domain intent APIs

Change-Id: I4b2ac854da7808a880ef0a37b3b08ef51da812e5
diff --git a/core/api/src/main/java/org/onosproject/net/domain/DomainService.java b/core/api/src/main/java/org/onosproject/net/domain/DomainService.java
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+/*
+ * 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.net.domain;
+
+import org.onosproject.net.DeviceId;
+
+import java.util.Set;
+
+/**
+ * Service to access domain topology elements.
+ */
+public interface DomainService {
+
+    /**
+     * Returns the set of domains that have an associated topology.
+     *
+     * @return set of domain identifiers
+     */
+    Set<DomainId> getDomainIds();
+
+    /**
+     * Returns the set of the device ids of the specified domain.
+     *
+     * @param domainId domain identifier
+     * @return set of device objects
+     */
+    Set<DeviceId> getDeviceIds(DomainId domainId);
+
+    /**
+     * Returns a domain given a device id.
+     *
+     * @param deviceId the device id
+     * @return null or the domain id of a device
+     */
+    DomainId getDomain(DeviceId deviceId);
+}
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