diff --git a/CMakeLists.txt b/CMakeLists.txt
index 04937a2840c0dcfa7b5ab1f9e2bc7358e05c8e02..b3eec5e149e26c6beb1ce408fe8ce58c4c9bc579 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -16,7 +16,6 @@ link_directories(${PROJECT_SOURCE_DIR}/thirdparty/local/lib)
 add_library(storage
         ${PROJECT_SOURCE_DIR}/visualdl/backend/storage/storage.cc
         ${PROJECT_SOURCE_DIR}/visualdl/backend/storage/storage.pb.cc)
-add_library(c_api ${PROJECT_SOURCE_DIR}/visualdl/backend/logic/c_api.cc)
 add_library(sdk ${PROJECT_SOURCE_DIR}/visualdl/backend/logic/sdk.cc)
 add_library(im ${PROJECT_SOURCE_DIR}/visualdl/backend/logic/im.cc)
 
@@ -29,4 +28,3 @@ add_executable(vl_test
         ${PROJECT_SOURCE_DIR}/visualdl/backend/test.cc
         ${PROJECT_SOURCE_DIR}/visualdl/backend/logic/im_test.cc)
 target_link_libraries(vl_test storage im gtest glog protobuf gflags)
-
diff --git a/visualdl/backend/logic/im.cc b/visualdl/backend/logic/im.cc
index 241ff469cb80faba724adbc49e7f179c7b28aabd..12fa5cd5b8c95b81e966b8c25f6234895dc5e63c 100644
--- a/visualdl/backend/logic/im.cc
+++ b/visualdl/backend/logic/im.cc
@@ -1,5 +1,5 @@
-#include <ctime>
 #include <glog/logging.h>
+#include <ctime>
 
 #include "visualdl/backend/logic/im.h"
 
@@ -45,11 +45,17 @@ void InformationMaintainer::AddRecord(const std::string &tag,
   auto *tablet = storage_.Find(tag);
   CHECK(tablet);
 
-  auto num_records = tablet->num_records();
+  auto num_records = tablet->total_records();
   const auto num_samples = tablet->num_samples();
-  const auto offset = ReserviorSample(num_samples, num_records + 1);
-  if (offset < 0)
-    return;
+
+  int offset;
+  // use reservoir sampling or not
+  if (num_samples > 0) {
+    offset = ReserviorSample(num_samples, num_records + 1);
+    if (offset < 0) return;
+  } else {
+    offset = num_records;
+  }
 
   storage::Record *record;
   if (offset >= num_records) {
@@ -59,13 +65,21 @@ void InformationMaintainer::AddRecord(const std::string &tag,
   }
 
   *record = data;
+  tablet->set_total_records(num_records + 1);
+}
 
-  tablet->set_num_records(num_records + 1);
+void InformationMaintainer::Clear() {
+  auto *data = storage().mutable_data();
+  data->clear_tablets();
+  data->clear_dir();
+  data->clear_timestamp();
 }
 
 void InformationMaintainer::PersistToDisk() {
   CHECK(!storage_.data().dir().empty()) << "path of storage should be set";
-  storage_.Save(storage_.data().dir());
+  // TODO make dir first
+  // MakeDir(storage_.data().dir());
+  storage_.Save(storage_.data().dir() + "/storage.pb");
 }
 
-} // namespace visualdl
+}  // namespace visualdl
diff --git a/visualdl/backend/logic/im.h b/visualdl/backend/logic/im.h
index b94102db08efb032f37e0e837bd379bb9f830569..dfb73a83cea3f6e4c98c5fe7565d669737e88bb9 100644
--- a/visualdl/backend/logic/im.h
+++ b/visualdl/backend/logic/im.h
@@ -29,14 +29,18 @@ public:
 
   /*
    * @tag: tag of the target Tablet.
-   * @type: type of target Tablet.
-   * @data: storage Record.
+   * @record: a record
    *
    * NOTE pass in the serialized protobuf message will trigger copying, but
    * simpler to support different Tablet data formats.
    */
   void AddRecord(const std::string &tag, const storage::Record &record);
 
+  /*
+   * delete all the information.
+   */
+  void Clear();
+
   /*
    * Save the Storage Protobuf to disk.
    */
diff --git a/visualdl/backend/logic/pybind.cc b/visualdl/backend/logic/pybind.cc
index 242c25d3e1a80a7704dcfddbaa62775ad1dbde20..2256542d880e2cc9199a4b9d6c27497491e8fb95 100644
--- a/visualdl/backend/logic/pybind.cc
+++ b/visualdl/backend/logic/pybind.cc
@@ -1,5 +1,6 @@
 #include <ctype.h>
 #include <pybind11/pybind11.h>
+#include <pybind11/stl.h>
 
 #include "visualdl/backend/logic/sdk.h"
 
@@ -10,19 +11,6 @@ PYBIND11_MODULE(core, m) {
   m.doc() = "visualdl python core API";
 
   py::class_<vs::TabletHelper>(m, "Tablet")
-      // interfaces for components
-      .def("add_scalar_int32",
-           &vs::TabletHelper::AddScalarRecord<int32_t>,
-           "add a scalar int32 record",
-           pybind11::arg("id"),
-           pybind11::arg("value"))
-      .def("add_scalar_int64",
-           &vs::TabletHelper::AddScalarRecord<int64_t>,
-           "add a scalar int64 record",
-           pybind11::arg("id"),
-           pybind11::arg("value"))
-      .def("add_scalar_float", &vs::TabletHelper::AddScalarRecord<float>)
-      .def("add_scalar_double", &vs::TabletHelper::AddScalarRecord<double>)
       // other member setter and getter
       .def("record_buffer", &vs::TabletHelper::record_buffer)
       .def("records_size", &vs::TabletHelper::records_size)
@@ -30,7 +18,23 @@ PYBIND11_MODULE(core, m) {
       .def("human_readable_buffer", &vs::TabletHelper::human_readable_buffer)
       .def("set_buffer",
            (void (vs::TabletHelper::*)(const std::string&)) &
-               vs::TabletHelper::SetBuffer);
+               vs::TabletHelper::SetBuffer)
+      // scalar interface
+      .def("as_int32_scalar",
+           [](const vs::TabletHelper& self) {
+             return vs::components::ScalarHelper<int32_t>(&self.data());
+           })
+      .def("as_int64_scalar",
+           [](const vs::TabletHelper& self) {
+             return vs::components::ScalarHelper<int64_t>(&self.data());
+           })
+      .def("as_float_scalar",
+           [](const vs::TabletHelper& self) {
+             return vs::components::ScalarHelper<float>(&self.data());
+           })
+      .def("as_double_scalar", [](const vs::TabletHelper& self) {
+        return vs::components::ScalarHelper<double>(&self.data());
+      });
 
   py::class_<vs::StorageHelper>(m, "Storage")
       .def("timestamp", &vs::StorageHelper::timestamp)
@@ -46,7 +50,24 @@ PYBIND11_MODULE(core, m) {
   py::class_<vs::ImHelper>(m, "Im")
       .def("storage", &vs::ImHelper::storage)
       .def("tablet", &vs::ImHelper::tablet)
-      .def("add_tablet", &vs::ImHelper::AddTablet);
+      .def("add_tablet", &vs::ImHelper::AddTablet)
+      .def("persist_to_disk", &vs::ImHelper::PersistToDisk)
+      .def("clear_tablets", &vs::ImHelper::ClearTablets);
 
   m.def("im", &vs::get_im, "global information-maintainer object.");
+
+// interfaces for components
+#define ADD_SCALAR_TYPED_INTERFACE(T, name__)                             \
+  py::class_<vs::components::ScalarHelper<T>>(m, #name__)                 \
+      .def("add_record", &vs::components::ScalarHelper<T>::AddRecord)     \
+      .def("set_captions", &vs::components::ScalarHelper<T>::SetCaptions) \
+      .def("get_records", &vs::components::ScalarHelper<T>::GetRecords)   \
+      .def("get_captions", &vs::components::ScalarHelper<T>::GetCaptions) \
+      .def("get_ids", &vs::components::ScalarHelper<T>::GetIds)           \
+      .def("get_timestamps", &vs::components::ScalarHelper<T>::GetTimestamps);
+  ADD_SCALAR_TYPED_INTERFACE(int32_t, ScalarInt32);
+  ADD_SCALAR_TYPED_INTERFACE(int64_t, ScalarInt64);
+  ADD_SCALAR_TYPED_INTERFACE(float, ScalarFloat);
+  ADD_SCALAR_TYPED_INTERFACE(double, ScalarDouble);
+#undef ADD_SCALAR_TYPED_INTERFACE
 }
diff --git a/visualdl/backend/logic/sdk.cc b/visualdl/backend/logic/sdk.cc
index 10406da6d7373c7efb54390cabdca8bdbffa7119..a2c7d638f847efc9af33487a725204a5b2a00df7 100644
--- a/visualdl/backend/logic/sdk.cc
+++ b/visualdl/backend/logic/sdk.cc
@@ -1,12 +1,13 @@
-#include <google/protobuf/text_format.h>
 #include "visualdl/backend/logic/sdk.h"
+#include <google/protobuf/text_format.h>
 
 namespace visualdl {
 
-#define IMPL_ENTRY_SET_OR_ADD(method__, ctype__, dtype__, opr__)               \
-  template <> void Entry<ctype__>::method__(ctype__ v) {                       \
-    entry->set_dtype(storage::DataType::dtype__);                              \
-    entry->opr__(v);                                                           \
+#define IMPL_ENTRY_SET_OR_ADD(method__, ctype__, dtype__, opr__) \
+  template <>                                                    \
+  void EntryHelper<ctype__>::method__(ctype__ v) {               \
+    entry->set_dtype(storage::DataType::dtype__);                \
+    entry->opr__(v);                                             \
   }
 
 IMPL_ENTRY_SET_OR_ADD(Set, int32_t, kInt32, set_i32);
@@ -16,9 +17,36 @@ IMPL_ENTRY_SET_OR_ADD(Set, float, kFloat, set_f);
 IMPL_ENTRY_SET_OR_ADD(Set, double, kDouble, set_d);
 IMPL_ENTRY_SET_OR_ADD(Add, int32_t, kInt32s, add_i32s);
 IMPL_ENTRY_SET_OR_ADD(Add, int64_t, kInt64s, add_i64s);
-IMPL_ENTRY_SET_OR_ADD(Add, bool, kBools, add_bs);
 IMPL_ENTRY_SET_OR_ADD(Add, float, kFloats, add_fs);
 IMPL_ENTRY_SET_OR_ADD(Add, double, kDoubles, add_ds);
+IMPL_ENTRY_SET_OR_ADD(Add, std::string, kStrings, add_ss);
+IMPL_ENTRY_SET_OR_ADD(Add, bool, kBools, add_bs);
+
+#define IMPL_ENTRY_GET(T, fieldname__) \
+  template <>                          \
+  T EntryHelper<T>::Get() const {      \
+    return entry->fieldname__();       \
+  }
+IMPL_ENTRY_GET(int32_t, i32);
+IMPL_ENTRY_GET(int64_t, i64);
+IMPL_ENTRY_GET(float, f);
+IMPL_ENTRY_GET(double, d);
+IMPL_ENTRY_GET(std::string, s);
+IMPL_ENTRY_GET(bool, b);
+
+#define IMPL_ENTRY_GET_MULTI(T, fieldname__)            \
+  template <>                                           \
+  std::vector<T> EntryHelper<T>::GetMulti() const {     \
+    return std::vector<T>(entry->fieldname__().begin(), \
+                          entry->fieldname__().end());  \
+  }
+
+IMPL_ENTRY_GET_MULTI(int32_t, i32s);
+IMPL_ENTRY_GET_MULTI(int64_t, i64s);
+IMPL_ENTRY_GET_MULTI(float, fs);
+IMPL_ENTRY_GET_MULTI(double, ds);
+IMPL_ENTRY_GET_MULTI(std::string, ss);
+IMPL_ENTRY_GET_MULTI(bool, bs);
 
 std::string StorageHelper::human_readable_buffer() const {
   std::string buffer;
@@ -32,4 +60,84 @@ std::string TabletHelper::human_readable_buffer() const {
   return buffer;
 }
 
-} // namespace visualdl
+void ImHelper::PersistToDisk() const {
+  InformationMaintainer::Global().PersistToDisk();
+}
+
+// implementations for components
+namespace components {
+
+template <typename T>
+void ScalarHelper<T>::SetCaptions(const std::vector<std::string> &captions) {
+  for (int i = 0; i < captions.size(); i++) {
+    data_->add_captions(captions[i]);
+  }
+}
+
+template <typename T>
+void ScalarHelper<T>::AddRecord(int id, const std::vector<T> &values) {
+  CHECK_NOTNULL(data_);
+  CHECK_GT(data_->captions_size(), 0UL) << "captions should be set first";
+  CHECK_EQ(data_->captions_size(), values.size())
+      << "number of values in a record should be compatible with the "
+         "captions";
+  // add record data
+  auto *record = data_->add_records();
+  auto *data = record->add_data();
+  EntryHelper<T> entry_helper(data);
+  for (auto v : values) {
+    entry_helper.Add(v);
+  }
+  // set record id
+  record->set_id(id);
+  // set record timestamp
+  record->set_timestamp(time(NULL));
+}
+
+template <typename T>
+std::vector<std::vector<T>> ScalarHelper<T>::GetRecords() const {
+  std::vector<std::vector<T>> result;
+  EntryHelper<T> entry_helper;
+  for (int i = 0; i < data_->records_size(); i++) {
+    auto *entry = data_->mutable_records(i)->mutable_data(0);
+    entry_helper(entry);
+    auto datas = entry_helper.GetMulti();
+    result.push_back(std::move(datas));
+  }
+  return result;
+}
+
+template <typename T>
+std::vector<int> ScalarHelper<T>::GetIds() const {
+  CHECK_NOTNULL(data_);
+  std::vector<int> result;
+  for (int i = 0; i < data_->records_size(); i++) {
+    result.push_back(data_->records(i).id());
+  }
+  return result;
+}
+
+template <typename T>
+std::vector<int> ScalarHelper<T>::GetTimestamps() const {
+  CHECK_NOTNULL(data_);
+  std::vector<int> result;
+  for (int i = 0; i < data_->records_size(); i++) {
+    result.push_back(data_->records(i).timestamp());
+  }
+  return result;
+}
+
+template <typename T>
+std::vector<std::string> ScalarHelper<T>::GetCaptions() const {
+  return std::vector<std::string>(data_->captions().begin(),
+                                  data_->captions().end());
+}
+
+template class ScalarHelper<int32_t>;
+template class ScalarHelper<int64_t>;
+template class ScalarHelper<float>;
+template class ScalarHelper<double>;
+
+}  // namespace components
+
+}  // namespace visualdl
diff --git a/visualdl/backend/logic/sdk.h b/visualdl/backend/logic/sdk.h
index c99958a7e11c129f860a983813f11076875788ce..54a504325a1905f3a58c4e9a96817c64775275ec 100644
--- a/visualdl/backend/logic/sdk.h
+++ b/visualdl/backend/logic/sdk.h
@@ -1,29 +1,67 @@
 #ifndef VISUALDL_BACKEND_LOGIC_SDK_H
 #define VISUALDL_BACKEND_LOGIC_SDK_H
-#include "visualdl/backend/logic/im.h"
 
+#include <glog/logging.h>
+#include <time.h>
 #include <map>
 
+#include "visualdl/backend/logic/im.h"
+
 namespace visualdl {
 
+/*
+ * Utility helper for storage::Entry.
+ */
+template <typename T>
+struct EntryHelper {
+  // use pointer to avoid copy
+  storage::Entry *entry{nullptr};
+
+  EntryHelper() {}
+  explicit EntryHelper(storage::Entry *entry) : entry(entry) {}
+  void operator()(storage::Entry *entry) { this->entry = entry; }
+
+  /*
+   * Set a single value.
+   */
+  void Set(T v);
+
+  /*
+   * Add a value to repeated message field.
+   */
+  void Add(T v);
+
+  /*
+   * Get a single value.
+   */
+  T Get() const;
+
+  /*
+   * Get repeated field.
+   */
+  std::vector<T> GetMulti() const;
+};
+
 class TabletHelper {
 public:
-  // method for each components
-  template <typename T>
-  void AddScalarRecord(int id, T value);
-
   // basic member getter and setter
-  std::string record_buffer(int idx) const { return data_->records(idx).SerializeAsString(); }
+  std::string record_buffer(int idx) const {
+    return data_->records(idx).SerializeAsString();
+  }
   size_t records_size() const { return data_->records_size(); }
   std::string buffer() const { return data_->SerializeAsString(); }
   std::string human_readable_buffer() const;
   void SetBuffer(const storage::Tablet &t) { *data_ = t; }
   void SetBuffer(const std::string &b) { data_->ParseFromString(b); }
+  storage::Tablet &data() const { return *data_; }
 
   // constructor that enable concurrency.
   TabletHelper(storage::Tablet *t) : data_(t) {}
   // data updater that resuage of one instance.
-  TabletHelper &operator()(storage::Tablet *t) { data_ = t; return *this; }
+  TabletHelper &operator()(storage::Tablet *t) {
+    data_ = t;
+    return *this;
+  }
 
 private:
   storage::Tablet *data_;
@@ -66,14 +104,46 @@ public:
     return TabletHelper(
         InformationMaintainer::Global().AddTablet(tag, num_samples));
   }
+  void ClearTablets() {
+    InformationMaintainer::Global().storage().mutable_data()->clear_tablets();
+  }
+
+  void PersistToDisk() const;
 };
 
-static ImHelper& get_im() {
+namespace components {
+
+/*
+ * Read and write support for Scalar component.
+ */
+template <typename T>
+class ScalarHelper {
+public:
+  ScalarHelper(storage::Tablet *tablet) : data_(tablet) {}
+
+  void SetCaptions(const std::vector<std::string> &captions);
+
+  void AddRecord(int id, const std::vector<T> &values);
+
+  std::vector<std::vector<T>> GetRecords() const;
+
+  std::vector<int> GetIds() const;
+
+  std::vector<int> GetTimestamps() const;
+
+  std::vector<std::string> GetCaptions() const;
+
+private:
+  storage::Tablet *data_;
+};
+
+}  // namespace components
+
+static ImHelper &get_im() {
   static ImHelper im;
   return im;
 }
 
-} // namespace visualdl
+}  // namespace visualdl
 
-#include "visualdl/backend/logic/sdk.hpp"
 #endif  // VISUALDL_BACKEND_LOGIC_SDK_H
diff --git a/visualdl/backend/logic/sdk.hpp b/visualdl/backend/logic/sdk.hpp
deleted file mode 100644
index 517abe3f8a1dbbd0aa307a5b1cc41224dd167ee3..0000000000000000000000000000000000000000
--- a/visualdl/backend/logic/sdk.hpp
+++ /dev/null
@@ -1,33 +0,0 @@
-#include "visualdl/backend/logic/im.h"
-
-namespace visualdl {
-
-/*
- * Utility helper for storage::Entry.
- */
-template <typename T> struct Entry {
-  // use pointer to avoid copy
-  storage::Entry *entry{nullptr};
-
-  Entry(storage::Entry *entry) : entry(entry) {}
-
-  /*
-   * Set a single value.
-   */
-  void Set(T v);
-
-  /*
-   * Add a value to repeated message field.
-   */
-  void Add(T v);
-};
-
-template <typename T>
-void TabletHelper::AddScalarRecord(int id, T value) {
-  auto* record = data_->add_records();
-  record->set_id(id);
-  Entry<T> entry_helper(record->mutable_data());
-  entry_helper.Set(value);
-}
-
-} // namespace visualdl
diff --git a/visualdl/backend/storage/storage.cc b/visualdl/backend/storage/storage.cc
index 5a89aa49b60abef9720ae29a1ecff8c7a29798c8..7a27448c7b9b773897acbe3910c34b98129fd60e 100644
--- a/visualdl/backend/storage/storage.cc
+++ b/visualdl/backend/storage/storage.cc
@@ -1,5 +1,5 @@
-#include <fstream>
 #include <glog/logging.h>
+#include <fstream>
 
 #include "visualdl/backend/storage/storage.h"
 
@@ -24,15 +24,15 @@ storage::Record *Storage::NewRecord(const std::string &tag) {
   CHECK(tablet) << "Tablet" << tag << " should be create first";
   auto *record = tablet->mutable_records()->Add();
   // increase num_records
-  int num_records = tablet->num_records();
-  tablet->set_num_records(num_records + 1);
+  int num_records = tablet->total_records();
+  tablet->set_total_records(num_records + 1);
   return record;
 }
 storage::Record *Storage::GetRecord(const std::string &tag, int offset) {
   auto *tablet = Find(tag);
   CHECK(tablet) << "Tablet" << tag << " should be create first";
 
-  auto num_records = tablet->num_records();
+  auto num_records = tablet->total_records();
   CHECK_LT(offset, num_records) << "invalid offset";
   return tablet->mutable_records()->Mutable(offset);
 }
@@ -60,4 +60,4 @@ void Storage::DeSerialize(const std::string &data) {
   proto_.ParseFromString(data);
 }
 
-} // namespace visualdl
+}  // namespace visualdl
diff --git a/visualdl/backend/storage/storage.proto b/visualdl/backend/storage/storage.proto
index 2b5729f83769f5ac73bc2bb38d72e6fce9f01f29..a38cb3ce3cf5e2b9523bbd7cb8167ef91770b1dd 100644
--- a/visualdl/backend/storage/storage.proto
+++ b/visualdl/backend/storage/storage.proto
@@ -2,88 +2,135 @@ syntax = "proto3";
 package storage;
 
 enum DataType {
-    // single entry
-    kInt32 = 0;
-    kInt64 = 1;
-    kFloat = 2;
-    kDouble = 3;
-    kString = 4;
-    kBool = 5;
-    // entrys
-    kInt64s = 6;
-    kFloats = 7;
-    kDoubles = 8;
-    kStrings = 9;
-    kInt32s = 10;
-    kBools = 11;
+  // single entry
+  kInt32 = 0;
+  kInt64 = 1;
+  kFloat = 2;
+  kDouble = 3;
+  kString = 4;
+  kBool = 5;
+  // entrys
+  kInt64s = 6;
+  kFloats = 7;
+  kDoubles = 8;
+  kStrings = 9;
+  kInt32s = 10;
+  kBools = 11;
 
-    kUnknown = 12;
+  kUnknown = 12;
 }
 
 // A data array, which type is `type`.
 message Entry {
-    // if all the entries in a record share the same data type, ignore this field
-    // and store type to `dtype` in `Record`.
-    DataType dtype = 1;
-    // single element
-    int32 i32 = 2;
-    int64 i64 = 3;
-    string s = 4;
-    float f = 5;
-    double d = 6;
-    bool b = 7;
-    // array
-    repeated int64 i64s = 8;
-    repeated float fs = 9;
-    repeated double ds = 10;
-    repeated int32 i32s = 11;
-    repeated bool bs = 12;
+  // if all the entries in a record share the same data type, ignore this field
+  // and store type to `dtype` in `Record`.
+  DataType dtype = 1;
+  // single element
+  int32 i32 = 2;
+  int64 i64 = 3;
+  string s = 4;
+  float f = 5;
+  double d = 6;
+  bool b = 7;
+  // array
+  repeated int64 i64s = 8;
+  repeated float fs = 9;
+  repeated double ds = 10;
+  repeated int32 i32s = 11;
+  repeated string ss = 12;
+  repeated bool bs = 13;
 }
 
+/*
+The Record proto is designed to represent any data structure for any component,
+for
+example, to store a record of Scalar component
+
+Record {
+  // training error is 0.1, testing error is 0.2
+  data = [0.1, 0.2],
+  timestamp = xxxx,
+  // step id
+  id = xxxx
+}
+
+to store a record of Image component
+
+Record {
+  // RBG pixel weights of a image
+  data = [[0.1, 0.2, ...], [...], [...]],
+  timestamp = xxxx,
+  // image shape
+  meta = [100, 200]
+}
+
+for other complex structure which have more fields than `timestamp`, `id` and
+meta, the additional fields
+can store in the `data` field, for it can store a list of values in different
+basic data types.
+
+A component handlers in logic layer should know how to write or load a record
+for the corresponding component.
+*/
 message Record {
-    Entry data = 1;
-    int64 timestamp = 2;
-    // store the count of writing operations to the tablet.
-    int64 id = 3;
-    DataType dtype = 4;
-    // shape or some other meta infomation for this record, if all the records
-    // share the same meta, just store one copy of meta in `Storage`, or create
-    // a unique copy for each `Record`.
-    Entry meta = 5;
+  // one record might have multiple fields, one specific component should know
+  // how
+  // to parse the records.
+  repeated Entry data = 1;
+  // NOTE the timestamp, id, dtype might be useless for that all the meta info
+  // can
+  // be stored in `data` field.
+  int64 timestamp = 2;
+  int64 id = 3;
+  DataType dtype = 4;
+  // shape or some other meta infomation for this record, if all the records
+  // share the same meta, just store one copy of meta in `Storage`, or create
+  // a unique copy for each `Record`.
+  Entry meta = 5;
 }
 
 /*
-A Tablet stores the records of a component which type is `component` and indidates as `tag`.
-The records will be saved in a file which name contains `tag`. During the running period,
-`num_records` will be accumulated, and `num_samples` indicates the size of sample set the
+A Tablet stores the records of a component which type is `component` and
+indidates as `tag`.
+The records will be saved in a file which name contains `tag`. During the
+running period,
+`num_records` will be accumulated, and `num_samples` indicates the size of
+sample set the
 reservoir sampling algorithm will collect.
 */
 message Tablet {
-    // the kinds of the components that supported
-    enum Type {
-        kScalar = 0;
-        kHistogram = 1;
-        kGraph = 2;
-    }
-    // type of the component, different component should have different storage format.
-    Type component = 1;
-    // records the total count of records, each Write operation should increate this value.
-    int64 num_records = 2;
-    // indicate the number of instances to sample, this should be a constant value.
-    int32 num_samples = 3;
-    repeated Record records = 4;
-    // store a meta infomation if all the records share.
-    Entry meta = 5;
-    // the unique identification for this `Tablet`.
-    string tag = 6;
+  // the kinds of the components that supported
+  enum Type {
+    kScalar = 0;
+    kHistogram = 1;
+    kGraph = 2;
+  }
+  // type of the component, different component should have different storage
+  // format.
+  Type component = 1;
+  // records the total count of records, each Write operation should increate
+  // this value.
+  int64 total_records = 2;
+  // indicate the number of instances to sample, this should be a constant
+  // value.
+  int32 num_samples = 3;
+  repeated Record records = 4;
+  // store a meta infomation if all the records share.
+  Entry meta = 5;
+  // the unique identification for this `Tablet`.
+  string tag = 6;
+  // one tablet might have multiple captions, for example, a scalar component
+  // might have
+  // two plots labeled "train" and "test".
+  repeated string captions = 7;
 }
 
 /*
 The Storage stores all the records.
 */
 message Storage {
-    // tags to Tablet, should be thread safe if fix the keys after initialization.
-    map<string, Tablet> tablets = 1;
-    string dir = 2;
-    int64 timestamp = 3;
+  // tags to Tablet, should be thread safe if fix the keys after initialization.
+  map<string, Tablet> tablets = 1;
+  string dir = 2;
+  int64 timestamp = 3;
 }
\ No newline at end of file
diff --git a/visualdl/backend/test.py b/visualdl/backend/test.py
index 8755ae7ff8a23587756fa8a8b76d568365c1744c..e7c1add36848626d7e4289d78ef3077a7d09a4ef 100644
--- a/visualdl/backend/test.py
+++ b/visualdl/backend/test.py
@@ -1,5 +1,6 @@
 import sys
 import unittest
+import numpy as np
 
 sys.path.append('../../build')
 import core
@@ -9,6 +10,7 @@ im = core.im()
 
 class StorageTester(unittest.TestCase):
     def setUp(self):
+        im.clear_tablets()
         self.storage = im.storage()
 
     def test_size(self):
@@ -34,15 +36,41 @@ class StorageTester(unittest.TestCase):
 
 class TabletTester(unittest.TestCase):
     def setUp(self):
+        im.clear_tablets()
         self.tablet = im.add_tablet("tag101", 20)
 
-    def test_add_scalar(self):
-        self.tablet.add_scalar_float(1, 0.3)
-        self.assertEqual(self.tablet.records_size(), 1)
-
     def test_human_readable_buffer(self):
         print self.tablet.human_readable_buffer()
 
+    def test_scalar(self):
+        scalar = self.tablet.as_float_scalar()
+        py_captions = ["train", "test"]
+        step_ids = [10, 20, 30]
+        py_records = [
+            [0.1, 0.2],
+            [0.2, 0.3],
+            [0.3, 0.4]
+        ]
+
+        scalar.set_captions(py_captions)
+        for i in range(len(py_records)):
+            scalar.add_record(step_ids[i], py_records[i])
+
+        records = scalar.get_records()
+        ids = scalar.get_ids()
+        for i in range(len(py_records)):
+            self.assertTrue(np.isclose(py_records[i], records[i]).all())
+            self.assertEqual(step_ids[i], ids[i])
+
+
+class ImTester(unittest.TestCase):
+    def test_persist(self):
+        im.clear_tablets()
+        tablet = im.add_tablet("tab0", 111)
+        self.assertEqual(im.storage().tablets_size(), 1)
+        im.storage().set_dir("./1")
+        im.persist_to_disk()
+
 
 if __name__ == '__main__':
     unittest.main()