diff --git a/core/api/src/main/java/org/onosproject/net/group/DefaultGroup.java b/core/api/src/main/java/org/onosproject/net/group/DefaultGroup.java
new file mode 100644
index 0000000..0e4cac1
--- /dev/null
+++ b/core/api/src/main/java/org/onosproject/net/group/DefaultGroup.java
@@ -0,0 +1,142 @@
+/*
+ * Copyright 2015 Open Networking Laboratory
+ *
+ * Licensed 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.onosproject.net.group;
+
+import static org.slf4j.LoggerFactory.getLogger;
+
+import org.onosproject.core.GroupId;
+import org.slf4j.Logger;
+
+/**
+ * ONOS implementation of default group that is stored in the system.
+ */
+public class DefaultGroup extends DefaultGroupDescription
+    implements Group, StoredGroupEntry {
+
+    private final Logger log = getLogger(getClass());
+
+    private GroupState state;
+    private long life;
+    private long packets;
+    private long bytes;
+    private GroupId id;
+
+    /**
+     * Default group object constructor with the parameters.
+     *
+     * @param id group identifier
+     * @param groupDesc group description parameters
+     */
+    public DefaultGroup(GroupId id, GroupDescription groupDesc) {
+        super(groupDesc);
+        this.id = id;
+        this.state = GroupState.PENDING_ADD;
+        this.life = 0;
+        this.packets = 0;
+        this.bytes = 0;
+    }
+
+    /**
+     * Returns group identifier associated with a group object.
+     *
+     * @return GroupId Group Identifier
+     */
+    @Override
+    public GroupId id() {
+        return this.id;
+    }
+
+    /**
+     * Returns current state of a group object.
+     *
+     * @return GroupState Group State
+     */
+    @Override
+    public GroupState state() {
+        return this.state;
+    }
+
+    /**
+     * Returns the number of milliseconds this group has been alive.
+     *
+     * @return number of millis
+     */
+    @Override
+    public long life() {
+        return this.life;
+    }
+
+    /**
+     * Returns the number of packets processed by this group.
+     *
+     * @return number of packets
+     */
+    @Override
+    public long packets() {
+        return this.packets;
+    }
+
+    /**
+     * Returns the number of bytes processed by this group.
+     *
+     * @return number of bytes
+     */
+    @Override
+    public long bytes() {
+        return this.bytes;
+    }
+
+    /**
+     * Sets the new state for this entry.
+     *
+     * @param newState new group entry state.
+     */
+    @Override
+    public void setState(Group.GroupState newState) {
+        this.state = newState;
+    }
+
+    /**
+     * Sets how long this entry has been entered in the system.
+     *
+     * @param life epoch time
+     */
+    @Override
+    public void setLife(long life) {
+        this.life = life;
+    }
+
+    /**
+     * Sets number of packets processed by this group entry.
+     *
+     * @param packets a long value
+     */
+    @Override
+    public void setPackets(long packets) {
+        this.packets = packets;
+    }
+
+    /**
+     * Sets number of bytes processed by this group entry.
+     *
+     * @param bytes a long value
+     */
+    @Override
+    public void setBytes(long bytes) {
+        this.bytes = bytes;
+    }
+
+}
diff --git a/core/api/src/main/java/org/onosproject/net/group/DefaultGroupBucket.java b/core/api/src/main/java/org/onosproject/net/group/DefaultGroupBucket.java
index 8c6eb63..3fab387 100644
--- a/core/api/src/main/java/org/onosproject/net/group/DefaultGroupBucket.java
+++ b/core/api/src/main/java/org/onosproject/net/group/DefaultGroupBucket.java
@@ -15,12 +15,12 @@
  */
 package org.onosproject.net.group;
 
-import static com.google.common.base.Preconditions.checkNotNull;
 import static com.google.common.base.Preconditions.checkArgument;
+import static com.google.common.base.Preconditions.checkNotNull;
 
+import org.onosproject.core.GroupId;
 import org.onosproject.net.PortNumber;
 import org.onosproject.net.flow.TrafficTreatment;
-import org.onosproject.core.GroupId;
 
 /**
  * Group bucket implementation. A group bucket is collection of
@@ -65,7 +65,6 @@
      * Creates indirect group bucket.
      *
      * @param treatment traffic treatment associated with group bucket
-     *
      * @return indirect group bucket object
      */
     public static GroupBucket createIndirectGroupBucket(
@@ -81,7 +80,6 @@
      * Creates select group bucket with weight as 1.
      *
      * @param treatment traffic treatment associated with group bucket
-     *
      * @return select group bucket object
      */
     public static GroupBucket createSelectGroupBucket(
@@ -98,7 +96,6 @@
      *
      * @param treatment traffic treatment associated with group bucket
      * @param weight weight associated with group bucket
-     *
      * @return select group bucket object
      */
     public static GroupBucket createSelectGroupBucket(
@@ -121,7 +118,6 @@
      * @param treatment traffic treatment associated with group bucket
      * @param watchPort port that determines the liveness of group bucket
      * @param watchGroup group that determines the liveness of group bucket
-     *
      * @return failover group bucket object
      */
     public static GroupBucket createFailoverGroupBucket(
@@ -142,7 +138,7 @@
     }
 
     /**
-     * Return list of Traffic instructions that are part of the bucket.
+     * Returns list of Traffic instructions that are part of the bucket.
      *
      * @return TrafficTreatment Traffic instruction list
      */
@@ -152,7 +148,7 @@
     }
 
     /**
-     * Return weight of select group bucket.
+     * Returns weight of select group bucket.
      *
      * @return short weight associated with a bucket
      */
@@ -162,7 +158,7 @@
     }
 
     /**
-     * Return port number used for liveness detection for a
+     * Returns port number used for liveness detection for a
      * failover bucket.
      *
      * @return PortNumber port number used for liveness detection
@@ -173,7 +169,7 @@
     }
 
     /**
-     * Return group identifier used for liveness detection for a
+     * Returns group identifier used for liveness detection for a
      * failover bucket.
      *
      * @return GroupId group identifier to be used for liveness detection
diff --git a/core/api/src/main/java/org/onosproject/net/group/DefaultGroupDescription.java b/core/api/src/main/java/org/onosproject/net/group/DefaultGroupDescription.java
index 46ccafd..25af506 100644
--- a/core/api/src/main/java/org/onosproject/net/group/DefaultGroupDescription.java
+++ b/core/api/src/main/java/org/onosproject/net/group/DefaultGroupDescription.java
@@ -20,6 +20,9 @@
 import org.onosproject.core.ApplicationId;
 import org.onosproject.net.DeviceId;
 
+/**
+ * Default implementation of group description interface.
+ */
 public class DefaultGroupDescription implements GroupDescription {
     private final GroupDescription.Type type;
     private final GroupBuckets buckets;
@@ -28,15 +31,15 @@
     private final DeviceId deviceId;
 
     /**
+     * Constructor to be used by north bound applications.
+     * NOTE: The caller of this subsystem MUST ensure the appCookie
+     * provided in this API is immutable
      *
      * @param deviceId device identifier
      * @param type type of the group
      * @param buckets immutable list of group bucket
      * @param appCookie immutable application cookie to be associated with the group
      * @param appId application id
-     *
-     * NOTE: The caller of this subsystem MUST ensure the appCookie
-     * provided in this API is immutable
      */
     public DefaultGroupDescription(DeviceId deviceId,
                                    GroupDescription.Type type,
@@ -51,7 +54,22 @@
     }
 
     /**
-     * Return type of a group object.
+     * Constructor to be used by group subsystem internal components.
+     * Creates group description object from another object of same type.
+     *
+     * @param groupDesc group description object
+     *
+     */
+    public DefaultGroupDescription(GroupDescription groupDesc) {
+        this.type = checkNotNull(groupDesc.type());
+        this.deviceId = checkNotNull(groupDesc.deviceId());
+        this.buckets = checkNotNull(groupDesc.buckets());
+        this.appCookie = checkNotNull(groupDesc.appCookie());
+        this.appId = checkNotNull(groupDesc.appId());
+    }
+
+    /**
+     * Returns type of a group object.
      *
      * @return GroupType group type
      */
@@ -61,7 +79,7 @@
     }
 
     /**
-     * Return device identifier on which this group object is created.
+     * Returns device identifier on which this group object is created.
      *
      * @return DeviceId device identifier
      */
@@ -71,7 +89,7 @@
     }
 
     /**
-     * Return application identifier that has created this group object.
+     * Returns application identifier that has created this group object.
      *
      * @return ApplicationId application identifier
      */
@@ -81,7 +99,7 @@
     }
 
     /**
-     * Return application cookie associated with a group object.
+     * Returns application cookie associated with a group object.
      *
      * @return GroupKey application cookie
      */
@@ -91,7 +109,7 @@
     }
 
     /**
-     * Return group buckets of a group.
+     * Returns group buckets of a group.
      *
      * @return GroupBuckets immutable list of group bucket
      */
diff --git a/core/api/src/main/java/org/onosproject/net/group/Group.java b/core/api/src/main/java/org/onosproject/net/group/Group.java
index 33a7969..f7fa507 100644
--- a/core/api/src/main/java/org/onosproject/net/group/Group.java
+++ b/core/api/src/main/java/org/onosproject/net/group/Group.java
@@ -23,35 +23,43 @@
 public interface Group extends GroupDescription {
     /**
      * State of the group object in ONOS.
-     * PENDING_ADD: group create request is processed by ONOS and
-     * not yet received the confirmation from data plane
-     * ADDED: group is created in the data plane
-     * PENDING_UPDATE: group update request is processed by ONOS and
-     * not received the confirmation from data plane post which state
-     * moves to ADDED state
-     * PENDING_DELETE: group delete request is processed by ONOS and
-     * not received the confirmation from data plane
      */
     public enum GroupState {
+        /**
+         * Group create request is processed by ONOS and not yet
+         * received the confirmation from data plane.
+         */
         PENDING_ADD,
+        /**
+         * Group is created in the data plane.
+         */
         ADDED,
+        /**
+         * Group update request is processed by ONOS and not
+         * received the confirmation from data plane post which
+         * state moves to ADDED state.
+         */
         PENDING_UPDATE,
+        /**
+         * Group delete request is processed by ONOS and not
+         * received the confirmation from data plane.
+         */
         PENDING_DELETE
     }
 
     /**
-     * Return group identifier associated with a group object.
+     * Returns group identifier associated with a group object.
      *
      * @return GroupId Group Identifier
      */
-    public GroupId id();
+    GroupId id();
 
     /**
-     * Return current state of a group object.
+     * Returns current state of a group object.
      *
      * @return GroupState Group State
      */
-    public GroupState state();
+    GroupState state();
 
     /**
      * Returns the number of milliseconds this group has been alive.
diff --git a/core/api/src/main/java/org/onosproject/net/group/GroupBucket.java b/core/api/src/main/java/org/onosproject/net/group/GroupBucket.java
index 3c2e1ec..2bf8882 100644
--- a/core/api/src/main/java/org/onosproject/net/group/GroupBucket.java
+++ b/core/api/src/main/java/org/onosproject/net/group/GroupBucket.java
@@ -15,11 +15,12 @@
  */
 package org.onosproject.net.group;
 
+import org.onosproject.core.GroupId;
 import org.onosproject.net.PortNumber;
 import org.onosproject.net.flow.TrafficTreatment;
-import org.onosproject.core.GroupId;
 
-/* Group Bucket definition. A default group Bucket is collection of
+/**
+ * Group Bucket definition. A default group Bucket is collection of
  * Instructions that can be performed on a traffic flow. A failover
  * group bucket is associated with a specific port or group that
  * controls its liveness. A select group bucket contains optional
@@ -27,28 +28,28 @@
  */
 public interface GroupBucket {
     /**
-     * Return group type of the bucket.
+     * Returns group type of the bucket.
      *
      * @return GroupType group type
      */
     public GroupDescription.Type type();
 
     /**
-     * Return list of Traffic instructions that are part of the bucket.
+     * Returns list of Traffic instructions that are part of the bucket.
      *
      * @return TrafficTreatment traffic instruction list
      */
     public TrafficTreatment treatment();
 
     /**
-     * Return weight of select group bucket.
+     * Returns weight of select group bucket.
      *
      * @return short weight associated with a bucket
      */
     public short weight();
 
     /**
-     * Return port number used for liveness detection for a
+     * Returns port number used for liveness detection for a
      * failover bucket.
      *
      * @return PortNumber port number used for liveness detection
@@ -56,7 +57,7 @@
     public PortNumber watchPort();
 
     /**
-     * Return group identifier used for liveness detection for a
+     * Returns group identifier used for liveness detection for a
      * failover bucket.
      *
      * @return GroupId group identifier to be used for liveness detection
diff --git a/core/api/src/main/java/org/onosproject/net/group/GroupBucketEntry.java b/core/api/src/main/java/org/onosproject/net/group/GroupBucketEntry.java
index c8805ad..f7a6617 100644
--- a/core/api/src/main/java/org/onosproject/net/group/GroupBucketEntry.java
+++ b/core/api/src/main/java/org/onosproject/net/group/GroupBucketEntry.java
@@ -15,20 +15,21 @@
  */
 package org.onosproject.net.group;
 
-/* Generic group bucket entry representation that is stored in a
+/**
+ * Generic group bucket entry representation that is stored in a
  * group object. A group bucket entry provides additional info of
  * group bucket like statistics...etc
  */
 public interface GroupBucketEntry extends GroupBucket {
     /**
-     * Return Number of packets processed by bucket.
+     * Returns Number of packets processed by bucket.
      *
      * @return long
      */
     public long packets();
 
     /**
-     * Return Number of bytes processed by bucket.
+     * Returns Number of bytes processed by bucket.
      *
      * @return long
      */
diff --git a/core/api/src/main/java/org/onosproject/net/group/GroupBuckets.java b/core/api/src/main/java/org/onosproject/net/group/GroupBuckets.java
index c4aaad2..10f4eca 100644
--- a/core/api/src/main/java/org/onosproject/net/group/GroupBuckets.java
+++ b/core/api/src/main/java/org/onosproject/net/group/GroupBuckets.java
@@ -19,9 +19,11 @@
 
 import java.util.List;
 
-
 import com.google.common.collect.ImmutableList;
 
+/**
+ * Immutable collection of group bucket.
+ */
 public final class GroupBuckets {
     private final List<GroupBucket> buckets;
 
@@ -35,7 +37,7 @@
     }
 
     /**
-     * Immutable list of group buckets.
+     * Returns immutable list of group buckets.
      *
      * @return list of group bucket
      */
diff --git a/core/api/src/main/java/org/onosproject/net/group/GroupDescription.java b/core/api/src/main/java/org/onosproject/net/group/GroupDescription.java
index e4ae7ed..74dcb16 100644
--- a/core/api/src/main/java/org/onosproject/net/group/GroupDescription.java
+++ b/core/api/src/main/java/org/onosproject/net/group/GroupDescription.java
@@ -47,35 +47,35 @@
     }
 
     /**
-     * Return type of a group object.
+     * Returns type of a group object.
      *
      * @return GroupType group type
      */
     public Type type();
 
     /**
-     * Return device identifier on which this group object is created.
+     * Returns device identifier on which this group object is created.
      *
      * @return DeviceId device identifier
      */
     public DeviceId deviceId();
 
     /**
-     * Return application identifier that has created this group object.
+     * Returns application identifier that has created this group object.
      *
      * @return ApplicationId application identifier
      */
     public ApplicationId appId();
 
     /**
-     * Return application cookie associated with a group object.
+     * Returns application cookie associated with a group object.
      *
      * @return GroupKey application cookie
      */
     public GroupKey appCookie();
 
     /**
-     * Return group buckets of a group.
+     * Returns group buckets of a group.
      *
      * @return GroupBuckets immutable list of group bucket
      */
diff --git a/core/api/src/main/java/org/onosproject/net/group/GroupEvent.java b/core/api/src/main/java/org/onosproject/net/group/GroupEvent.java
index 8bbe742..d9d8a97 100644
--- a/core/api/src/main/java/org/onosproject/net/group/GroupEvent.java
+++ b/core/api/src/main/java/org/onosproject/net/group/GroupEvent.java
@@ -18,7 +18,7 @@
 import org.onosproject.event.AbstractEvent;
 
 /**
- * Describes flow rule event.
+ * Describes group events.
  */
 public class GroupEvent extends AbstractEvent<GroupEvent.Type, Group> {
 
@@ -48,6 +48,10 @@
          */
         GROUP_ADD_REQUESTED,
         /*
+         * Signifies that a request to update Group has been added to the store.
+         */
+        GROUP_UPDATE_REQUESTED,
+        /*
          * Signifies that a request to delete Group has been added to the store.
          */
         GROUP_REMOVE_REQUESTED,
diff --git a/core/api/src/main/java/org/onosproject/net/group/GroupKey.java b/core/api/src/main/java/org/onosproject/net/group/GroupKey.java
index 17cb560..da8d449 100644
--- a/core/api/src/main/java/org/onosproject/net/group/GroupKey.java
+++ b/core/api/src/main/java/org/onosproject/net/group/GroupKey.java
@@ -15,8 +15,9 @@
  */
 package org.onosproject.net.group;
 
-/* Representation of generalized Key that would be used to store
- * groups in <Key, Value> store. Implementation of this interface
+/**
+ * Representation of generalized Key that would be used to store
+ * groups in &lt; Key, Value &gt; store. Implementation of this interface
  * MUST override "equals()" and "hashcode()" methods.
  */
 public interface GroupKey  {
diff --git a/core/api/src/main/java/org/onosproject/net/group/GroupOperation.java b/core/api/src/main/java/org/onosproject/net/group/GroupOperation.java
index a99ed07..44d7e88 100644
--- a/core/api/src/main/java/org/onosproject/net/group/GroupOperation.java
+++ b/core/api/src/main/java/org/onosproject/net/group/GroupOperation.java
@@ -19,6 +19,11 @@
 
 import org.onosproject.core.GroupId;
 
+/**
+ * Group operation definition to be used between core and provider
+ * layers of group subsystem.
+ *
+ */
 public final class GroupOperation {
     private final Type opType;
     private final GroupId groupId;
@@ -64,7 +69,6 @@
      * @param groupId group Identifier
      * @param groupType type of the group
      * @param buckets immutable list of group buckets to be part of group
-     *
      * @return add group operation object
      */
     public static GroupOperation createAddGroupOperation(GroupId groupId,
@@ -80,7 +84,6 @@
      * @param groupId group Identifier
      * @param groupType type of the group
      * @param buckets immutable list of group buckets to be part of group
-     *
      * @return modify group operation object
      */
     public static GroupOperation createModifyGroupOperation(GroupId groupId,
@@ -96,7 +99,6 @@
      *
      * @param groupId group Identifier
      * @param groupType type of the group
-     *
      * @return delete group operation object
      */
     public static GroupOperation createDeleteGroupOperation(GroupId groupId,
@@ -106,7 +108,7 @@
     }
 
     /**
-     * Return group operation type.
+     * Returns group operation type.
      *
      * @return GroupOpType group operation type
      */
@@ -115,7 +117,7 @@
     }
 
     /**
-     * Return group identifier attribute of the operation.
+     * Returns group identifier attribute of the operation.
      *
      * @return GroupId group identifier
      */
@@ -124,7 +126,7 @@
     }
 
     /**
-     * Return group type attribute of the operation.
+     * Returns group type attribute of the operation.
      *
      * @return GroupType group type
      */
@@ -133,7 +135,7 @@
     }
 
     /**
-     * Return group buckets associated with the operation.
+     * Returns group buckets associated with the operation.
      *
      * @return GroupBuckets group buckets
      */
diff --git a/core/api/src/main/java/org/onosproject/net/group/GroupOperations.java b/core/api/src/main/java/org/onosproject/net/group/GroupOperations.java
index 629ecd3..bc03628 100644
--- a/core/api/src/main/java/org/onosproject/net/group/GroupOperations.java
+++ b/core/api/src/main/java/org/onosproject/net/group/GroupOperations.java
@@ -19,9 +19,13 @@
 
 import java.util.List;
 
-
 import com.google.common.collect.ImmutableList;
 
+/**
+ * Immutable collection of group operation to be used between
+ * core and provider layers of group subsystem.
+ *
+ */
 public final class GroupOperations {
     private final List<GroupOperation> operations;
 
@@ -35,7 +39,7 @@
     }
 
     /**
-     * Immutable list of group operation.
+     * Returns immutable list of group operation.
      *
      * @return list of group operation
      */
diff --git a/core/api/src/main/java/org/onosproject/net/group/GroupProvider.java b/core/api/src/main/java/org/onosproject/net/group/GroupProvider.java
index 35d949f..6757e66 100644
--- a/core/api/src/main/java/org/onosproject/net/group/GroupProvider.java
+++ b/core/api/src/main/java/org/onosproject/net/group/GroupProvider.java
@@ -19,12 +19,12 @@
 import org.onosproject.net.provider.Provider;
 
 /**
- * Abstraction of a flow rule provider.
+ * Abstraction of group provider.
  */
 public interface GroupProvider extends Provider {
 
     /**
-     * Perform a group operation in the specified device with the
+     * Performs a batch of group operation in the specified device with the
      * specified parameters.
      *
      * @param deviceId device identifier on which the batch of group
diff --git a/core/api/src/main/java/org/onosproject/net/group/GroupProviderService.java b/core/api/src/main/java/org/onosproject/net/group/GroupProviderService.java
index bfa0522..26c7bb1 100644
--- a/core/api/src/main/java/org/onosproject/net/group/GroupProviderService.java
+++ b/core/api/src/main/java/org/onosproject/net/group/GroupProviderService.java
@@ -26,6 +26,11 @@
  */
 public interface GroupProviderService extends ProviderService<GroupProvider> {
 
+    /**
+     * Notifies core if any failure from data plane during group operations.
+     *
+     * @param operation offended group operation
+     */
     void groupOperationFailed(GroupOperation operation);
 
     /**
diff --git a/core/api/src/main/java/org/onosproject/net/group/GroupService.java b/core/api/src/main/java/org/onosproject/net/group/GroupService.java
index eb733e1..1fd9984 100644
--- a/core/api/src/main/java/org/onosproject/net/group/GroupService.java
+++ b/core/api/src/main/java/org/onosproject/net/group/GroupService.java
@@ -36,7 +36,7 @@
 public interface GroupService {
 
     /**
-     * Create a group in the specified device with the provided buckets.
+     * Creates a group in the specified device with the provided buckets.
      * This API provides an option for application to associate a cookie
      * while creating a group, so that applications can look-up the
      * groups based on the cookies. These Groups will be retained by
@@ -55,7 +55,7 @@
     void addGroup(GroupDescription groupDesc);
 
     /**
-     * Return a group object associated to an application cookie.
+     * Returns a group object associated to an application cookie.
      *
      * NOTE1: The presence of group object in the system does not
      * guarantee that the "group" is actually created in device.
@@ -64,14 +64,13 @@
      *
      * @param deviceId device identifier
      * @param appCookie application cookie to be used for lookup
-     *
      * @return group associated with the application cookie or
      *               NULL if Group is not found for the provided cookie
      */
     Group getGroup(DeviceId deviceId, GroupKey appCookie);
 
     /**
-     * Append buckets to existing group. The caller can optionally
+     * Appends buckets to existing group. The caller can optionally
      * associate a new cookie during this updation. GROUP_UPDATED or
      * GROUP_UPDATE_FAILED notifications would be provided along with
      * cookie depending on the result of the operation on the device
@@ -89,7 +88,7 @@
                            ApplicationId appId);
 
     /**
-     * Remove buckets from existing group. The caller can optionally
+     * Removes buckets from existing group. The caller can optionally
      * associate a new cookie during this updation. GROUP_UPDATED or
      * GROUP_UPDATE_FAILED notifications would be provided along with
      * cookie depending on the result of the operation on the device
@@ -107,7 +106,7 @@
                                 ApplicationId appId);
 
     /**
-     * Delete a group associated to an application cookie.
+     * Deletes a group associated to an application cookie.
      * GROUP_DELETED or GROUP_DELETE_FAILED notifications would be
      * provided along with cookie depending on the result of the
      * operation on the device
@@ -119,12 +118,11 @@
     void removeGroup(Device deviceId, GroupKey appCookie, ApplicationId appId);
 
     /**
-     * Retrieve all groups created by an application in the specified device
+     * Retrieves all groups created by an application in the specified device
      * as seen by current controller instance.
      *
      * @param deviceId device identifier
      * @param appId application id
-     *
      * @return collection of immutable group objects created by the application
      */
     Iterable<Group> getGroups(Device deviceId, ApplicationId appId);
diff --git a/core/api/src/main/java/org/onosproject/net/group/GroupStore.java b/core/api/src/main/java/org/onosproject/net/group/GroupStore.java
new file mode 100644
index 0000000..22914f9
--- /dev/null
+++ b/core/api/src/main/java/org/onosproject/net/group/GroupStore.java
@@ -0,0 +1,105 @@
+/*
+ * Copyright 2015 Open Networking Laboratory
+ *
+ * Licensed 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.onosproject.net.group;
+
+import org.onosproject.net.DeviceId;
+import org.onosproject.store.Store;
+
+/**
+ * Manages inventory of groups per device; not intended for direct use.
+ */
+public interface GroupStore extends Store<GroupEvent, GroupStoreDelegate> {
+
+    public enum UpdateType {
+        /**
+         * Modify existing group entry by adding provided information.
+         */
+        ADD,
+        /**
+         * Modify existing group by removing provided information from it.
+         */
+        REMOVE
+    }
+
+    /**
+     * Returns the number of groups for the specified device in the store.
+     *
+     * @param deviceId the device ID
+     * @return number of groups for the specified device
+     */
+    int getGroupCount(DeviceId deviceId);
+
+    /**
+     * Returns the groups associated with a device.
+     *
+     * @param deviceId the device ID
+     * @return the group entries
+     */
+    Iterable<Group> getGroups(DeviceId deviceId);
+
+    /**
+     * Returns the stored group entry.
+     *
+     * @param deviceId the device ID
+     * @param appCookie the group key
+     * @return a group associated with the key
+     */
+    Group getGroup(DeviceId deviceId, GroupKey appCookie);
+
+    /**
+     * Stores a new group entry using the information from group description.
+     *
+     * @param groupDesc group description to be used to store group entry
+     */
+    void storeGroupDescription(GroupDescription groupDesc);
+
+    /**
+     * Updates the existing group entry with the information
+     * from group description.
+     *
+     * @param deviceId the device ID
+     * @param oldAppCookie the current group key
+     * @param type update type
+     * @param newGroupDesc group description with updates
+     */
+    void updateGroupDescription(DeviceId deviceId,
+                                GroupKey oldAppCookie,
+                                UpdateType type,
+                                GroupDescription newGroupDesc);
+
+    /**
+     * Triggers deleting the existing group entry.
+     *
+     * @param deviceId the device ID
+     * @param appCookie the group key
+     */
+    void deleteGroupDescription(DeviceId deviceId,
+                                GroupKey appCookie);
+
+    /**
+     * Stores a new group entry, or updates an existing entry.
+     *
+     * @param group group entry
+     */
+    void addOrUpdateGroupEntry(Group group);
+
+    /**
+     * Removes the group entry from store.
+     *
+     * @param group group entry
+     */
+    void removeGroupEntry(Group group);
+}
diff --git a/core/api/src/main/java/org/onosproject/net/group/GroupStoreDelegate.java b/core/api/src/main/java/org/onosproject/net/group/GroupStoreDelegate.java
new file mode 100644
index 0000000..308ebb1
--- /dev/null
+++ b/core/api/src/main/java/org/onosproject/net/group/GroupStoreDelegate.java
@@ -0,0 +1,24 @@
+/*
+ * Copyright 2015 Open Networking Laboratory
+ *
+ * Licensed 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.onosproject.net.group;
+
+import org.onosproject.store.StoreDelegate;
+
+/**
+ * Group store delegate abstraction.
+ */
+public interface GroupStoreDelegate extends StoreDelegate<GroupEvent> {
+}
diff --git a/core/api/src/main/java/org/onosproject/net/group/StoredGroupEntry.java b/core/api/src/main/java/org/onosproject/net/group/StoredGroupEntry.java
new file mode 100644
index 0000000..b3557b4
--- /dev/null
+++ b/core/api/src/main/java/org/onosproject/net/group/StoredGroupEntry.java
@@ -0,0 +1,52 @@
+/*
+ * Copyright 2015 Open Networking Laboratory
+ *
+ * Licensed 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.onosproject.net.group;
+
+/**
+ * Interface that defines set methods for a group entry
+ * that is stored in the system.
+ */
+public interface StoredGroupEntry extends Group {
+
+    /**
+     * Sets the new state for this entry.
+     *
+     * @param newState new group entry state.
+     */
+    void setState(Group.GroupState newState);
+
+    /**
+     * Sets how long this entry has been entered in the system.
+     *
+     * @param life epoch time
+     */
+    void setLife(long life);
+
+    /**
+     * Sets number of packets processed by this group entry.
+     *
+     * @param packets a long value
+     */
+    void setPackets(long packets);
+
+    /**
+     * Sets number of bytes processed by this group entry.
+     *
+     * @param bytes a long value
+     */
+    void setBytes(long bytes);
+
+}
diff --git a/core/store/dist/src/main/java/org/onosproject/store/group/impl/package-info.java b/core/store/dist/src/main/java/org/onosproject/store/group/impl/package-info.java
new file mode 100644
index 0000000..603712f
--- /dev/null
+++ b/core/store/dist/src/main/java/org/onosproject/store/group/impl/package-info.java
@@ -0,0 +1,19 @@
+/*
+ * Copyright 2014 Open Networking Laboratory
+ *
+ * Licensed 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.
+ */
+/**
+ * Implementation of the group store.
+ */
+package org.onosproject.store.group.impl;
\ No newline at end of file
diff --git a/core/store/trivial/src/main/java/org/onosproject/store/trivial/impl/SimpleGroupStore.java b/core/store/trivial/src/main/java/org/onosproject/store/trivial/impl/SimpleGroupStore.java
new file mode 100644
index 0000000..c82ebc2
--- /dev/null
+++ b/core/store/trivial/src/main/java/org/onosproject/store/trivial/impl/SimpleGroupStore.java
@@ -0,0 +1,365 @@
+/*
+ * Copyright 2015 Open Networking Laboratory
+ *
+ * Licensed 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.onosproject.store.trivial.impl;
+
+import static org.apache.commons.lang3.concurrent.ConcurrentUtils.createIfAbsentUnchecked;
+import static org.slf4j.LoggerFactory.getLogger;
+
+import java.util.ArrayList;
+import java.util.List;
+import java.util.concurrent.ConcurrentHashMap;
+import java.util.concurrent.ConcurrentMap;
+import java.util.concurrent.atomic.AtomicInteger;
+
+import org.apache.felix.scr.annotations.Activate;
+import org.apache.felix.scr.annotations.Component;
+import org.apache.felix.scr.annotations.Deactivate;
+import org.apache.felix.scr.annotations.Service;
+import org.onlab.util.NewConcurrentHashMap;
+import org.onosproject.core.DefaultGroupId;
+import org.onosproject.core.GroupId;
+import org.onosproject.net.DeviceId;
+import org.onosproject.net.group.DefaultGroup;
+import org.onosproject.net.group.DefaultGroupDescription;
+import org.onosproject.net.group.Group;
+import org.onosproject.net.group.Group.GroupState;
+import org.onosproject.net.group.GroupBucket;
+import org.onosproject.net.group.GroupBuckets;
+import org.onosproject.net.group.GroupDescription;
+import org.onosproject.net.group.GroupEvent;
+import org.onosproject.net.group.GroupEvent.Type;
+import org.onosproject.net.group.GroupKey;
+import org.onosproject.net.group.GroupStore;
+import org.onosproject.net.group.GroupStoreDelegate;
+import org.onosproject.net.group.StoredGroupEntry;
+import org.onosproject.store.AbstractStore;
+import org.slf4j.Logger;
+
+import com.google.common.base.Function;
+import com.google.common.collect.FluentIterable;
+
+/**
+ * Manages inventory of group entries using trivial in-memory implementation.
+ */
+@Component(immediate = true)
+@Service
+public class SimpleGroupStore
+        extends AbstractStore<GroupEvent, GroupStoreDelegate>
+        implements GroupStore {
+
+    private final Logger log = getLogger(getClass());
+
+    // inner Map is per device group table
+    private final ConcurrentMap<DeviceId, ConcurrentMap<GroupKey, StoredGroupEntry>>
+            groupEntriesByKey = new ConcurrentHashMap<>();
+    private final ConcurrentMap<DeviceId, ConcurrentMap<GroupId, StoredGroupEntry>>
+            groupEntriesById = new ConcurrentHashMap<>();
+
+    private final AtomicInteger groupIdGen = new AtomicInteger();
+
+    @Activate
+    public void activate() {
+        log.info("Started");
+    }
+
+    @Deactivate
+    public void deactivate() {
+        groupEntriesByKey.clear();
+        groupEntriesById.clear();
+        log.info("Stopped");
+    }
+
+    private static NewConcurrentHashMap<GroupKey, StoredGroupEntry> lazyEmptyGroupKeyTable() {
+        return NewConcurrentHashMap.<GroupKey, StoredGroupEntry>ifNeeded();
+    }
+
+    private static NewConcurrentHashMap<GroupId, StoredGroupEntry> lazyEmptyGroupIdTable() {
+        return NewConcurrentHashMap.<GroupId, StoredGroupEntry>ifNeeded();
+    }
+
+    /**
+     * Returns the group key table for specified device.
+     *
+     * @param deviceId identifier of the device
+     * @return Map representing group key table of given device.
+     */
+    private ConcurrentMap<GroupKey, StoredGroupEntry> getGroupKeyTable(DeviceId deviceId) {
+        return createIfAbsentUnchecked(groupEntriesByKey,
+                                       deviceId, lazyEmptyGroupKeyTable());
+    }
+
+    /**
+     * Returns the group id table for specified device.
+     *
+     * @param deviceId identifier of the device
+     * @return Map representing group key table of given device.
+     */
+    private ConcurrentMap<GroupId, StoredGroupEntry> getGroupIdTable(DeviceId deviceId) {
+        return createIfAbsentUnchecked(groupEntriesById,
+                                       deviceId, lazyEmptyGroupIdTable());
+    }
+
+    /**
+     * Returns the number of groups for the specified device in the store.
+     *
+     * @return number of groups for the specified device
+     */
+    @Override
+    public int getGroupCount(DeviceId deviceId) {
+        return (groupEntriesByKey.get(deviceId) != null) ?
+                 groupEntriesByKey.get(deviceId).size() : 0;
+    }
+
+    /**
+     * Returns the groups associated with a device.
+     *
+     * @param deviceId the device ID
+     *
+     * @return the group entries
+     */
+    @Override
+    public Iterable<Group> getGroups(DeviceId deviceId) {
+        // flatten and make iterator unmodifiable
+        if (groupEntriesByKey.get(deviceId) != null) {
+            return FluentIterable.from(groupEntriesByKey.get(deviceId).values())
+                .transform(
+                        new Function<StoredGroupEntry, Group>() {
+
+                            @Override
+                            public Group apply(
+                                    StoredGroupEntry input) {
+                                return input;
+                            }
+                        });
+        } else {
+            return null;
+        }
+    }
+
+    /**
+     * Returns the stored group entry.
+     *
+     * @param deviceId the device ID
+     * @param appCookie the group key
+     *
+     * @return a group associated with the key
+     */
+    @Override
+    public Group getGroup(DeviceId deviceId, GroupKey appCookie) {
+        return (groupEntriesByKey.get(deviceId) != null) ?
+                      groupEntriesByKey.get(deviceId).get(appCookie) :
+                      null;
+    }
+
+    /**
+     * Stores a new group entry using the information from group description.
+     *
+     * @param groupDesc group description to be used to create group entry
+     */
+    @Override
+    public void storeGroupDescription(GroupDescription groupDesc) {
+        /* Check if a group is existing with the same key */
+        if (getGroup(groupDesc.deviceId(), groupDesc.appCookie()) != null) {
+            return;
+        }
+
+        /* Get a new group identifier */
+        GroupId id = new DefaultGroupId(groupIdGen.incrementAndGet());
+        /* Create a group entry object */
+        StoredGroupEntry group = new DefaultGroup(id, groupDesc);
+        /* Insert the newly created group entry into concurrent key and id maps */
+        ConcurrentMap<GroupKey, StoredGroupEntry> keyTable =
+                getGroupKeyTable(groupDesc.deviceId());
+        keyTable.put(groupDesc.appCookie(), group);
+        ConcurrentMap<GroupId, StoredGroupEntry> idTable =
+                getGroupIdTable(groupDesc.deviceId());
+        idTable.put(id, group);
+        notifyDelegate(new GroupEvent(GroupEvent.Type.GROUP_ADD_REQUESTED,
+                                      group));
+    }
+
+    /**
+     * Updates the existing group entry with the information
+     * from group description.
+     *
+     * @param deviceId the device ID
+     * @param oldAppCookie the current group key
+     * @param type update type
+     * @param newGroupDesc group description with updates
+     */
+    @Override
+    public void updateGroupDescription(DeviceId deviceId,
+                                GroupKey oldAppCookie,
+                                UpdateType type,
+                                GroupDescription newGroupDesc) {
+        /* Check if a group is existing with the provided key */
+        Group oldGroup = getGroup(deviceId, oldAppCookie);
+        if (oldGroup == null) {
+            return;
+        }
+
+        List<GroupBucket> newBucketList = getUpdatedBucketList(oldGroup,
+                                                               type,
+                                               newGroupDesc.buckets());
+        if (newBucketList != null) {
+            /* Create a new group object from the old group */
+            GroupBuckets updatedBuckets = new GroupBuckets(newBucketList);
+            GroupDescription updatedGroupDesc = new DefaultGroupDescription(
+                                                        oldGroup.deviceId(),
+                                                        oldGroup.type(),
+                                                        updatedBuckets,
+                                                        newGroupDesc.appCookie(),
+                                                        oldGroup.appId());
+            StoredGroupEntry newGroup = new DefaultGroup(oldGroup.id(),
+                                                     updatedGroupDesc);
+            newGroup.setState(GroupState.PENDING_UPDATE);
+            newGroup.setLife(oldGroup.life());
+            newGroup.setPackets(oldGroup.packets());
+            newGroup.setBytes(oldGroup.bytes());
+            /* Remove the old entry from maps and add new entry
+             * using new key
+             */
+            ConcurrentMap<GroupKey, StoredGroupEntry> keyTable =
+                    getGroupKeyTable(oldGroup.deviceId());
+            ConcurrentMap<GroupId, StoredGroupEntry> idTable =
+                    getGroupIdTable(oldGroup.deviceId());
+            keyTable.remove(oldGroup.appCookie());
+            idTable.remove(oldGroup.id());
+            keyTable.put(newGroup.appCookie(), newGroup);
+            idTable.put(newGroup.id(), newGroup);
+            notifyDelegate(new GroupEvent(Type.GROUP_UPDATE_REQUESTED, newGroup));
+        }
+    }
+
+    private List<GroupBucket> getUpdatedBucketList(Group oldGroup,
+                                   UpdateType type,
+                                   GroupBuckets buckets) {
+        GroupBuckets oldBuckets = oldGroup.buckets();
+        List<GroupBucket> newBucketList = new ArrayList<GroupBucket>(
+                oldBuckets.buckets());
+        boolean groupDescUpdated = false;
+
+        if (type == UpdateType.ADD) {
+            /* Check if the any of the new buckets are part of the
+             * old bucket list
+             */
+            for (GroupBucket addBucket:buckets.buckets()) {
+                if (!newBucketList.contains(addBucket)) {
+                    newBucketList.add(addBucket);
+                    groupDescUpdated = true;
+                }
+            }
+        } else if (type == UpdateType.REMOVE) {
+            /* Check if the to be removed buckets are part of the
+             * old bucket list
+             */
+            for (GroupBucket removeBucket:buckets.buckets()) {
+                if (newBucketList.contains(removeBucket)) {
+                    newBucketList.remove(removeBucket);
+                    groupDescUpdated = true;
+                }
+            }
+        }
+
+        if (groupDescUpdated) {
+            return newBucketList;
+        } else {
+            return null;
+        }
+    }
+
+    /**
+     * Triggers deleting the existing group entry.
+     *
+     * @param deviceId the device ID
+     * @param appCookie the group key
+     */
+    @Override
+    public void deleteGroupDescription(DeviceId deviceId,
+                                GroupKey appCookie) {
+        /* Check if a group is existing with the provided key */
+        StoredGroupEntry existing = (groupEntriesByKey.get(deviceId) != null) ?
+                           groupEntriesByKey.get(deviceId).get(appCookie) :
+                           null;
+        if (existing == null) {
+            return;
+        }
+
+        synchronized (existing) {
+            existing.setState(GroupState.PENDING_DELETE);
+        }
+        notifyDelegate(new GroupEvent(Type.GROUP_REMOVE_REQUESTED, existing));
+    }
+
+    /**
+     * Stores a new group entry, or updates an existing entry.
+     *
+     * @param group group entry
+     */
+    @Override
+    public void addOrUpdateGroupEntry(Group group) {
+        // check if this new entry is an update to an existing entry
+        StoredGroupEntry existing = (groupEntriesById.get(
+                      group.deviceId()) != null) ?
+                      groupEntriesById.get(group.deviceId()).get(group.id()) :
+                      null;
+        GroupEvent event = null;
+
+        if (existing != null) {
+            synchronized (existing) {
+                existing.setLife(group.life());
+                existing.setPackets(group.packets());
+                existing.setBytes(group.bytes());
+                if (existing.state() == GroupState.PENDING_ADD) {
+                    existing.setState(GroupState.ADDED);
+                    event = new GroupEvent(Type.GROUP_ADDED, existing);
+                } else {
+                    if (existing.state() == GroupState.PENDING_UPDATE) {
+                        existing.setState(GroupState.PENDING_UPDATE);
+                    }
+                    event = new GroupEvent(Type.GROUP_UPDATED, existing);
+                }
+            }
+        }
+
+        if (event != null) {
+            notifyDelegate(event);
+        }
+    }
+
+    /**
+     * Removes the group entry from store.
+     *
+     * @param group group entry
+     */
+    @Override
+    public void removeGroupEntry(Group group) {
+        StoredGroupEntry existing = (groupEntriesById.get(
+                         group.deviceId()) != null) ?
+                         groupEntriesById.get(group.deviceId()).get(group.id()) :
+                         null;
+
+        if (existing != null) {
+            ConcurrentMap<GroupKey, StoredGroupEntry> keyTable =
+                    getGroupKeyTable(existing.deviceId());
+            ConcurrentMap<GroupId, StoredGroupEntry> idTable =
+                    getGroupIdTable(existing.deviceId());
+            idTable.remove(existing.id());
+            keyTable.remove(existing.appCookie());
+            notifyDelegate(new GroupEvent(Type.GROUP_REMOVED, existing));
+        }
+    }
+}
diff --git a/core/store/trivial/src/test/java/org/onosproject/store/trivial/impl/SimpleGroupStoreTest.java b/core/store/trivial/src/test/java/org/onosproject/store/trivial/impl/SimpleGroupStoreTest.java
new file mode 100644
index 0000000..b1f03f4
--- /dev/null
+++ b/core/store/trivial/src/test/java/org/onosproject/store/trivial/impl/SimpleGroupStoreTest.java
@@ -0,0 +1,314 @@
+/*
+ * Copyright 2014 Open Networking Laboratory
+ *
+ * Licensed 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.onosproject.store.trivial.impl;
+
+import static org.junit.Assert.assertEquals;
+import static org.onosproject.net.DeviceId.deviceId;
+
+import java.util.ArrayList;
+import java.util.List;
+
+import org.junit.After;
+import org.junit.Before;
+import org.junit.Test;
+import org.onlab.packet.MacAddress;
+import org.onosproject.core.ApplicationId;
+import org.onosproject.core.DefaultApplicationId;
+import org.onosproject.core.GroupId;
+import org.onosproject.net.DeviceId;
+import org.onosproject.net.PortNumber;
+import org.onosproject.net.flow.DefaultTrafficTreatment;
+import org.onosproject.net.flow.TrafficTreatment;
+import org.onosproject.net.group.DefaultGroupBucket;
+import org.onosproject.net.group.DefaultGroupDescription;
+import org.onosproject.net.group.Group;
+import org.onosproject.net.group.GroupBucket;
+import org.onosproject.net.group.GroupBuckets;
+import org.onosproject.net.group.GroupDescription;
+import org.onosproject.net.group.GroupEvent;
+import org.onosproject.net.group.GroupKey;
+import org.onosproject.net.group.GroupStoreDelegate;
+import org.onosproject.net.group.GroupStore.UpdateType;
+
+/**
+ * Test of the simple DeviceStore implementation.
+ */
+public class SimpleGroupStoreTest {
+
+    private SimpleGroupStore simpleGroupStore;
+
+    public static final DeviceId D1 = deviceId("of:1");
+
+    @Before
+    public void setUp() throws Exception {
+        simpleGroupStore = new SimpleGroupStore();
+        simpleGroupStore.activate();
+    }
+
+    @After
+    public void tearDown() throws Exception {
+        simpleGroupStore.deactivate();
+    }
+
+    public class TestGroupKey implements GroupKey {
+        private String groupId;
+
+        public TestGroupKey(String id) {
+            this.groupId = id;
+        }
+
+        public String id() {
+            return this.groupId;
+        }
+
+        @Override
+        public int hashCode() {
+            return groupId.hashCode();
+        }
+
+        @Override
+        public boolean equals(Object obj) {
+            if (obj instanceof TestGroupKey) {
+                return this.groupId.equals(((TestGroupKey) obj).id());
+            }
+            return false;
+        }
+    }
+
+    private class InternalGroupStoreDelegate
+                implements GroupStoreDelegate {
+        private GroupId createdGroupId = null;
+        private GroupKey createdGroupKey;
+        private GroupBuckets createdBuckets;
+        private GroupEvent.Type expectedEvent;
+
+        public InternalGroupStoreDelegate(GroupKey key,
+                                          GroupBuckets buckets,
+                                          GroupEvent.Type expectedEvent) {
+            this.createdBuckets = buckets;
+            this.createdGroupKey = key;
+            this.expectedEvent = expectedEvent;
+        }
+        @Override
+        public void notify(GroupEvent event) {
+            assertEquals(expectedEvent, event.type());
+            assertEquals(Group.Type.SELECT, event.subject().type());
+            assertEquals(D1, event.subject().deviceId());
+            assertEquals(createdGroupKey, event.subject().appCookie());
+            assertEquals(createdBuckets.buckets(), event.subject().buckets().buckets());
+            if (expectedEvent == GroupEvent.Type.GROUP_ADD_REQUESTED) {
+                createdGroupId = event.subject().id();
+                assertEquals(Group.GroupState.PENDING_ADD,
+                             event.subject().state());
+            } else if (expectedEvent == GroupEvent.Type.GROUP_ADDED) {
+                createdGroupId = event.subject().id();
+                assertEquals(Group.GroupState.ADDED,
+                             event.subject().state());
+            } else if (expectedEvent == GroupEvent.Type.GROUP_UPDATE_REQUESTED) {
+                assertEquals(Group.GroupState.PENDING_UPDATE,
+                             event.subject().state());
+            } else if (expectedEvent == GroupEvent.Type.GROUP_REMOVE_REQUESTED) {
+                assertEquals(Group.GroupState.PENDING_DELETE,
+                             event.subject().state());
+            } else if (expectedEvent == GroupEvent.Type.GROUP_REMOVED) {
+                createdGroupId = event.subject().id();
+                assertEquals(Group.GroupState.PENDING_DELETE,
+                             event.subject().state());
+            }
+        }
+
+        public void verifyGroupId(GroupId id) {
+            assertEquals(createdGroupId, id);
+        }
+    }
+
+    @Test
+    public void testGroupStoreOperations() {
+        ApplicationId appId =
+                new DefaultApplicationId(2, "org.groupstore.test");
+        TestGroupKey key = new TestGroupKey("group1");
+        PortNumber[] ports = {PortNumber.portNumber(31),
+                              PortNumber.portNumber(32)};
+        List<PortNumber> outPorts = new ArrayList<PortNumber>();
+        outPorts.add(ports[0]);
+        outPorts.add(ports[1]);
+
+        List<GroupBucket> buckets = new ArrayList<GroupBucket>();
+        for (PortNumber portNumber: outPorts) {
+            TrafficTreatment.Builder tBuilder = DefaultTrafficTreatment.builder();
+            tBuilder.setOutput(portNumber)
+                    .setEthDst(MacAddress.valueOf("00:00:00:00:00:02"))
+                    .setEthSrc(MacAddress.valueOf("00:00:00:00:00:01"))
+                    .pushMpls()
+                    .setMpls(106);
+            buckets.add(DefaultGroupBucket.createSelectGroupBucket(
+                                                        tBuilder.build()));
+        }
+        GroupBuckets groupBuckets = new GroupBuckets(buckets);
+        GroupDescription groupDesc = new DefaultGroupDescription(
+                                                 D1,
+                                                 Group.Type.SELECT,
+                                                 groupBuckets,
+                                                 key,
+                                                 appId);
+        InternalGroupStoreDelegate checkStoreGroupDelegate =
+                new InternalGroupStoreDelegate(key,
+                                               groupBuckets,
+                                               GroupEvent.Type.GROUP_ADD_REQUESTED);
+        simpleGroupStore.setDelegate(checkStoreGroupDelegate);
+        /* Testing storeGroup operation */
+        simpleGroupStore.storeGroupDescription(groupDesc);
+
+        /* Testing getGroupCount operation */
+        assertEquals(1, simpleGroupStore.getGroupCount(D1));
+
+        /* Testing getGroup operation */
+        Group createdGroup = simpleGroupStore.getGroup(D1, key);
+        checkStoreGroupDelegate.verifyGroupId(createdGroup.id());
+
+        /* Testing getGroups operation */
+        Iterable<Group> createdGroups = simpleGroupStore.getGroups(D1);
+        int groupCount = 0;
+        for (Group group:createdGroups) {
+            checkStoreGroupDelegate.verifyGroupId(group.id());
+            groupCount++;
+        }
+        assertEquals(1, groupCount);
+        simpleGroupStore.unsetDelegate(checkStoreGroupDelegate);
+
+        /* Testing addOrUpdateGroupEntry operation from southbound */
+        InternalGroupStoreDelegate addGroupEntryDelegate =
+                new InternalGroupStoreDelegate(key,
+                                               groupBuckets,
+                                               GroupEvent.Type.GROUP_ADDED);
+        simpleGroupStore.setDelegate(addGroupEntryDelegate);
+        simpleGroupStore.addOrUpdateGroupEntry(createdGroup);
+        simpleGroupStore.unsetDelegate(addGroupEntryDelegate);
+
+        /* Testing updateGroupDescription for ADD operation from northbound */
+        TestGroupKey addKey = new TestGroupKey("group1AddBuckets");
+        PortNumber[] newNeighborPorts = {PortNumber.portNumber(41),
+                                         PortNumber.portNumber(42)};
+        List<PortNumber> newOutPorts = new ArrayList<PortNumber>();
+        newOutPorts.add(newNeighborPorts[0]);
+        newOutPorts.add(newNeighborPorts[1]);
+
+        List<GroupBucket> toAddBuckets = new ArrayList<GroupBucket>();
+        for (PortNumber portNumber: newOutPorts) {
+            TrafficTreatment.Builder tBuilder = DefaultTrafficTreatment.builder();
+            tBuilder.setOutput(portNumber)
+                    .setEthDst(MacAddress.valueOf("00:00:00:00:00:03"))
+                    .setEthSrc(MacAddress.valueOf("00:00:00:00:00:01"))
+                    .pushMpls()
+                    .setMpls(106);
+            toAddBuckets.add(DefaultGroupBucket.createSelectGroupBucket(
+                                                        tBuilder.build()));
+        }
+        GroupBuckets toAddGroupBuckets = new GroupBuckets(toAddBuckets);
+        buckets.addAll(toAddBuckets);
+        GroupBuckets updatedGroupBuckets = new GroupBuckets(buckets);
+        InternalGroupStoreDelegate updateGroupDescDelegate =
+                new InternalGroupStoreDelegate(addKey,
+                                               updatedGroupBuckets,
+                                               GroupEvent.Type.GROUP_UPDATE_REQUESTED);
+        simpleGroupStore.setDelegate(updateGroupDescDelegate);
+        GroupDescription newGroupDesc = new DefaultGroupDescription(
+                                                 D1,
+                                                 Group.Type.SELECT,
+                                                 toAddGroupBuckets,
+                                                 addKey,
+                                                 appId);
+        simpleGroupStore.updateGroupDescription(D1,
+                                                key,
+                                                UpdateType.ADD,
+                                                newGroupDesc);
+        simpleGroupStore.unsetDelegate(updateGroupDescDelegate);
+
+        /* Testing updateGroupDescription for REMOVE operation from northbound */
+        TestGroupKey removeKey = new TestGroupKey("group1RemoveBuckets");
+        List<GroupBucket> toRemoveBuckets = new ArrayList<GroupBucket>();
+        toRemoveBuckets.add(updatedGroupBuckets.buckets().get(0));
+        toRemoveBuckets.add(updatedGroupBuckets.buckets().get(1));
+        GroupBuckets toRemoveGroupBuckets = new GroupBuckets(toRemoveBuckets);
+        List<GroupBucket> remainingBuckets = new ArrayList<GroupBucket>();
+        remainingBuckets.add(updatedGroupBuckets.buckets().get(2));
+        remainingBuckets.add(updatedGroupBuckets.buckets().get(3));
+        GroupBuckets remainingGroupBuckets = new GroupBuckets(remainingBuckets);
+        InternalGroupStoreDelegate removeGroupDescDelegate =
+                new InternalGroupStoreDelegate(removeKey,
+                                               remainingGroupBuckets,
+                                               GroupEvent.Type.GROUP_UPDATE_REQUESTED);
+        simpleGroupStore.setDelegate(removeGroupDescDelegate);
+        GroupDescription removeGroupDesc = new DefaultGroupDescription(
+                                                        D1,
+                                                        Group.Type.SELECT,
+                                                        toRemoveGroupBuckets,
+                                                        removeKey,
+                                                        appId);
+        simpleGroupStore.updateGroupDescription(D1,
+                                                addKey,
+                                                UpdateType.REMOVE,
+                                                removeGroupDesc);
+        simpleGroupStore.unsetDelegate(removeGroupDescDelegate);
+
+        /* Testing getGroup operation */
+        Group existingGroup = simpleGroupStore.getGroup(D1, removeKey);
+        checkStoreGroupDelegate.verifyGroupId(existingGroup.id());
+
+        /* Testing addOrUpdateGroupEntry operation from southbound */
+        InternalGroupStoreDelegate updateGroupEntryDelegate =
+                new InternalGroupStoreDelegate(removeKey,
+                                               remainingGroupBuckets,
+                                               GroupEvent.Type.GROUP_UPDATED);
+        simpleGroupStore.setDelegate(updateGroupEntryDelegate);
+        simpleGroupStore.addOrUpdateGroupEntry(existingGroup);
+        simpleGroupStore.unsetDelegate(updateGroupEntryDelegate);
+
+        /* Testing deleteGroupDescription operation from northbound */
+        InternalGroupStoreDelegate deleteGroupDescDelegate =
+                new InternalGroupStoreDelegate(removeKey,
+                                               remainingGroupBuckets,
+                                               GroupEvent.Type.GROUP_REMOVE_REQUESTED);
+        simpleGroupStore.setDelegate(deleteGroupDescDelegate);
+        simpleGroupStore.deleteGroupDescription(D1, removeKey);
+        simpleGroupStore.unsetDelegate(deleteGroupDescDelegate);
+
+        /* Testing removeGroupEntry operation from southbound */
+        InternalGroupStoreDelegate removeGroupEntryDelegate =
+                new InternalGroupStoreDelegate(removeKey,
+                                               remainingGroupBuckets,
+                                               GroupEvent.Type.GROUP_REMOVED);
+        simpleGroupStore.setDelegate(removeGroupEntryDelegate);
+        simpleGroupStore.removeGroupEntry(existingGroup);
+
+        /* Testing getGroup operation */
+        existingGroup = simpleGroupStore.getGroup(D1, removeKey);
+        assertEquals(null, existingGroup);
+        Iterable<Group> existingGroups  = simpleGroupStore.getGroups(D1);
+        groupCount = 0;
+        for (Group tmp:existingGroups) {
+            /* To avoid warning */
+            assertEquals(null, tmp);
+            groupCount++;
+        }
+        assertEquals(0, groupCount);
+        assertEquals(0, simpleGroupStore.getGroupCount(D1));
+
+        simpleGroupStore.unsetDelegate(removeGroupEntryDelegate);
+
+    }
+}
+