adding constaints to intent API
diff --git a/core/api/src/main/java/org/onlab/onos/net/intent/Constraint.java b/core/api/src/main/java/org/onlab/onos/net/intent/Constraint.java
new file mode 100644
index 0000000..9004aa6
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+++ b/core/api/src/main/java/org/onlab/onos/net/intent/Constraint.java
@@ -0,0 +1,51 @@
+/*
+ * 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.onlab.onos.net.intent;
+
+import org.onlab.onos.net.Link;
+import org.onlab.onos.net.Path;
+import org.onlab.onos.net.resource.LinkResourceService;
+
+/**
+ * Representation of a connectivity constraint capable of evaluating a link
+ * and determining the cost of traversing that link in the context of this
+ * constraint.
+ */
+public interface Constraint {
+
+ // TODO: Consider separating cost vs viability.
+
+ /**
+ * Evaluates the specified link and provides the cost for its traversal.
+ *
+ * @param link link to be evaluated
+ * @param resourceService resource service for validating availability of
+ * link resources
+ * @return cost of link traversal
+ */
+ double cost(Link link, LinkResourceService resourceService);
+
+ /**
+ * Validates that the specified path satisfies the constraint.
+ *
+ * @param path path to be validated
+ * @param resourceService resource service for validating availability of
+ * link resources
+ * @return cost of link traversal
+ */
+ boolean validate(Path path, LinkResourceService resourceService);
+
+}