diff --git a/maker/java/src/main/java/org/lionsoul/ip2region/xdb/Maker.java b/maker/java/src/main/java/org/lionsoul/ip2region/xdb/Maker.java
index b28c829..23f0d47 100644
--- a/maker/java/src/main/java/org/lionsoul/ip2region/xdb/Maker.java
+++ b/maker/java/src/main/java/org/lionsoul/ip2region/xdb/Maker.java
@@ -5,7 +5,62 @@
 // @Author Lion <chenxin619315@gmail.com>
 // @Date   2022/07/12
 
+// --- Ip2Region v2.0 data structure
+//
+// +----------------+--------------------------+---------------+--------------+
+// | header space   | vector speed up index    |  data payload | block index  |
+// +----------------+--------------------------+---------------+--------------+
+// | 256 bytes      | 512 KiB (fixed)          | dynamic size  | dynamic size |
+// +----------------+--------------------------+---------------+--------------+
+//
+// 1. padding space : for header info like block index ptr, version, release date eg ... or any other temporary needs.
+// -- 2bytes: version number, different version means structure update, it fixed to 2 for now
+// -- 2bytes: index algorithm code.
+// -- 4bytes: generate unix timestamp (version)
+// -- 4bytes: index block start ptr
+// -- 4bytes: index block end ptr
+//
+//
+// 2. data block : region or whatever data info.
+// 3. segment index block : binary index block.
+// 4. vector index block  : fixed index info for block index search speed up.
+// space structure table:
+// -- 0   -> | 1rt super block | 2nd super block | 3rd super block | ... | 255th super block
+// -- 1   -> | 1rt super block | 2nd super block | 3rd super block | ... | 255th super block
+// -- 2   -> | 1rt super block | 2nd super block | 3rd super block | ... | 255th super block
+// -- ...
+// -- 255 -> | 1rt super block | 2nd super block | 3rd super block | ... | 255th super block
+//
+//
+// super block structure:
+// +-----------------------+----------------------+
+// | first index block ptr | last index block ptr |
+// +-----------------------+----------------------+
+//
+// data entry structure:
+// +--------------------+-----------------------+
+// | 2bytes (for desc)	| dynamic length		|
+// +--------------------+-----------------------+
+//  data length   whatever in bytes
+//
+// index entry structure
+// +------------+-----------+---------------+------------+
+// | 4bytes		| 4bytes	| 2bytes		| 4 bytes    |
+// +------------+-----------+---------------+------------+
+//  start ip 	  end ip	  data length     data ptr
+
 package org.lionsoul.ip2region.xdb;
 
 public class Maker {
+    // constants define
+    public static final int VersionNo = 2;
+    public static final int HeaderInfoLength = 256;
+    public static final int VectorIndexRows = 256;
+    public static final int VectorIndexCols = 256;
+    public static final int VectorIndexSize = 8;
+    public static final int SegmentIndexSize = 14;
+
+    public Maker() {
+    }
+
 }