeature.getFrameworkProperties().containsKey("updated"));
+        assertEquals("updated entry", targetFeature.getFrameworkProperties().get("updated"));
+    }
+
+}