[Paper Review] Personalized Top-N Sequential Recommendation via Convolutional Sequence Embedding (WSDM’18)
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This document summarizes a research paper on personalized top-N sequential recommendation using convolutional sequence embedding. The paper proposes a model called Caser that uses horizontal and vertical convolutional filters to capture sequential patterns at different levels from user behavior data. Caser outperforms previous methods by modeling both general user preferences and sequential patterns in a unified framework. The document provides details on Caser's network architecture, training approach, and evaluation on real-world datasets showing it achieves better performance than baseline methods.
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[Paper Review] Personalized Top-N Sequential Recommendation via Convolutional Sequence Embedding (WSDM’18)
- 1. January 8, 2020 Page 1/27 Personalized Top-N Sequential Recommendation via Convolutional Sequence Embedding (WSDM’18) Jihoo Kim [email protected] Dept. of Computer and Software, Hanyang University Jiaxi Tang, Ke Wang Simon Fraser University
- 2. January 8, 2020 Page 2/27 Jiaxi Tang PhD Student School of Computing Science Simon Fraser University Intern at Google AI Research & Machine Intelligence Team Ke Wang Professor School of Computing Science Simon Fraser University PhD, Georgia Institute of Technology MS, Georgia Institute of Technology Recent papers Towards Neural Mixture Recommender for Long Range Dependent User Sequences (WWW’19) Jiaxi Tang*, Francois Belletti*, Sagar Jain, Minmin Chen, Alex Beutel, Can Xu and Ed H. Chi Ranking Distillation: Learning Compact Ranking Models With High Performance for Recommender System (KDD’18) Jiaxi Tang, Ke Wang Author
- 3. January 8, 2020 Page 3/27 Minimum qualifications: • Currently enrolled in a Master’s or PhD degree in Computer Science or a related technical field. • Experience (classroom/work) in Natural Language Understanding, Neural Networks, Computer Vision, Machine Learning, Deep Learning, Algorithmic Foundations of Optimization, Data Science, Data Mining and/or Machine Intelligence/Artificial Intelligence. • Experience with one or more general purpose programming languages: Java, C++ or Python. • Experience with research communities and/or efforts, including having published papers (being listed as author) at conferences (e.g. NIPS, ICML, ACL, CVPR, etc). About the job Research and Machine Intelligence is a high impact team that’s building the next generation of intelligence and language understanding for all Google products. To achieve this, we’re working on projects that utilize the latest techniques in Artificial Intelligence, Machine Learning (including Deep Learning approaches like Google AI) and Natural Language Understanding. We impact products across Google including Search, Maps and Google Now. https://careers.google.com/jobs/results/136271419680924358-research-intern-2020/ Google AI Research Intern
- 4. January 8, 2020 Page 4/27 Contents 1. Introduction 1.1 Top-N Sequential Recommendation 1.2 Limitations of Previous Work 1.3 Contributions 2. Related Work 3. Proposed Methodology 3.1 Embedding Look-up 3.2 Convolutional Layers 3.3 Fully-connected Layers 3.4 Network Training 3.5 Recommendation 4. Experiments 4.1 Experimental Setup 4.2 Performance Comparison 4.3 Network Visualization
- 5. January 8, 2020 Page 5/27 User’s long term and static behaviors User’s short term and dynamic behaviors General preferences Sequential patterns < always After buying an iPhone, buy phone accessories “I love Apple’s products” vs recent next <Motivation> 1. Introduction
- 6. January 8, 2020 Page 6/27 1.1 Top-N Sequential Recommendation Users Items Sequence order General preferences Sequential patterns Input Output A list of items for user u <Top-N Sequential Recommendation> <Notations> 1. Introduction
- 7. January 8, 2020 Page 7/27 1.2 Limitations of Previous Work <Markov chain based model> 1) FPMC (Factorized Personalized Markov Chains) WWW’10 2) Fossil (Factorized Sequential Prediction with Item Similarity Model) ICDM’16 <Two major limitations> 1) Fail to model union-level* sequential patterns. 2) Fail to allow skip behaviors**. milk flour *Union-Level? butter… … **Skip behaviors? … airport hotel rest- aurant bar attr- action not necessary … Figure 1 1. Introduction
- 8. January 8, 2020 Page 8/27 1.2 Limitations of Previous Work To provide evidences of union-level influences and skip behaviors minimum support count = 5 minimum confidence = 50% X Y sequence Figure 2 Sequential Association Rules → 1. Introduction
- 9. January 8, 2020 Page 9/27 1.3 Contributions Caser (ConvolutionAl Sequence Embedding Recommendation Model) • Caser uses horizontal and vertical convolutional filters to capture sequential patterns at point-level, union-level, and of skip behaviors. • Caser models both users’ general preferences and sequential patterns, and generalizes several existing state-of-the-art methods in a single unified framework. • Caser outperforms state-of-the-art methods for top-N sequential recommendation on real life data sets. 1. Introduction
- 10. January 8, 2020 Page 10/27 • Sequential pattern mining depends on the explicit representation of patterns, thus, could miss patterns in unobserved states. (= could miss implicit patterns) • CNN has been used to extract users’ preferences from their reviews. None of these works is for sequential recommendation. • RNN was used for session-based recommendation. It may not work well in sequential recommendation, because not all adjacent actions have dependency relationships. • Temporal recommendation is related but different problem. (Session-based is also different) (ex. Recommend coffee in the morning, instead of evening.) 2. Related Work
- 11. January 8, 2020 Page 11/27 Figure 3 <Network Architecture of Caser> 3. Proposed Methodology
- 12. January 8, 2020 Page 12/27 The user 𝒖’s sequence every 𝑳 successive items as input their next 𝑻 items as the targets window of size 𝑳 + 𝑻 The embedding for item 𝒊 d is the number of latent dimensions 𝑺 𝟏 𝒖 𝑺 𝟐 𝒖 𝑺 𝟑 𝒖 𝑺 𝟒 𝒖 𝑺 𝟓 𝒖 𝑬(𝒖,𝟑) = 𝑸 𝑺 𝟏 𝒖 𝑸 𝑺 𝟐 𝒖 𝑬(𝒖,𝟒) = 𝑸 𝑺 𝟐 𝒖 𝑸 𝑺 𝟑 𝒖 𝑬(𝒖,𝟓) = 𝑸 𝑺 𝟑 𝒖 𝑸 𝑺 𝟒 𝒖 3.1 Embedding Look-up 3. Proposed Methodology
- 13. January 8, 2020 Page 13/27 image local features = 𝑳 × 𝒅 matrix 𝑬 = sequential pattern Figure 4 Unlike image recognition, “image” 𝑬 is not given… and must be learnt 3.2 Convolutional Layers 3. Proposed Methodology
- 14. January 8, 2020 Page 14/27 𝑳 = 𝟒 𝒉 = 𝟐 𝒅 = 𝟑 𝑭 𝒌 ∈ ℝ 𝟐×𝟑 𝒊 = 𝟏 𝒊 = 𝑳 − 𝒉 + 𝟏 = 𝟒 − 𝟐 + 𝟏 = 𝟑 𝑬 𝟏:𝟐 𝑬 𝟐:𝟑 𝑬 𝟑:𝟒 inner product activation function 𝑖-th convolution value <Max Pooling><Horizontal Filter> 𝑳 = 𝟒 𝒅 = 𝟑 ෩𝑭 𝒌 ∈ ℝ 𝟒×𝟏 <Vertical Filter> → weighted sum → no max pooling 3. Proposed Methodology 𝑘-th filter # of filter height of filter Convolution value (by 𝑭 𝒌 )
- 15. January 8, 2020 Page 15/27 activation function convolutional sequence embedding 3.3 Fully-connected Layers the probability of how likely user 𝒖 will interact with item 𝒊 at time step 𝒕 3. Proposed Methodology
- 16. January 8, 2020 Page 16/27 union-level sequential patterns point-level sequential patterns short-term sequential patterns long-term general preferences 3. Proposed Methodology
- 17. January 8, 2020 Page 17/27 3.4 Network Training To train the network, we transform the values of the output layers to probabilities sigmoid function the collection of the time steps for which we would like to make predictions for user 𝒖 the likelihood of all sequences in the dataset 3. Proposed Methodology
- 18. January 8, 2020 Page 18/27 3.4 Network Training To further capture skip behaviors, we could consider the next 𝑻 target items Taking the negative logarithm of likelihood, we get the objective function “binary cross-entropy loss” model parameters hyper-parameters are learned by minimizing the loss function (13) are tuned on the validation set via grid search 3. Proposed Methodology
- 19. January 8, 2020 Page 19/27 3.5 Recommendation After obtaining the trained neural network, to make recommendations for a user 𝒖 at time step 𝒕 We recommend 𝑵 items that have the highest values in the output layer 𝒖 𝒖’s last 𝑳 items’ embedding 𝑬(𝒖,𝒕) 𝒖’s latent embedding 𝑷 𝒖 Input Output 3. Proposed Methodology
- 20. January 8, 2020 Page 20/27 4.1 Experimental Setup <Datasets> Amazon data was not used, due to its SI 0.0026 for ‘Office Products’ 0.0019 for ‘Clothing’ / ‘Shoes’ / ‘Jewelry’ / ‘Video Games’ 70% 10% 20% validation testtraining sequence 4. Experiments
- 21. January 8, 2020 Page 21/27 <Evaluation Metrics> 4.1 Experimental Setup MAP(Mean Average Precision): the average of AP for all users Precision, Recall top 𝑵 predicted items for a user the last 20% of actions in user’s sequence (= test set) 4. Experiments
- 22. January 8, 2020 Page 22/27 4.2 Performance Comparison 4. Experiments
- 23. January 8, 2020 Page 23/27 4.2 Performance Comparison <Influence of hyper-parameter 𝒅, 𝑳, 𝑻,> 4. Experiments
- 24. January 8, 2020 Page 24/27 4.2 Performance Comparison <Analysis of Caser Components> 𝒉 denotes horizontal convolutional layer 𝒗 denotes vertical convolutional layer 𝒑 denotes personalization Any missing component is represented by setting its corresponding 𝒐, 𝒐, 𝑷 𝒖 to zero. 4. Experiments
- 25. January 8, 2020 Page 25/27 4.3 Network Visualization Caser puts more emphasis on recent actions, demonstrating a major difference from the conventional top-N recommendation. <Vertical convolutional filters> 4. Experiments
- 26. January 8, 2020 Page 26/27 4.3 Network Visualization <Horizontal convolutional filters> <Previous Sequence> 𝑺 𝟏 (13th Warrior) History 𝑺 𝟐 (American Beauty), Romance 𝑺 𝟑 (Star Trek), Action & SF 𝑺 𝟒 (Star Trek III) 𝑺 𝟓 (Star Trek IV) <Predictions> 𝑹 𝟏 (Mad Max) 𝑹 𝟐 (Star War) 𝑹 𝟑 (Star Trek) >> Ground Truth 4. Experiments
- 27. January 8, 2020 Page 27/27 Thank you! Q & A