Techniques for Context-Aware and Cold-Start Recommendations
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Transcript of Techniques for Context-Aware and Cold-Start Recommendations
![Page 1: Techniques for Context-Aware and Cold-Start Recommendations](https://reader031.fdocuments.in/reader031/viewer/2022030314/589bf5a81a28ab40348b626b/html5/thumbnails/1.jpg)
PhD Thesis Defense, 28th Ph.D. Cycle, May 2016
Techniques for Context-Aware and Cold-Start Recommendations
Matthias BraunhoferSupervisor: Prof. Francesco Ricci
Free University of Bozen - BolzanoPiazza Domenicani 3, 39100 Bolzano, Italy
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PhD Thesis Defense, 28th Ph.D. Cycle, May 2016
Outline
2
• Context-Aware Recommenders and the Cold-Start Problem
• State of the Art
• South Tyrol Suggests Application Scenario
• Hybrid Context-Aware Recommendation Algorithms
• Active Learning for Context-Aware Recommenders
• Conclusions and Future Work
![Page 3: Techniques for Context-Aware and Cold-Start Recommendations](https://reader031.fdocuments.in/reader031/viewer/2022030314/589bf5a81a28ab40348b626b/html5/thumbnails/3.jpg)
PhD Thesis Defense, 28th Ph.D. Cycle, May 2016
Outline
2
• Context-Aware Recommenders and the Cold-Start Problem
• State of the Art
• South Tyrol Suggests Application Scenario
• Hybrid Context-Aware Recommendation Algorithms
• Active Learning for Context-Aware Recommenders
• Conclusions and Future Work
![Page 4: Techniques for Context-Aware and Cold-Start Recommendations](https://reader031.fdocuments.in/reader031/viewer/2022030314/589bf5a81a28ab40348b626b/html5/thumbnails/4.jpg)
PhD Thesis Defense, 28th Ph.D. Cycle, May 2016
• Recommender Systems (RSs) are information filtering and decision support tools suggesting interesting items to the user based on feedback
• Explicit feedback (e.g., ratings) vs. implicit feedback (e.g., browsing history)
• Two popular approaches:
• Collaborative Filtering (CF)
• Content-based
Recommender Systems
3
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PhD Thesis Defense, 28th Ph.D. Cycle, May 2016
Context is Essential
• Main idea: users can experience the same item differently depending on the current contextual situation (e.g., weather, season, mood)
• RSs must take into account this information to deliver more useful (perceived) recommendations
4
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PhD Thesis Defense, 28th Ph.D. Cycle, May 2016
Context-Aware Recommender Systems
• Context-Aware Recommender Systems (CARSs) improve traditional RSs by adapting their suggestions to the contextual situations of the user and the recommended items
• Example: Google Now
5
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PhD Thesis Defense, 28th Ph.D. Cycle, May 2016
Cold-Start Problem
• CARSs suffer from the cold-start problem
• New user problem: How do you recommend to a new user?
• New item problem: How do you recommend a new item with no ratings?
• New context problem: How do you recommend in a new context?
6
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PhD Thesis Defense, 28th Ph.D. Cycle, May 2016
Cold-Start Problem
• CARSs suffer from the cold-start problem
• New user problem: How do you recommend to a new user?
• New item problem: How do you recommend a new item with no ratings?
• New context problem: How do you recommend in a new context?
6
1 ? 1 ?
2 5 ?
? 3 ?
3 ? 5 ?
2 5 ?
? 3 ?
5 ? 5 ?
4 5 4 ?
? 3 5 ?
1 ? 12 5? 3
3 ? 52 5? 3
5 ? 54 5 4? 3 5? ? ?
? ? ?1 ? 1
2 5
? 3
3 ? 5
2 5
? 3
5 ? 5
4 5 4
? 3 5
Focus of this research
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PhD Thesis Defense, 28th Ph.D. Cycle, May 2016
Outline
7
• Context-Aware Recommenders and the Cold-Start Problem
• State of the Art
• South Tyrol Suggests Application Scenario
• Hybrid Context-Aware Recommendation Algorithms
• Active Learning for Context-Aware Recommenders
• Conclusions and Future Work
![Page 10: Techniques for Context-Aware and Cold-Start Recommendations](https://reader031.fdocuments.in/reader031/viewer/2022030314/589bf5a81a28ab40348b626b/html5/thumbnails/10.jpg)
PhD Thesis Defense, 28th Ph.D. Cycle, May 2016
Approaches for Cold-Starting CARSs
8
Cold-starting CARSs
8
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PhD Thesis Defense, 28th Ph.D. Cycle, May 2016
Approaches for Cold-Starting CARSs
8
Cold-starting CARSs
… using additional knowledge sources
… better using existing knowledge
8
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PhD Thesis Defense, 28th Ph.D. Cycle, May 2016
Approaches for Cold-Starting CARSs
8
Cold-starting CARSs
… using additional knowledge sources
… better using existing knowledge
Active learning (Elahi et al., 2013)
8
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PhD Thesis Defense, 28th Ph.D. Cycle, May 2016
Approaches for Cold-Starting CARSs
8
Cold-starting CARSs
… using additional knowledge sources
… better using existing knowledge
Active learning (Elahi et al., 2013)
Cross-domain rec. (Enrich et al., 2013)
8
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PhD Thesis Defense, 28th Ph.D. Cycle, May 2016
Approaches for Cold-Starting CARSs
8
Cold-starting CARSs
… using additional knowledge sources
… better using existing knowledge
Active learning (Elahi et al., 2013)
Cross-domain rec. (Enrich et al., 2013)
Implicit feedback (Koren, 2008)
8
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PhD Thesis Defense, 28th Ph.D. Cycle, May 2016
Approaches for Cold-Starting CARSs
8
Cold-starting CARSs
… using additional knowledge sources
… better using existing knowledge
Active learning (Elahi et al., 2013)
Cross-domain rec. (Enrich et al., 2013)
User / item attributes (Musto et al., 2013)
Implicit feedback (Koren, 2008)
8
![Page 16: Techniques for Context-Aware and Cold-Start Recommendations](https://reader031.fdocuments.in/reader031/viewer/2022030314/589bf5a81a28ab40348b626b/html5/thumbnails/16.jpg)
PhD Thesis Defense, 28th Ph.D. Cycle, May 2016
Approaches for Cold-Starting CARSs
8
Cold-starting CARSs
… using additional knowledge sources
… better using existing knowledge
Active learning (Elahi et al., 2013)
Cross-domain rec. (Enrich et al., 2013)
User / item attributes (Musto et al., 2013)
Selective context acquisition (Baltrunas et al., 2012)
Implicit feedback (Koren, 2008)
8
![Page 17: Techniques for Context-Aware and Cold-Start Recommendations](https://reader031.fdocuments.in/reader031/viewer/2022030314/589bf5a81a28ab40348b626b/html5/thumbnails/17.jpg)
PhD Thesis Defense, 28th Ph.D. Cycle, May 2016
Approaches for Cold-Starting CARSs
8
Cold-starting CARSs
… using additional knowledge sources
… better using existing knowledge
Active learning (Elahi et al., 2013)
Cross-domain rec. (Enrich et al., 2013)
User / item attributes (Musto et al., 2013)
Selective context acquisition (Baltrunas et al., 2012)
Context hierarchy / similarity (Codina et al., 2013)
Implicit feedback (Koren, 2008)
8
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PhD Thesis Defense, 28th Ph.D. Cycle, May 2016
Outline
9
• Context-Aware Recommenders and the Cold-Start Problem
• State of the Art
• South Tyrol Suggests Application Scenario
• Hybrid Context-Aware Recommendation Algorithms
• Active Learning for Context-Aware Recommenders
• Conclusions and Future Work
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PhD Thesis Defense, 28th Ph.D. Cycle, May 2016
Interaction with the System
10
Welcome screen
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PhD Thesis Defense, 28th Ph.D. Cycle, May 2016
Interaction with the System
10
Registration screen
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PhD Thesis Defense, 28th Ph.D. Cycle, May 2016
Interaction with the System
10
Personality questionnaire
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PhD Thesis Defense, 28th Ph.D. Cycle, May 2016
Interaction with the System
10
Questionnaire results
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PhD Thesis Defense, 28th Ph.D. Cycle, May 2016
Interaction with the System
10
Slide-out navigation menu
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PhD Thesis Defense, 28th Ph.D. Cycle, May 2016
Interaction with the System
10
Suggestions screen
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PhD Thesis Defense, 28th Ph.D. Cycle, May 2016
Interaction with the System
10
Active learning
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PhD Thesis Defense, 28th Ph.D. Cycle, May 2016
Interaction with the System
10
Details screen
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PhD Thesis Defense, 28th Ph.D. Cycle, May 2016
Interaction with the System
10
Routing screen
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PhD Thesis Defense, 28th Ph.D. Cycle, May 2016
Interaction with the System
10
Profile page
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PhD Thesis Defense, 28th Ph.D. Cycle, May 2016
Research Hypotheses Tested through User Studies
11
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PhD Thesis Defense, 28th Ph.D. Cycle, May 2016
Research Hypotheses Tested through User Studies
• Personality is useful to elicit more ratings from new users than some state-of-the-art AL strategies based on heuristics
11
![Page 31: Techniques for Context-Aware and Cold-Start Recommendations](https://reader031.fdocuments.in/reader031/viewer/2022030314/589bf5a81a28ab40348b626b/html5/thumbnails/31.jpg)
PhD Thesis Defense, 28th Ph.D. Cycle, May 2016
Research Hypotheses Tested through User Studies
• Personality is useful to elicit more ratings from new users than some state-of-the-art AL strategies based on heuristics
• Personality can be exploited for eliciting ratings from new users that lead to an improved system prediction accuracy
11
![Page 32: Techniques for Context-Aware and Cold-Start Recommendations](https://reader031.fdocuments.in/reader031/viewer/2022030314/589bf5a81a28ab40348b626b/html5/thumbnails/32.jpg)
PhD Thesis Defense, 28th Ph.D. Cycle, May 2016
Research Hypotheses Tested through User Studies
• Personality is useful to elicit more ratings from new users than some state-of-the-art AL strategies based on heuristics
• Personality can be exploited for eliciting ratings from new users that lead to an improved system prediction accuracy
• Personality can be helpful to acquire ratings from new users which result in recommendations better tailored to the user’s context
11
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PhD Thesis Defense, 28th Ph.D. Cycle, May 2016
Research Hypotheses Tested with Offline Experiments
12
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PhD Thesis Defense, 28th Ph.D. Cycle, May 2016
Research Hypotheses Tested with Offline Experiments
• Hybrid CARS algorithms are beneficial for delivering accurate context-aware rating predictions in cold-start situations
12
![Page 35: Techniques for Context-Aware and Cold-Start Recommendations](https://reader031.fdocuments.in/reader031/viewer/2022030314/589bf5a81a28ab40348b626b/html5/thumbnails/35.jpg)
PhD Thesis Defense, 28th Ph.D. Cycle, May 2016
Research Hypotheses Tested with Offline Experiments
• Hybrid CARS algorithms are beneficial for delivering accurate context-aware rating predictions in cold-start situations
• Hybrid CARS algorithms can achieve a high recommendation ranking quality in cold-start situations
12
![Page 36: Techniques for Context-Aware and Cold-Start Recommendations](https://reader031.fdocuments.in/reader031/viewer/2022030314/589bf5a81a28ab40348b626b/html5/thumbnails/36.jpg)
PhD Thesis Defense, 28th Ph.D. Cycle, May 2016
Research Hypotheses Tested with Offline Experiments
• Hybrid CARS algorithms are beneficial for delivering accurate context-aware rating predictions in cold-start situations
• Hybrid CARS algorithms can achieve a high recommendation ranking quality in cold-start situations
• Parsimonious and adaptive context acquisition can save time and effort of the user by effectively identifying what contextual factors to acquire upon rating an item
12
![Page 37: Techniques for Context-Aware and Cold-Start Recommendations](https://reader031.fdocuments.in/reader031/viewer/2022030314/589bf5a81a28ab40348b626b/html5/thumbnails/37.jpg)
PhD Thesis Defense, 28th Ph.D. Cycle, May 2016
Outline
13
• Context-Aware Recommenders and the Cold-Start Problem
• State of the Art
• South Tyrol Suggests Application Scenario
• Hybrid Context-Aware Recommendation Algorithms
• Active Learning for Context-Aware Recommenders
• Conclusions and Future Work
![Page 38: Techniques for Context-Aware and Cold-Start Recommendations](https://reader031.fdocuments.in/reader031/viewer/2022030314/589bf5a81a28ab40348b626b/html5/thumbnails/38.jpg)
PhD Thesis Defense, 28th Ph.D. Cycle, May 2016
Hybrid Context-Aware Recommenders
14
• Conjecture: it is possible to adaptively combine multiple CARS algorithms in order to take advantage of their strengths and alleviate their drawbacks in different cold-start situations
• Example:
(user, item, context) tuple
CARS 1
CARS 2
Hybridization Final score
Score
Score
Hybrid CARS
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PhD Thesis Defense, 28th Ph.D. Cycle, May 2016
• Matrix Factorization (MF) predicts unknown ratings by discovering some latent features that determine how a user rates an item; items similar to the target user in this latent space are recommended
Matrix Factorization Methods
15
r11 r12 r13 r14
r21 r22 r23 r24
r31 r32 r33 r34
r41 r42 r43 r44
r51 r52 r53 r54
a b c
xyz=
r q p5 x 4 matrix 5 x 3 matrix 3 x 4 matrix
r42 = (a, b, c) · (x, y, z) = a * x + b * y + c * z
ȓui = qiTpu
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PhD Thesis Defense, 28th Ph.D. Cycle, May 2016
• Matrix Factorization (MF) predicts unknown ratings by discovering some latent features that determine how a user rates an item; items similar to the target user in this latent space are recommended
Matrix Factorization Methods
15
r11 r12 r13 r14
r21 r22 r23 r24
r31 r32 r33 r34
r41 r42 r43 r44
r51 r52 r53 r54
a b c
xyz=
r q p5 x 4 matrix 5 x 3 matrix 3 x 4 matrix
r42 = (a, b, c) · (x, y, z) = a * x + b * y + c * z
ȓui = qiTpuRating prediction
![Page 41: Techniques for Context-Aware and Cold-Start Recommendations](https://reader031.fdocuments.in/reader031/viewer/2022030314/589bf5a81a28ab40348b626b/html5/thumbnails/41.jpg)
PhD Thesis Defense, 28th Ph.D. Cycle, May 2016
• Matrix Factorization (MF) predicts unknown ratings by discovering some latent features that determine how a user rates an item; items similar to the target user in this latent space are recommended
Matrix Factorization Methods
15
r11 r12 r13 r14
r21 r22 r23 r24
r31 r32 r33 r34
r41 r42 r43 r44
r51 r52 r53 r54
a b c
xyz=
r q p5 x 4 matrix 5 x 3 matrix 3 x 4 matrix
r42 = (a, b, c) · (x, y, z) = a * x + b * y + c * z
ȓui = qiTpu
Item preference factor vector
![Page 42: Techniques for Context-Aware and Cold-Start Recommendations](https://reader031.fdocuments.in/reader031/viewer/2022030314/589bf5a81a28ab40348b626b/html5/thumbnails/42.jpg)
PhD Thesis Defense, 28th Ph.D. Cycle, May 2016
• Matrix Factorization (MF) predicts unknown ratings by discovering some latent features that determine how a user rates an item; items similar to the target user in this latent space are recommended
Matrix Factorization Methods
15
r11 r12 r13 r14
r21 r22 r23 r24
r31 r32 r33 r34
r41 r42 r43 r44
r51 r52 r53 r54
a b c
xyz=
r q p5 x 4 matrix 5 x 3 matrix 3 x 4 matrix
r42 = (a, b, c) · (x, y, z) = a * x + b * y + c * z
ȓui = qiTpu User preference factor vector
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PhD Thesis Defense, 28th Ph.D. Cycle, May 2016
• CAMF-CC (Context-Aware Matrix Factorization for item categories) is a variant of CAMF that extends standard MF by incorporating baseline parameters for contextual condition-item category pairs
Basic CARS Algorithms CAMF-CC (Baltrunas et al., 2011)
16
ruic1...ck = qiT pu + ri + bu + btcj
j=1
k
∑t∈T (i )∑
qi latent factor vector of item ipu latent factor vector of user u average rating for item ibu baseline for user uT(i) set of categories associated to item ibtcj baseline for item category-contextual condition tcj
ri
![Page 44: Techniques for Context-Aware and Cold-Start Recommendations](https://reader031.fdocuments.in/reader031/viewer/2022030314/589bf5a81a28ab40348b626b/html5/thumbnails/44.jpg)
PhD Thesis Defense, 28th Ph.D. Cycle, May 2016
• CAMF-CC (Context-Aware Matrix Factorization for item categories) is a variant of CAMF that extends standard MF by incorporating baseline parameters for contextual condition-item category pairs
Basic CARS Algorithms CAMF-CC (Baltrunas et al., 2011)
16
ruic1...ck = qiT pu + ri + bu + btcj
j=1
k
∑t∈T (i )∑
qi latent factor vector of item ipu latent factor vector of user u average rating for item ibu baseline for user uT(i) set of categories associated to item ibtcj baseline for item category-contextual condition tcj
ri
![Page 45: Techniques for Context-Aware and Cold-Start Recommendations](https://reader031.fdocuments.in/reader031/viewer/2022030314/589bf5a81a28ab40348b626b/html5/thumbnails/45.jpg)
PhD Thesis Defense, 28th Ph.D. Cycle, May 2016
• CAMF-CC (Context-Aware Matrix Factorization for item categories) is a variant of CAMF that extends standard MF by incorporating baseline parameters for contextual condition-item category pairs
Basic CARS Algorithms CAMF-CC (Baltrunas et al., 2011)
16
ruic1...ck = qiT pu + ri + bu + btcj
j=1
k
∑t∈T (i )∑
qi latent factor vector of item ipu latent factor vector of user u average rating for item ibu baseline for user uT(i) set of categories associated to item ibtcj baseline for item category-contextual condition tcj
ri
![Page 46: Techniques for Context-Aware and Cold-Start Recommendations](https://reader031.fdocuments.in/reader031/viewer/2022030314/589bf5a81a28ab40348b626b/html5/thumbnails/46.jpg)
PhD Thesis Defense, 28th Ph.D. Cycle, May 2016
• CAMF-CC (Context-Aware Matrix Factorization for item categories) is a variant of CAMF that extends standard MF by incorporating baseline parameters for contextual condition-item category pairs
Basic CARS Algorithms CAMF-CC (Baltrunas et al., 2011)
16
ruic1...ck = qiT pu + ri + bu + btcj
j=1
k
∑t∈T (i )∑
qi latent factor vector of item ipu latent factor vector of user u average rating for item ibu baseline for user uT(i) set of categories associated to item ibtcj baseline for item category-contextual condition tcj
ri
![Page 47: Techniques for Context-Aware and Cold-Start Recommendations](https://reader031.fdocuments.in/reader031/viewer/2022030314/589bf5a81a28ab40348b626b/html5/thumbnails/47.jpg)
PhD Thesis Defense, 28th Ph.D. Cycle, May 2016
• CAMF-CC (Context-Aware Matrix Factorization for item categories) is a variant of CAMF that extends standard MF by incorporating baseline parameters for contextual condition-item category pairs
Basic CARS Algorithms CAMF-CC (Baltrunas et al., 2011)
16
ruic1...ck = qiT pu + ri + bu + btcj
j=1
k
∑t∈T (i )∑
qi latent factor vector of item ipu latent factor vector of user u average rating for item ibu baseline for user uT(i) set of categories associated to item ibtcj baseline for item category-contextual condition tcj
ri
![Page 48: Techniques for Context-Aware and Cold-Start Recommendations](https://reader031.fdocuments.in/reader031/viewer/2022030314/589bf5a81a28ab40348b626b/html5/thumbnails/48.jpg)
PhD Thesis Defense, 28th Ph.D. Cycle, May 2016
Basic CARS Algorithms SPF (Codina et al., 2013)
17
• SPF (Semantic Pre-Filtering) is a contextual pre-filtering method that, given a target contextual situation, uses a standard MF model learnt from all the ratings tagged with contextual situations identical or similar to the target one
• Conjecture: learning the prediction model on a larger number of ratings, even if not obtained exactly in the target context, will help
• Key step: similarity calculation
1 -0.5 2 1
-2 0.5 -2 -1.5
-2 0.5 -1 -1
Condition-to-item co-occurrence matrix
1 -0.96 -0.84
-0.96 1 0.96
-0.84 0.96 1
Cosine similarity between conditions
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PhD Thesis Defense, 28th Ph.D. Cycle, May 2016
Basic CARS Algorithms Content-based CAMF-CC
18
• It is a novel variant of CAMF-CC that incorporates additional sources of information about the items, e.g., category or genre information
• Conjecture: alleviates the new item problem of CAMF-CC
ruic1...ck = (qi + xa )a∈A(i )∑ T
pu + ri + bu + btcjj=1
k
∑t∈T (i )∑
qi latent factor vector of item iA(i) set of item attributes xa latent factor vector of item attribute apu latent factor vector of user u average rating for item ibu baseline for user uT(i) set of categories associated to item ibtcj baseline for item category-contextual condition tcj
ri
![Page 50: Techniques for Context-Aware and Cold-Start Recommendations](https://reader031.fdocuments.in/reader031/viewer/2022030314/589bf5a81a28ab40348b626b/html5/thumbnails/50.jpg)
PhD Thesis Defense, 28th Ph.D. Cycle, May 2016
Basic CARS Algorithms Content-based CAMF-CC
18
• It is a novel variant of CAMF-CC that incorporates additional sources of information about the items, e.g., category or genre information
• Conjecture: alleviates the new item problem of CAMF-CC
ruic1...ck = (qi + xa )a∈A(i )∑ T
pu + ri + bu + btcjj=1
k
∑t∈T (i )∑
qi latent factor vector of item iA(i) set of item attributes xa latent factor vector of item attribute apu latent factor vector of user u average rating for item ibu baseline for user uT(i) set of categories associated to item ibtcj baseline for item category-contextual condition tcj
ri
![Page 51: Techniques for Context-Aware and Cold-Start Recommendations](https://reader031.fdocuments.in/reader031/viewer/2022030314/589bf5a81a28ab40348b626b/html5/thumbnails/51.jpg)
PhD Thesis Defense, 28th Ph.D. Cycle, May 2016
Basic CARS Algorithms Demographics-based CAMF-CC
19
• It is a novel variant of CAMF-CC that profiles users through known user attributes (e.g., age group, gender, personality traits)
• Conjecture: alleviates the new user problem of CAMF-CC
ruic1...ck = qiT (pu + ya )
a∈A(u )∑ + ri + bu + btcj
j=1
k
∑t∈T (i )∑
qi latent factor vector of item ipu latent factor vector of user uA(u) set of user attributesya latent factor vector of user attribute a overall average ratingbu baseline for user uT(i) set of categories associated to item ibtcj baseline for item category-contextual condition tcj
ri
![Page 52: Techniques for Context-Aware and Cold-Start Recommendations](https://reader031.fdocuments.in/reader031/viewer/2022030314/589bf5a81a28ab40348b626b/html5/thumbnails/52.jpg)
PhD Thesis Defense, 28th Ph.D. Cycle, May 2016
Basic CARS Algorithms Demographics-based CAMF-CC
19
• It is a novel variant of CAMF-CC that profiles users through known user attributes (e.g., age group, gender, personality traits)
• Conjecture: alleviates the new user problem of CAMF-CC
ruic1...ck = qiT (pu + ya )
a∈A(u )∑ + ri + bu + btcj
j=1
k
∑t∈T (i )∑
qi latent factor vector of item ipu latent factor vector of user uA(u) set of user attributesya latent factor vector of user attribute a overall average ratingbu baseline for user uT(i) set of categories associated to item ibtcj baseline for item category-contextual condition tcj
ri
![Page 53: Techniques for Context-Aware and Cold-Start Recommendations](https://reader031.fdocuments.in/reader031/viewer/2022030314/589bf5a81a28ab40348b626b/html5/thumbnails/53.jpg)
PhD Thesis Defense, 28th Ph.D. Cycle, May 2016
Hybrid CARS Algorithms Heuristic Switching
• Heuristic Switching uses a stable heuristic to switch between a set of basic CARS algorithms depending on the encountered cold-start situation
• Conjecture: better tackles specific cold-start situations found in CARSs
20
R1: Use content-based CAMF-CC for a new item.
R2: Use demographics-based CAMF-CC for a new user.
R3: Average the predictions of content-based CAMF-CC and demographics-based CAMF-CC for new contextual situations or mixtures of cold-start cases.
![Page 54: Techniques for Context-Aware and Cold-Start Recommendations](https://reader031.fdocuments.in/reader031/viewer/2022030314/589bf5a81a28ab40348b626b/html5/thumbnails/54.jpg)
PhD Thesis Defense, 28th Ph.D. Cycle, May 2016
• Adaptive Weighted adaptively sums the predictions of the basic algorithms weighted by their estimated accuracies for the user, item and contextual situation in question
• Extends the two-dimensional adaptive RS presented in (Bjørkøy, 2011)
• Conjecture: optimizes adaptation of differently performing CARS algorithms
Hybrid CARS Algorithms Adaptive Weighted (1/2)
21
r
…
∑
…
r1 r 2 r m
a1 a2 am
![Page 55: Techniques for Context-Aware and Cold-Start Recommendations](https://reader031.fdocuments.in/reader031/viewer/2022030314/589bf5a81a28ab40348b626b/html5/thumbnails/55.jpg)
PhD Thesis Defense, 28th Ph.D. Cycle, May 2016
Hybrid CARS Algorithms Adaptive Weighted (2/2)
22
• Builds for each basic CARS algorithm a new user-item-context error tensor whose entries are the known deviations (errors) of the CARS predictions from the true ratings
• Uses a separate CARS error prediction model for each of these error tensors to predict the errors (accuracies) on a particular (user, item, context) tuple
euic1...ck = (qi + xcici∈IC∑ )T (pu + ycu
cu∈UC∑ )+ ei + bu
qi latent factor vector of item ipu latent factor vector of user uIC subset of item-related contextual conditionsxci latent factor vector of contextual condition ciUC subset of user-related contextual conditionsycu latent factor vector of contextual condition cu average error for item ibu baseline for user uei
![Page 56: Techniques for Context-Aware and Cold-Start Recommendations](https://reader031.fdocuments.in/reader031/viewer/2022030314/589bf5a81a28ab40348b626b/html5/thumbnails/56.jpg)
PhD Thesis Defense, 28th Ph.D. Cycle, May 2016
Hybrid CARS Algorithms Adaptive Weighted (2/2)
22
• Builds for each basic CARS algorithm a new user-item-context error tensor whose entries are the known deviations (errors) of the CARS predictions from the true ratings
• Uses a separate CARS error prediction model for each of these error tensors to predict the errors (accuracies) on a particular (user, item, context) tuple
euic1...ck = (qi + xcici∈IC∑ )T (pu + ycu
cu∈UC∑ )+ ei + bu
qi latent factor vector of item ipu latent factor vector of user uIC subset of item-related contextual conditionsxci latent factor vector of contextual condition ciUC subset of user-related contextual conditionsycu latent factor vector of contextual condition cu average error for item ibu baseline for user uei
![Page 57: Techniques for Context-Aware and Cold-Start Recommendations](https://reader031.fdocuments.in/reader031/viewer/2022030314/589bf5a81a28ab40348b626b/html5/thumbnails/57.jpg)
PhD Thesis Defense, 28th Ph.D. Cycle, May 2016
Hybrid CARS Algorithms Adaptive Weighted (2/2)
22
• Builds for each basic CARS algorithm a new user-item-context error tensor whose entries are the known deviations (errors) of the CARS predictions from the true ratings
• Uses a separate CARS error prediction model for each of these error tensors to predict the errors (accuracies) on a particular (user, item, context) tuple
euic1...ck = (qi + xcici∈IC∑ )T (pu + ycu
cu∈UC∑ )+ ei + bu
qi latent factor vector of item ipu latent factor vector of user uIC subset of item-related contextual conditionsxci latent factor vector of contextual condition ciUC subset of user-related contextual conditionsycu latent factor vector of contextual condition cu average error for item ibu baseline for user uei
![Page 58: Techniques for Context-Aware and Cold-Start Recommendations](https://reader031.fdocuments.in/reader031/viewer/2022030314/589bf5a81a28ab40348b626b/html5/thumbnails/58.jpg)
PhD Thesis Defense, 28th Ph.D. Cycle, May 2016
Hybrid CARS Algorithms Adaptive Weighted (2/2)
22
• Builds for each basic CARS algorithm a new user-item-context error tensor whose entries are the known deviations (errors) of the CARS predictions from the true ratings
• Uses a separate CARS error prediction model for each of these error tensors to predict the errors (accuracies) on a particular (user, item, context) tuple
euic1...ck = (qi + xcici∈IC∑ )T (pu + ycu
cu∈UC∑ )+ ei + bu
qi latent factor vector of item ipu latent factor vector of user uIC subset of item-related contextual conditionsxci latent factor vector of contextual condition ciUC subset of user-related contextual conditionsycu latent factor vector of contextual condition cu average error for item ibu baseline for user uei
![Page 59: Techniques for Context-Aware and Cold-Start Recommendations](https://reader031.fdocuments.in/reader031/viewer/2022030314/589bf5a81a28ab40348b626b/html5/thumbnails/59.jpg)
PhD Thesis Defense, 28th Ph.D. Cycle, May 2016
Hybrid CARS Algorithms Adaptive Weighted (2/2)
22
• Builds for each basic CARS algorithm a new user-item-context error tensor whose entries are the known deviations (errors) of the CARS predictions from the true ratings
• Uses a separate CARS error prediction model for each of these error tensors to predict the errors (accuracies) on a particular (user, item, context) tuple
euic1...ck = (qi + xcici∈IC∑ )T (pu + ycu
cu∈UC∑ )+ ei + bu
qi latent factor vector of item ipu latent factor vector of user uIC subset of item-related contextual conditionsxci latent factor vector of contextual condition ciUC subset of user-related contextual conditionsycu latent factor vector of contextual condition cu average error for item ibu baseline for user uei
![Page 60: Techniques for Context-Aware and Cold-Start Recommendations](https://reader031.fdocuments.in/reader031/viewer/2022030314/589bf5a81a28ab40348b626b/html5/thumbnails/60.jpg)
PhD Thesis Defense, 28th Ph.D. Cycle, May 2016
Hybrid CARS Algorithms Adaptive Weighted (2/2)
22
• Builds for each basic CARS algorithm a new user-item-context error tensor whose entries are the known deviations (errors) of the CARS predictions from the true ratings
• Uses a separate CARS error prediction model for each of these error tensors to predict the errors (accuracies) on a particular (user, item, context) tuple
euic1...ck = (qi + xcici∈IC∑ )T (pu + ycu
cu∈UC∑ )+ ei + bu
qi latent factor vector of item ipu latent factor vector of user uIC subset of item-related contextual conditionsxci latent factor vector of contextual condition ciUC subset of user-related contextual conditionsycu latent factor vector of contextual condition cu average error for item ibu baseline for user uei
![Page 61: Techniques for Context-Aware and Cold-Start Recommendations](https://reader031.fdocuments.in/reader031/viewer/2022030314/589bf5a81a28ab40348b626b/html5/thumbnails/61.jpg)
PhD Thesis Defense, 28th Ph.D. Cycle, May 2016
Hybrid CARS Algorithms Adaptive Weighted (2/2)
22
• Builds for each basic CARS algorithm a new user-item-context error tensor whose entries are the known deviations (errors) of the CARS predictions from the true ratings
• Uses a separate CARS error prediction model for each of these error tensors to predict the errors (accuracies) on a particular (user, item, context) tuple
euic1...ck = (qi + xcici∈IC∑ )T (pu + ycu
cu∈UC∑ )+ ei + bu
qi latent factor vector of item ipu latent factor vector of user uIC subset of item-related contextual conditionsxci latent factor vector of contextual condition ciUC subset of user-related contextual conditionsycu latent factor vector of contextual condition cu average error for item ibu baseline for user uei
![Page 62: Techniques for Context-Aware and Cold-Start Recommendations](https://reader031.fdocuments.in/reader031/viewer/2022030314/589bf5a81a28ab40348b626b/html5/thumbnails/62.jpg)
PhD Thesis Defense, 28th Ph.D. Cycle, May 2016
Hybrid CARS Algorithms Feature Weighted (1/2)
23
• Feature Weighted adaptively sums the weighted predictions of the basic algorithms with weights estimated using meta-features, i.e., the number of user, item and context ratings
• Is inspired by the Feature-Weighted Linear Stacking (FWLS) algorithm (Sill et al., 2009)
• Conjecture: exploits cold-start conditions under which performance differences between the CARS algorithms can be observed
v11
a1
…
r
∑
r1 r m
∑ ∑
…
…
…
…
f1 fn f1 fn
v11 vn
1 v1m vn
m
![Page 63: Techniques for Context-Aware and Cold-Start Recommendations](https://reader031.fdocuments.in/reader031/viewer/2022030314/589bf5a81a28ab40348b626b/html5/thumbnails/63.jpg)
PhD Thesis Defense, 28th Ph.D. Cycle, May 2016
Hybrid CARS Algorithms Feature Weighted (2/2)
24
• It extends standard linear stacking, which is a method for linearly combining the predictions of different models m ∈ M:
• Feature Weighted models the weight ŵm as a linear function of some meta-features f ∈ F:
• The rating prediction function is rewritten as:
ruic1...ck = wm
m∈M∑ ruic1...ck
m
wm = v fm
f∈F∑ f (u,i,c1,...,ck )
ruic1...ck = ( v fm
f∈F∑ f (u,i,c1,...,ck ))
m∈M∑ ruic1...ck
m
ruic1...ckm
![Page 64: Techniques for Context-Aware and Cold-Start Recommendations](https://reader031.fdocuments.in/reader031/viewer/2022030314/589bf5a81a28ab40348b626b/html5/thumbnails/64.jpg)
PhD Thesis Defense, 28th Ph.D. Cycle, May 2016
Hybrid CARS Algorithms Feature Weighted (2/2)
24
• It extends standard linear stacking, which is a method for linearly combining the predictions of different models m ∈ M:
• Feature Weighted models the weight ŵm as a linear function of some meta-features f ∈ F:
• The rating prediction function is rewritten as:
ruic1...ck = wm
m∈M∑ ruic1...ck
m
wm = v fm
f∈F∑ f (u,i,c1,...,ck )
ruic1...ck = ( v fm
f∈F∑ f (u,i,c1,...,ck ))
m∈M∑ ruic1...ck
m
ruic1...ckm
![Page 65: Techniques for Context-Aware and Cold-Start Recommendations](https://reader031.fdocuments.in/reader031/viewer/2022030314/589bf5a81a28ab40348b626b/html5/thumbnails/65.jpg)
PhD Thesis Defense, 28th Ph.D. Cycle, May 2016
Hybrid CARS Algorithms Feature Weighted (2/2)
24
• It extends standard linear stacking, which is a method for linearly combining the predictions of different models m ∈ M:
• Feature Weighted models the weight ŵm as a linear function of some meta-features f ∈ F:
• The rating prediction function is rewritten as:
ruic1...ck = wm
m∈M∑ ruic1...ck
m
wm = v fm
f∈F∑ f (u,i,c1,...,ck )
ruic1...ck = ( v fm
f∈F∑ f (u,i,c1,...,ck ))
m∈M∑ ruic1...ck
m
ruic1...ckm
![Page 66: Techniques for Context-Aware and Cold-Start Recommendations](https://reader031.fdocuments.in/reader031/viewer/2022030314/589bf5a81a28ab40348b626b/html5/thumbnails/66.jpg)
PhD Thesis Defense, 28th Ph.D. Cycle, May 2016
Hybrid CARS Algorithms Feature Weighted (2/2)
24
• It extends standard linear stacking, which is a method for linearly combining the predictions of different models m ∈ M:
• Feature Weighted models the weight ŵm as a linear function of some meta-features f ∈ F:
• The rating prediction function is rewritten as:
ruic1...ck = wm
m∈M∑ ruic1...ck
m
wm = v fm
f∈F∑ f (u,i,c1,...,ck )
ruic1...ck = ( v fm
f∈F∑ f (u,i,c1,...,ck ))
m∈M∑ ruic1...ck
m
ruic1...ckm
![Page 67: Techniques for Context-Aware and Cold-Start Recommendations](https://reader031.fdocuments.in/reader031/viewer/2022030314/589bf5a81a28ab40348b626b/html5/thumbnails/67.jpg)
PhD Thesis Defense, 28th Ph.D. Cycle, May 2016
Hybrid CARS Algorithms Feature Weighted (2/2)
24
• It extends standard linear stacking, which is a method for linearly combining the predictions of different models m ∈ M:
• Feature Weighted models the weight ŵm as a linear function of some meta-features f ∈ F:
• The rating prediction function is rewritten as:
ruic1...ck = wm
m∈M∑ ruic1...ck
m
wm = v fm
f∈F∑ f (u,i,c1,...,ck )
ruic1...ck = ( v fm
f∈F∑ f (u,i,c1,...,ck ))
m∈M∑ ruic1...ck
m
ruic1...ckm
![Page 68: Techniques for Context-Aware and Cold-Start Recommendations](https://reader031.fdocuments.in/reader031/viewer/2022030314/589bf5a81a28ab40348b626b/html5/thumbnails/68.jpg)
PhD Thesis Defense, 28th Ph.D. Cycle, May 2016
Hybrid CARS Algorithms Feature Weighted (2/2)
24
• It extends standard linear stacking, which is a method for linearly combining the predictions of different models m ∈ M:
• Feature Weighted models the weight ŵm as a linear function of some meta-features f ∈ F:
• The rating prediction function is rewritten as:
ruic1...ck = wm
m∈M∑ ruic1...ck
m
wm = v fm
f∈F∑ f (u,i,c1,...,ck )
ruic1...ck = ( v fm
f∈F∑ f (u,i,c1,...,ck ))
m∈M∑ ruic1...ck
m
ruic1...ckm
![Page 69: Techniques for Context-Aware and Cold-Start Recommendations](https://reader031.fdocuments.in/reader031/viewer/2022030314/589bf5a81a28ab40348b626b/html5/thumbnails/69.jpg)
PhD Thesis Defense, 28th Ph.D. Cycle, May 2016
Evaluation Used Datasets
25
• 4 contextually-tagged rating datasets
STS (Braunhofer et al.,
2013)
CoMoDa (Odić et al.,
2013)
Music (Baltrunas et al.,
2011)
TripAdvisor (www.tripadvisor.
com)
Domain POIs Movies Music POIsRating scale 1-5 1-5 1-5 1-5Ratings 2,534 2,296 4,012 7,154Users 325 121 43 5,487Items 249 1,232 139 1,263Contextual factors 14 12 8 3Contextual conditions 57 49 26 31Contextual situations 931 1,969 26 512User attributes 7 4 10 2Item features 1 7 2 2
![Page 70: Techniques for Context-Aware and Cold-Start Recommendations](https://reader031.fdocuments.in/reader031/viewer/2022030314/589bf5a81a28ab40348b626b/html5/thumbnails/70.jpg)
PhD Thesis Defense, 28th Ph.D. Cycle, May 2016
Evaluation Evaluation Procedure
26
• Randomly divide the entities (i.e., users, items or contexts) into 10 cross-validation folds
• For each fold k = 1, 2, …, 10
• Use all the ratings except those coming from entities in fold k as training set to build the prediction models
• Calculate the Mean Absolute Error (MAE) and normalized Discounted Cumulative Gain (nDCG) on the test ratings for the entities in fold k
• Advantage: allows to test the models on really cold entities
• Disadvantage: can’t test for different degrees of coldness
![Page 71: Techniques for Context-Aware and Cold-Start Recommendations](https://reader031.fdocuments.in/reader031/viewer/2022030314/589bf5a81a28ab40348b626b/html5/thumbnails/71.jpg)
PhD Thesis Defense, 28th Ph.D. Cycle, May 2016
Results Recommendation for New Users
27
Basic CARS Algorithms
MAE
0.5
0.6
0.7
0.8
0.9
1.0
1.1
1.2
1.3
STS CoMoDa Music TripAdvisor
CAMF-CC SPF Content-CAMF-CC Demographics-CAMF-CC
* *
*
* *
* *
Hybrid CARS Algorithms
MAE
diff
to b
est b
asic
alg
orith
m-0.08-0.06-0.04-0.020.000.020.040.060.080.100.12
STS CoMoDa Music TripAdvisor
Average Weighted Heuristic SwitchingAdaptive Weighted Feature Weighted
*
Stars denote significant differences w.r.t. CAMF-CC (p < 0.05)
Stars denote significant differences w.r.t. best basic CARS algorithm(p < 0.05)
![Page 72: Techniques for Context-Aware and Cold-Start Recommendations](https://reader031.fdocuments.in/reader031/viewer/2022030314/589bf5a81a28ab40348b626b/html5/thumbnails/72.jpg)
PhD Thesis Defense, 28th Ph.D. Cycle, May 2016
Results Recommendation for New Items
28
Stars denote significant differences w.r.t. CAMF-CC (p < 0.05)
Stars denote significant differences w.r.t. best basic CARS algorithm(p < 0.05)
Basic CARS Algorithms
MAE
0.5
0.6
0.7
0.8
0.9
1.0
1.1
1.2
1.3
STS CoMoDa Music TripAdvisor
CAMF-CC SPF Content-CAMF-CC Demographics-CAMF-CC
* *
* **
*
*
*
* *
Hybrid CARS Algorithms
MAE
diff
to b
est b
asic
alg
orith
m-0.08-0.06-0.04-0.020.000.020.040.060.080.100.12
STS CoMoDa Music TripAdvisor
Average Weighted Heuristic SwitchingAdaptive Weighted Feature Weighted
* *
*
**
![Page 73: Techniques for Context-Aware and Cold-Start Recommendations](https://reader031.fdocuments.in/reader031/viewer/2022030314/589bf5a81a28ab40348b626b/html5/thumbnails/73.jpg)
PhD Thesis Defense, 28th Ph.D. Cycle, May 2016
Results Recommendation under New Contexts
29
Basic CARS Algorithms
MAE
0.5
0.6
0.7
0.8
0.9
1.0
1.1
1.2
1.3
STS CoMoDa Music TripAdvisor
CAMF-CC SPF Content-CAMF-CC Demographics-CAMF-CC
**
* *
** *
Stars denote significant differences w.r.t. CAMF-CC (p < 0.05)
Stars denote significant differences w.r.t. best basic CARS algorithm(p < 0.05)
Hybrid CARS Algorithms
MAE
diff
to b
est b
asic
alg
orith
m-0.08-0.06-0.04-0.020.000.020.040.060.080.100.12
STS CoMoDa Music TripAdvisor
Average Weighted Heuristic SwitchingAdaptive Weighted Feature Weighted
* *
**
*
* **
![Page 74: Techniques for Context-Aware and Cold-Start Recommendations](https://reader031.fdocuments.in/reader031/viewer/2022030314/589bf5a81a28ab40348b626b/html5/thumbnails/74.jpg)
PhD Thesis Defense, 28th Ph.D. Cycle, May 2016
Summary
30
Algorithm Pros ConsAverage Weighted
• Simple and fast to train • Sensitive to poorly performing basic algorithms
• Works only when all basic algorithms are performing equally well
![Page 75: Techniques for Context-Aware and Cold-Start Recommendations](https://reader031.fdocuments.in/reader031/viewer/2022030314/589bf5a81a28ab40348b626b/html5/thumbnails/75.jpg)
PhD Thesis Defense, 28th Ph.D. Cycle, May 2016
Summary
30
Algorithm Pros ConsAverage Weighted
• Simple and fast to train • Sensitive to poorly performing basic algorithms
• Works only when all basic algorithms are performing equally well
Heuristic Switching
• Simple and fast to train • Can avoid the impact of poorly performing
basic algorithms
• Depends on the manual choice of the heuristic
![Page 76: Techniques for Context-Aware and Cold-Start Recommendations](https://reader031.fdocuments.in/reader031/viewer/2022030314/589bf5a81a28ab40348b626b/html5/thumbnails/76.jpg)
PhD Thesis Defense, 28th Ph.D. Cycle, May 2016
Summary
30
Algorithm Pros ConsAverage Weighted
• Simple and fast to train • Sensitive to poorly performing basic algorithms
• Works only when all basic algorithms are performing equally well
Heuristic Switching
• Simple and fast to train • Can avoid the impact of poorly performing
basic algorithms
• Depends on the manual choice of the heuristic
Adaptive Weighted
• Adaptively combines the basic algorithms based on their strengths and weaknesses
• Complex and slow to train • Sensitive to the training set used • Optimized for error minimization • Sensitive to poorly performing basic
algorithms
![Page 77: Techniques for Context-Aware and Cold-Start Recommendations](https://reader031.fdocuments.in/reader031/viewer/2022030314/589bf5a81a28ab40348b626b/html5/thumbnails/77.jpg)
PhD Thesis Defense, 28th Ph.D. Cycle, May 2016
Summary
30
Algorithm Pros ConsAverage Weighted
• Simple and fast to train • Sensitive to poorly performing basic algorithms
• Works only when all basic algorithms are performing equally well
Heuristic Switching
• Simple and fast to train • Can avoid the impact of poorly performing
basic algorithms
• Depends on the manual choice of the heuristic
Adaptive Weighted
• Adaptively combines the basic algorithms based on their strengths and weaknesses
• Complex and slow to train • Sensitive to the training set used • Optimized for error minimization • Sensitive to poorly performing basic
algorithmsFeature Weighted
• Adaptively combines the basic algorithms based on their strengths and weaknesses
• Robust in all cold-start cases
• Complex and slow to train • Sensitive to the training set used • Optimized for error minimization
![Page 78: Techniques for Context-Aware and Cold-Start Recommendations](https://reader031.fdocuments.in/reader031/viewer/2022030314/589bf5a81a28ab40348b626b/html5/thumbnails/78.jpg)
PhD Thesis Defense, 28th Ph.D. Cycle, May 2016
Outline
31
• Context-Aware Recommenders and the Cold-Start Problem
• State of the Art
• South Tyrol Suggests Application Scenario
• Hybrid Context-Aware Recommendation Algorithms
• Active Learning for Context-Aware Recommenders
• Conclusions and Future Work
![Page 79: Techniques for Context-Aware and Cold-Start Recommendations](https://reader031.fdocuments.in/reader031/viewer/2022030314/589bf5a81a28ab40348b626b/html5/thumbnails/79.jpg)
PhD Thesis Defense, 28th Ph.D. Cycle, May 2016
• Conjecture: Active Learning (AL), which identifies the most useful items for the target user to rate, can be improved for CARSs by leveraging the user’s personality and by identifying the most useful contextual factors to be entered upon rating these items
Active Learning for CARSs
32
item ratings
item ratings request
approximatedfunction
supervised learning
Active Learning
Passive Learning
user
![Page 80: Techniques for Context-Aware and Cold-Start Recommendations](https://reader031.fdocuments.in/reader031/viewer/2022030314/589bf5a81a28ab40348b626b/html5/thumbnails/80.jpg)
PhD Thesis Defense, 28th Ph.D. Cycle, May 2016
• Conjecture: Active Learning (AL), which identifies the most useful items for the target user to rate, can be improved for CARSs by leveraging the user’s personality and by identifying the most useful contextual factors to be entered upon rating these items
Active Learning for CARSs
32
item ratings
item ratings request
approximatedfunction
supervised learning
Active Learning
Passive Learning
personality (Big-5)
user
![Page 81: Techniques for Context-Aware and Cold-Start Recommendations](https://reader031.fdocuments.in/reader031/viewer/2022030314/589bf5a81a28ab40348b626b/html5/thumbnails/81.jpg)
PhD Thesis Defense, 28th Ph.D. Cycle, May 2016
• Conjecture: Active Learning (AL), which identifies the most useful items for the target user to rate, can be improved for CARSs by leveraging the user’s personality and by identifying the most useful contextual factors to be entered upon rating these items
Active Learning for CARSs
32
item ratings
item ratings request
approximatedfunction
supervised learning
Active Learning
Passive Learning
personality (Big-5)
user
+ context data
+ context data request
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PhD Thesis Defense, 28th Ph.D. Cycle, May 2016
Using Personality in Active Learning
• Main idea: people with similar personality are likely to have similar interests (Rentfrow & Gosling, 2003), and thus the incorporation of human personality can help in predicting the items that can be rated by a user
33
Neuroticism Conscientious-ness
Openness
ExtraversionAgreeableness Big Five Personality
Traits
![Page 83: Techniques for Context-Aware and Cold-Start Recommendations](https://reader031.fdocuments.in/reader031/viewer/2022030314/589bf5a81a28ab40348b626b/html5/thumbnails/83.jpg)
PhD Thesis Defense, 28th Ph.D. Cycle, May 2016
Personality-Based Binary Prediction
• Input: Target user u. Maximum number of items to be returned N. Binary user-item rating matrix B. Candidate set of items to be rated Cu
• Output: List of M <= N top-scoring items for which user u is requested to provide ratings
34
qi latent factor vector of item ipu latent factor vector of user uA(u) set of user u’s attributes (i.e., Big-5 scores)ya latent factor vector of user attribute a average binary rating for item ibu baseline for user uxi
xui = qiT (pu + ya )
a∈A(u )∑ + xi + bu
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PhD Thesis Defense, 28th Ph.D. Cycle, May 2016
Personality-Based Binary Prediction
• Input: Target user u. Maximum number of items to be returned N. Binary user-item rating matrix B. Candidate set of items to be rated Cu
• Output: List of M <= N top-scoring items for which user u is requested to provide ratings
34
qi latent factor vector of item ipu latent factor vector of user uA(u) set of user u’s attributes (i.e., Big-5 scores)ya latent factor vector of user attribute a average binary rating for item ibu baseline for user uxi
xui = qiT (pu + ya )
a∈A(u )∑ + xi + bu
![Page 85: Techniques for Context-Aware and Cold-Start Recommendations](https://reader031.fdocuments.in/reader031/viewer/2022030314/589bf5a81a28ab40348b626b/html5/thumbnails/85.jpg)
PhD Thesis Defense, 28th Ph.D. Cycle, May 2016
Personality-Based Binary Prediction
• Input: Target user u. Maximum number of items to be returned N. Binary user-item rating matrix B. Candidate set of items to be rated Cu
• Output: List of M <= N top-scoring items for which user u is requested to provide ratings
34
qi latent factor vector of item ipu latent factor vector of user uA(u) set of user u’s attributes (i.e., Big-5 scores)ya latent factor vector of user attribute a average binary rating for item ibu baseline for user uxi
xui = qiT (pu + ya )
a∈A(u )∑ + xi + bu
![Page 86: Techniques for Context-Aware and Cold-Start Recommendations](https://reader031.fdocuments.in/reader031/viewer/2022030314/589bf5a81a28ab40348b626b/html5/thumbnails/86.jpg)
PhD Thesis Defense, 28th Ph.D. Cycle, May 2016
Parsimonious & Adaptive Context Acquisition
• Main idea: for each user-item pair (u, i), identify the contextual factors that when acquired with u’s rating for i improve most the long term performance of the recommender
• Heuristic: acquire the contextual factors that have the largest impact on rating prediction
• Challenge: how to quantify these impacts?
35
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PhD Thesis Defense, 28th Ph.D. Cycle, May 2016
CARS Prediction Model
• We use the new variant of CAMF that we already successfully employed to estimate the rating prediction accuracy of a CARS algorithm
• Advantage: allows to capture latent correlations and patterns between a potentially wide range of knowledge sources ⟹ ideal to derive the usefulness of contextual factors
36
ruic1...ck = (qi + xaa∈A(i )∪C (i )∑ )T ⋅(pu + yb
b∈A(u )∪C (u )∑ )+ ri + bu
qi latent factor vector of item iA(i) set of conventional item attributes (e.g., genre)C(i) set of contextual item attributes (e.g., weather)xa latent factor vector of item attribute apu latent factor vector of user uA(u) set of conventional user attributes (e.g., age)C(u) set of contextual user attributes (e.g., mood)yb latent factor vector of user attribute bṝi average rating for item ibu baseline for user u
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PhD Thesis Defense, 28th Ph.D. Cycle, May 2016
Largest Deviation
• Given (u, i), it first measures the “impact” of each contextual condition cj ∈ Cj
by calculating the absolute deviation between the rating prediction when the condition holds (i.e., ȓuicj) and the predicted context-free rating (i.e., ȓui):
where fcj is the normalized frequency of cj
• Finally, it computes for each factor the average of these deviation scores, and selects the contextual factors with the largest average scores
37
wuicj= fcj ruic j − rui ,
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PhD Thesis Defense, 28th Ph.D. Cycle, May 2016
Largest Deviation
• Given (u, i), it first measures the “impact” of each contextual condition cj ∈ Cj
by calculating the absolute deviation between the rating prediction when the condition holds (i.e., ȓuicj) and the predicted context-free rating (i.e., ȓui):
where fcj is the normalized frequency of cj
• Finally, it computes for each factor the average of these deviation scores, and selects the contextual factors with the largest average scores
37
wuicj= fcj ruic j − rui ,
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PhD Thesis Defense, 28th Ph.D. Cycle, May 2016
Largest Deviation
• Given (u, i), it first measures the “impact” of each contextual condition cj ∈ Cj
by calculating the absolute deviation between the rating prediction when the condition holds (i.e., ȓuicj) and the predicted context-free rating (i.e., ȓui):
where fcj is the normalized frequency of cj
• Finally, it computes for each factor the average of these deviation scores, and selects the contextual factors with the largest average scores
37
wuicj= fcj ruic j − rui ,
![Page 91: Techniques for Context-Aware and Cold-Start Recommendations](https://reader031.fdocuments.in/reader031/viewer/2022030314/589bf5a81a28ab40348b626b/html5/thumbnails/91.jpg)
PhD Thesis Defense, 28th Ph.D. Cycle, May 2016
Largest Deviation
• Given (u, i), it first measures the “impact” of each contextual condition cj ∈ Cj
by calculating the absolute deviation between the rating prediction when the condition holds (i.e., ȓuicj) and the predicted context-free rating (i.e., ȓui):
where fcj is the normalized frequency of cj
• Finally, it computes for each factor the average of these deviation scores, and selects the contextual factors with the largest average scores
37
wuicj= fcj ruic j − rui ,
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PhD Thesis Defense, 28th Ph.D. Cycle, May 2016
Experiments 1 and 2
• 2 user studies involving 108 subjects in the 1st and 51 subjects in the 2nd
• Compared personality-based binary prediction with log(popularity) * entropy and random
• Personality-based binary prediction performed best in terms of:
• Number of acquired ratings
• Rating prediction accuracy
• Quality of context-aware recommendations
38
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PhD Thesis Defense, 28th Ph.D. Cycle, May 2016
Experiment 3 Datasets
39
• 3 contextually-tagged rating datasets
CoMoDa (Odić et al.,
2013)
TripAdvisor (www.tripadvisor.
com)
STS (Braunhofer et al.,
2013)
Domain Movies POIs POIsRating scale 1-5 1-5 1-5Ratings 2,098 4,147 2,534Users 112 3,916 325Items 1,189 569 249Contextual factors 12 3 14Contextual conditions 49 31 57Avg. # of conditions / rating 12 3 1.49User attributes 4 2 7Item features 7 2 1
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PhD Thesis Defense, 28th Ph.D. Cycle, May 2016
Experiment 3 Evaluation Procedure
40
• Repeated random sub-sampling validation (20 times):
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PhD Thesis Defense, 28th Ph.D. Cycle, May 2016
Experiment 3 Evaluation Procedure
40
25% 50% 25%
Training set Candidate set Testing set
• Repeated random sub-sampling validation (20 times):
• Randomly partition the ratings into three subsets
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PhD Thesis Defense, 28th Ph.D. Cycle, May 2016
• For each user-item pair (u,i) in the candidate set, compute the N most relevant contextual factors and transfer the corresponding rating and context information ruic in the candidate set to the training set as ruic' with c' ⊆ c containing the associated contextual conditions for these factors, if any
Experiment 3 Evaluation Procedure
40
25% 50% 25%
Training set Candidate set Testing set
• Repeated random sub-sampling validation (20 times):
• Randomly partition the ratings into three subsets
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PhD Thesis Defense, 28th Ph.D. Cycle, May 2016
• For each user-item pair (u,i) in the candidate set, compute the N most relevant contextual factors and transfer the corresponding rating and context information ruic in the candidate set to the training set as ruic' with c' ⊆ c containing the associated contextual conditions for these factors, if any
Experiment 3 Evaluation Procedure
40
25% 50% 25%
Training set Candidate set Testing set
• Repeated random sub-sampling validation (20 times):
• Randomly partition the ratings into three subsets
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PhD Thesis Defense, 28th Ph.D. Cycle, May 2016
• For each user-item pair (u,i) in the candidate set, compute the N most relevant contextual factors and transfer the corresponding rating and context information ruic in the candidate set to the training set as ruic' with c' ⊆ c containing the associated contextual conditions for these factors, if any
Experiment 3 Evaluation Procedure
40
25% 50% 25%
Training set Candidate set Testing set
• Repeated random sub-sampling validation (20 times):
• Randomly partition the ratings into three subsets
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PhD Thesis Defense, 28th Ph.D. Cycle, May 2016
• For each user-item pair (u,i) in the candidate set, compute the N most relevant contextual factors and transfer the corresponding rating and context information ruic in the candidate set to the training set as ruic' with c' ⊆ c containing the associated contextual conditions for these factors, if any
Experiment 3 Evaluation Procedure
40
25% 50% 25%
Training set Candidate set Testing set
• Repeated random sub-sampling validation (20 times):
• Randomly partition the ratings into three subsets
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PhD Thesis Defense, 28th Ph.D. Cycle, May 2016
• For each user-item pair (u,i) in the candidate set, compute the N most relevant contextual factors and transfer the corresponding rating and context information ruic in the candidate set to the training set as ruic' with c' ⊆ c containing the associated contextual conditions for these factors, if any
Experiment 3 Evaluation Procedure
40
25% 50% 25%
Training set Candidate set Testing set
• Repeated random sub-sampling validation (20 times):
• Randomly partition the ratings into three subsets
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PhD Thesis Defense, 28th Ph.D. Cycle, May 2016
• For each user-item pair (u,i) in the candidate set, compute the N most relevant contextual factors and transfer the corresponding rating and context information ruic in the candidate set to the training set as ruic' with c' ⊆ c containing the associated contextual conditions for these factors, if any
Experiment 3 Evaluation Procedure
40
25% 50% 25%
Training set Candidate set Testing set
• Repeated random sub-sampling validation (20 times):
• Randomly partition the ratings into three subsets
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PhD Thesis Defense, 28th Ph.D. Cycle, May 2016
• Measure user-averaged MAE (U-MAE), Precision@10 and Recall@10 on the testing set, after training the prediction model on the new extended training set
• For each user-item pair (u,i) in the candidate set, compute the N most relevant contextual factors and transfer the corresponding rating and context information ruic in the candidate set to the training set as ruic' with c' ⊆ c containing the associated contextual conditions for these factors, if any
Experiment 3 Evaluation Procedure
40
25% 50% 25%
Training set Candidate set Testing set
• Repeated random sub-sampling validation (20 times):
• Randomly partition the ratings into three subsets
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PhD Thesis Defense, 28th Ph.D. Cycle, May 2016
• Measure user-averaged MAE (U-MAE), Precision@10 and Recall@10 on the testing set, after training the prediction model on the new extended training set
• For each user-item pair (u,i) in the candidate set, compute the N most relevant contextual factors and transfer the corresponding rating and context information ruic in the candidate set to the training set as ruic' with c' ⊆ c containing the associated contextual conditions for these factors, if any
Experiment 3 Evaluation Procedure
40
25% 50% 25%
Training set Candidate set Testing set
• Repeated random sub-sampling validation (20 times):
• Randomly partition the ratings into three subsets
• Repeat
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PhD Thesis Defense, 28th Ph.D. Cycle, May 2016
Experiment 3 Evaluation Procedure: Example
41
user-item pairtop two contextual factors
rating transferred to training set
++
=
rating in candidate set
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PhD Thesis Defense, 28th Ph.D. Cycle, May 2016
Experiment 3 Evaluation Procedure: Example
41
(Alice, Skiing)top two contextual factors
rating transferred to training set
++
=
rating in candidate set
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PhD Thesis Defense, 28th Ph.D. Cycle, May 2016
Experiment 3 Evaluation Procedure: Example
41
(Alice, Skiing)Season and Weather
rating transferred to training set
++
=
rating in candidate set
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PhD Thesis Defense, 28th Ph.D. Cycle, May 2016
Experiment 3 Evaluation Procedure: Example
41
(Alice, Skiing)Season and Weather
rating transferred to training set
rAlice Skiing Winter Sunny Warm Morning = 5++
=
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PhD Thesis Defense, 28th Ph.D. Cycle, May 2016
Experiment 3 Evaluation Procedure: Example
41
(Alice, Skiing)Season and Weather
rAlice Skiing Winter Sunny Warm Morning = 5
rAlice Skiing Winter Sunny = 5
++
=
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PhD Thesis Defense, 28th Ph.D. Cycle, May 2016
Experiment 3 Baseline Methods for Evaluation
42
• Mutual Information: given a user-item pair (u,i), computes the relevance for a contextual factor Cj as the mutual information between ratings for items belonging to i’s category (Baltrunas et al., 2012)
• Freeman-Halton Test: calculates the relevance of Cj using the Freeman-Halton test (Odić et al., 2013)
• Minimum Redundancy Maximum Relevance (mRMR): ranks each Cj according to its relevance to the rating variable and redundancy to other contextual factors (Peng et al., 2005)
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PhD Thesis Defense, 28th Ph.D. Cycle, May 2016
Experiment 3 Results: Prediction Accuracy
43
CoMoDa
U-M
AE
0.710.720.730.740.750.760.770.780.790.800.810.82
1 2 3 4
Mutual Information Freeman-Halton mRMR Largest Deviation All factors
STS
0.900.910.920.930.940.950.960.970.980.991.00
1 2 3 4
Stars denote significant improvements of Largest Deviation over the other considered algorithms (p < 0.05)
*
* * * *
* * *
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PhD Thesis Defense, 28th Ph.D. Cycle, May 2016
Experiment 3 Results: Ranking Quality
44
CoMoDa
Prec
isio
n@10
0.0000
0.0002
0.0004
0.0006
0.0008
0.0010
0.0012
0.0014
0.0016
1 2 3 4
Mutual Information Freeman-Halton mRMR Largest Deviation All factors
STS
0.0050.0060.0070.0080.0090.0100.0110.0120.0130.0140.0150.016
1 2 3 4
**
**
*
** *
Stars denote significant improvements of Largest Deviation over the other considered algorithms (p < 0.05)
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PhD Thesis Defense, 28th Ph.D. Cycle, May 2016
Experiment 3 Results: # of Acquired Conditions
45
STS
Avg
# of
acq
uire
d co
nditi
ons
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1 2 3 4
Mutual Information Freeman-Halton mRMR Largest Deviation All factors
* * * * * * * ** * *
*
Stars denote significant improvements of Largest Deviation over the other considered algorithms (p < 0.05)
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PhD Thesis Defense, 28th Ph.D. Cycle, May 2016
Outline
46
• Context-Aware Recommenders and the Cold-Start Problem
• State of the Art
• South Tyrol Suggests Application Scenario
• Hybrid Context-Aware Recommendation Algorithms
• Active Learning for Context-Aware Recommenders
• Conclusions and Future Work
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PhD Thesis Defense, 28th Ph.D. Cycle, May 2016
Conclusions
• Novel hybrid recommendation algorithms that, in many cases, effectively alleviate the cold-start problem of CARS
• New personality-based Active Learning rating acquisition algorithm that can better estimate what items a (new) user is able to rate
• Novel parsimonious and adaptive context acquisition algorithm that can identify what contextual factors to acquire from the user upon rating an item, thus minimizing the user’s rating effort
• Comprehensive evaluation of the proposed solutions in cold-start scenarios
47
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PhD Thesis Defense, 28th Ph.D. Cycle, May 2016
Future Work
• Additional experiments and datasets
• Improvement of proposed algorithms
• Proactive Active Learning
• Sequential Active Learning
• Gamification approaches
48
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PhD Thesis Defense, 28th Ph.D. Cycle, May 2016
Publications Journal Papers
Fernández-Tobías, I., Braunhofer, M., Elahi, M., Cantador, I., & Ricci, F. (2016). Alleviating the New User Problem in Collaborative Filtering by Exploiting Personality Information. User Modeling and User-Adapted Interaction, 1-35. http://dx.doi.org/10.1007/s11257-016-9172-z
Braunhofer, M., Elahi, M., & Ricci, F. (2014). Techniques for cold-starting context-aware mobile recommender systems for tourism. Intelligenza Artificiale, 8(2), 129-143. http://dx.doi.org/10.3233/IA-140069
Braunhofer, M., Kaminskas, M., & Ricci, F. (2013). Location-aware music recommendation. International Journal of Multimedia Information Retrieval, 2(1), 31-44. http://dx.doi.org/10.1007/s13735-012-0032-2
49
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PhD Thesis Defense, 28th Ph.D. Cycle, May 2016
Publications Conference Papers
Nasery, M., Braunhofer, M., & Ricci, F. (2016). Recommendations with Optimal Combination of Feature-Based and Item-Based Preferences. To appear in User Modeling, Adaptation, and Personalization. Halifax, Canada: Springer International Publishing
Braunhofer, M., & Ricci, F. (2016). Contextual Information Elicitation in Travel Recommender Systems. In Information and Communication Technologies in Tourism 2016 (pp. 579-592). Bilbao, Spain: Springer International Publishing. http://dx.doi.org/10.1007/978-3-319-28231-2_42 (Second Best Research Paper Award)Braunhofer, M., Elahi, M., & Ricci, F. (2015). User Personality and the New User Problem in a Context-Aware Points of Interest Recommender System. In Information and Communication Technologies in Tourism 2015 (pp. 537-549). Lugano, Switzerland: Springer International Publishing. http://dx.doi.org/10.1007/978-3-319-14343-9_39
Braunhofer, M., Elahi, M., & Ricci, F. (2014). Usability Assessment of a Context-Aware and Personality-Based Mobile Recommender System. In E-Commerce and Web Technologies (pp. 77-88). Munich, Germany: Springer International Publishing. http://dx.doi.org/10.1007/978-3-319-10491-1_9
Braunhofer, M., Elahi, M., Ge, M., & Ricci, F. (2014). Context Dependent Preference Acquisition with Personality-Based Active Learning in Mobile Recommender Systems. In Learning and Collaboration Technologies. Technology-Rich Environments for Learning and Collaboration, Held as Part of HCI International 2014 (pp. 105-116). Heraklion, Crete, Greece: Springer International Publishing. http://dx.doi.org/10.1007/978-3-319-07485-6_11
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PhD Thesis Defense, 28th Ph.D. Cycle, May 2016
Publications Conference Papers (contd.)
Braunhofer, M., Codina, V., & Ricci, F. (2014). Switching hybrid for cold-starting context-aware recommender systems. In Proceedings of the 8th ACM Conference on Recommender systems (pp. 349-352). Foster City, Silicon Valley, California, USA: ACM. http://dx.doi.org/10.1145/2645710.2645757
Braunhofer, M., Elahi, M., Ricci, F., & Schievenin, T. (2013). Context-aware points of interest suggestion with dynamic weather data management. In Information and Communication Technologies in Tourism 2014 (pp. 87-100). Dublin, Ireland: Springer International Publishing. http://dx.doi.org/10.1007/978-3-319-03973-2_7
Elahi, M., Braunhofer, M., Ricci, F., & Tkalcic, M. (2013). Personality-based active learning for collaborative filtering recommender systems. In AI*IA 2013: Advances in Artificial Intelligence (pp. 360-371). Turin, Italy: Springer International Publishing. http://dx.doi.org/10.1007/978-3-319-03524-6_31
Enrich, M., Braunhofer, M., & Ricci, F. (2013). Cold-Start Management with Cross-Domain Collaborative Filtering and Tags. In E-Commerce and Web Technologies (pp. 101-112). Prague, Czech Republic: Springer Berlin Heidelberg. http://dx.doi.org/10.1007/978-3-642-39878-0_10
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PhD Thesis Defense, 28th Ph.D. Cycle, May 2016
Publications Workshop, Demo & Doctoral Consortium Papers
Braunhofer, M., Fernández-Tobías, I., & Ricci, F. (2015). Parsimonious and Adaptive Contextual Information Acquisition in Recommender Systems. In Proceedings of the Joint Workshop on Interfaces and Human Decision Making for Recommender Systems, IntRS 2015, co-located with ACM Conference on Recommender Systems (RecSys 2015). Vienna, Austria: ACM.
Braunhofer, M., Ricci, F., Lamche, B., & Wörndl, W. (2015). A Context-Aware Model for Proactive Recommender Systems in the Tourism Domain. In Proceedings of the 17th International Conference on Human-Computer Interaction with Mobile Devices and Services Adjunct (pp. 1070-1075). Copenhagen, Denmark: ACM. http://dx.doi.org/10.1145/2786567.2794332
Braunhofer, M. (2014). Hybridisation techniques for cold-starting context-aware recommender systems. In Proceedings of the 8th ACM Conference on Recommender systems, Doctoral Symposium (pp. 405-408). Foster City, Silicon Valley, California, USA: ACM. http://dx.doi.org/10.1145/2645710.2653360
Braunhofer, M. (2014). Hybrid solution of the cold-start problem in context-aware recommender systems. In User Modeling, Adaptation, and Personalization, Doctoral Consortium (pp. 484-489). Aalborg, Denmark: Springer International Publishing. http://dx.doi.org/10.1007/978-3-319-08786-3_44
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PhD Thesis Defense, 28th Ph.D. Cycle, May 2016
Publications Workshop, Demo & Doctoral Consortium Papers (contd.)
Braunhofer, M., Elahi, M., & Ricci, F. (2014). STS: A Context-Aware Mobile Recommender System for Places of Interest. In Extended Proceedings of User Modeling, Adaptation, and Personalization (pp. 75-80). Aalborg, Denmark.
Braunhofer, M., Elahi, M., Ge, M., Ricci, F., & Schievenin, T. (2013). STS: Design of Weather-Aware Mobile Recommender Systems in Tourism. In Proceedings of the First International Workshop on Intelligent User Interfaces: Artificial Intelligence meets Human Computer Interaction (AI*HCI 2013). A workshop of the XIII International Conference of the Italian Association for Artificial Intelligence (AI*IA 2013). Turin, Italy.
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PhD Thesis Defense, 28th Ph.D. Cycle, May 2016
Questions?
Thank you.