diff --git a/apps/workflow/api/src/main/java/org/onosproject/workflow/api/AbstractWorkflow.java b/apps/workflow/api/src/main/java/org/onosproject/workflow/api/AbstractWorkflow.java
index 8a5f2b8..5fb8943 100644
--- a/apps/workflow/api/src/main/java/org/onosproject/workflow/api/AbstractWorkflow.java
+++ b/apps/workflow/api/src/main/java/org/onosproject/workflow/api/AbstractWorkflow.java
@@ -42,11 +42,19 @@
 
     @Override
     public WorkflowContext buildContext(Workplace workplace, DataModelTree data) throws WorkflowException {
-        return new DefaultWorkflowContext(id, workplace.name(), data);
+        return DefaultWorkflowContext.builder()
+                .workflowId(id)
+                .workplaceName(workplace.name())
+                .data(data)
+                .build();
     }
 
     @Override
     public WorkflowContext buildSystemContext(Workplace workplace, DataModelTree data) throws WorkflowException {
-        return new SystemWorkflowContext(id, workplace.name(), data);
+        return SystemWorkflowContext.systemBuilder()
+                .workflowId(id)
+                .workplaceName(workplace.name())
+                .data(data)
+                .build();
     }
 }
diff --git a/apps/workflow/api/src/main/java/org/onosproject/workflow/api/CheckCondition.java b/apps/workflow/api/src/main/java/org/onosproject/workflow/api/CheckCondition.java
new file mode 100644
index 0000000..7419583
--- /dev/null
+++ b/apps/workflow/api/src/main/java/org/onosproject/workflow/api/CheckCondition.java
@@ -0,0 +1,44 @@
+/*
+ * Copyright 2018-present Open Networking Foundation
+ *
+ * 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.workflow.api;
+
+
+/**
+ * Static convenience class that help a whether it was invoked correctly(whether its preconditions have been met).
+ * Methods of this class generally accept a boolean expression which is expected to be true.
+ * When false (or null) is passed instead, the Preconditions method throws an workflow exception.
+ */
+public final class CheckCondition {
+
+    /**
+     * Private class of check condition.
+     */
+    private CheckCondition() {
+    }
+
+    /**
+     * Checks the condition, and if it is false, it raises workflow exception with exception message.
+     * @param condition condition to check. A boolean expression is located on here.
+     * @param exceptionMessage exception message for workflow exception
+     * @throws WorkflowException workflow exception
+     */
+    public static void check(boolean condition, String exceptionMessage) throws WorkflowException {
+        if (!condition) {
+            throw new WorkflowException(exceptionMessage);
+        }
+    }
+
+}
diff --git a/apps/workflow/api/src/main/java/org/onosproject/workflow/api/ContextEventMapStore.java b/apps/workflow/api/src/main/java/org/onosproject/workflow/api/ContextEventMapStore.java
index c26b3be..6d0f0fb 100644
--- a/apps/workflow/api/src/main/java/org/onosproject/workflow/api/ContextEventMapStore.java
+++ b/apps/workflow/api/src/main/java/org/onosproject/workflow/api/ContextEventMapStore.java
@@ -32,11 +32,11 @@
      * @param eventType the class name of event
      * @param eventHint event hint string value of the event
      * @param contextName workflow context name
-     * @param workletType the class name of worklet
+     * @param programCounterString the program counter of workflow
      * @throws WorkflowException workflow exception
      */
     void registerEventMap(String eventType, String eventHint,
-                          String contextName, String workletType) throws WorkflowException;
+                          String contextName, String programCounterString) throws WorkflowException;
 
     /**
      * Unregisters workflow context event mapping.
diff --git a/apps/workflow/api/src/main/java/org/onosproject/workflow/api/DataModelTree.java b/apps/workflow/api/src/main/java/org/onosproject/workflow/api/DataModelTree.java
index 3236164..f7ada8d 100644
--- a/apps/workflow/api/src/main/java/org/onosproject/workflow/api/DataModelTree.java
+++ b/apps/workflow/api/src/main/java/org/onosproject/workflow/api/DataModelTree.java
@@ -59,5 +59,12 @@
      * @throws WorkflowException workflow exception
      */
     DataModelTree alloc(String path, Nodetype leaftype) throws WorkflowException;
+
+    /**
+     * Remove node on the path.
+     * @param path data model tree path
+     * @throws WorkflowException workflow exception
+     */
+    void remove(String path) throws WorkflowException;
 }
 
diff --git a/apps/workflow/api/src/main/java/org/onosproject/workflow/api/DefaultRpcDescription.java b/apps/workflow/api/src/main/java/org/onosproject/workflow/api/DefaultRpcDescription.java
index 4a4715e..6f9d3c3 100644
--- a/apps/workflow/api/src/main/java/org/onosproject/workflow/api/DefaultRpcDescription.java
+++ b/apps/workflow/api/src/main/java/org/onosproject/workflow/api/DefaultRpcDescription.java
@@ -20,6 +20,8 @@
 import com.fasterxml.jackson.databind.node.TextNode;
 import com.google.common.base.MoreObjects;
 
+import static org.onosproject.workflow.api.CheckCondition.check;
+
 /**
  * Class of workflow RPC description.
  */
@@ -169,8 +171,12 @@
         /**
          * Builds workplace RPC description from builder.
          * @return instance of workflow RPC description
+         * @throws WorkflowException workflow exception
          */
-        public DefaultRpcDescription build() {
+        public DefaultRpcDescription build() throws WorkflowException {
+            check(op != null, "op is invalid");
+            check(params != null, "params is invalid");
+            check(id != null, "id is invalid");
             return new DefaultRpcDescription(this);
         }
     }
diff --git a/apps/workflow/api/src/main/java/org/onosproject/workflow/api/DefaultWorkflowContext.java b/apps/workflow/api/src/main/java/org/onosproject/workflow/api/DefaultWorkflowContext.java
index e16376f..05c564a 100644
--- a/apps/workflow/api/src/main/java/org/onosproject/workflow/api/DefaultWorkflowContext.java
+++ b/apps/workflow/api/src/main/java/org/onosproject/workflow/api/DefaultWorkflowContext.java
@@ -16,10 +16,14 @@
 package org.onosproject.workflow.api;
 
 import com.google.common.base.MoreObjects;
+import org.onlab.osgi.DefaultServiceDirectory;
+import org.onlab.osgi.ServiceNotFoundException;
 import org.onosproject.event.Event;
 
 import java.net.URI;
 
+import static org.onosproject.workflow.api.CheckCondition.check;
+
 /**
  * Default implementation of WorkflowContext.
  */
@@ -41,9 +45,9 @@
     private WorkflowState state;
 
     /**
-     * Current worklet of the workflow.
+     * Current program counter of the workflow.
      */
-    private String current;
+    private ProgramCounter current;
 
     /**
      * Cause of workflow exception.
@@ -87,16 +91,14 @@
 
     /**
      * Constructor of DefaultWorkflowContext.
-     * @param workflowId ID of workflow
-     * @param workplaceName name of workplace
-     * @param data data model tree
+     * @param builder default workflow context builder
      */
-    public DefaultWorkflowContext(URI workflowId, String workplaceName, DataModelTree data) {
-        super(data);
-        this.workflowId = workflowId;
-        this.workplaceName = workplaceName;
+    protected DefaultWorkflowContext(Builder builder) {
+        super(builder.data);
+        this.workflowId = builder.workflowId;
+        this.workplaceName = builder.workplaceName;
         this.state = WorkflowState.IDLE;
-        this.current = Worklet.Common.INIT.name();
+        this.current = ProgramCounter.INIT_PC;
     }
 
     /**
@@ -140,13 +142,13 @@
     }
 
     @Override
-    public String current() {
+    public ProgramCounter current() {
         return this.current;
     }
 
     @Override
-    public void setCurrent(Worklet worklet) {
-        this.current = worklet.tag();
+    public void setCurrent(ProgramCounter pc) {
+        this.current = pc;
     }
 
     @Override
@@ -228,6 +230,16 @@
         return workplaceStore;
     }
 
+    public <T> T getService(Class<T> serviceClass) throws WorkflowException {
+        T service;
+        try {
+            service = DefaultServiceDirectory.getService(serviceClass);
+        } catch (ServiceNotFoundException e) {
+            throw new WorkflowException(e);
+        }
+        return service;
+    }
+
     @Override
     public String toString() {
         return MoreObjects.toStringHelper(getClass())
@@ -239,4 +251,75 @@
                 .add("cause", cause())
                 .toString();
     }
+
+    /**
+     * Gets builder instance.
+     * @return builder instance
+     */
+    public static final Builder builder() {
+        return new Builder();
+    }
+
+    /**
+     * Builder for default workflow context.
+     */
+    public static class Builder {
+
+        /**
+         * ID of workflow.
+         */
+        private URI workflowId;
+
+        /**
+         * Workplace name of the workflow.
+         */
+        private String workplaceName;
+
+        /**
+         * Data model tree.
+         */
+        private DataModelTree data;
+
+        /**
+         * Sets workflow id.
+         * @param workflowId workflow id
+         * @return builder
+         */
+        public Builder workflowId(URI workflowId) {
+            this.workflowId = workflowId;
+            return this;
+        }
+
+        /**
+         * Sets workplace name.
+         * @param workplaceName workplace name
+         * @return builder
+         */
+        public Builder workplaceName(String workplaceName) {
+            this.workplaceName = workplaceName;
+            return this;
+        }
+
+        /**
+         * Sets data model tree.
+         * @param data data model tree
+         * @return builder
+         */
+        public Builder data(DataModelTree data) {
+            this.data = data;
+            return this;
+        }
+
+        /**
+         * Builds default workflow context.
+         * @return instance of default workflow context
+         * @throws WorkflowException workflow exception
+         */
+        public DefaultWorkflowContext build() throws WorkflowException {
+            check(data != null, "Invalid data model tree");
+            check(workflowId != null, "Invalid workflowId");
+            check(workplaceName != null, "Invalid workplaceName");
+            return new DefaultWorkflowContext(this);
+        }
+    }
 }
diff --git a/apps/workflow/api/src/main/java/org/onosproject/workflow/api/DefaultWorkflowDescription.java b/apps/workflow/api/src/main/java/org/onosproject/workflow/api/DefaultWorkflowDescription.java
index c9ded60..13a8f46 100644
--- a/apps/workflow/api/src/main/java/org/onosproject/workflow/api/DefaultWorkflowDescription.java
+++ b/apps/workflow/api/src/main/java/org/onosproject/workflow/api/DefaultWorkflowDescription.java
@@ -24,6 +24,8 @@
 
 import java.net.URI;
 
+import static org.onosproject.workflow.api.CheckCondition.check;
+
 
 /**
  * Class for default workflow description.
@@ -201,8 +203,12 @@
         /**
          * Builds workflow description from builder.
          * @return instance of workflow description
+         * @throws WorkflowException workflow exception
          */
-        public DefaultWorkflowDescription build() {
+        public DefaultWorkflowDescription build() throws WorkflowException {
+            check(workplaceName != null, "workplaceName is invalid");
+            check(id != null, "id is invalid");
+            check(data != null, "data is invalid");
             return new DefaultWorkflowDescription(this);
         }
     }
diff --git a/apps/workflow/api/src/main/java/org/onosproject/workflow/api/DefaultWorkplaceDescription.java b/apps/workflow/api/src/main/java/org/onosproject/workflow/api/DefaultWorkplaceDescription.java
index 95da550..e8125f7 100644
--- a/apps/workflow/api/src/main/java/org/onosproject/workflow/api/DefaultWorkplaceDescription.java
+++ b/apps/workflow/api/src/main/java/org/onosproject/workflow/api/DefaultWorkplaceDescription.java
@@ -27,6 +27,8 @@
 import java.util.List;
 import java.util.Optional;
 
+import static org.onosproject.workflow.api.CheckCondition.check;
+
 /**
  * Class for default workplace description.
  */
@@ -161,8 +163,10 @@
         /**
          * Builds workplace description from builder.
          * @return instance of workflow description
+         * @throws WorkflowException workflow exception
          */
-        public DefaultWorkplaceDescription build() {
+        public DefaultWorkplaceDescription build() throws WorkflowException {
+            check(name != null, "name is invalid");
             return new DefaultWorkplaceDescription(this);
         }
     }
diff --git a/apps/workflow/api/src/main/java/org/onosproject/workflow/api/EventHintSupplier.java b/apps/workflow/api/src/main/java/org/onosproject/workflow/api/EventHintSupplier.java
index 3ad1847..076bfc0 100644
--- a/apps/workflow/api/src/main/java/org/onosproject/workflow/api/EventHintSupplier.java
+++ b/apps/workflow/api/src/main/java/org/onosproject/workflow/api/EventHintSupplier.java
@@ -22,5 +22,5 @@
  */
 @FunctionalInterface
 public interface EventHintSupplier {
-    String apply(Event event);
+    String apply(Event event) throws Throwable;
 }
diff --git a/apps/workflow/api/src/main/java/org/onosproject/workflow/api/EventTask.java b/apps/workflow/api/src/main/java/org/onosproject/workflow/api/EventTask.java
index 3b2b30a..c2af3e6 100644
--- a/apps/workflow/api/src/main/java/org/onosproject/workflow/api/EventTask.java
+++ b/apps/workflow/api/src/main/java/org/onosproject/workflow/api/EventTask.java
@@ -20,6 +20,8 @@
 
 import java.util.Objects;
 
+import static org.onosproject.workflow.api.CheckCondition.check;
+
 /**
  * Class for event task.
  */
@@ -91,7 +93,7 @@
     public String toString() {
         return MoreObjects.toStringHelper(getClass())
                 .add("context", context())
-                .add("workletType", workletType())
+                .add("programCounter", programCounter())
                 .add("event", event())
                 .add("eventHint", eventHint())
                 .toString();
@@ -147,16 +149,19 @@
         }
 
         @Override
-        public Builder workletType(String workletType) {
-            super.workletType(workletType);
+        public Builder programCounter(ProgramCounter programCounter) {
+            super.programCounter(programCounter);
             return this;
         }
 
         /**
          * Builds EventTask.
          * @return instance of EventTask
+         * @throws WorkflowException workflow exception
          */
-        public EventTask build() {
+        public EventTask build() throws WorkflowException {
+            check(event != null, "event is invalid");
+            check(eventHint != null, "eventHint is invalid");
             return new EventTask(this);
         }
     }
diff --git a/apps/workflow/api/src/main/java/org/onosproject/workflow/api/EventTimeoutTask.java b/apps/workflow/api/src/main/java/org/onosproject/workflow/api/EventTimeoutTask.java
index 92516d4..9aa870d 100644
--- a/apps/workflow/api/src/main/java/org/onosproject/workflow/api/EventTimeoutTask.java
+++ b/apps/workflow/api/src/main/java/org/onosproject/workflow/api/EventTimeoutTask.java
@@ -19,6 +19,8 @@
 
 import java.util.Objects;
 
+import static org.onosproject.workflow.api.CheckCondition.check;
+
 /**
  * Class for event timeout task.
  */
@@ -81,7 +83,7 @@
     public String toString() {
         return MoreObjects.toStringHelper(getClass())
                 .add("context", context())
-                .add("workletType", workletType())
+                .add("programCounter", programCounter())
                 .add("eventType", eventType())
                 .add("eventHint", eventHint())
                 .toString();
@@ -136,16 +138,19 @@
         }
 
         @Override
-        public Builder workletType(String workletType) {
-            super.workletType(workletType);
+        public Builder programCounter(ProgramCounter programCounter) {
+            super.programCounter(programCounter);
             return this;
         }
 
         /**
          * Builds EventTimeoutTask.
          * @return instance of EventTimeoutTask
+         * @throws WorkflowException workflow exception
          */
-        public EventTimeoutTask build() {
+        public EventTimeoutTask build() throws WorkflowException {
+            check(eventType != null, "eventType is invalid");
+            check(eventHint != null, "eventType is invalid");
             return new EventTimeoutTask(this);
         }
     }
diff --git a/apps/workflow/api/src/main/java/org/onosproject/workflow/api/HandlerTask.java b/apps/workflow/api/src/main/java/org/onosproject/workflow/api/HandlerTask.java
index 106466b..94203bc 100644
--- a/apps/workflow/api/src/main/java/org/onosproject/workflow/api/HandlerTask.java
+++ b/apps/workflow/api/src/main/java/org/onosproject/workflow/api/HandlerTask.java
@@ -28,9 +28,9 @@
     private final WorkflowContext context;
 
     /**
-     * Worklet type of handler task.
+     * Program counter of handler task.
      */
-    private final String workletType;
+    private final ProgramCounter programCounter;
 
     /**
      * Constructor for handler task.
@@ -38,7 +38,7 @@
      */
     protected HandlerTask(Builder builder) {
         this.context = builder.context;
-        this.workletType = builder.workletType;
+        this.programCounter = builder.programCounter;
     }
 
     /**
@@ -50,18 +50,18 @@
     }
 
     /**
-     * Returns worklet type name of this handler task.
-     * @return worklet type
+     * Returns program counter of this handler task.
+     * @return program counter
      */
-    public String workletType() {
-        return workletType;
+    public ProgramCounter programCounter() {
+        return programCounter;
     }
 
     @Override
     public String toString() {
         return MoreObjects.toStringHelper(getClass())
                 .add("context", context())
-                .add("workletType", workletType())
+                .add("programCounter", programCounter())
                 .toString();
     }
 
@@ -70,7 +70,7 @@
      */
     public static class Builder {
         protected WorkflowContext context;
-        protected String workletType;
+        protected ProgramCounter programCounter;
 
         /**
          * Sets workflow context of handler task.
@@ -83,12 +83,12 @@
         }
 
         /**
-         * Sets worklet type of handler task.
-         * @param workletType worklet type
+         * Sets program counter of handler task.
+         * @param programCounter program counter of handler type
          * @return builder of handler task
          */
-        public Builder workletType(String workletType) {
-            this.workletType = workletType;
+        public Builder programCounter(ProgramCounter programCounter) {
+            this.programCounter = programCounter;
             return this;
         }
     }
diff --git a/apps/workflow/api/src/main/java/org/onosproject/workflow/api/ImmutableListWorkflow.java b/apps/workflow/api/src/main/java/org/onosproject/workflow/api/ImmutableListWorkflow.java
index b5ea456..e948a7a 100644
--- a/apps/workflow/api/src/main/java/org/onosproject/workflow/api/ImmutableListWorkflow.java
+++ b/apps/workflow/api/src/main/java/org/onosproject/workflow/api/ImmutableListWorkflow.java
@@ -29,6 +29,8 @@
 import java.util.Objects;
 import java.util.Set;
 
+import static org.onosproject.workflow.api.CheckCondition.check;
+
 /**
  * Class for immutable list workflow.
  */
@@ -49,6 +51,8 @@
      */
     private Set<WorkflowAttribute> attributes;
 
+    private static JsonDataModelInjector dataModelInjector = new JsonDataModelInjector();
+
     /**
      * Constructor of ImmutableListWorkflow.
      * @param builder builder of ImmutableListWorkflow
@@ -71,10 +75,14 @@
 
 
     @Override
-    public Worklet next(WorkflowContext context) throws WorkflowException {
+    public ProgramCounter next(WorkflowContext context) throws WorkflowException {
 
         int cnt = 0;
-        for (int i = 0; i < workletTypeList.size(); i++) {
+
+        ProgramCounter pc = context.current();
+        check(pc != null, "Invalid program counter");
+
+        for (int i = pc.workletIndex(); i < workletTypeList.size(); i++) {
 
             if (cnt++ > Worklet.MAX_WORKS) {
                 throw new WorkflowException("Maximum worklet execution exceeded");
@@ -83,7 +91,7 @@
             String workletType = workletTypeList.get(i);
 
             if (Worklet.Common.COMPLETED.tag().equals(workletType)) {
-                return Worklet.Common.COMPLETED;
+                return ProgramCounter.valueOf(workletType, i);
             }
 
             if (Worklet.Common.INIT.tag().equals(workletType)) {
@@ -109,17 +117,35 @@
                 continue;
 
             } else {
+                // isNext is read only. It does not perform 'inhale'.
+                dataModelInjector.inject(worklet, context);
                 if (worklet.isNext(context)) {
-                    return worklet;
+                    return ProgramCounter.valueOf(workletType, i);
                 }
             }
         }
-        return Worklet.Common.COMPLETED;
+        throw new WorkflowException("workflow reached to end but not COMPLETED");
+    }
+
+    @Override
+    public ProgramCounter increased(ProgramCounter pc) throws WorkflowException {
+
+        int increaedIndex = pc.workletIndex() + 1;
+        if (increaedIndex >= workletTypeList.size()) {
+            throw new WorkflowException("Out of bound in program counter(" + pc + ")");
+        }
+
+        String workletType = workletTypeList.get(increaedIndex);
+        return ProgramCounter.valueOf(workletType, increaedIndex);
     }
 
     @Override
     public Worklet getWorkletInstance(String workletType) throws WorkflowException {
 
+        if (Worklet.Common.COMPLETED.tag().equals(workletType)) {
+            return Worklet.Common.COMPLETED;
+        }
+
         WorkflowStore store;
         try {
              store = DefaultServiceDirectory.getService(WorkflowStore.class);
diff --git a/apps/workflow/api/src/main/java/org/onosproject/workflow/api/JsonDataModel.java b/apps/workflow/api/src/main/java/org/onosproject/workflow/api/JsonDataModel.java
new file mode 100644
index 0000000..1dc8e52
--- /dev/null
+++ b/apps/workflow/api/src/main/java/org/onosproject/workflow/api/JsonDataModel.java
@@ -0,0 +1,50 @@
+/*
+ * Copyright 2018-present Open Networking Foundation
+ *
+ * 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.workflow.api;
+
+import com.fasterxml.jackson.databind.JsonNode;
+
+import java.lang.annotation.ElementType;
+import java.lang.annotation.Retention;
+import java.lang.annotation.RetentionPolicy;
+import java.lang.annotation.Target;
+
+@Target(ElementType.FIELD)
+@Retention(RetentionPolicy.RUNTIME)
+
+/**
+ * Annotation for injecting json data model on work-let execution context.
+ */
+public @interface JsonDataModel {
+
+    /**
+     * Path of data model.
+     * @return path of data model
+     */
+    String path() default "/";
+
+    /**
+     * Type of data model.
+     * @return type of data model
+     */
+    Class<?> type() default JsonNode.class;
+
+    /**
+     * Representing whether this data model is optional or not.
+     * @return optional or not
+     */
+    boolean optional() default false;
+}
diff --git a/apps/workflow/api/src/main/java/org/onosproject/workflow/api/JsonDataModelInjector.java b/apps/workflow/api/src/main/java/org/onosproject/workflow/api/JsonDataModelInjector.java
new file mode 100644
index 0000000..d76aa52
--- /dev/null
+++ b/apps/workflow/api/src/main/java/org/onosproject/workflow/api/JsonDataModelInjector.java
@@ -0,0 +1,589 @@
+/*
+ * Copyright 2018-present Open Networking Foundation
+ *
+ * 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.workflow.api;
+
+import com.fasterxml.jackson.databind.JsonNode;
+import com.fasterxml.jackson.databind.node.ArrayNode;
+import com.fasterxml.jackson.databind.node.BooleanNode;
+import com.fasterxml.jackson.databind.node.IntNode;
+import com.fasterxml.jackson.databind.node.MissingNode;
+import com.fasterxml.jackson.databind.node.ObjectNode;
+import com.fasterxml.jackson.databind.node.TextNode;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import java.lang.annotation.Annotation;
+import java.lang.reflect.Field;
+import java.util.ArrayList;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+import java.util.Objects;
+
+/**
+ * Class for injecting json data model on the work-let execution context.
+ */
+public class JsonDataModelInjector {
+
+    private static final Logger log = LoggerFactory.getLogger(JsonDataModelInjector.class);
+
+    /**
+     * Injects data model to work-let.
+     * @param worklet work-let to be injected
+     * @param context workflow context
+     * @throws WorkflowException workflow exception
+     */
+    public void inject(Worklet worklet, WorkflowContext context) throws WorkflowException {
+
+        handle(worklet, context, this::injectModel);
+    }
+
+    /**
+     * Inhales data model from work-let.
+     * @param worklet work-let to be inhaled
+     * @param context workflow context
+     * @throws WorkflowException workflow exception
+     */
+    public void inhale(Worklet worklet, WorkflowContext context) throws WorkflowException {
+
+        handle(worklet, context, this::inhaleModel);
+    }
+
+    private void handle(Worklet worklet, WorkflowContext context, DataModelFieldBehavior func)
+            throws WorkflowException {
+        Class cl = worklet.getClass();
+        List<Field> fields = getInheritedFields(cl);
+        if (Objects.isNull(fields)) {
+            log.error("Invalid fields on {}", cl);
+            return;
+        }
+
+        for (Field field: fields) {
+            Annotation[] annotations = field.getAnnotations();
+            if (Objects.isNull(annotations)) {
+                continue;
+            }
+            for (Annotation annotation: annotations) {
+                if (!(annotation instanceof JsonDataModel)) {
+                    continue;
+                }
+                JsonDataModel model = (JsonDataModel) annotation;
+                func.apply(worklet, context, field, model);
+            }
+        }
+    }
+
+    private static List<Field> getInheritedFields(Class<?> type) {
+        List<Field> fields = new ArrayList<Field>();
+
+        Class<?> cl = type;
+        while (cl != null && cl != Object.class) {
+            for (Field field : cl.getDeclaredFields()) {
+                if (!field.isSynthetic()) {
+                    fields.add(field);
+                }
+            }
+            cl = cl.getSuperclass();
+        }
+        return fields;
+    }
+
+    /**
+     * Functional interface for json data model annotated field behavior.
+     */
+    @FunctionalInterface
+    public interface DataModelFieldBehavior {
+        void apply(Worklet worklet, WorkflowContext context, Field field, JsonDataModel model)
+                throws WorkflowException;
+    }
+
+    private static Map<Class, DataModelFieldBehavior> injectTypeMap = new HashMap<>();
+    static {
+        injectTypeMap.put(String.class, JsonDataModelInjector::injectText);
+        injectTypeMap.put(Integer.class, JsonDataModelInjector::injectInteger);
+        injectTypeMap.put(Boolean.class, JsonDataModelInjector::injectBoolean);
+        injectTypeMap.put(JsonNode.class, JsonDataModelInjector::injectJsonNode);
+        injectTypeMap.put(ArrayNode.class, JsonDataModelInjector::injectArrayNode);
+        injectTypeMap.put(ObjectNode.class, JsonDataModelInjector::injectObjectNode);
+    }
+
+    /**
+     * Injects data model on the filed of work-let.
+     * @param worklet work-let
+     * @param context workflow context
+     * @param field the field of work-let
+     * @param model data model for the field
+     * @throws WorkflowException workflow exception
+     */
+    private void injectModel(Worklet worklet, WorkflowContext context, Field field, JsonDataModel model)
+            throws WorkflowException {
+
+        DataModelFieldBehavior behavior = injectTypeMap.get(model.type());
+        if (Objects.isNull(behavior)) {
+            throw new WorkflowException("Not supported type(" + model.type() + ")");
+        }
+        behavior.apply(worklet, context, field, model);
+    }
+
+    /**
+     * Injects text data model on the filed of work-let.
+     * @param worklet work-let
+     * @param context workflow context
+     * @param field the field of work-let
+     * @param model text data model for the field
+     * @throws WorkflowException workflow exception
+     */
+    private static void injectText(Worklet worklet, WorkflowContext context, Field field, JsonDataModel model)
+            throws WorkflowException {
+
+        String text = ((JsonDataModelTree) context.data()).textAt(model.path());
+        if (Objects.isNull(text)) {
+            if (model.optional()) {
+                return;
+            }
+            throw new WorkflowException("Invalid text data model on (" + model.path() + ")");
+        }
+
+        if (!(Objects.equals(field.getType(), String.class))) {
+            throw new WorkflowException("Target field (" + field + ") is not String");
+        }
+
+        try {
+            field.setAccessible(true);
+            field.set(worklet, text);
+        } catch (IllegalAccessException e) {
+            throw new WorkflowException(e);
+        }
+    }
+
+    /**
+     * Injects integer data model on the filed of work-let.
+     * @param worklet work-let
+     * @param context workflow context
+     * @param field the field of work-let
+     * @param model integer data model for the field
+     * @throws WorkflowException workflow exception
+     */
+    private static void injectInteger(Worklet worklet, WorkflowContext context, Field field, JsonDataModel model)
+            throws WorkflowException {
+
+        Integer number = ((JsonDataModelTree) context.data()).intAt(model.path());
+        if (Objects.isNull(number)) {
+            if (model.optional()) {
+                return;
+            }
+            throw new WorkflowException("Invalid number data model on (" + model.path() + ")");
+        }
+
+        if (!(Objects.equals(field.getType(), Integer.class))) {
+            throw new WorkflowException("Target field (" + field + ") is not Integer");
+        }
+
+        try {
+            field.setAccessible(true);
+            field.set(worklet, number);
+        } catch (IllegalAccessException e) {
+            throw new WorkflowException(e);
+        }
+    }
+
+    /**
+     * Injects boolean data model on the filed of work-let.
+     * @param worklet work-let
+     * @param context workflow context
+     * @param field the field of work-let
+     * @param model boolean data model for the field
+     * @throws WorkflowException workflow exception
+     */
+    private static void injectBoolean(Worklet worklet, WorkflowContext context, Field field, JsonDataModel model)
+            throws WorkflowException {
+
+        Boolean bool = ((JsonDataModelTree) context.data()).booleanAt(model.path());
+        if (Objects.isNull(bool)) {
+            if (model.optional()) {
+                return;
+            }
+            throw new WorkflowException("Invalid boolean data model on (" + model.path() + ")");
+        }
+
+        if (!(Objects.equals(field.getType(), Boolean.class))) {
+            throw new WorkflowException("Target field (" + field + ") is not Boolean");
+        }
+
+        try {
+            field.setAccessible(true);
+            field.set(worklet, bool);
+        } catch (IllegalAccessException e) {
+            throw new WorkflowException(e);
+        }
+    }
+
+    /**
+     * Injects json node data model on the filed of work-let.
+     * @param worklet work-let
+     * @param context workflow context
+     * @param field the field of work-let
+     * @param model json node data model for the field
+     * @throws WorkflowException workflow exception
+     */
+    private static void injectJsonNode(Worklet worklet, WorkflowContext context, Field field, JsonDataModel model)
+            throws WorkflowException {
+
+        JsonNode jsonNode = ((JsonDataModelTree) context.data()).nodeAt(model.path());
+        if (Objects.isNull(jsonNode)) {
+            if (model.optional()) {
+                return;
+            }
+            throw new WorkflowException("Invalid json node data model on (" + model.path() + ")");
+        }
+
+        if (!(Objects.equals(field.getType(), JsonNode.class))) {
+            throw new WorkflowException("Target field (" + field + ") is not JsonNode");
+        }
+
+        try {
+            field.setAccessible(true);
+            field.set(worklet, jsonNode);
+        } catch (IllegalAccessException e) {
+            throw new WorkflowException(e);
+        }
+    }
+
+    /**
+     * Injects json array node data model on the filed of work-let.
+     * @param worklet work-let
+     * @param context workflow context
+     * @param field the field of work-let
+     * @param model json array node data model for the field
+     * @throws WorkflowException workflow exception
+     */
+    private static void injectArrayNode(Worklet worklet, WorkflowContext context, Field field, JsonDataModel model)
+            throws WorkflowException {
+
+        ArrayNode arrayNode = ((JsonDataModelTree) context.data()).arrayAt(model.path());
+        if (Objects.isNull(arrayNode)) {
+            if (model.optional()) {
+                return;
+            }
+            throw new WorkflowException("Invalid array node data model on (" + model.path() + ")");
+        }
+
+        if (!(Objects.equals(field.getType(), ArrayNode.class))) {
+            throw new WorkflowException("Target field (" + field + ") is not ArrayNode");
+        }
+
+        try {
+            field.setAccessible(true);
+            field.set(worklet, arrayNode);
+        } catch (IllegalAccessException e) {
+            throw new WorkflowException(e);
+        }
+    }
+
+    /**
+     * Injects json object node data model on the filed of work-let.
+     * @param worklet work-let
+     * @param context workflow context
+     * @param field the field of work-let
+     * @param model json object node data model for the field
+     * @throws WorkflowException workflow exception
+     */
+    private static void injectObjectNode(Worklet worklet, WorkflowContext context, Field field, JsonDataModel model)
+            throws WorkflowException {
+
+        ObjectNode objNode = ((JsonDataModelTree) context.data()).objectAt(model.path());
+        if (Objects.isNull(objNode)) {
+            if (model.optional()) {
+                return;
+            }
+            throw new WorkflowException("Invalid object node data model on (" + model.path() + ")");
+        }
+
+        if (!(Objects.equals(field.getType(), ObjectNode.class))) {
+            throw new WorkflowException("Target field (" + field + ") is not ObjectNode");
+        }
+
+        try {
+            field.setAccessible(true);
+            field.set(worklet, objNode);
+        } catch (IllegalAccessException e) {
+            throw new WorkflowException(e);
+        }
+    }
+
+    private static Map<Class, DataModelFieldBehavior> inhaleTypeMap = new HashMap<>();
+    static {
+        inhaleTypeMap.put(String.class, JsonDataModelInjector::inhaleText);
+        inhaleTypeMap.put(Integer.class, JsonDataModelInjector::inhaleInteger);
+        inhaleTypeMap.put(Boolean.class, JsonDataModelInjector::inhaleBoolean);
+        inhaleTypeMap.put(JsonNode.class, JsonDataModelInjector::inhaleJsonNode);
+        inhaleTypeMap.put(ArrayNode.class, JsonDataModelInjector::inhaleArrayNode);
+        inhaleTypeMap.put(ObjectNode.class, JsonDataModelInjector::inhaleObjectNode);
+    }
+
+    /**
+     * Inhales data model on the filed of work-let.
+     * @param worklet work-let
+     * @param context workflow context
+     * @param field the field of work-let
+     * @param model data model for the field
+     * @throws WorkflowException workflow exception
+     */
+    private void inhaleModel(Worklet worklet, WorkflowContext context, Field field, JsonDataModel model)
+            throws WorkflowException {
+
+        DataModelFieldBehavior behavior = inhaleTypeMap.get(model.type());
+        if (Objects.isNull(behavior)) {
+            throw new WorkflowException("Not supported type(" + model.type() + ")");
+        }
+        behavior.apply(worklet, context, field, model);
+    }
+
+    /**
+     * Inhales text data model on the filed of work-let.
+     * @param worklet work-let
+     * @param context workflow context
+     * @param field the field of work-let
+     * @param model text data model for the field
+     * @throws WorkflowException workflow exception
+     */
+    private static void inhaleText(Worklet worklet, WorkflowContext context, Field field, JsonDataModel model)
+            throws WorkflowException {
+
+        if (!(Objects.equals(field.getType(), String.class))) {
+            throw new WorkflowException("Target field (" + field + ") is not String");
+        }
+
+        String text;
+        try {
+            field.setAccessible(true);
+            text = (String) field.get(worklet);
+        } catch (IllegalAccessException e) {
+            throw new WorkflowException(e);
+        }
+
+        if (Objects.isNull(text)) {
+            return;
+        }
+
+        JsonDataModelTree tree = (JsonDataModelTree) context.data();
+        JsonNode jsonNode = tree.nodeAt(model.path());
+
+        if (Objects.isNull(jsonNode) || jsonNode instanceof MissingNode) {
+            tree.setAt(model.path(), text);
+        } else if (!(jsonNode instanceof TextNode)) {
+            throw new WorkflowException("Invalid text data model on (" + model.path() + ")");
+        } else {
+            tree.remove(model.path());
+            tree.setAt(model.path(), text);
+        }
+    }
+
+    /**
+     * Inhales integer data model on the filed of work-let.
+     * @param worklet work-let
+     * @param context workflow context
+     * @param field the field of work-let
+     * @param model integer data model for the field
+     * @throws WorkflowException workflow exception
+     */
+    private static void inhaleInteger(Worklet worklet, WorkflowContext context, Field field, JsonDataModel model)
+            throws WorkflowException {
+
+        if (!(Objects.equals(field.getType(), Integer.class))) {
+            throw new WorkflowException("Target field (" + field + ") is not Integer");
+        }
+
+        Integer number;
+        try {
+            field.setAccessible(true);
+            number = (Integer) field.get(worklet);
+        } catch (IllegalAccessException e) {
+            throw new WorkflowException(e);
+        }
+
+        if (Objects.isNull(number)) {
+            return;
+        }
+
+        JsonDataModelTree tree = (JsonDataModelTree) context.data();
+        JsonNode jsonNode = tree.nodeAt(model.path());
+
+        if (Objects.isNull(jsonNode) || jsonNode instanceof MissingNode) {
+            tree.setAt(model.path(), number);
+        } else if (!(jsonNode instanceof IntNode)) {
+            throw new WorkflowException("Invalid integer data model on (" + model.path() + ")");
+        } else {
+            tree.remove(model.path());
+            tree.setAt(model.path(), number);
+        }
+    }
+
+    /**
+     * Inhales boolean data model on the filed of work-let.
+     * @param worklet work-let
+     * @param context workflow context
+     * @param field the field of work-let
+     * @param model boolean data model for the field
+     * @throws WorkflowException workflow exception
+     */
+    private static void inhaleBoolean(Worklet worklet, WorkflowContext context, Field field, JsonDataModel model)
+            throws WorkflowException {
+
+        if (!(Objects.equals(field.getType(), Boolean.class))) {
+            throw new WorkflowException("Target field (" + field + ") is not Boolean");
+        }
+
+        Boolean bool;
+        try {
+            field.setAccessible(true);
+            bool = (Boolean) field.get(worklet);
+        } catch (IllegalAccessException e) {
+            throw new WorkflowException(e);
+        }
+
+        if (Objects.isNull(bool)) {
+            return;
+        }
+
+        JsonDataModelTree tree = (JsonDataModelTree) context.data();
+        JsonNode jsonNode = tree.nodeAt(model.path());
+
+        if (Objects.isNull(jsonNode) || jsonNode instanceof MissingNode) {
+            tree.setAt(model.path(), bool);
+        } else if (!(jsonNode instanceof BooleanNode)) {
+            throw new WorkflowException("Invalid boolean data model on (" + model.path() + ")");
+        } else {
+            tree.remove(model.path());
+            tree.setAt(model.path(), bool);
+        }
+    }
+
+    /**
+     * Inhales json node data model on the filed of work-let.
+     * @param worklet work-let
+     * @param context workflow context
+     * @param field the field of work-let
+     * @param model json node data model for the field
+     * @throws WorkflowException workflow exception
+     */
+    private static void inhaleJsonNode(Worklet worklet, WorkflowContext context, Field field, JsonDataModel model)
+            throws WorkflowException {
+
+        if (!(Objects.equals(field.getType(), JsonNode.class))) {
+            throw new WorkflowException("Target field (" + field + ") is not JsonNode");
+        }
+
+        JsonNode tgtJsonNode;
+        try {
+            field.setAccessible(true);
+            tgtJsonNode = (JsonNode) field.get(worklet);
+        } catch (IllegalAccessException e) {
+            throw new WorkflowException(e);
+        }
+
+        if (Objects.isNull(tgtJsonNode)) {
+            return;
+        }
+
+        JsonDataModelTree tree = (JsonDataModelTree) context.data();
+        JsonNode jsonNode = tree.nodeAt(model.path());
+
+        if (Objects.isNull(jsonNode) || jsonNode instanceof MissingNode) {
+            tree.attach(model.path(), new JsonDataModelTree(tgtJsonNode));
+        } else if (!(jsonNode instanceof JsonNode)) {
+            throw new WorkflowException("Invalid json node data model on (" + model.path() + ")");
+        } else {
+            // do nothing
+        }
+    }
+
+    /**
+     * Inhales json array node data model on the filed of work-let.
+     * @param worklet work-let
+     * @param context workflow context
+     * @param field the field of work-let
+     * @param model json array node data model for the field
+     * @throws WorkflowException workflow exception
+     */
+    private static void inhaleArrayNode(Worklet worklet, WorkflowContext context, Field field, JsonDataModel model)
+            throws WorkflowException {
+        if (!(Objects.equals(field.getType(), ArrayNode.class))) {
+            throw new WorkflowException("Target field (" + field + ") is not ArrayNode");
+        }
+
+        ArrayNode tgtArrayNode;
+        try {
+            field.setAccessible(true);
+            tgtArrayNode = (ArrayNode) field.get(worklet);
+        } catch (IllegalAccessException e) {
+            throw new WorkflowException(e);
+        }
+
+        if (Objects.isNull(tgtArrayNode)) {
+            return;
+        }
+
+        JsonDataModelTree tree = (JsonDataModelTree) context.data();
+        JsonNode jsonNode = tree.nodeAt(model.path());
+
+        if (Objects.isNull(jsonNode) || jsonNode instanceof MissingNode) {
+            tree.attach(model.path(), new JsonDataModelTree(tgtArrayNode));
+        } else if (!(jsonNode instanceof ArrayNode)) {
+            throw new WorkflowException("Invalid array node data model on (" + model.path() + ")");
+        } else {
+            // do nothing
+        }
+    }
+
+    /**
+     * Inhales json object node data model on the filed of work-let.
+     * @param worklet work-let
+     * @param context workflow context
+     * @param field the field of work-let
+     * @param model json object node data model for the field
+     * @throws WorkflowException workflow exception
+     */
+    private static void inhaleObjectNode(Worklet worklet, WorkflowContext context, Field field, JsonDataModel model)
+            throws WorkflowException {
+        if (!(Objects.equals(field.getType(), ObjectNode.class))) {
+            throw new WorkflowException("Target field (" + field + ") is not ObjectNode");
+        }
+
+        ObjectNode tgtObjNode;
+        try {
+            field.setAccessible(true);
+            tgtObjNode = (ObjectNode) field.get(worklet);
+        } catch (IllegalAccessException e) {
+            throw new WorkflowException(e);
+        }
+
+        if (Objects.isNull(tgtObjNode)) {
+            return;
+        }
+
+        JsonDataModelTree tree = (JsonDataModelTree) context.data();
+        JsonNode jsonNode = tree.nodeAt(model.path());
+
+        if (Objects.isNull(jsonNode) || jsonNode instanceof MissingNode) {
+            tree.attach(model.path(), new JsonDataModelTree(tgtObjNode));
+        } else if (!(jsonNode instanceof ObjectNode)) {
+            throw new WorkflowException("Invalid object node data model on (" + model.path() + ")");
+        } else {
+            // do nothing
+        }
+    }
+}
diff --git a/apps/workflow/api/src/main/java/org/onosproject/workflow/api/JsonDataModelTree.java b/apps/workflow/api/src/main/java/org/onosproject/workflow/api/JsonDataModelTree.java
index 3a74bd2..7ee1be7 100644
--- a/apps/workflow/api/src/main/java/org/onosproject/workflow/api/JsonDataModelTree.java
+++ b/apps/workflow/api/src/main/java/org/onosproject/workflow/api/JsonDataModelTree.java
@@ -21,11 +21,17 @@
 import com.fasterxml.jackson.databind.JsonNode;
 import com.fasterxml.jackson.databind.ObjectMapper;
 import com.fasterxml.jackson.databind.node.ArrayNode;
+import com.fasterxml.jackson.databind.node.BooleanNode;
+import com.fasterxml.jackson.databind.node.IntNode;
 import com.fasterxml.jackson.databind.node.JsonNodeFactory;
 import com.fasterxml.jackson.databind.node.JsonNodeType;
 import com.fasterxml.jackson.databind.node.MissingNode;
+import com.fasterxml.jackson.databind.node.NumericNode;
 import com.fasterxml.jackson.databind.node.ObjectNode;
+import com.fasterxml.jackson.databind.node.TextNode;
 import com.google.common.base.MoreObjects;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
 
 import java.util.Objects;
 
@@ -34,6 +40,8 @@
  */
 public final class JsonDataModelTree implements DataModelTree {
 
+    private static final Logger log = LoggerFactory.getLogger(JsonDataModelTree.class);
+
     /**
      * Root node of json data model tree.
      */
@@ -65,30 +73,88 @@
 
     @Override
     public void attach(String path, DataModelTree tree) throws WorkflowException {
+
         if (root == null || root instanceof MissingNode) {
             throw new WorkflowException("Invalid root node");
         }
 
         JsonPointer ptr = JsonPointer.compile(path);
-        JsonNode node = root.at(ptr);
-        if (!(node instanceof MissingNode)) {
-            throw new WorkflowException("Path(" + path + ") has already subtree(" + node + ")");
-        }
 
         if (!(tree instanceof JsonDataModelTree)) {
             throw new WorkflowException("Invalid subTree(" + tree + ")");
         }
         JsonNode attachingNode = ((JsonDataModelTree) tree).root();
 
-        alloc(ptr.head(), Nodetype.MAP);
-        JsonNode parentNode = root.at(ptr.head());
+        attach(ptr, attachingNode);
+    }
 
-        if (!parentNode.isObject()) {
-            throw new WorkflowException("Invalid parentNode type(" + parentNode.getNodeType() + ")");
+    private void attach(JsonPointer ptr, JsonNode attachingNode) throws WorkflowException {
+
+        JsonNode node = root.at(ptr);
+        if (!(node instanceof MissingNode)) {
+            throw new WorkflowException("Path(" + ptr + ") has already subtree(" + node + ")");
         }
 
-        String key = ptr.last().getMatchingProperty();
-        ((ObjectNode) parentNode).put(key, attachingNode);
+        if (ptr.last().getMatchingIndex() != -1) {
+
+            alloc(ptr.head(), Nodetype.ARRAY);
+            JsonNode parentNode = root.at(ptr.head());
+            if (!parentNode.isArray()) {
+                throw new WorkflowException("Invalid parentNode type(" + parentNode.getNodeType() + " != Array)");
+            }
+            int index = ptr.last().getMatchingIndex();
+            ((ArrayNode) parentNode).insert(index, attachingNode);
+
+        } else if (ptr.last().getMatchingProperty() != null) {
+
+            alloc(ptr.head(), Nodetype.MAP);
+            JsonNode parentNode = root.at(ptr.head());
+            if (!parentNode.isObject()) {
+                throw new WorkflowException("Invalid parentNode type(" + parentNode.getNodeType() + " != Object)");
+            }
+            String key = ptr.last().getMatchingProperty();
+            ((ObjectNode) parentNode).put(key, attachingNode);
+
+        } else {
+            throw new WorkflowException("Invalid path(" + ptr + ")");
+        }
+    }
+
+    @Override
+    public void remove(String path) throws WorkflowException {
+        JsonPointer ptr = JsonPointer.compile(path);
+        remove(ptr);
+    }
+
+    private void remove(JsonPointer ptr) throws WorkflowException {
+
+        JsonNode node = root.at(ptr);
+        if (node instanceof MissingNode) {
+            log.warn("{} does not have valid node", ptr);
+            return;
+        }
+
+        if (ptr.last().getMatchingIndex() != -1) {
+
+            JsonNode parentNode = root.at(ptr.head());
+            if (!parentNode.isArray()) {
+                throw new WorkflowException("Invalid parentNode type(" + parentNode.getNodeType() + " != Array)");
+            }
+            int index = ptr.last().getMatchingIndex();
+            ((ArrayNode) parentNode).remove(index);
+
+        } else if (ptr.last().getMatchingProperty() != null) {
+
+            JsonNode parentNode = root.at(ptr.head());
+            if (!parentNode.isObject()) {
+                throw new WorkflowException("Invalid parentNode type(" + parentNode.getNodeType() + " != Object)");
+            }
+            String key = ptr.last().getMatchingProperty();
+            ((ObjectNode) parentNode).remove(key);
+
+        } else {
+            throw new WorkflowException("Invalid path(" + ptr + ")");
+        }
     }
 
     @Override
@@ -200,6 +266,9 @@
             throw new WorkflowException("Invalid root node");
         }
         JsonNode node = root.at(ptr);
+        if (node instanceof MissingNode) {
+            return null;
+        }
         if (!(node instanceof ObjectNode)) {
             throw new WorkflowException("Invalid node(" + node + ") at " + ptr);
         }
@@ -228,6 +297,9 @@
             throw new WorkflowException("Invalid root node");
         }
         JsonNode node = root.at(ptr);
+        if (node instanceof MissingNode) {
+            return null;
+        }
         if (!(node instanceof ArrayNode)) {
             throw new WorkflowException("Invalid node(" + node + ") at " + ptr);
         }
@@ -235,6 +307,165 @@
     }
 
     /**
+     * Gets text node on specific path.
+     * @param path path of json node
+     * @return text on specific path
+     * @throws WorkflowException workflow exception
+     */
+    public String textAt(String path) throws WorkflowException {
+        JsonPointer ptr = JsonPointer.compile(path);
+        return textAt(ptr);
+    }
+
+    /**
+     * Gets text on specific json pointer.
+     * @param ptr json pointer
+     * @return text on specific json pointer
+     * @throws WorkflowException workflow exception
+     */
+    public String textAt(JsonPointer ptr) throws WorkflowException {
+        if (root == null || root instanceof MissingNode) {
+            throw new WorkflowException("Invalid root node");
+        }
+        JsonNode node = root.at(ptr);
+        if (node instanceof MissingNode) {
+            return null;
+        }
+        if (!(node instanceof TextNode)) {
+            throw new WorkflowException("Invalid node(" + node + ") at " + ptr);
+        }
+        return ((TextNode) node).asText();
+    }
+
+    /**
+     * Gets integer node on specific path.
+     * @param path path of json node
+     * @return integer on specific path
+     * @throws WorkflowException workflow exception
+     */
+    public Integer intAt(String path) throws WorkflowException {
+        JsonPointer ptr = JsonPointer.compile(path);
+        return intAt(ptr);
+    }
+
+    /**
+     * Gets integer on specific json pointer.
+     * @param ptr json pointer
+     * @return integer on specific json pointer
+     * @throws WorkflowException workflow exception
+     */
+    public Integer intAt(JsonPointer ptr) throws WorkflowException {
+        if (root == null || root instanceof MissingNode) {
+            throw new WorkflowException("Invalid root node");
+        }
+        JsonNode node = root.at(ptr);
+        if (node instanceof MissingNode) {
+            return null;
+        }
+        if (!(node instanceof NumericNode)) {
+            throw new WorkflowException("Invalid node(" + node + ") at " + ptr);
+        }
+        return ((NumericNode) node).asInt();
+    }
+
+    /**
+     * Gets boolean on specific path.
+     * @param path path of json node
+     * @return boolean on specific path
+     * @throws WorkflowException workflow exception
+     */
+    public Boolean booleanAt(String path) throws WorkflowException {
+        JsonPointer ptr = JsonPointer.compile(path);
+        return booleanAt(ptr);
+    }
+
+    /**
+     * Gets boolean on specific json pointer.
+     * @param ptr json pointer
+     * @return boolean on specific json pointer
+     * @throws WorkflowException workflow exception
+     */
+    public Boolean booleanAt(JsonPointer ptr) throws WorkflowException {
+        if (root == null || root instanceof MissingNode) {
+            throw new WorkflowException("Invalid root node");
+        }
+        JsonNode node = root.at(ptr);
+        if (node instanceof MissingNode) {
+            return null;
+        }
+        if (!(node instanceof BooleanNode)) {
+            throw new WorkflowException("Invalid node(" + node + ") at " + ptr);
+        }
+        return ((BooleanNode) node).asBoolean();
+    }
+
+    /**
+     * Sets text on specific json path.
+     * @param path json path
+     * @param text text to set
+     * @throws WorkflowException workflow exception
+     */
+    public void setAt(String path, String text) throws WorkflowException {
+        JsonPointer ptr = JsonPointer.compile(path);
+        setAt(ptr, text);
+    }
+
+    /**
+     * Sets text on the specific json pointer.
+     * @param ptr json pointer
+     * @param text text to set
+     * @throws WorkflowException workflow exception
+     */
+    public void setAt(JsonPointer ptr, String text) throws WorkflowException {
+        TextNode textNode = TextNode.valueOf(text);
+        attach(ptr, textNode);
+    }
+
+    /**
+     * Sets boolean on specific json path.
+     * @param path json path
+     * @param isTrue boolean to set
+     * @throws WorkflowException workflow exception
+     */
+    public void setAt(String path, Boolean isTrue) throws WorkflowException {
+        JsonPointer ptr = JsonPointer.compile(path);
+        setAt(ptr, isTrue);
+    }
+
+    /**
+     * Sets boolean on the specific json pointer.
+     * @param ptr json pointer
+     * @param isTrue boolean to set
+     * @throws WorkflowException workflow exception
+     */
+    public void setAt(JsonPointer ptr, Boolean isTrue) throws WorkflowException {
+        BooleanNode booleanNode = BooleanNode.valueOf(isTrue);
+        attach(ptr, booleanNode);
+    }
+
+    /**
+     * Sets integer on specific json path.
+     * @param path json path
+     * @param number number to set
+     * @throws WorkflowException workflow exception
+     */
+    public void setAt(String path, Integer number) throws WorkflowException {
+        JsonPointer ptr = JsonPointer.compile(path);
+        setAt(ptr, number);
+    }
+
+    /**
+     * Sets integer on the specific json pointer.
+     * @param ptr json pointer
+     * @param number number to set
+     * @throws WorkflowException workflow exception
+     */
+    public void setAt(JsonPointer ptr, Integer number) throws WorkflowException {
+        IntNode intNode = IntNode.valueOf(number);
+        attach(ptr, intNode);
+    }
+
+    /**
      * Allocates json data model tree on json pointer path with specific leaf type.
      * @param node current json node in the json tree path
      * @param ptr json pointer
@@ -245,11 +476,11 @@
     private JsonNode alloc(JsonNode node, JsonPointer ptr, JsonNodeType leaftype) throws WorkflowException {
 
         if (ptr.matches()) {
-            if (node instanceof MissingNode) {
+            if (node == null || node instanceof MissingNode) {
                 node = createEmpty(leaftype);
             } else {
                 //TODO: checking existing node type is matched with leaftype
-                if (Objects.equals(node.getNodeType(), leaftype)) {
+                if (!Objects.equals(node.getNodeType(), leaftype)) {
                     throw new WorkflowException("Requesting leaftype(" + leaftype + ") is not matched with "
                             + "existing nodetype(" + node.getNodeType() + ") for " + ptr);
                 }
@@ -258,7 +489,7 @@
         }
 
         if (ptr.getMatchingIndex() != -1) {
-            if (node instanceof MissingNode) {
+            if (node == null || node instanceof MissingNode) {
                 node = createEmpty(JsonNodeType.ARRAY);
             }
             JsonNode child = alloc(node.get(ptr.getMatchingIndex()), ptr.tail(), leaftype);
@@ -266,7 +497,7 @@
                 ((ArrayNode) node).insert(ptr.getMatchingIndex(), child);
             }
         } else if (ptr.getMatchingProperty() != null) {
-            if (node instanceof MissingNode) {
+            if (node == null || node instanceof MissingNode) {
                 node = createEmpty(JsonNodeType.OBJECT);
             }
             JsonNode child = alloc(node.get(ptr.getMatchingProperty()), ptr.tail(), leaftype);
@@ -304,7 +535,7 @@
         try {
             str = (new ObjectMapper()).writerWithDefaultPrettyPrinter().writeValueAsString(root);
         } catch (JsonProcessingException e) {
-            e.printStackTrace();
+            log.error("Exception: ", e);
         }
         return str;
     }
@@ -312,7 +543,7 @@
     @Override
     public String toString() {
         return MoreObjects.toStringHelper(getClass())
-                .add("json", formattedRootString())
+                .add("json", root)
                 .toString();
     }
 }
diff --git a/apps/workflow/api/src/main/java/org/onosproject/workflow/api/ProgramCounter.java b/apps/workflow/api/src/main/java/org/onosproject/workflow/api/ProgramCounter.java
new file mode 100644
index 0000000..6af50e0
--- /dev/null
+++ b/apps/workflow/api/src/main/java/org/onosproject/workflow/api/ProgramCounter.java
@@ -0,0 +1,114 @@
+/*
+ * Copyright 2018-present Open Networking Foundation
+ *
+ * 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.workflow.api;
+
+import java.util.Objects;
+import java.util.regex.Matcher;
+import java.util.regex.Pattern;
+
+/**
+ * An interface representing workflow program counter.
+ */
+public final class ProgramCounter {
+
+    public static final ProgramCounter INIT_PC = ProgramCounter.valueOf(Worklet.Common.INIT.name(), 0);
+
+    /**
+     * index of the worklet.
+     */
+    private int workletIndex;
+
+    /**
+     * Type of worklet.
+     */
+    private String workletType;
+
+    /**
+     * Index of worklet.
+     * @return index of worklet
+     */
+    public int workletIndex() {
+        return this.workletIndex;
+    }
+
+    /**
+     * Type of worklet.
+     * @return type of worklet
+     */
+    public String workletType() {
+        return this.workletType;
+    }
+
+    /**
+     * Constructor of workflow Program Counter.
+     * @param workletType type of worklet
+     * @param workletIndex index of worklet
+     */
+    private ProgramCounter(String workletType, int workletIndex) {
+        this.workletType = workletType;
+        this.workletIndex = workletIndex;
+    }
+
+    @Override
+    public int hashCode() {
+        return Objects.hash(this.toString());
+    }
+
+    @Override
+    public boolean equals(Object obj) {
+        if (obj == this) {
+            return true;
+        }
+        if (!(obj instanceof ProgramCounter)) {
+            return false;
+        }
+        return Objects.equals(this.workletType(), ((ProgramCounter) obj).workletType())
+                && Objects.equals(this.workletIndex(), ((ProgramCounter) obj).workletIndex());
+    }
+
+    @Override
+    public String toString() {
+        return String.format("(%d)%s", workletIndex, workletType);
+    }
+
+    /**
+     * Builder of workflow Program Counter.
+     * @param workletType type of worklet
+     * @param workletIndex index of worklet
+     * @return program counter
+     */
+    public static ProgramCounter valueOf(String workletType, int workletIndex) {
+        return new ProgramCounter(workletType, workletIndex);
+    }
+
+    /**
+     * Builder of workflow Program Counter.
+     * @param strProgramCounter string format for program counter
+     * @return program counter
+     */
+    public static ProgramCounter valueOf(String strProgramCounter) {
+
+        Matcher m = Pattern.compile("\\((\\d+)\\)(.+)").matcher(strProgramCounter);
+
+        if (!m.matches()) {
+            throw new IllegalArgumentException("Malformed program counter string");
+        }
+
+        return new ProgramCounter(m.group(2), Integer.parseInt(m.group(1)));
+    }
+
+}
+
diff --git a/apps/workflow/api/src/main/java/org/onosproject/workflow/api/SystemWorkflowContext.java b/apps/workflow/api/src/main/java/org/onosproject/workflow/api/SystemWorkflowContext.java
index 5642c97..4cc15bd 100644
--- a/apps/workflow/api/src/main/java/org/onosproject/workflow/api/SystemWorkflowContext.java
+++ b/apps/workflow/api/src/main/java/org/onosproject/workflow/api/SystemWorkflowContext.java
@@ -17,8 +17,6 @@
 
 import com.google.common.base.MoreObjects;
 
-import java.net.URI;
-
 /**
  * WorkflowContext for system workflow.
  */
@@ -36,12 +34,10 @@
 
     /**
      * The constructor of SystemWorkflowContext.
-     * @param workflowId id of workflow
-     * @param workplaceName workplace name
-     * @param data data model tree
+     * @param builder builder of SystemWorkflowContext
      */
-    public SystemWorkflowContext(URI workflowId, String workplaceName, DataModelTree data) {
-        super(workflowId, workplaceName, data);
+    public SystemWorkflowContext(Builder builder) {
+        super(builder);
         timestamp = System.currentTimeMillis();
         //initial distributor(It can be changed)
         distributor = name();
@@ -78,4 +74,27 @@
                 .add("cause", cause())
                 .toString();
     }
+
+    /**
+     * Gets systemBuilder instance.
+     * @return systemBuilder instance
+     */
+    public static final Builder systemBuilder() {
+        return new Builder();
+    }
+
+    /**
+     * Builder for system workflow context.
+     */
+    public static class Builder extends DefaultWorkflowContext.Builder {
+
+        /**
+         * Builds system workflow context.
+         * @return instance of default workflow context.
+         */
+        public SystemWorkflowContext build() {
+            return new SystemWorkflowContext(this);
+        }
+    }
+
 }
diff --git a/apps/workflow/api/src/main/java/org/onosproject/workflow/api/TimeoutTask.java b/apps/workflow/api/src/main/java/org/onosproject/workflow/api/TimeoutTask.java
index 5b98bd1..180d9eb 100644
--- a/apps/workflow/api/src/main/java/org/onosproject/workflow/api/TimeoutTask.java
+++ b/apps/workflow/api/src/main/java/org/onosproject/workflow/api/TimeoutTask.java
@@ -17,6 +17,8 @@
 
 import com.google.common.base.MoreObjects;
 
+import static org.onosproject.workflow.api.CheckCondition.check;
+
 
 public final class TimeoutTask extends HandlerTask {
 
@@ -28,7 +30,7 @@
     public String toString() {
         return MoreObjects.toStringHelper(getClass())
                 .add("context", context())
-                .add("workletType", workletType())
+                .add("programCounter", programCounter())
                 .toString();
     }
 
@@ -51,16 +53,19 @@
         }
 
         @Override
-        public Builder workletType(String workletType) {
-            super.workletType(workletType);
+        public Builder programCounter(ProgramCounter programCounter) {
+            super.programCounter(programCounter);
             return this;
         }
 
         /**
          * Builds TimeoutTask.
          * @return instance of TimeoutTask
+         * @throws WorkflowException workflow exception
          */
-        public TimeoutTask build() {
+        public TimeoutTask build() throws WorkflowException {
+            check(context != null, "context is invalid");
+            check(programCounter != null, "programCounter is invalid");
             return new TimeoutTask(this);
         }
     }
diff --git a/apps/workflow/api/src/main/java/org/onosproject/workflow/api/TimerChain.java b/apps/workflow/api/src/main/java/org/onosproject/workflow/api/TimerChain.java
index 1118568..afa2ac6 100644
--- a/apps/workflow/api/src/main/java/org/onosproject/workflow/api/TimerChain.java
+++ b/apps/workflow/api/src/main/java/org/onosproject/workflow/api/TimerChain.java
@@ -32,6 +32,13 @@
     private TimerChainTask impendingTask;
 
     /**
+     * Constructor of timer chain.
+     */
+    public TimerChain() {
+
+    }
+
+    /**
      * Schedules timer event.
      * @param afterMs millisecond which time event happens.
      * @param runnable runnable to be executed after 'afterMs'
@@ -55,7 +62,7 @@
      */
     private void schedule(TimerChainTask task) {
         synchronized (this) {
-            if (taskQueue.size() == 0) {
+            if (taskQueue.isEmpty()) {
                 scheduleImpending(task);
                 return;
             }
@@ -124,7 +131,7 @@
      * @return timer chain task
      */
     public TimerChainTask head() {
-        if (taskQueue.size() > 0) {
+        if (!taskQueue.isEmpty()) {
             return taskQueue.peek();
         } else {
             return null;
@@ -136,7 +143,7 @@
      * @return timer chain task
      */
     public TimerChainTask pop() {
-        if (taskQueue.size() > 0) {
+        if (!taskQueue.isEmpty()) {
             return taskQueue.poll();
         } else {
             return null;
@@ -186,7 +193,6 @@
             TimerChainTask nextTask;
             synchronized (timerchain) {
                 if (timerchain.impendingTask() != this) {
-                    System.out.println("Invalid impendingTask");
                     runnable().run();
                     return;
                 }
diff --git a/apps/workflow/api/src/main/java/org/onosproject/workflow/api/Workflow.java b/apps/workflow/api/src/main/java/org/onosproject/workflow/api/Workflow.java
index 95e6e08..96e623f 100644
--- a/apps/workflow/api/src/main/java/org/onosproject/workflow/api/Workflow.java
+++ b/apps/workflow/api/src/main/java/org/onosproject/workflow/api/Workflow.java
@@ -38,12 +38,20 @@
     Worklet init(WorkflowContext context) throws WorkflowException;
 
     /**
-     * Returns next worklet.
+     * Returns next program counter.
      * @param context workflow context
-     * @return next worklet
+     * @return next program counter
      * @throws WorkflowException workflow exception
      */
-    Worklet next(WorkflowContext context) throws WorkflowException;
+    ProgramCounter next(WorkflowContext context) throws WorkflowException;
+
+    /**
+     * Gets increased program coounter.
+     * @param pc program counter
+     * @return increased program counter
+     * @throws WorkflowException workflow exception
+     */
+    ProgramCounter increased(ProgramCounter pc) throws WorkflowException;
 
     /**
      * Returns instance of worklet.
diff --git a/apps/workflow/api/src/main/java/org/onosproject/workflow/api/WorkflowContext.java b/apps/workflow/api/src/main/java/org/onosproject/workflow/api/WorkflowContext.java
index 12d4673..9f0b4fe 100644
--- a/apps/workflow/api/src/main/java/org/onosproject/workflow/api/WorkflowContext.java
+++ b/apps/workflow/api/src/main/java/org/onosproject/workflow/api/WorkflowContext.java
@@ -57,16 +57,16 @@
     public abstract void setState(WorkflowState state);
 
     /**
-     * Sets the current worklet of workflow context.
-     * @param worklet current worklet
+     * Sets the current program counter of workflow context.
+     * @param pc current program counter
      */
-    public abstract void setCurrent(Worklet worklet);
+    public abstract void setCurrent(ProgramCounter pc);
 
     /**
-     * Returns the class name of current worklet.
-     * @return the class name of current worklet
+     * Returns the current program counter of workflow.
+     * @return the current program counter of workflow
      */
-    public abstract String current();
+    public abstract ProgramCounter current();
 
     /**
      * Returns the cause string of exception state.
@@ -163,4 +163,13 @@
      * @return workplace store
      */
     public abstract WorkplaceStore workplaceStore();
+
+    /**
+     * Get service.
+     * @param serviceClass service class
+     * @param <T> service class type
+     * @return service reference
+     * @throws WorkflowException workflow exception
+     */
+    public abstract <T> T getService(Class<T> serviceClass) throws WorkflowException;
 }
diff --git a/apps/workflow/api/src/main/java/org/onosproject/workflow/api/WorkflowExecutionService.java b/apps/workflow/api/src/main/java/org/onosproject/workflow/api/WorkflowExecutionService.java
index ad9f731..9f609b3 100644
--- a/apps/workflow/api/src/main/java/org/onosproject/workflow/api/WorkflowExecutionService.java
+++ b/apps/workflow/api/src/main/java/org/onosproject/workflow/api/WorkflowExecutionService.java
@@ -30,6 +30,12 @@
     void execInitWorklet(WorkflowContext context);
 
     /**
+     * Evals workflow context.
+     * @param contextName the name of workflow context
+     */
+    void eval(String contextName);
+
+    /**
      * Triggers workflow event map.
      * @param event triggering event
      * @param generator event hint generation method reference
@@ -41,10 +47,9 @@
      * @param eventType event type (class name of event)
      * @param eventHint event hint value
      * @param contextName workflow context name to be called by this event map
-     * @param workletType worklet type to be called by this event map
+     * @param programCounterString worklet type to be called by this event map
      * @throws WorkflowException workflow exception
      */
     void registerEventMap(Class<? extends Event> eventType, String eventHint,
-                          String contextName, String workletType) throws WorkflowException;
-
+                          String contextName, String programCounterString) throws WorkflowException;
 }
diff --git a/apps/workflow/api/src/main/java/org/onosproject/workflow/api/Worklet.java b/apps/workflow/api/src/main/java/org/onosproject/workflow/api/Worklet.java
index 386fa38..c4b4fb2 100644
--- a/apps/workflow/api/src/main/java/org/onosproject/workflow/api/Worklet.java
+++ b/apps/workflow/api/src/main/java/org/onosproject/workflow/api/Worklet.java
@@ -23,7 +23,7 @@
  */
 public interface Worklet {
 
-    int MAX_WORKS = 1000;
+    int MAX_WORKS = 10000;
 
     /**
      * Returns tag name of worklet. class name is usually used.