--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/main/java/jp/ac/u_ryukyu/ie/cr/tatsuki/jungle/store/index/ParentIndex.java	Sat Nov 22 12:54:28 2014 +0900
@@ -0,0 +1,43 @@
+package jp.ac.u_ryukyu.ie.cr.tatsuki.jungle.store.index;
+
+import jp.ac.u_ryukyu.ie.cr.shoshi.jungle.store.impl.TreeNode;
+import jp.ac.u_ryukyu.ie.cr.shoshi.jungle.util.TreeMapOrd;
+import fj.data.Option;
+import fj.data.TreeMap;
+
+public class ParentIndex {
+  
+  private final TreeMap<TreeNode, TreeNode> parentIndex;
+
+  public ParentIndex() {
+    parentIndex = TreeMap.empty(TreeMapOrd.treeNodeOrd);
+  }
+
+  public ParentIndex(TreeMap<TreeNode, TreeNode> parentIndex) {
+    this.parentIndex = parentIndex;
+  }
+  
+  public ParentIndex(ParentIndex parentIndex) {
+    this.parentIndex = parentIndex.getParentIndex();
+  }
+
+  private TreeMap<TreeNode, TreeNode> getParentIndex() {
+    return parentIndex;
+  }
+
+  public Option<TreeNode> get(TreeNode child) {
+    Option<TreeNode> parentOp = parentIndex.get(child);
+    return parentOp;
+  }
+  
+  public ParentIndex set(TreeNode child, TreeNode parent){
+    TreeMap<TreeNode, TreeNode> newParentIndex = parentIndex.set(child,parent);
+    return new ParentIndex(newParentIndex);
+  }
+  
+  public ParentIndex delete(TreeNode child) {
+    TreeMap<TreeNode, TreeNode> newParentIndex = parentIndex.delete(child);
+     return new ParentIndex(newParentIndex);
+  }
+
+}