diff --git a/skywalking-commons/skywalking-trace/src/main/java/com/a/eye/skywalking/trace/LogData.java b/skywalking-commons/skywalking-trace/src/main/java/com/a/eye/skywalking/trace/LogData.java
index 250bc2516badaf13b9901d5d2031486b94dcb1b7..576aa680c0740c0f65e09677f9af1dde9b39a418 100644
--- a/skywalking-commons/skywalking-trace/src/main/java/com/a/eye/skywalking/trace/LogData.java
+++ b/skywalking-commons/skywalking-trace/src/main/java/com/a/eye/skywalking/trace/LogData.java
@@ -1,5 +1,6 @@
 package com.a.eye.skywalking.trace;
 
+import java.util.Collections;
 import java.util.Map;
 
 /**
@@ -21,6 +22,6 @@ public class LogData {
     }
 
     public Map<String, ?> getFields() {
-        return fields;
+        return Collections.unmodifiableMap(fields);
     }
 }
diff --git a/skywalking-commons/skywalking-trace/src/main/java/com/a/eye/skywalking/trace/Span.java b/skywalking-commons/skywalking-trace/src/main/java/com/a/eye/skywalking/trace/Span.java
index 5261d59ffee646b48069ab422bfad8b596a3154a..e447142200c0d810602acf7ff56edf9a2e453894 100644
--- a/skywalking-commons/skywalking-trace/src/main/java/com/a/eye/skywalking/trace/Span.java
+++ b/skywalking-commons/skywalking-trace/src/main/java/com/a/eye/skywalking/trace/Span.java
@@ -12,19 +12,8 @@ import java.util.Map;
  * Span is a concept from OpenTracing Spec, also from Google Dapper Paper.
  * Traces in OpenTracing are defined implicitly by their Spans.
  *
- * [Span A]  ←←←(the root span)
- * |
- * +------+------+
- * |             |
- * [Span B]      [Span C] ←←←(Span C is a `ChildOf` Span A)
- * |             |
- * [Span D]      +---+-------+
- * |           |
- * [Span E]    [Span F] >>> [Span G] >>> [Span H]
- * ↑
- * ↑
- * ↑
- * (Span G `FollowsFrom` Span F)
+ * Know more things about span concept:
+ * {@see https://github.com/opentracing/specification/blob/master/specification.md#the-opentracing-data-model}
  *
  * Created by wusheng on 2017/2/17.
  */
@@ -192,9 +181,7 @@ public class Span {
         exceptionFields.put("message", t.getMessage());
         exceptionFields.put("stack", ThrowableTransformer.INSTANCE.convert2String(t, 4000));
 
-        logs.add(new LogData(System.currentTimeMillis(), exceptionFields));
-
-        return this;
+        return log(exceptionFields);
     }
 
     private enum ThrowableTransformer {
diff --git a/skywalking-commons/skywalking-trace/src/main/java/com/a/eye/skywalking/trace/tag/Tags.java b/skywalking-commons/skywalking-trace/src/main/java/com/a/eye/skywalking/trace/tag/Tags.java
index 94d33874e9cb87c3eb44e56a6907716933c2f8ee..d0881dc1b4e97121f24e261dfe8b6e94c9d8eb16 100644
--- a/skywalking-commons/skywalking-trace/src/main/java/com/a/eye/skywalking/trace/tag/Tags.java
+++ b/skywalking-commons/skywalking-trace/src/main/java/com/a/eye/skywalking/trace/tag/Tags.java
@@ -29,20 +29,45 @@ public final class Tags {
     public static final class SPAN_KIND{
         private static StringTag SPAN_KIND_TAG = new StringTag("span.kind");
 
+        private static final String DB_KIND = "db";
+        private static final String RPC_KIND = "rpc";
+        private static final String NOSQL_KIND = "nosql";
+        private static final String HTTP_KIND = "http";
+
         public static void asDBAccess(Span span){
-            SPAN_KIND_TAG.set(span, "db");
+            SPAN_KIND_TAG.set(span, DB_KIND);
         }
 
         public static void asRPC(Span span){
-            SPAN_KIND_TAG.set(span, "rpc");
+            SPAN_KIND_TAG.set(span, RPC_KIND);
         }
 
         public static void asNoSQL(Span span){
-            SPAN_KIND_TAG.set(span, "nosql");
+            SPAN_KIND_TAG.set(span, NOSQL_KIND);
         }
 
         public static void asHttp(Span span){
-            SPAN_KIND_TAG.set(span, "http");
+            SPAN_KIND_TAG.set(span, HTTP_KIND);
+        }
+
+        public static String get(Span span){
+            return SPAN_KIND_TAG.get(span);
+        }
+
+        public static boolean isDBAccess(Span span){
+            return DB_KIND.equals(get(span));
+        }
+
+        public static boolean isRPC(Span span){
+            return RPC_KIND.equals(get(span));
+        }
+
+        public static boolean isNoSQL(Span span){
+            return NOSQL_KIND.equals(get(span));
+        }
+
+        public static boolean isHttp(Span span){
+            return HTTP_KIND.equals(get(span));
         }
     }
 
diff --git a/skywalking-commons/skywalking-trace/src/test/java/com/a/eye/skywalking/trace/SpanTestCase.java b/skywalking-commons/skywalking-trace/src/test/java/com/a/eye/skywalking/trace/SpanTestCase.java
index d57cf2d22296c00bcfffc568882057c223b62e04..f26b22f232ddc4759570849c1ac7c3d4b5f2833e 100644
--- a/skywalking-commons/skywalking-trace/src/test/java/com/a/eye/skywalking/trace/SpanTestCase.java
+++ b/skywalking-commons/skywalking-trace/src/test/java/com/a/eye/skywalking/trace/SpanTestCase.java
@@ -2,6 +2,7 @@ package com.a.eye.skywalking.trace;
 
 import com.a.eye.skywalking.trace.tag.Tags;
 import java.util.Collections;
+import java.util.List;
 import java.util.Map;
 import org.junit.Assert;
 import org.junit.Test;
@@ -37,7 +38,7 @@ public class SpanTestCase {
     @Test
     public void testSetTag() {
         Span span1 = new Span(0, "serviceA");
-        Tags.SPAN_KIND.set(span1, "client");
+        Tags.SPAN_KIND.asHttp(span1);
         Tags.COMPONENT.set(span1, "Spring");
         Tags.PEER_HOST_IPV4.set(span1, ipToInt("127.0.0.1"));
         Tags.ERROR.set(span1, true);
@@ -48,7 +49,7 @@ public class SpanTestCase {
 
         Map<String, Object> tags = span1.getTags();
         Assert.assertEquals(8, tags.size());
-        Assert.assertEquals("client", Tags.SPAN_KIND.get(span1));
+        Assert.assertTrue(Tags.SPAN_KIND.isHttp(span1));
         Assert.assertEquals("127.0.0.1", intToIp(Tags.PEER_HOST_IPV4.get(span1)));
         Assert.assertTrue(Tags.ERROR.get(span1));
     }
@@ -82,4 +83,16 @@ public class SpanTestCase {
         sb.append(String.valueOf((longIp & 0x000000FF)));
         return sb.toString();
     }
+
+    @Test
+    public void testLogException(){
+        Span span1 = new Span(0, "serviceA");
+        Exception exp = new Exception("exception msg");
+        span1.log(exp);
+        List<LogData> logs = span1.getLogs();
+
+        Assert.assertEquals("java.lang.Exception", logs.get(0).getFields().get("error.kind"));
+        Assert.assertEquals("exception msg", logs.get(0).getFields().get("message"));
+        Assert.assertNotNull(logs.get(0).getFields().get("stack"));
+    }
 }