1 INTRODUCTION

2 TAXONOMY  
2.1 Notations  
2.2 The Proposed Two-level Taxonomy  
2.3 Method-based Categorization under Different Recommendation Scenarios  

3 SCENARIO 1: USER NON-OVERLAP & ITEM NON-OVERLAP  

4 SCENARIO 2: USER PARTIAL OVERLAP & ITEM NON-OVERLAP  

5 SCENARIO 3: USER FULL OVERLAP & ITEM NON-OVERLAP  

6 DATASETS FOR CROSS-DOMAIN RECOMMENDATION  
6.1 Datasets with Multiple Domains  
6.2 Datasets with Single Domain  

7 FUTURE DIRECTIONS AND CHALLENGES  
7.1 Exploring Unstudied Recommendation Scenarios  
7.2 Adopting the Latest Advances in Deep Learning  
7.3 Exploring Robustness of Recommendation  
7.4 Scalability of Deep Cross-domain Recommendation Models  
7.5 Explainability of Cross-Domain Recommendation  

8 CONCLUSION