diff --git a/core/api/src/main/java/org/onosproject/ui/model/topo/UiCluster.java b/core/api/src/main/java/org/onosproject/ui/model/topo/UiCluster.java
deleted file mode 100644
index 40de28c..0000000
--- a/core/api/src/main/java/org/onosproject/ui/model/topo/UiCluster.java
+++ /dev/null
@@ -1,92 +0,0 @@
-/*
- *  Copyright 2016-present 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.ui.model.topo;
-
-import org.onosproject.cluster.NodeId;
-
-import java.util.ArrayList;
-import java.util.HashMap;
-import java.util.List;
-import java.util.Map;
-
-/**
- * Encapsulates the notion of the ONOS cluster.
- */
-class UiCluster extends UiElement {
-
-    private static final String DEFAULT_CLUSTER_ID = "CLUSTER-0";
-
-    private final List<UiClusterMember> members = new ArrayList<>();
-    private final Map<NodeId, UiClusterMember> lookup = new HashMap<>();
-
-    @Override
-    public String toString() {
-        return String.valueOf(size()) + "-member cluster";
-    }
-
-    /**
-     * Removes all cluster members.
-     */
-    void clear() {
-        members.clear();
-    }
-
-    /**
-     * Returns the cluster member with the given identifier, or null if no
-     * such member exists.
-     *
-     * @param id identifier of member to find
-     * @return corresponding member
-     */
-    public UiClusterMember find(NodeId id) {
-        return lookup.get(id);
-    }
-
-    /**
-     * Adds the given member to the cluster.
-     *
-     * @param member member to add
-     */
-    public void add(UiClusterMember member) {
-        members.add(member);
-        lookup.put(member.id(), member);
-    }
-
-    /**
-     * Removes the given member from the cluster.
-     *
-     * @param member member to remove
-     */
-    public void remove(UiClusterMember member) {
-        members.remove(member);
-        lookup.remove(member.id());
-    }
-
-    /**
-     * Returns the number of members in the cluster.
-     *
-     * @return number of members
-     */
-    public int size() {
-        return members.size();
-    }
-
-    @Override
-    public String idAsString() {
-        return DEFAULT_CLUSTER_ID;
-    }
-}
diff --git a/core/api/src/main/java/org/onosproject/ui/model/topo/UiClusterMember.java b/core/api/src/main/java/org/onosproject/ui/model/topo/UiClusterMember.java
index 1cc9234..d8803ab 100644
--- a/core/api/src/main/java/org/onosproject/ui/model/topo/UiClusterMember.java
+++ b/core/api/src/main/java/org/onosproject/ui/model/topo/UiClusterMember.java
@@ -19,6 +19,11 @@
 import org.onlab.packet.IpAddress;
 import org.onosproject.cluster.ControllerNode;
 import org.onosproject.cluster.NodeId;
+import org.onosproject.net.DeviceId;
+
+import java.util.Collections;
+import java.util.HashSet;
+import java.util.Set;
 
 import static org.onosproject.cluster.ControllerNode.State.INACTIVE;
 
@@ -27,18 +32,21 @@
  */
 public class UiClusterMember extends UiElement {
 
+    private final UiTopology topology;
     private final ControllerNode cnode;
 
-    private int deviceCount = 0;
     private ControllerNode.State state = INACTIVE;
+    private final Set<DeviceId> mastership = new HashSet<>();
 
     /**
-     * Constructs a cluster member, with a reference to the specified
-     * controller node instance.
+     * Constructs a UI cluster member, with a reference to the parent
+     * topology instance and the specified controller node instance.
      *
-     * @param cnode underlying controller node.
+     * @param topology parent topology containing this cluster member
+     * @param cnode    underlying controller node.
      */
-    public UiClusterMember(ControllerNode cnode) {
+    public UiClusterMember(UiTopology topology, ControllerNode cnode) {
+        this.topology = topology;
         this.cnode = cnode;
     }
 
@@ -47,10 +55,23 @@
         return "UiClusterMember{" + cnode +
                 ", online=" + isOnline() +
                 ", ready=" + isReady() +
-                ", #devices=" + deviceCount +
+                ", #devices=" + deviceCount() +
                 "}";
     }
 
+    @Override
+    public String idAsString() {
+        return id().toString();
+    }
+
+    /**
+     * Returns the controller node instance backing this UI cluster member.
+     *
+     * @return the backing controller node instance
+     */
+    public ControllerNode backingNode() {
+        return cnode;
+    }
 
     /**
      * Sets the state of this cluster member.
@@ -61,14 +82,15 @@
         this.state = state;
     }
 
-
     /**
-     * Sets the number of devices for which this cluster member is master.
+     * Sets the collection of identities of devices for which this
+     * controller node is master.
      *
-     * @param deviceCount number of devices
+     * @param mastership device IDs
      */
-    public void setDeviceCount(int deviceCount) {
-        this.deviceCount = deviceCount;
+    public void setMastership(Set<DeviceId> mastership) {
+        this.mastership.clear();
+        this.mastership.addAll(mastership);
     }
 
     /**
@@ -113,11 +135,26 @@
      * @return number of devices for which this member is master
      */
     public int deviceCount() {
-        return deviceCount;
+        return mastership.size();
     }
 
-    @Override
-    public String idAsString() {
-        return id().toString();
+    /**
+     * Returns the list of devices for which this cluster member is master.
+     *
+     * @return list of devices for which this member is master
+     */
+    public Set<DeviceId> masterOf() {
+        return Collections.unmodifiableSet(mastership);
+    }
+
+    /**
+     * Returns true if the specified device is one for which this cluster
+     * member is master.
+     *
+     * @param deviceId device ID
+     * @return true if this cluster member is master for the given device
+     */
+    public boolean masterOf(DeviceId deviceId) {
+        return mastership.contains(deviceId);
     }
 }
diff --git a/core/api/src/main/java/org/onosproject/ui/model/topo/UiDevice.java b/core/api/src/main/java/org/onosproject/ui/model/topo/UiDevice.java
index 88d86d0..bb59752 100644
--- a/core/api/src/main/java/org/onosproject/ui/model/topo/UiDevice.java
+++ b/core/api/src/main/java/org/onosproject/ui/model/topo/UiDevice.java
@@ -16,21 +16,53 @@
 
 package org.onosproject.ui.model.topo;
 
+import com.google.common.base.MoreObjects;
 import org.onosproject.net.Device;
 import org.onosproject.net.DeviceId;
+import org.onosproject.net.region.RegionId;
 
 /**
  * Represents a device.
  */
 public class UiDevice extends UiNode {
 
-    private Device device;
+    private final UiTopology topology;
+    private final Device device;
+
+    private RegionId regionId;
+
+    /**
+     * Creates a new UI device.
+     *
+     * @param topology parent topology
+     * @param device   backing device
+     */
+    public UiDevice(UiTopology topology, Device device) {
+        this.topology = topology;
+        this.device = device;
+    }
+
+    /**
+     * Sets the ID of the region to which this device belongs.
+     *
+     * @param regionId region identifier
+     */
+    public void setRegionId(RegionId regionId) {
+        this.regionId = regionId;
+    }
 
     @Override
-    protected void destroy() {
-        device = null;
+    public String toString() {
+        return MoreObjects.toStringHelper(this)
+                .add("id", id())
+                .add("region", regionId)
+                .toString();
     }
 
+    //    @Override
+//    protected void destroy() {
+//    }
+
     /**
      * Returns the identity of the device.
      *
@@ -44,4 +76,22 @@
     public String idAsString() {
         return id().toString();
     }
+
+    /**
+     * Returns the device instance backing this UI device.
+     *
+     * @return the backing device instance
+     */
+    public Device backingDevice() {
+        return device;
+    }
+
+    /**
+     * Returns the UI region to which this device belongs.
+     *
+     * @return the UI region
+     */
+    public UiRegion uiRegion() {
+        return topology.findRegion(regionId);
+    }
 }
diff --git a/core/api/src/main/java/org/onosproject/ui/model/topo/UiElement.java b/core/api/src/main/java/org/onosproject/ui/model/topo/UiElement.java
index f0c2684..558f206 100644
--- a/core/api/src/main/java/org/onosproject/ui/model/topo/UiElement.java
+++ b/core/api/src/main/java/org/onosproject/ui/model/topo/UiElement.java
@@ -35,4 +35,15 @@
      * @return the element unique identifier
      */
     public abstract String idAsString();
+
+    /**
+     * Returns a friendly name to be used for display purposes.
+     * This default implementation returns the result of calling
+     * {@link #idAsString()}.
+     *
+     * @return the friendly name
+     */
+    public String name() {
+        return idAsString();
+    }
 }
diff --git a/core/api/src/main/java/org/onosproject/ui/model/topo/UiHost.java b/core/api/src/main/java/org/onosproject/ui/model/topo/UiHost.java
index 9a9e24a..e80836a 100644
--- a/core/api/src/main/java/org/onosproject/ui/model/topo/UiHost.java
+++ b/core/api/src/main/java/org/onosproject/ui/model/topo/UiHost.java
@@ -16,19 +16,49 @@
 
 package org.onosproject.ui.model.topo;
 
+import org.onosproject.net.DeviceId;
 import org.onosproject.net.Host;
 import org.onosproject.net.HostId;
+import org.onosproject.net.PortNumber;
+
+import static com.google.common.base.MoreObjects.toStringHelper;
 
 /**
  * Represents an end-station host.
  */
 public class UiHost extends UiNode {
 
-    private Host host;
+    private final UiTopology topology;
+    private final Host host;
+
+    // Host location
+    private DeviceId locDevice;
+    private PortNumber locPort;
+
+    private UiLinkId edgeLinkId;
+
+    /**
+     * Creates a new UI host.
+     *
+     * @param topology parent topology
+     * @param host     backing host
+     */
+    public UiHost(UiTopology topology, Host host) {
+        this.topology = topology;
+        this.host = host;
+    }
+
+//    @Override
+//    protected void destroy() {
+//    }
 
     @Override
-    protected void destroy() {
-        host = null;
+    public String toString() {
+        return toStringHelper(this)
+                .add("id", id())
+                .add("dev", locDevice)
+                .add("port", locPort)
+                .toString();
     }
 
     /**
@@ -44,4 +74,44 @@
     public String idAsString() {
         return id().toString();
     }
+
+    /**
+     * Sets the host's current location.
+     *
+     * @param deviceId ID of device
+     * @param port     port number
+     */
+    public void setLocation(DeviceId deviceId, PortNumber port) {
+        locDevice = deviceId;
+        locPort = port;
+    }
+
+    /**
+     * Sets the ID of the edge link between this host and the device to which
+     * it connects.
+     *
+     * @param id edge link identifier to set
+     */
+    public void setEdgeLinkId(UiLinkId id) {
+        this.edgeLinkId = id;
+    }
+
+    /**
+     * Returns the host instance backing this UI host.
+     *
+     * @return the backing host instance
+     */
+    public Host backingHost() {
+        return host;
+    }
+
+    /**
+     * Identifier for the edge link between this host and the device to which
+     * it is connected.
+     *
+     * @return edge link identifier
+     */
+    public UiLinkId edgeLinkId() {
+        return null;
+    }
 }
diff --git a/core/api/src/main/java/org/onosproject/ui/model/topo/UiLayer.java b/core/api/src/main/java/org/onosproject/ui/model/topo/UiLayer.java
new file mode 100644
index 0000000..30d16f6
--- /dev/null
+++ b/core/api/src/main/java/org/onosproject/ui/model/topo/UiLayer.java
@@ -0,0 +1,34 @@
+/*
+ * Copyright 2016-present 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.ui.model.topo;
+
+/**
+ * Designates the logical layer of the network that an element belongs to.
+ */
+public enum UiLayer {
+    PACKET, OPTICAL;
+
+    /**
+     * Returns the default layer (for those elements that do not explicitly
+     * define which layer they belong to).
+     *
+     * @return default layer
+     */
+    public static UiLayer defaultLayer() {
+        return PACKET;
+    }
+}
diff --git a/core/api/src/main/java/org/onosproject/ui/model/topo/UiLink.java b/core/api/src/main/java/org/onosproject/ui/model/topo/UiLink.java
index 99d6144..b386c5e 100644
--- a/core/api/src/main/java/org/onosproject/ui/model/topo/UiLink.java
+++ b/core/api/src/main/java/org/onosproject/ui/model/topo/UiLink.java
@@ -16,26 +16,61 @@
 
 package org.onosproject.ui.model.topo;
 
-import org.onosproject.net.Device;
+import org.onosproject.net.DeviceId;
 import org.onosproject.net.EdgeLink;
 import org.onosproject.net.Link;
 
 import java.util.Set;
 
+import static com.google.common.base.MoreObjects.toStringHelper;
+
 /**
- * Represents a bi-directional link backed by two uni-directional links.
+ * Represents a link (line between two elements). This may have one of
+ * several forms:
+ * <ul>
+ * <li>
+ * An infrastructure link:
+ * two backing unidirectional links between two devices.
+ * </li>
+ * <li>
+ * An edge link:
+ * representing the connection between a host and a device.
+ * </li>
+ * <li>
+ * An aggregation link:
+ * representing multiple underlying UI link instances.
+ * </li>
+ * </ul>
  */
 public class UiLink extends UiElement {
 
+    private static final String E_UNASSOC =
+            "backing link not associated with this UI link: ";
+
+    private final UiTopology topology;
+    private final UiLinkId id;
+
+    /**
+     * Creates a UI link.
+     *
+     * @param topology parent topology
+     * @param id       canonicalized link identifier
+     */
+    public UiLink(UiTopology topology, UiLinkId id) {
+        this.topology = topology;
+        this.id = id;
+    }
+
     // devices at either end of this link
-    private Device deviceA;
-    private Device deviceB;
+    private DeviceId deviceA;
+    private DeviceId deviceB;
 
     // two unidirectional links underlying this link...
     private Link linkAtoB;
     private Link linkBtoA;
 
     // ==OR== : private (synthetic) host link
+    private DeviceId edgeDevice;
     private EdgeLink edgeLink;
 
     // ==OR== : set of underlying UI links that this link aggregates
@@ -43,6 +78,13 @@
 
 
     @Override
+    public String toString() {
+        return toStringHelper(this)
+                .add("id", id)
+                .toString();
+    }
+
+    @Override
     protected void destroy() {
         deviceA = null;
         deviceB = null;
@@ -55,9 +97,84 @@
         }
     }
 
+    /**
+     * Returns the canonicalized link identifier for this link.
+     *
+     * @return the link identifier
+     */
+    public UiLinkId id() {
+        return id;
+    }
+
     @Override
     public String idAsString() {
-        // TODO
-        return null;
+        return id.toString();
+    }
+
+    /**
+     * Attaches the given backing link to this UI link. This method will
+     * throw an exception if this UI link is not representative of the
+     * supplied link.
+     *
+     * @param link backing link to attach
+     * @throws IllegalArgumentException if the link is not appropriate
+     */
+    public void attachBackingLink(Link link) {
+        UiLinkId.Direction d = id.directionOf(link);
+
+        if (d == UiLinkId.Direction.A_TO_B) {
+            linkAtoB = link;
+            deviceA = link.src().deviceId();
+            deviceB = link.dst().deviceId();
+
+        } else if (d == UiLinkId.Direction.B_TO_A) {
+            linkBtoA = link;
+            deviceB = link.src().deviceId();
+            deviceA = link.dst().deviceId();
+
+        } else {
+            throw new IllegalArgumentException(E_UNASSOC + link);
+        }
+    }
+
+    /**
+     * Detaches the given backing link from this UI link, returning true if the
+     * reverse link is still attached, or false otherwise.
+     *
+     * @param link the backing link to detach
+     * @return true if other link still attached, false otherwise
+     * @throws IllegalArgumentException if the link is not appropriate
+     */
+    public boolean detachBackingLink(Link link) {
+        UiLinkId.Direction d = id.directionOf(link);
+        if (d == UiLinkId.Direction.A_TO_B) {
+            linkAtoB = null;
+            return linkBtoA != null;
+        }
+        if (d == UiLinkId.Direction.B_TO_A) {
+            linkBtoA = null;
+            return linkAtoB != null;
+        }
+        throw new IllegalArgumentException(E_UNASSOC + link);
+    }
+
+    /**
+     * Attaches the given edge link to this UI link. This method will
+     * throw an exception if this UI link is not representative of the
+     * supplied link.
+     *
+     * @param elink edge link to attach
+     * @throws IllegalArgumentException if the link is not appropriate
+     */
+    public void attachEdgeLink(EdgeLink elink) {
+        UiLinkId.Direction d = id.directionOf(elink);
+        // Expected direction of edge links is A-to-B (Host to device)
+        // but checking not null is sufficient
+        if (d == null) {
+            throw new IllegalArgumentException(E_UNASSOC + elink);
+        }
+
+        edgeLink = elink;
+        edgeDevice = elink.hostLocation().deviceId();
     }
 }
diff --git a/core/api/src/main/java/org/onosproject/ui/model/topo/UiLinkId.java b/core/api/src/main/java/org/onosproject/ui/model/topo/UiLinkId.java
new file mode 100644
index 0000000..070052d
--- /dev/null
+++ b/core/api/src/main/java/org/onosproject/ui/model/topo/UiLinkId.java
@@ -0,0 +1,139 @@
+/*
+ * Copyright 2016-present 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.ui.model.topo;
+
+import org.onosproject.net.ConnectPoint;
+import org.onosproject.net.ElementId;
+import org.onosproject.net.Link;
+
+/**
+ * A canonical representation of an identifier for {@link UiLink}s.
+ */
+public final class UiLinkId {
+
+    /**
+     * Designates the directionality of an underlying (uni-directional) link.
+     */
+    public enum Direction {
+        A_TO_B,
+        B_TO_A
+    }
+
+    private static final String ID_DELIMITER = "~";
+
+    private final ElementId idA;
+    private final ElementId idB;
+    private final String idStr;
+
+    /**
+     * Creates a UI link identifier. It is expected that A comes before B when
+     * the two identifiers are naturally sorted, thus providing a representation
+     * which is invariant to whether A or B is source or destination of the
+     * underlying link.
+     *
+     * @param a first element ID
+     * @param b second element ID
+     */
+    private UiLinkId(ElementId a, ElementId b) {
+        idA = a;
+        idB = b;
+
+        idStr = a.toString() + ID_DELIMITER + b.toString();
+    }
+
+    @Override
+    public String toString() {
+        return idStr;
+    }
+
+    /**
+     * Returns the identifier of the first element.
+     *
+     * @return first element identity
+     */
+    public ElementId elementA() {
+        return idA;
+    }
+
+    /**
+     * Returns the identifier of the second element.
+     *
+     * @return second element identity
+     */
+    public ElementId elementB() {
+        return idB;
+    }
+
+    @Override
+    public boolean equals(Object o) {
+        if (this == o) {
+            return true;
+        }
+        if (o == null || getClass() != o.getClass()) {
+            return false;
+        }
+
+        UiLinkId uiLinkId = (UiLinkId) o;
+        return idStr.equals(uiLinkId.idStr);
+    }
+
+    @Override
+    public int hashCode() {
+        return idStr.hashCode();
+    }
+
+    /**
+     * Returns the direction of the given link, or null if this link ID does
+     * not correspond to the given link.
+     *
+     * @param link the link to examine
+     * @return corresponding direction
+     */
+    Direction directionOf(Link link) {
+        ConnectPoint src = link.src();
+        ElementId srcId = src.elementId();
+        return idA.equals(srcId) ? Direction.A_TO_B
+                : idB.equals(srcId) ? Direction.B_TO_A
+                : null;
+    }
+
+    /**
+     * Generates the canonical link identifier for the given link.
+     *
+     * @param link link for which the identifier is required
+     * @return link identifier
+     * @throws NullPointerException if any of the required fields are null
+     */
+    public static UiLinkId uiLinkId(Link link) {
+        ConnectPoint src = link.src();
+        ConnectPoint dst = link.dst();
+        if (src == null || dst == null) {
+            throw new NullPointerException("null src or dst connect point: " + link);
+        }
+
+        ElementId srcId = src.elementId();
+        ElementId dstId = dst.elementId();
+        if (srcId == null || dstId == null) {
+            throw new NullPointerException("null element ID in connect point: " + link);
+        }
+
+        // canonicalize
+        int comp = srcId.toString().compareTo(dstId.toString());
+        return comp <= 0 ? new UiLinkId(srcId, dstId)
+                : new UiLinkId(dstId, srcId);
+    }
+}
diff --git a/core/api/src/main/java/org/onosproject/ui/model/topo/UiRegion.java b/core/api/src/main/java/org/onosproject/ui/model/topo/UiRegion.java
index 488c37b..0bcaa58 100644
--- a/core/api/src/main/java/org/onosproject/ui/model/topo/UiRegion.java
+++ b/core/api/src/main/java/org/onosproject/ui/model/topo/UiRegion.java
@@ -16,35 +16,46 @@
 
 package org.onosproject.ui.model.topo;
 
+import org.onosproject.net.DeviceId;
+import org.onosproject.net.HostId;
 import org.onosproject.net.region.Region;
 import org.onosproject.net.region.RegionId;
 
+import java.util.HashSet;
 import java.util.Set;
-import java.util.TreeSet;
+
+import static com.google.common.base.MoreObjects.toStringHelper;
 
 /**
  * Represents a region.
  */
 public class UiRegion extends UiNode {
 
-    private final Set<UiDevice> uiDevices = new TreeSet<>();
-    private final Set<UiHost> uiHosts = new TreeSet<>();
-    private final Set<UiLink> uiLinks = new TreeSet<>();
+    // loose bindings to things in this region
+    private final Set<DeviceId> deviceIds = new HashSet<>();
+    private final Set<HostId> hostIds = new HashSet<>();
+    private final Set<UiLinkId> uiLinkIds = new HashSet<>();
 
-    private Region region;
+    private final UiTopology topology;
 
+    private final Region region;
+
+    /**
+     * Constructs a UI region, with a reference to the specified backing region.
+     *
+     * @param topology parent topology
+     * @param region   backing region
+     */
+    public UiRegion(UiTopology topology, Region region) {
+        this.topology = topology;
+        this.region = region;
+    }
 
     @Override
     protected void destroy() {
-        uiDevices.forEach(UiDevice::destroy);
-        uiHosts.forEach(UiHost::destroy);
-        uiLinks.forEach(UiLink::destroy);
-
-        uiDevices.clear();
-        uiHosts.clear();
-        uiLinks.clear();
-
-        region = null;
+        deviceIds.clear();
+        hostIds.clear();
+        uiLinkIds.clear();
     }
 
     /**
@@ -60,4 +71,75 @@
     public String idAsString() {
         return id().toString();
     }
+
+    @Override
+    public String name() {
+        return region.name();
+    }
+
+    /**
+     * Returns the region instance backing this UI region.
+     *
+     * @return the backing region instance
+     */
+    public Region backingRegion() {
+        return region;
+    }
+
+    /**
+     * Make sure we have only these devices in the region.
+     *
+     * @param devices devices in the region
+     */
+    public void reconcileDevices(Set<DeviceId> devices) {
+        deviceIds.clear();
+        deviceIds.addAll(devices);
+    }
+
+    @Override
+    public String toString() {
+        return toStringHelper(this)
+                .add("id", id())
+                .add("name", name())
+                .add("devices", deviceIds)
+                .add("#hosts", hostIds.size())
+                .add("#links", uiLinkIds.size())
+                .toString();
+    }
+
+    /**
+     * Returns the region's type.
+     *
+     * @return region type
+     */
+    public Region.Type type() {
+        return region.type();
+    }
+
+    /**
+     * Returns the devices in this region.
+     *
+     * @return the devices in this region
+     */
+    public Set<UiDevice> devices() {
+        return topology.deviceSet(deviceIds);
+    }
+
+    /**
+     * Returns the hosts in this region.
+     *
+     * @return the hosts in this region
+     */
+    public Set<UiHost> hosts() {
+        return topology.hostSet(hostIds);
+    }
+
+    /**
+     * Returns the links in this region.
+     *
+     * @return the links in this region
+     */
+    public Set<UiLink> links() {
+        return topology.linkSet(uiLinkIds);
+    }
 }
diff --git a/core/api/src/main/java/org/onosproject/ui/model/topo/UiTopology.java b/core/api/src/main/java/org/onosproject/ui/model/topo/UiTopology.java
index a8b5b06..3a11fcf 100644
--- a/core/api/src/main/java/org/onosproject/ui/model/topo/UiTopology.java
+++ b/core/api/src/main/java/org/onosproject/ui/model/topo/UiTopology.java
@@ -17,27 +17,54 @@
 package org.onosproject.ui.model.topo;
 
 import org.onosproject.cluster.NodeId;
+import org.onosproject.net.DeviceId;
+import org.onosproject.net.HostId;
+import org.onosproject.net.region.RegionId;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
+import java.util.HashMap;
+import java.util.HashSet;
+import java.util.Map;
 import java.util.Set;
-import java.util.TreeSet;
+
+import static com.google.common.base.MoreObjects.toStringHelper;
 
 /**
  * Represents the overall network topology.
  */
 public class UiTopology extends UiElement {
 
+    private static final String E_UNMAPPED =
+            "Attempting to retrieve unmapped {}: {}";
+
     private static final String DEFAULT_TOPOLOGY_ID = "TOPOLOGY-0";
 
     private static final Logger log = LoggerFactory.getLogger(UiTopology.class);
 
-    private final UiCluster uiCluster = new UiCluster();
-    private final Set<UiRegion> uiRegions = new TreeSet<>();
+
+    // top level mappings of topology elements by ID
+    private final Map<NodeId, UiClusterMember> cnodeLookup = new HashMap<>();
+    private final Map<RegionId, UiRegion> regionLookup = new HashMap<>();
+    private final Map<DeviceId, UiDevice> deviceLookup = new HashMap<>();
+    private final Map<HostId, UiHost> hostLookup = new HashMap<>();
+    private final Map<UiLinkId, UiLink> linkLookup = new HashMap<>();
+
 
     @Override
     public String toString() {
-        return "Topology: " + uiCluster + ", " + uiRegions.size() + " regions";
+        return toStringHelper(this)
+                .add("#cnodes", clusterMemberCount())
+                .add("#regions", regionCount())
+                .add("#devices", deviceLookup.size())
+                .add("#hosts", hostLookup.size())
+                .add("#links", linkLookup.size())
+                .toString();
+    }
+
+    @Override
+    public String idAsString() {
+        return DEFAULT_TOPOLOGY_ID;
     }
 
     /**
@@ -46,19 +73,22 @@
      */
     public void clear() {
         log.debug("clearing topology model");
-        uiRegions.clear();
-        uiCluster.clear();
+        cnodeLookup.clear();
+        regionLookup.clear();
+        deviceLookup.clear();
+        hostLookup.clear();
+        linkLookup.clear();
     }
 
     /**
      * Returns the cluster member with the given identifier, or null if no
-     * such member.
+     * such member exists.
      *
      * @param id cluster node identifier
-     * @return the cluster member with that identifier
+     * @return corresponding UI cluster member
      */
     public UiClusterMember findClusterMember(NodeId id) {
-        return uiCluster.find(id);
+        return cnodeLookup.get(id);
     }
 
     /**
@@ -67,7 +97,7 @@
      * @param member cluster member to add
      */
     public void add(UiClusterMember member) {
-        uiCluster.add(member);
+        cnodeLookup.put(member.id(), member);
     }
 
     /**
@@ -76,7 +106,10 @@
      * @param member cluster member to remove
      */
     public void remove(UiClusterMember member) {
-        uiCluster.remove(member);
+        UiClusterMember m = cnodeLookup.remove(member.id());
+        if (m != null) {
+            m.destroy();
+        }
     }
 
     /**
@@ -85,7 +118,18 @@
      * @return number of cluster members
      */
     public int clusterMemberCount() {
-        return uiCluster.size();
+        return cnodeLookup.size();
+    }
+
+    /**
+     * Returns the region with the specified identifier, or null if
+     * no such region exists.
+     *
+     * @param id region identifier
+     * @return corresponding UI region
+     */
+    public UiRegion findRegion(RegionId id) {
+        return regionLookup.get(id);
     }
 
     /**
@@ -94,11 +138,182 @@
      * @return number of regions
      */
     public int regionCount() {
-        return uiRegions.size();
+        return regionLookup.size();
     }
 
-    @Override
-    public String idAsString() {
-        return DEFAULT_TOPOLOGY_ID;
+    /**
+     * Adds the given region to the topology model.
+     *
+     * @param uiRegion region to add
+     */
+    public void add(UiRegion uiRegion) {
+        regionLookup.put(uiRegion.id(), uiRegion);
     }
+
+    /**
+     * Removes the given region from the topology model.
+     *
+     * @param uiRegion region to remove
+     */
+    public void remove(UiRegion uiRegion) {
+        regionLookup.remove(uiRegion.id());
+    }
+
+    /**
+     * Returns the device with the specified identifier, or null if
+     * no such device exists.
+     *
+     * @param id device identifier
+     * @return corresponding UI device
+     */
+    public UiDevice findDevice(DeviceId id) {
+        return deviceLookup.get(id);
+    }
+
+    /**
+     * Adds the given device to the topology model.
+     *
+     * @param uiDevice device to add
+     */
+    public void add(UiDevice uiDevice) {
+        deviceLookup.put(uiDevice.id(), uiDevice);
+    }
+
+    /**
+     * Removes the given device from the topology model.
+     *
+     * @param uiDevice device to remove
+     */
+    public void remove(UiDevice uiDevice) {
+        UiDevice d = deviceLookup.remove(uiDevice.id());
+        if (d != null) {
+            d.destroy();
+        }
+    }
+
+    /**
+     * Returns the link with the specified identifier, or null if no such
+     * link exists.
+     *
+     * @param id the canonicalized link identifier
+     * @return corresponding UI link
+     */
+    public UiLink findLink(UiLinkId id) {
+        return linkLookup.get(id);
+    }
+
+    /**
+     * Adds the given UI link to the topology model.
+     *
+     * @param uiLink link to add
+     */
+    public void add(UiLink uiLink) {
+        linkLookup.put(uiLink.id(), uiLink);
+    }
+
+    /**
+     * Removes the given UI link from the model.
+     *
+     * @param uiLink link to remove
+     */
+    public void remove(UiLink uiLink) {
+        UiLink link = linkLookup.get(uiLink.id());
+        if (link != null) {
+            link.destroy();
+        }
+    }
+
+    /**
+     * Returns the host with the specified identifier, or null if no such
+     * host exists.
+     *
+     * @param id host identifier
+     * @return corresponding UI host
+     */
+    public UiHost findHost(HostId id) {
+        return hostLookup.get(id);
+    }
+
+    /**
+     * Adds the given host to the topology model.
+     *
+     * @param uiHost host to add
+     */
+    public void add(UiHost uiHost) {
+        hostLookup.put(uiHost.id(), uiHost);
+    }
+
+    /**
+     * Removes the given host from the topology model.
+     *
+     * @param uiHost host to remove
+     */
+    public void remove(UiHost uiHost) {
+        UiHost h = hostLookup.remove(uiHost.id());
+        if (h != null) {
+            h.destroy();
+        }
+    }
+
+    // ==
+    // package private methods for supporting linkage amongst topology entities
+    // ==
+
+    /**
+     * Returns the set of UI devices with the given identifiers.
+     *
+     * @param deviceIds device identifiers
+     * @return set of matching UI device instances
+     */
+    Set<UiDevice> deviceSet(Set<DeviceId> deviceIds) {
+        Set<UiDevice> uiDevices = new HashSet<>();
+        for (DeviceId id : deviceIds) {
+            UiDevice d = deviceLookup.get(id);
+            if (d != null) {
+                uiDevices.add(d);
+            } else {
+                log.warn(E_UNMAPPED, "device", id);
+            }
+        }
+        return uiDevices;
+    }
+
+    /**
+     * Returns the set of UI hosts with the given identifiers.
+     *
+     * @param hostIds host identifiers
+     * @return set of matching UI host instances
+     */
+    Set<UiHost> hostSet(Set<HostId> hostIds) {
+        Set<UiHost> uiHosts = new HashSet<>();
+        for (HostId id : hostIds) {
+            UiHost h = hostLookup.get(id);
+            if (h != null) {
+                uiHosts.add(h);
+            } else {
+                log.warn(E_UNMAPPED, "host", id);
+            }
+        }
+        return uiHosts;
+    }
+
+    /**
+     * Returns the set of UI links with the given identifiers.
+     *
+     * @param uiLinkIds link identifiers
+     * @return set of matching UI link instances
+     */
+    Set<UiLink> linkSet(Set<UiLinkId> uiLinkIds) {
+        Set<UiLink> uiLinks = new HashSet<>();
+        for (UiLinkId id : uiLinkIds) {
+            UiLink link = linkLookup.get(id);
+            if (link != null) {
+                uiLinks.add(link);
+            } else {
+                log.warn(E_UNMAPPED, "link", id);
+            }
+        }
+        return uiLinks;
+    }
+
 }