diff --git a/.travis.yml b/.travis.yml
index 441d2e1..f48f640 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -4,7 +4,7 @@ node_js:
 
 before_script:
   - npm install -g gulp
-  - rvm install ruby-2.2.3
+  - rvm install ruby
   - gem install scss_lint
 
 script:
diff --git a/gulpfile.js b/gulpfile.js
index 45d2830..35ad06d 100644
--- a/gulpfile.js
+++ b/gulpfile.js
@@ -38,7 +38,9 @@ gulp.task('default', ['lint', 'build', 'build-doc']);
 // Do everything.
 gulp.task('all', function(cb) {
   runSequence(
-    'clean',
+    'dist',
     ['lint', 'compile-all', 'build-doc'],
+    'dist',
+    'build',
     cb);
 });
diff --git a/src/data/data.js b/src/data/data.js
index f6f423b..6d6c50a 100644
--- a/src/data/data.js
+++ b/src/data/data.js
@@ -20,12 +20,6 @@ visflow.TabularData;
 /** @const */
 visflow.data = {};
 
-/**
- * Counter to set process based dataIds.
- * @type {number}
- */
-visflow.data.counter = 0;
-
 /**
  * Dimension index of item table index.
  * @const {number}
@@ -35,6 +29,9 @@ visflow.data.INDEX_DIM = -1;
 /** @const {string} */
 visflow.data.INDEX_TEXT = '[index]';
 
+/** @const {string} */
+visflow.data.EMPTY_DATA_ID = 'empty';
+
 /**
  * @typedef {{
  *   id: number,
@@ -121,12 +118,7 @@ visflow.data.registerData = function(data) {
     visflow.error('attempt register null/empty data');
     return;
   }
-  if (!(data.hash in visflow.data.hashToData)) {
-    visflow.data.hashToData[data.hash] = data;
-    data.dataId = ++visflow.data.counter;
-  } else {
-    data.dataId = visflow.data.hashToData[data.hash].dataId;
-  }
+  visflow.data.hashToData[data.hash] = data;
 };
 
 /**
@@ -141,7 +133,7 @@ visflow.Data = function(data) {
       dimensionTypes: [],
       dimensionDuplicate: [],
       values: [],
-      dataId: 0,
+      dataId: visflow.data.EMPTY_DATA_ID,
       type: ''
     });
     return;
@@ -169,9 +161,10 @@ visflow.Data = function(data) {
 
   /**
    * Data id assigned by the running system instance.
-   * @type {number}
+   * Use hash value as data id to identify data changes.
+   * @type {string}
    */
-  this.dataId = data.dataId;
+  this.dataId = data.hash;
 
   /**
    * Type of data. It will be a hash value of the data's dimensions and
diff --git a/src/filter/index.js b/src/filter/index.js
index 97b5eea..d641be3 100644
--- a/src/filter/index.js
+++ b/src/filter/index.js
@@ -18,9 +18,9 @@ visflow.Filter = function(params) {
 
   /**
    * Last processed data id. By default it is empty data.
-   * @protected {number}
+   * @protected {string}
    */
-  this.lastDataId = 0;
+  this.lastDataId = visflow.data.EMPTY_DATA_ID;
 };
 
 _.inherit(visflow.Filter, visflow.Node);
@@ -51,7 +51,7 @@ visflow.Filter.prototype.deserialize = function(save) {
   visflow.Filter.base.deserialize.call(this, save);
   this.lastDataId = save.lastDataId;
   if (this.lastDataId == null) {
-    this.lastDataId = 0;
+    this.lastDataId = visflow.data.EMPTY_DATA_ID;
     visflow.warning('filter lastDataId not saved');
   }
 };
diff --git a/src/value/value-extractor/index.js b/src/value/value-extractor/index.js
index 4a5e816..397b8eb 100644
--- a/src/value/value-extractor/index.js
+++ b/src/value/value-extractor/index.js
@@ -27,10 +27,10 @@ visflow.ValueExtractor = function(params) {
   };
 
   /**
-   * Last applied data id. Default is empty data (0).
-   * @protected {number}
+   * Last applied data id. Default is empty data.
+   * @protected {string}
    */
-  this.lastDataId = 0;
+  this.lastDataId = visflow.data.EMPTY_DATA_ID;
 };
 
 _.inherit(visflow.ValueExtractor, visflow.Node);
diff --git a/src/visualization/index.js b/src/visualization/index.js
index a4e9fe3..8a44511 100644
--- a/src/visualization/index.js
+++ b/src/visualization/index.js
@@ -55,10 +55,10 @@ visflow.Visualization = function(params) {
   this.brushPoints = [];
 
   /**
-   * Last used dataset ID.
-   * @protected {number}
+   * Last used dataset ID. Default is empty data.
+   * @protected {string}
    */
-  this.lastDataId = 0;  // Default: empty data
+  this.lastDataId = visflow.data.EMPTY_DATA_ID;
 
   /**
    * Whether rendering should be using transition. When the view is resized,
@@ -112,7 +112,7 @@ visflow.Visualization.prototype.deserialize = function(save) {
   this.lastDataId = save.lastDataId;
   if (this.lastDataId == null) {
     visflow.error('lastDataId not saved in visualization');
-    this.lastDataId = 0;
+    this.lastDataId = visflow.data.EMPTY_DATA_ID;
   }
   this.fillOptions(this.options, this.visualizationOptions());
 };
diff --git a/src/visualization/network/index.js b/src/visualization/network/index.js
index 67fcdf3..27b939a 100644
--- a/src/visualization/network/index.js
+++ b/src/visualization/network/index.js
@@ -83,9 +83,9 @@ visflow.Network = function(params) {
 
   /**
    * Last data id for edges.
-   * @protected {number}
+   * @protected {string}
    */
-  this.lastEdgeDataId = 0;
+  this.lastEdgeDataId = visflow.data.EMPTY_DATA_ID;
 
   // Navigation state.
   /** @private {!Array<number>} */