diff --git a/native/jni/com_android_inputmethod_latin_BinaryDictionary.cpp b/native/jni/com_android_inputmethod_latin_BinaryDictionary.cpp
index 19aeb28..da8c2ac 100644
--- a/native/jni/com_android_inputmethod_latin_BinaryDictionary.cpp
+++ b/native/jni/com_android_inputmethod_latin_BinaryDictionary.cpp
@@ -373,7 +373,8 @@
     }
     // Use 1 for count to indicate the word has inputted.
     const UnigramProperty unigramProperty(isBeginningOfSentence, isNotAWord,
-            isBlacklisted, probability, timestamp, 0 /* level */, 1 /* count */, &shortcuts);
+            isBlacklisted, probability, HistoricalInfo(timestamp, 0 /* level */, 1 /* count */),
+            &shortcuts);
     return dictionary->addUnigramEntry(CodePointArrayView(codePoints, codePointCount),
             &unigramProperty);
 }
@@ -405,7 +406,7 @@
     env->GetIntArrayRegion(word, 0, wordLength, wordCodePoints);
     // Use 1 for count to indicate the ngram has inputted.
     const NgramProperty ngramProperty(CodePointArrayView(wordCodePoints, wordLength).toVector(),
-            probability, timestamp, 0 /* level */, 1 /* count */);
+            probability, HistoricalInfo(timestamp, 0 /* level */, 1 /* count */));
     return dictionary->addNgramEntry(&prevWordsInfo, &ngramProperty);
 }
 
@@ -494,8 +495,8 @@
         }
         // Use 1 for count to indicate the word has inputted.
         const UnigramProperty unigramProperty(false /* isBeginningOfSentence */, isNotAWord,
-                isBlacklisted, unigramProbability, timestamp, 0 /* level */, 1 /* count */,
-                &shortcuts);
+                isBlacklisted, unigramProbability,
+                HistoricalInfo(timestamp, 0 /* level */, 1 /* count */), &shortcuts);
         dictionary->addUnigramEntry(CodePointArrayView(word1CodePoints, word1Length),
                 &unigramProperty);
         if (word0) {
@@ -503,7 +504,7 @@
             // Use 1 for count to indicate the bigram has inputted.
             const NgramProperty ngramProperty(
                     CodePointArrayView(word1CodePoints, word1Length).toVector(),
-                    bigramProbability, timestamp, 0 /* level */, 1 /* count */);
+                    bigramProbability, HistoricalInfo(timestamp, 0 /* level */, 1 /* count */));
             const PrevWordsInfo prevWordsInfo(word0CodePoints, word0Length,
                     false /* isBeginningOfSentence */);
             dictionary->addNgramEntry(&prevWordsInfo, &ngramProperty);
diff --git a/native/jni/src/suggest/policyimpl/dictionary/utils/historical_info.h b/native/jni/src/suggest/core/dictionary/property/historical_info.h
similarity index 85%
rename from native/jni/src/suggest/policyimpl/dictionary/utils/historical_info.h
rename to native/jni/src/suggest/core/dictionary/property/historical_info.h
index 428ca86..5ed9ebf 100644
--- a/native/jni/src/suggest/policyimpl/dictionary/utils/historical_info.h
+++ b/native/jni/src/suggest/core/dictionary/property/historical_info.h
@@ -34,7 +34,7 @@
         return mTimestamp != NOT_A_TIMESTAMP;
     }
 
-    int getTimeStamp() const {
+    int getTimestamp() const {
         return mTimestamp;
     }
 
@@ -47,12 +47,12 @@
     }
 
  private:
-    // Copy constructor is public to use this class as a type of return value.
-    DISALLOW_ASSIGNMENT_OPERATOR(HistoricalInfo);
+    // Default copy constructor and assign operator are used for using in std::vector.
 
-    const int mTimestamp;
-    const int mLevel;
-    const int mCount;
+    // TODO: Make members const.
+    int mTimestamp;
+    int mLevel;
+    int mCount;
 };
 } // namespace latinime
 #endif /* LATINIME_HISTORICAL_INFO_H */
diff --git a/native/jni/src/suggest/core/dictionary/property/ngram_property.h b/native/jni/src/suggest/core/dictionary/property/ngram_property.h
index 5d822fa..49f683b 100644
--- a/native/jni/src/suggest/core/dictionary/property/ngram_property.h
+++ b/native/jni/src/suggest/core/dictionary/property/ngram_property.h
@@ -20,15 +20,16 @@
 #include <vector>
 
 #include "defines.h"
+#include "suggest/core/dictionary/property/historical_info.h"
 
 namespace latinime {
 
 class NgramProperty {
  public:
     NgramProperty(const std::vector<int> &&targetCodePoints, const int probability,
-            const int timestamp, const int level, const int count)
+            const HistoricalInfo &historicalInfo)
             : mTargetCodePoints(std::move(targetCodePoints)), mProbability(probability),
-              mTimestamp(timestamp), mLevel(level), mCount(count) {}
+              mHistoricalInfo(historicalInfo) {}
 
     const std::vector<int> *getTargetCodePoints() const {
         return &mTargetCodePoints;
@@ -38,16 +39,8 @@
         return mProbability;
     }
 
-    int getTimestamp() const {
-        return mTimestamp;
-    }
-
-    int getLevel() const {
-        return mLevel;
-    }
-
-    int getCount() const {
-        return mCount;
+    const HistoricalInfo getHistoricalInfo() const {
+        return mHistoricalInfo;
     }
 
  private:
@@ -57,9 +50,7 @@
     // TODO: Make members const.
     std::vector<int> mTargetCodePoints;
     int mProbability;
-    int mTimestamp;
-    int mLevel;
-    int mCount;
+    HistoricalInfo mHistoricalInfo;
 };
 } // namespace latinime
 #endif // LATINIME_NGRAM_PROPERTY_H
diff --git a/native/jni/src/suggest/core/dictionary/property/unigram_property.h b/native/jni/src/suggest/core/dictionary/property/unigram_property.h
index b7e7d66..4c61f96 100644
--- a/native/jni/src/suggest/core/dictionary/property/unigram_property.h
+++ b/native/jni/src/suggest/core/dictionary/property/unigram_property.h
@@ -20,6 +20,7 @@
 #include <vector>
 
 #include "defines.h"
+#include "suggest/core/dictionary/property/historical_info.h"
 
 namespace latinime {
 
@@ -50,15 +51,14 @@
 
     UnigramProperty()
             : mRepresentsBeginningOfSentence(false), mIsNotAWord(false), mIsBlacklisted(false),
-              mProbability(NOT_A_PROBABILITY), mTimestamp(NOT_A_TIMESTAMP), mLevel(0), mCount(0),
-              mShortcuts() {}
+              mProbability(NOT_A_PROBABILITY), mHistoricalInfo(), mShortcuts() {}
 
     UnigramProperty(const bool representsBeginningOfSentence, const bool isNotAWord,
-            const bool isBlacklisted, const int probability, const int timestamp, const int level,
-            const int count, const std::vector<ShortcutProperty> *const shortcuts)
+            const bool isBlacklisted, const int probability, const HistoricalInfo &historicalInfo,
+            const std::vector<ShortcutProperty> *const shortcuts)
             : mRepresentsBeginningOfSentence(representsBeginningOfSentence),
               mIsNotAWord(isNotAWord), mIsBlacklisted(isBlacklisted), mProbability(probability),
-              mTimestamp(timestamp), mLevel(level), mCount(count), mShortcuts(*shortcuts) {}
+              mHistoricalInfo(historicalInfo), mShortcuts(*shortcuts) {}
 
     bool representsBeginningOfSentence() const {
         return mRepresentsBeginningOfSentence;
@@ -85,16 +85,8 @@
         return mProbability;
     }
 
-    int getTimestamp() const {
-        return mTimestamp;
-    }
-
-    int getLevel() const {
-        return mLevel;
-    }
-
-    int getCount() const {
-        return mCount;
+    const HistoricalInfo getHistoricalInfo() const {
+        return mHistoricalInfo;
     }
 
     const std::vector<ShortcutProperty> &getShortcuts() const {
@@ -110,10 +102,7 @@
     bool mIsNotAWord;
     bool mIsBlacklisted;
     int mProbability;
-    // Historical information
-    int mTimestamp;
-    int mLevel;
-    int mCount;
+    HistoricalInfo mHistoricalInfo;
     std::vector<ShortcutProperty> mShortcuts;
 };
 } // namespace latinime
diff --git a/native/jni/src/suggest/core/dictionary/property/word_property.cpp b/native/jni/src/suggest/core/dictionary/property/word_property.cpp
index e3406fa..caac8fe 100644
--- a/native/jni/src/suggest/core/dictionary/property/word_property.cpp
+++ b/native/jni/src/suggest/core/dictionary/property/word_property.cpp
@@ -17,6 +17,7 @@
 #include "suggest/core/dictionary/property/word_property.h"
 
 #include "utils/jni_data_utils.h"
+#include "suggest/core/dictionary/property/historical_info.h"
 
 namespace latinime {
 
@@ -31,8 +32,9 @@
             !mNgrams.empty(), mUnigramProperty.hasShortcuts(),
             mUnigramProperty.representsBeginningOfSentence()};
     env->SetBooleanArrayRegion(outFlags, 0 /* start */, NELEMS(flags), flags);
-    int probabilityInfo[] = {mUnigramProperty.getProbability(), mUnigramProperty.getTimestamp(),
-            mUnigramProperty.getLevel(), mUnigramProperty.getCount()};
+    const HistoricalInfo &historicalInfo = mUnigramProperty.getHistoricalInfo();
+    int probabilityInfo[] = {mUnigramProperty.getProbability(), historicalInfo.getTimestamp(),
+            historicalInfo.getLevel(), historicalInfo.getCount()};
     env->SetIntArrayRegion(outProbabilityInfo, 0 /* start */, NELEMS(probabilityInfo),
             probabilityInfo);
 
@@ -51,10 +53,10 @@
                 false /* needsNullTermination */);
         env->CallBooleanMethod(outBigramTargets, addMethodId, bigramWord1CodePointArray);
         env->DeleteLocalRef(bigramWord1CodePointArray);
-
+        const HistoricalInfo &ngramHistoricalInfo = ngramProperty.getHistoricalInfo();
         int bigramProbabilityInfo[] = {ngramProperty.getProbability(),
-                ngramProperty.getTimestamp(), ngramProperty.getLevel(),
-                ngramProperty.getCount()};
+                ngramHistoricalInfo.getTimestamp(), ngramHistoricalInfo.getLevel(),
+                ngramHistoricalInfo.getCount()};
         jintArray bigramProbabilityInfoArray = env->NewIntArray(NELEMS(bigramProbabilityInfo));
         env->SetIntArrayRegion(bigramProbabilityInfoArray, 0 /* start */,
                 NELEMS(bigramProbabilityInfo), bigramProbabilityInfo);
diff --git a/native/jni/src/suggest/policyimpl/dictionary/structure/backward/v402/bigram/ver4_bigram_list_policy.cpp b/native/jni/src/suggest/policyimpl/dictionary/structure/backward/v402/bigram/ver4_bigram_list_policy.cpp
index c639770..bc0f47f 100644
--- a/native/jni/src/suggest/policyimpl/dictionary/structure/backward/v402/bigram/ver4_bigram_list_policy.cpp
+++ b/native/jni/src/suggest/policyimpl/dictionary/structure/backward/v402/bigram/ver4_bigram_list_policy.cpp
@@ -267,8 +267,7 @@
         const NgramProperty *const ngramProperty) const {
     // TODO: Consolidate historical info and probability.
     if (mHeaderPolicy->hasHistoricalInfoOfWords()) {
-        const HistoricalInfo historicalInfoForUpdate(ngramProperty->getTimestamp(),
-                ngramProperty->getLevel(), ngramProperty->getCount());
+        const HistoricalInfo &historicalInfoForUpdate = ngramProperty->getHistoricalInfo();
         const HistoricalInfo updatedHistoricalInfo =
                 ForgettingCurveUtils::createUpdatedHistoricalInfo(
                         originalBigramEntry->getHistoricalInfo(), ngramProperty->getProbability(),
diff --git a/native/jni/src/suggest/policyimpl/dictionary/structure/backward/v402/content/bigram_dict_content.cpp b/native/jni/src/suggest/policyimpl/dictionary/structure/backward/v402/content/bigram_dict_content.cpp
index e2dd93c..9e1adff 100644
--- a/native/jni/src/suggest/policyimpl/dictionary/structure/backward/v402/content/bigram_dict_content.cpp
+++ b/native/jni/src/suggest/policyimpl/dictionary/structure/backward/v402/content/bigram_dict_content.cpp
@@ -83,10 +83,10 @@
     }
     if (mHasHistoricalInfo) {
         const HistoricalInfo *const historicalInfo = bigramEntryToWrite->getHistoricalInfo();
-        if (!bigramListBuffer->writeUintAndAdvancePosition(historicalInfo->getTimeStamp(),
+        if (!bigramListBuffer->writeUintAndAdvancePosition(historicalInfo->getTimestamp(),
                 Ver4DictConstants::TIME_STAMP_FIELD_SIZE, entryWritingPos)) {
             AKLOGE("Cannot write bigram timestamps. pos: %d, timestamp: %d", *entryWritingPos,
-                    historicalInfo->getTimeStamp());
+                    historicalInfo->getTimestamp());
             return false;
         }
         if (!bigramListBuffer->writeUintAndAdvancePosition(historicalInfo->getLevel(),
diff --git a/native/jni/src/suggest/policyimpl/dictionary/structure/backward/v402/content/bigram_entry.h b/native/jni/src/suggest/policyimpl/dictionary/structure/backward/v402/content/bigram_entry.h
index 40968b4..480095a 100644
--- a/native/jni/src/suggest/policyimpl/dictionary/structure/backward/v402/content/bigram_entry.h
+++ b/native/jni/src/suggest/policyimpl/dictionary/structure/backward/v402/content/bigram_entry.h
@@ -25,8 +25,8 @@
 #define LATINIME_BACKWARD_V402_BIGRAM_ENTRY_H
 
 #include "defines.h"
+#include "suggest/core/dictionary/property/historical_info.h"
 #include "suggest/policyimpl/dictionary/structure/backward/v402/ver4_dict_constants.h"
-#include "suggest/policyimpl/dictionary/utils/historical_info.h"
 
 namespace latinime {
 namespace backward {
diff --git a/native/jni/src/suggest/policyimpl/dictionary/structure/backward/v402/content/probability_dict_content.cpp b/native/jni/src/suggest/policyimpl/dictionary/structure/backward/v402/content/probability_dict_content.cpp
index c671647..4a740d4 100644
--- a/native/jni/src/suggest/policyimpl/dictionary/structure/backward/v402/content/probability_dict_content.cpp
+++ b/native/jni/src/suggest/policyimpl/dictionary/structure/backward/v402/content/probability_dict_content.cpp
@@ -147,7 +147,7 @@
     }
     if (mHasHistoricalInfo) {
         const HistoricalInfo *const historicalInfo = probabilityEntry->getHistoricalInfo();
-        if (!bufferToWrite->writeUintAndAdvancePosition(historicalInfo->getTimeStamp(),
+        if (!bufferToWrite->writeUintAndAdvancePosition(historicalInfo->getTimestamp(),
                 Ver4DictConstants::TIME_STAMP_FIELD_SIZE, &writingPos)) {
             AKLOGE("Cannot write timestamp in probability dict content. pos: %d", writingPos);
             return false;
diff --git a/native/jni/src/suggest/policyimpl/dictionary/structure/backward/v402/content/probability_entry.h b/native/jni/src/suggest/policyimpl/dictionary/structure/backward/v402/content/probability_entry.h
index 8ccfa33..4111a49 100644
--- a/native/jni/src/suggest/policyimpl/dictionary/structure/backward/v402/content/probability_entry.h
+++ b/native/jni/src/suggest/policyimpl/dictionary/structure/backward/v402/content/probability_entry.h
@@ -25,8 +25,8 @@
 #define LATINIME_BACKWARD_V402_PROBABILITY_ENTRY_H
 
 #include "defines.h"
+#include "suggest/core/dictionary/property/historical_info.h"
 #include "suggest/policyimpl/dictionary/structure/backward/v402/ver4_dict_constants.h"
-#include "suggest/policyimpl/dictionary/utils/historical_info.h"
 
 namespace latinime {
 namespace backward {
diff --git a/native/jni/src/suggest/policyimpl/dictionary/structure/backward/v402/ver4_patricia_trie_node_writer.cpp b/native/jni/src/suggest/policyimpl/dictionary/structure/backward/v402/ver4_patricia_trie_node_writer.cpp
index 6827c3e..8d16974 100644
--- a/native/jni/src/suggest/policyimpl/dictionary/structure/backward/v402/ver4_patricia_trie_node_writer.cpp
+++ b/native/jni/src/suggest/policyimpl/dictionary/structure/backward/v402/ver4_patricia_trie_node_writer.cpp
@@ -396,8 +396,7 @@
         const UnigramProperty *const unigramProperty) const {
     // TODO: Consolidate historical info and probability.
     if (mHeaderPolicy->hasHistoricalInfoOfWords()) {
-        const HistoricalInfo historicalInfoForUpdate(unigramProperty->getTimestamp(),
-                unigramProperty->getLevel(), unigramProperty->getCount());
+        const HistoricalInfo &historicalInfoForUpdate = unigramProperty->getHistoricalInfo();
         const HistoricalInfo updatedHistoricalInfo =
                 ForgettingCurveUtils::createUpdatedHistoricalInfo(
                         originalProbabilityEntry->getHistoricalInfo(),
diff --git a/native/jni/src/suggest/policyimpl/dictionary/structure/backward/v402/ver4_patricia_trie_policy.cpp b/native/jni/src/suggest/policyimpl/dictionary/structure/backward/v402/ver4_patricia_trie_policy.cpp
index 9631cf1..40e393c 100644
--- a/native/jni/src/suggest/policyimpl/dictionary/structure/backward/v402/ver4_patricia_trie_policy.cpp
+++ b/native/jni/src/suggest/policyimpl/dictionary/structure/backward/v402/ver4_patricia_trie_policy.cpp
@@ -343,7 +343,7 @@
             const UnigramProperty beginningOfSentenceUnigramProperty(
                     true /* representsBeginningOfSentence */, true /* isNotAWord */,
                     false /* isBlacklisted */, MAX_PROBABILITY /* probability */,
-                    NOT_A_TIMESTAMP /* timestamp */, 0 /* level */, 0 /* count */, &shortcuts);
+                    HistoricalInfo(), &shortcuts);
             if (!addUnigramEntry(prevWordsInfo->getNthPrevWordCodePoints(1 /* n */),
                     &beginningOfSentenceUnigramProperty)) {
                 AKLOGE("Cannot add unigram entry for the beginning-of-sentence.");
@@ -528,8 +528,7 @@
                     bigramEntry.getProbability();
             ngrams.emplace_back(
                     CodePointArrayView(bigramWord1CodePoints, codePointCount).toVector(),
-                    probability, historicalInfo->getTimeStamp(), historicalInfo->getLevel(),
-                    historicalInfo->getCount());
+                    probability, *historicalInfo);
         }
     }
     // Fetch shortcut information.
@@ -552,8 +551,7 @@
     }
     const UnigramProperty unigramProperty(ptNodeParams.representsBeginningOfSentence(),
             ptNodeParams.isNotAWord(), ptNodeParams.isBlacklisted(), ptNodeParams.getProbability(),
-            historicalInfo->getTimeStamp(), historicalInfo->getLevel(),
-            historicalInfo->getCount(), &shortcuts);
+            *historicalInfo, &shortcuts);
     return WordProperty(wordCodePoints.toVector(), &unigramProperty, &ngrams);
 }
 
diff --git a/native/jni/src/suggest/policyimpl/dictionary/structure/backward/v402/ver4_patricia_trie_writing_helper.cpp b/native/jni/src/suggest/policyimpl/dictionary/structure/backward/v402/ver4_patricia_trie_writing_helper.cpp
index 3fb4caa..2887dc6 100644
--- a/native/jni/src/suggest/policyimpl/dictionary/structure/backward/v402/ver4_patricia_trie_writing_helper.cpp
+++ b/native/jni/src/suggest/policyimpl/dictionary/structure/backward/v402/ver4_patricia_trie_writing_helper.cpp
@@ -216,7 +216,7 @@
                         probabilityEntry.getHistoricalInfo(), mBuffers->getHeaderPolicy()) :
                 probabilityEntry.getProbability();
         priorityQueue.push(DictProbability(terminalPos, probability,
-                probabilityEntry.getHistoricalInfo()->getTimeStamp()));
+                probabilityEntry.getHistoricalInfo()->getTimestamp()));
     }
 
     // Delete unigrams.
@@ -263,7 +263,7 @@
                             bigramEntry.getHistoricalInfo(), mBuffers->getHeaderPolicy()) :
                     bigramEntry.getProbability();
             priorityQueue.push(DictProbability(entryPos, probability,
-                    bigramEntry.getHistoricalInfo()->getTimeStamp()));
+                    bigramEntry.getHistoricalInfo()->getTimestamp()));
         }
     }
 
diff --git a/native/jni/src/suggest/policyimpl/dictionary/structure/v2/patricia_trie_policy.cpp b/native/jni/src/suggest/policyimpl/dictionary/structure/v2/patricia_trie_policy.cpp
index 49095d0..7800758 100644
--- a/native/jni/src/suggest/policyimpl/dictionary/structure/v2/patricia_trie_policy.cpp
+++ b/native/jni/src/suggest/policyimpl/dictionary/structure/v2/patricia_trie_policy.cpp
@@ -452,7 +452,7 @@
             const int probability = getProbability(word1Probability, bigramsIt.getProbability());
             ngrams.emplace_back(
                     CodePointArrayView(bigramWord1CodePoints, word1CodePointCount).toVector(),
-                    probability, NOT_A_TIMESTAMP /* timestamp */, 0 /* level */, 0 /* count */);
+                    probability, HistoricalInfo());
         }
     }
     // Fetch shortcut information.
@@ -477,7 +477,7 @@
     }
     const UnigramProperty unigramProperty(ptNodeParams.representsBeginningOfSentence(),
             ptNodeParams.isNotAWord(), ptNodeParams.isBlacklisted(), ptNodeParams.getProbability(),
-            NOT_A_TIMESTAMP /* timestamp */, 0 /* level */, 0 /* count */, &shortcuts);
+            HistoricalInfo(), &shortcuts);
     return WordProperty(wordCodePoints.toVector(), &unigramProperty, &ngrams);
 }
 
diff --git a/native/jni/src/suggest/policyimpl/dictionary/structure/v4/content/language_model_dict_content.cpp b/native/jni/src/suggest/policyimpl/dictionary/structure/v4/content/language_model_dict_content.cpp
index 1392302..956dabb 100644
--- a/native/jni/src/suggest/policyimpl/dictionary/structure/v4/content/language_model_dict_content.cpp
+++ b/native/jni/src/suggest/policyimpl/dictionary/structure/v4/content/language_model_dict_content.cpp
@@ -296,7 +296,7 @@
                 ForgettingCurveUtils::decodeProbability(probabilityEntry.getHistoricalInfo(),
                         headerPolicy) : probabilityEntry.getProbability();
         outEntryInfo->emplace_back(probability,
-                probabilityEntry.getHistoricalInfo()->getTimeStamp(),
+                probabilityEntry.getHistoricalInfo()->getTimestamp(),
                 entry.key(), targetLevel, prevWordIds->data());
     }
     return true;
diff --git a/native/jni/src/suggest/policyimpl/dictionary/structure/v4/content/probability_entry.h b/native/jni/src/suggest/policyimpl/dictionary/structure/v4/content/probability_entry.h
index fd52e57..fa14156 100644
--- a/native/jni/src/suggest/policyimpl/dictionary/structure/v4/content/probability_entry.h
+++ b/native/jni/src/suggest/policyimpl/dictionary/structure/v4/content/probability_entry.h
@@ -21,10 +21,10 @@
 #include <cstdint>
 
 #include "defines.h"
+#include "suggest/core/dictionary/property/historical_info.h"
 #include "suggest/core/dictionary/property/ngram_property.h"
 #include "suggest/core/dictionary/property/unigram_property.h"
 #include "suggest/policyimpl/dictionary/structure/v4/ver4_dict_constants.h"
-#include "suggest/policyimpl/dictionary/utils/historical_info.h"
 
 namespace latinime {
 
@@ -53,15 +53,13 @@
                     unigramProperty->isNotAWord(), unigramProperty->isBlacklisted(),
                     unigramProperty->isPossiblyOffensive())),
               mProbability(unigramProperty->getProbability()),
-              mHistoricalInfo(unigramProperty->getTimestamp(), unigramProperty->getLevel(),
-                      unigramProperty->getCount()) {}
+              mHistoricalInfo(unigramProperty->getHistoricalInfo()) {}
 
     // Create from ngram property.
     // TODO: Set flags.
     ProbabilityEntry(const NgramProperty *const ngramProperty)
             : mFlags(0), mProbability(ngramProperty->getProbability()),
-              mHistoricalInfo(ngramProperty->getTimestamp(), ngramProperty->getLevel(),
-                      ngramProperty->getCount()) {}
+              mHistoricalInfo(ngramProperty->getHistoricalInfo()) {}
 
     bool isValid() const {
         return (mFlags & Ver4DictConstants::FLAG_NOT_A_VALID_ENTRY) == 0;
@@ -103,7 +101,7 @@
         uint64_t encodedEntry = static_cast<uint64_t>(mFlags);
         if (hasHistoricalInfo) {
             encodedEntry = (encodedEntry << (Ver4DictConstants::TIME_STAMP_FIELD_SIZE * CHAR_BIT))
-                    ^ static_cast<uint64_t>(mHistoricalInfo.getTimeStamp());
+                    ^ static_cast<uint64_t>(mHistoricalInfo.getTimestamp());
             encodedEntry = (encodedEntry << (Ver4DictConstants::WORD_LEVEL_FIELD_SIZE * CHAR_BIT))
                     ^ static_cast<uint64_t>(mHistoricalInfo.getLevel());
             encodedEntry = (encodedEntry << (Ver4DictConstants::WORD_COUNT_FIELD_SIZE * CHAR_BIT))
diff --git a/native/jni/src/suggest/policyimpl/dictionary/structure/v4/ver4_patricia_trie_policy.cpp b/native/jni/src/suggest/policyimpl/dictionary/structure/v4/ver4_patricia_trie_policy.cpp
index d46acf5..0badabf 100644
--- a/native/jni/src/suggest/policyimpl/dictionary/structure/v4/ver4_patricia_trie_policy.cpp
+++ b/native/jni/src/suggest/policyimpl/dictionary/structure/v4/ver4_patricia_trie_policy.cpp
@@ -302,7 +302,7 @@
         const UnigramProperty beginningOfSentenceUnigramProperty(
                 true /* representsBeginningOfSentence */, true /* isNotAWord */,
                 false /* isBlacklisted */, MAX_PROBABILITY /* probability */,
-                NOT_A_TIMESTAMP /* timestamp */, 0 /* level */, 0 /* count */, &shortcuts);
+                HistoricalInfo(), &shortcuts);
         if (!addUnigramEntry(prevWordsInfo->getNthPrevWordCodePoints(1 /* n */),
                 &beginningOfSentenceUnigramProperty)) {
             AKLOGE("Cannot add unigram entry for the beginning-of-sentence.");
@@ -464,8 +464,7 @@
                 ForgettingCurveUtils::decodeProbability(historicalInfo, mHeaderPolicy) :
                 probabilityEntry.getProbability();
         ngrams.emplace_back(CodePointArrayView(bigramWord1CodePoints, codePointCount).toVector(),
-                probability, historicalInfo->getTimeStamp(), historicalInfo->getLevel(),
-                historicalInfo->getCount());
+                probability, *historicalInfo);
     }
     // Fetch shortcut information.
     std::vector<UnigramProperty::ShortcutProperty> shortcuts;
@@ -487,8 +486,7 @@
     }
     const UnigramProperty unigramProperty(probabilityEntry.representsBeginningOfSentence(),
             probabilityEntry.isNotAWord(), probabilityEntry.isBlacklisted(),
-            probabilityEntry.getProbability(), historicalInfo->getTimeStamp(),
-            historicalInfo->getLevel(), historicalInfo->getCount(), &shortcuts);
+            probabilityEntry.getProbability(), *historicalInfo, &shortcuts);
     return WordProperty(wordCodePoints.toVector(), &unigramProperty, &ngrams);
 }
 
diff --git a/native/jni/src/suggest/policyimpl/dictionary/utils/forgetting_curve_utils.cpp b/native/jni/src/suggest/policyimpl/dictionary/utils/forgetting_curve_utils.cpp
index fed0ae7..af4bc18 100644
--- a/native/jni/src/suggest/policyimpl/dictionary/utils/forgetting_curve_utils.cpp
+++ b/native/jni/src/suggest/policyimpl/dictionary/utils/forgetting_curve_utils.cpp
@@ -43,7 +43,7 @@
 /* static */ const HistoricalInfo ForgettingCurveUtils::createUpdatedHistoricalInfo(
         const HistoricalInfo *const originalHistoricalInfo, const int newProbability,
         const HistoricalInfo *const newHistoricalInfo, const HeaderPolicy *const headerPolicy) {
-    const int timestamp = newHistoricalInfo->getTimeStamp();
+    const int timestamp = newHistoricalInfo->getTimestamp();
     if (newProbability != NOT_A_PROBABILITY && originalHistoricalInfo->getLevel() == 0) {
         // Add entry as a valid word.
         const int level = clampToVisibleEntryLevelRange(newHistoricalInfo->getLevel());
@@ -78,7 +78,7 @@
 
 /* static */ int ForgettingCurveUtils::decodeProbability(
         const HistoricalInfo *const historicalInfo, const HeaderPolicy *const headerPolicy) {
-    const int elapsedTimeStepCount = getElapsedTimeStepCount(historicalInfo->getTimeStamp(),
+    const int elapsedTimeStepCount = getElapsedTimeStepCount(historicalInfo->getTimestamp(),
             headerPolicy->getForgettingCurveDurationToLevelDown());
     return sProbabilityTable.getProbability(
             headerPolicy->getForgettingCurveProbabilityValuesTableId(),
@@ -102,7 +102,7 @@
 /* static */ bool ForgettingCurveUtils::needsToKeep(const HistoricalInfo *const historicalInfo,
         const HeaderPolicy *const headerPolicy) {
     return historicalInfo->getLevel() > 0
-            || getElapsedTimeStepCount(historicalInfo->getTimeStamp(),
+            || getElapsedTimeStepCount(historicalInfo->getTimestamp(),
                     headerPolicy->getForgettingCurveDurationToLevelDown())
                             < DISCARD_LEVEL_ZERO_ENTRY_TIME_STEP_COUNT_THRESHOLD;
 }
@@ -110,12 +110,12 @@
 /* static */ const HistoricalInfo ForgettingCurveUtils::createHistoricalInfoToSave(
         const HistoricalInfo *const originalHistoricalInfo,
         const HeaderPolicy *const headerPolicy) {
-    if (originalHistoricalInfo->getTimeStamp() == NOT_A_TIMESTAMP) {
+    if (originalHistoricalInfo->getTimestamp() == NOT_A_TIMESTAMP) {
         return HistoricalInfo();
     }
     const int durationToLevelDownInSeconds = headerPolicy->getForgettingCurveDurationToLevelDown();
     const int elapsedTimeStep = getElapsedTimeStepCount(
-            originalHistoricalInfo->getTimeStamp(), durationToLevelDownInSeconds);
+            originalHistoricalInfo->getTimestamp(), durationToLevelDownInSeconds);
     if (elapsedTimeStep <= MAX_ELAPSED_TIME_STEP_COUNT) {
         // No need to update historical info.
         return *originalHistoricalInfo;
@@ -124,7 +124,7 @@
     const int maxLevelDownAmonut = elapsedTimeStep / (MAX_ELAPSED_TIME_STEP_COUNT + 1);
     const int levelDownAmount = (maxLevelDownAmonut >= originalHistoricalInfo->getLevel()) ?
             originalHistoricalInfo->getLevel() : maxLevelDownAmonut;
-    const int adjustedTimestampInSeconds = originalHistoricalInfo->getTimeStamp() +
+    const int adjustedTimestampInSeconds = originalHistoricalInfo->getTimestamp() +
             levelDownAmount * durationToLevelDownInSeconds;
     return HistoricalInfo(adjustedTimestampInSeconds,
             originalHistoricalInfo->getLevel() - levelDownAmount, 0 /* count */);
diff --git a/native/jni/src/suggest/policyimpl/dictionary/utils/forgetting_curve_utils.h b/native/jni/src/suggest/policyimpl/dictionary/utils/forgetting_curve_utils.h
index 313eb6b..10abb40 100644
--- a/native/jni/src/suggest/policyimpl/dictionary/utils/forgetting_curve_utils.h
+++ b/native/jni/src/suggest/policyimpl/dictionary/utils/forgetting_curve_utils.h
@@ -20,7 +20,7 @@
 #include <vector>
 
 #include "defines.h"
-#include "suggest/policyimpl/dictionary/utils/historical_info.h"
+#include "suggest/core/dictionary/property/historical_info.h"
 
 namespace latinime {
 
diff --git a/native/jni/tests/suggest/policyimpl/dictionary/structure/v4/content/language_model_dict_content_test.cpp b/native/jni/tests/suggest/policyimpl/dictionary/structure/v4/content/language_model_dict_content_test.cpp
index daa32c3..4469dc7 100644
--- a/native/jni/tests/suggest/policyimpl/dictionary/structure/v4/content/language_model_dict_content_test.cpp
+++ b/native/jni/tests/suggest/policyimpl/dictionary/structure/v4/content/language_model_dict_content_test.cpp
@@ -60,7 +60,7 @@
     languageModelDictContent.setProbabilityEntry(wordId, &probabilityEntry);
     const ProbabilityEntry entry = languageModelDictContent.getProbabilityEntry(wordId);
     EXPECT_EQ(flag, entry.getFlags());
-    EXPECT_EQ(timestamp, entry.getHistoricalInfo()->getTimeStamp());
+    EXPECT_EQ(timestamp, entry.getHistoricalInfo()->getTimestamp());
     EXPECT_EQ(level, entry.getHistoricalInfo()->getLevel());
     EXPECT_EQ(count, entry.getHistoricalInfo()->getCount());
 
diff --git a/native/jni/tests/suggest/policyimpl/dictionary/structure/v4/content/probability_entry_test.cpp b/native/jni/tests/suggest/policyimpl/dictionary/structure/v4/content/probability_entry_test.cpp
index f0494f3..260b347 100644
--- a/native/jni/tests/suggest/policyimpl/dictionary/structure/v4/content/probability_entry_test.cpp
+++ b/native/jni/tests/suggest/policyimpl/dictionary/structure/v4/content/probability_entry_test.cpp
@@ -51,7 +51,7 @@
             ProbabilityEntry::decode(encodedEntry, true /* hasHistoricalInfo */);
 
     EXPECT_EQ(flag, decodedEntry.getFlags());
-    EXPECT_EQ(timestamp, decodedEntry.getHistoricalInfo()->getTimeStamp());
+    EXPECT_EQ(timestamp, decodedEntry.getHistoricalInfo()->getTimestamp());
     EXPECT_EQ(level, decodedEntry.getHistoricalInfo()->getLevel());
     EXPECT_EQ(count, decodedEntry.getHistoricalInfo()->getCount());
 }