Add Knowlege distillation to Tutorial.md (#4)

update Tutorial.md with knowledge distillation tasks

Tutorial.md

@@ -12,6 +12,11 @@
     * [Task 4: Regression](#task-4)
     * [Task 5: Sentiment Analysis](#task-5)
     * [Task 6: Question Paraphrase](#task-6)
+    * [Task 7: Knowledge Distillation for Model Compression](#task-7)
+        1. [Compression for Query Binary Classifier](#task-7.1)
+        2. [Compression for Text Matching Model](#task-7.2)
+        3. [Compression for Slot Filling Model](#task-7.3)
+        4. [Compression for MRC Model](#task-7.4)
 * [Advanced Usage](#advanced-usage)
     * [Extra Feature Support](#extra-feature)
     * [Learning Rate Decay](#lr-decay)
@@ -382,6 +387,61 @@ This task is to determine whether a pair of questions are semantically equivalen
     
     *Tips: the model file and train log file can be found in JSON config file's outputs/save_base_dir.*
 
+### <span id="task-7">Task 7: Knowledge Distillation for Model Compression</span>
+
+Knowledge Distillation is a common method to compress model in order to improve inference speed. Here are some reference papers:
+- [Distilling the Knowledge in a Neural Network](https://arxiv.org/abs/1503.02531)
+- [Model Compression with Multi-Task Knowledge Distillation for Web-scale Question Answering System](https://arxiv.org/abs/1904.09636)
+
+#### <span id="task-7.1">7.1: Compression for Query Binary Classifier</span>
+This task is to train a query regression model to learn from a heavy teacher model such as BERT based query classifier model. The training process is to minimized the score difference between the student model output and teacher model output. 
+- ***Dataset***
+*PROJECT_ROOT/dataset/knowledge_distillation/query_binary_classifier*:
+    * *train.tsv* and *valid.tsv*: two columns, namely **Query** and **Score**. 
+    **Score** is the output score of a heavy teacher model (BERT base finetune model), which is the soft label to be learned by student model as knowledge. 
+    * *test.tsv*: two columns, namely **Query** and **Label**. 
+    **Label** is a binary value which 0 means negtive and 1 means positive.     
+
+        In the meanwhile, you can also replace with your own dataset for compression task trainning.
+
+- ***Usage***
+
+    1. Train student model
+    ```bash
+    cd PROJECT_ROOT
+    python train.py --conf_path=model_zoo/nlp_tasks/knowledge_distillation/conf_kdqbc_bilstmattn_cnn.json
+    ```
+
+    2. Test student model
+    ```bash
+    cd PROJECT_ROOT
+    python test.py --conf_path=models/kdqbc_bilstmattn_cnn/train/conf_kdqbc_bilstmattn_cnn.json --previous_model_path models/kdqbc_bilstmattn_cnn/train/model.nb --predict_output_path models/kdqbc_bilstmattn_cnn/test/test.tsv --test_data_path dataset/knowledge_distillation/query_binary_classifier/test.tsv
+    ```
+
+    3. Calculate AUC metric
+    ```bash
+    cd PROJECT_ROOT
+    python tools/AUC.py --input_file models/kdqbc_bilstmattn_cnn/test/test.tsv --predict_index 2 --label_index 1 
+    ```
+
+     *Tips: you can try different models by running different JSON config files.*
+
+- ***Result***
+
+    The AUC of student model is very close to that of teacher model and its inference speed is 3.5X~4X times faster. 
+
+    |Model|AUC|
+    |-----|---|
+    |Teacher|0.9112|
+    |Student-BiLSTMAttn+TextCNN (NeuronBlocks)|0.8941|
+
+    *Tips: the model file and train log file can be found in JSON config file's outputs/save_base_dir.*
+
+#### <span id="task-7.2">7.2: Compression for Text Matching Model (ongoing)</span>
+#### <span id="task-7.3">7.3: Compression for Slot Filling Model (ongoing)</span>
+#### <span id="task-7.4">7.4: Compression for MRC (ongoing)</span>
+
+
 ## <span id="advanced-usage">Advanced Usage</span>
 
 After building a model, the next goal is to train a model with good performance. It depends on a highly expressive model and tricks of the model training. NeuronBlocks provides some tricks of model training.