1 Introduction  
1.1 Overview  
2 Query Strategies  
2.1 Informativeness  
2.2 Representativeness  
2.3 Hybrid  
3 Query and Annotation  
3.1 AL for Structured Prediction  
3.2 Annotation Cost  
4 Model and Learning  
4.1 Model Mismatch  
4.2 Learning  
5 Starting and Stopping AL  
5.1 Starting AL  
5.2 Stopping AL  
6 Other Aspects  
7 Related Topics and Future Directions  
7.1 Related Topics  
7.2 Future Directions  
Limitations