CN112836130A - Context-aware recommendation system and method based on federated learning - Google Patents

Context-aware recommendation system and method based on federated learning Download PDF

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CN112836130A
CN112836130A CN202110192913.8A CN202110192913A CN112836130A CN 112836130 A CN112836130 A CN 112836130A CN 202110192913 A CN202110192913 A CN 202110192913A CN 112836130 A CN112836130 A CN 112836130A
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邵杰
阿里·瓦格尔
王衍松
邓智毅
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Abstract

The invention discloses a context awareness recommendation system and method based on federal learning, which provides a user-defined data cooperation protocol module, splices user scoring data and context information through the module to obtain user data containing the context information and sends the user data to a client. The client trains a local recommendation model according to the user data and the server weight parameters, and sends the local model weight parameters to the central server. And the central server aggregates the local model weight parameters of all the clients to obtain new server weight parameters, and completes a round of training. And training the local recommendation model for multiple times until the local recommendation model converges. And the trained local recommendation model is used for processing the new user data to obtain the recommendation content of the user. According to the invention, the federal learning technology is applied to the recommendation system, and the context information is combined in the recommendation system, so that the higher recommendation accuracy is realized while the user privacy is protected.

Description

Context-aware recommendation system and method based on federated learning
Technical Field
The invention relates to the field of recommendation systems, in particular to a context-aware recommendation system and method based on federal learning.
Background
In the field of recommendation systems, the traditional privacy protection methods mainly include data anonymization, encryption technology and differential privacy. The data anonymization technology is a method for carrying out anonymization processing on data in a data set, firstly, attributes of each piece of data are divided into 3 classes, identification attributes of an individual are uniquely identified, and standard identification attributes and sensitive attributes needing to be protected of the individual can be determined by combining the identification attributes. The identification attribute of the data set after anonymization processing is hidden, and meanwhile, the identification attribute is aligned to perform certain fuzzification (such as changing the age into a range, removing the last two digits of a zip code and the like) so that sensitive data is protected. The encryption technology requires a large additional calculation cost, complicated steps and a low overall resource utilization rate. The differential privacy technology is a privacy protection method which is popular in recent years, noise is added into a data set, so that even if the data set is changed in a small range, the probability distribution of result values obtained by inquiring the data set is basically unchanged, and information leakage caused by differential attack is effectively prevented. However, similar to data anonymization, differential privacy requires a large amount of randomization to be added to the query results, resulting in a drastic drop in data availability and a loss of information contained in the data.
The traditional privacy protection method plays a certain role in protecting user data, but when the methods are applied to a recommendation system, huge calculation overhead is caused, the accuracy of results is greatly influenced, and the training iterative upgrade process of artificial intelligence algorithms such as a recommendation algorithm cannot be well fitted. Federal learning, which is rapidly developed in recent years, is just a training framework suitable for privacy protection in deep learning. It was proposed by google researcher McMahan et al in 2016. Initially used to train a handset input prediction model without the user data leaving the home. Later, its central idea was refined and called federal learning. The Federal learning assumption comprises a plurality of training participants and a central server, the central server distributes the model to each participant, and the participants only need to train locally and return updated model parameters to the central server to complete a model updating process. Federal learning ensures that user data does not leave the user local storage device, and the privacy protection capability is greatly improved.
In addition, in the field of recommendation systems, context-aware recommendation systems have gained widespread attention. It is noted that the user's selection is not only dependent on people with similar interests, but also closely related to the context information when selecting a particular item, such as time, location, social interaction, etc. when selecting. Working as an early proxy, 'Adomavicius G, Sankaranarayana R, Sen S, et al, incorporation textual Information in recommendation Systems using a multidimensional analysis of Information J. ACM Transformations On Information Systems (TOIS),2005,23(1):103-145,' introduces the importance of contextual Information and a multidimensional method to incorporate contextual Information into the recommendation process. Meanwhile, the importance of the time dynamics of the data set to the recommendation result is gradually noticed, and some work of integrating the time features into the recommendation model also achieves good results. Recently, many researchers have taken advantage of deep learning to make context-based recommendations. In addition to the importance of contextual information in deep learning models, privacy disclosure is a major drawback from the user's perspective. Serious consequences can arise if the recommender system has full access to all of the contextual attributes and the attackers can collectively obtain or infer such information.
Therefore, applying the federal learning framework in recommendation system algorithms to improve privacy protection is a natural idea. The early representatives worked on the federal collaborative filtering recommendation model, which was thought to be very simple, separating the item vector from the user vector, with the item vector being located on a central server and the user vector being stored locally on the user. Subsequently, there are also algorithms based on meta-learning to make joint recommendations. Recently, the paper 'Tan B, Liu B, Zheng V, et al.A Federated Recommender System for on-line Services [ C ]// Fourtenth ACM Conference on Recommender systems.2020:579 @ 581' proposes a Federated recommendation System for Online Services that trains recommendation models based on data from multiple parties without exposing personal information of each party. The model includes a data layer, an algorithm layer, a service layer, and an interface layer. Authors also discuss various online applications such as content recommendations, product recommendations, and online advertising through the proposed model. Meanwhile, the paper ' Muhammad K, Wang Q, O ' Reilly-Morgan D, et al.Fedfast: Going beyond average for failure training of fed recognized systems [ C ]// Proceedings of the 26th ACM SIGKDD International Conference on Knowledge Discovery & Data mining.2020:1234-1242 ' proposes another technique to accelerate the distributed learning of recommended tasks. It completes the early training process by sampling from a group of different customers in each training run and applying active aggregation to propagate the updated model to other customers. While some existing approaches have utilized federal learning to improve the reliability of recommendations, they do not make good use of contextual information.
Disclosure of Invention
Aiming at the defects in the prior art, the context-aware recommendation system and method based on the federal learning provided by the invention solve the problem that the existing recommendation system using the federal learning framework does not well utilize the context information by applying the federal learning technology to the recommendation system and combining the context information in the recommendation system, and the invention realizes that the privacy of users is protected and simultaneously has higher recommendation accuracy.
In order to achieve the purpose of the invention, the invention adopts the technical scheme that: a federal learning based context aware recommendation system comprising: a central server and a plurality of clients;
the central server is respectively connected with a plurality of clients; the central server comprises: a global recommendation model; each of the clients includes thereon: a local recommendation model and a user-defined data cooperation protocol module;
the local recommendation model is used for performing federal learning training by using user data output by a user defined protocol (UDCP) and model weight parameters sent by the global recommendation model to obtain a trained local recommendation model; and the trained local recommendation model is used for processing new user data to obtain the recommendation content of the user.
Further, the user-defined data cooperation protocol module is used for splicing the user context information, the article context information, the scoring history and the time records of the scoring history to obtain user data containing the context information, a user can freely select whether the spliced data contains the user context information or the article context information in the process, and then the module sends the user data to each client during each iteration; each client is used for training a local recommendation model according to the user data and the server model weight parameters sent by the global recommendation model of the central server, completing one-time training of the local recommendation model, and sending the obtained local model weight parameters to the central server; the global recommendation model of the central server is used for aggregating the local model weight parameters sent by all the clients to obtain new server model weight parameters, sending the new server model weight parameters to the local recommendation model, performing secondary training on the local recommendation model, and training the local recommendation model for multiple times until the local recommendation model converges to obtain a trained local recommendation model; and the trained local recommendation model is used for processing new user data to obtain the recommendation content of the user.
The beneficial effects of the above further scheme are: the user-defined data cooperation protocol module effectively utilizes various context information, and associates the context information with the historical scoring behavior data of the user, so that the availability of the user data is greatly enhanced. Meanwhile, the most important point is that the user can control the specific degree of combination of personal data and the recommended model through the user-defined data cooperation protocol module, so that the personal privacy of the user is protected.
Further, the loss function of the local recommendation model is:
Figure BDA0002945858840000051
wherein L isi(θ) is the average loss function of the ith local recommendation model over all samples of the ith user, DiRepresenting items scored by a user
Figure BDA0002945858840000052
The total number of (a) and (b),
Figure BDA0002945858840000053
to input the local recommendation model during the training process,
Figure BDA0002945858840000054
j is the number of the local data,
Figure BDA0002945858840000055
the local model weight parameter for the t-th iteration,
Figure BDA0002945858840000056
is the MSE Loss function.
Further, the local model weight parameter
Figure BDA0002945858840000057
The calculation formula at each client is:
Figure BDA0002945858840000058
Figure BDA0002945858840000059
wherein,
Figure BDA00029458588400000510
is the directional weight parameter for the t-1 th iteration, alpha is the learning rate,
Figure BDA00029458588400000511
is a gradient factor, beta is a learning rate,
Figure BDA00029458588400000512
for a test set containing context-embedded information,
Figure BDA00029458588400000513
a training set containing context embedded information.
Further, the calculation formula of the server-side model weight parameter is as follows:
Figure BDA00029458588400000514
Figure BDA00029458588400000515
wherein,
Figure BDA00029458588400000516
a server model weight parameter for the t-th iteration, N is the number of clients, WiThe weight occupied by each client is large.
A context-aware recommendation method based on federated learning comprises the following steps:
s1, constructing a user-defined data cooperation protocol module between the local data and the local recommendation model of each client;
s2, splicing user context information, article context information, scoring history and time records of the scoring history in the local data by adopting a user-defined data cooperation protocol module to obtain user data;
s3, distributing the initial value of the server model weight parameter to each client through the central server;
s4, inputting the initial values of the user data and the server model weight parameters into a local recommendation model of the client, and training the local recommendation model;
s5, sending the local model weight parameters obtained by training on the local recommendation model back to the central server;
s6, receiving the local model weight parameters sent back by all the clients through the central server, carrying out aggregation processing on all the local model weight parameters through a weighting method based on the global recommendation model to obtain cached server model weight parameters, and taking the cached server model weight parameters as new server model weight parameter initial values;
s7, jumping to the step S3, and circularly executing the step S3 to the step S6 until the local recommendation model converges, and ending the federal learning process to obtain a trained local recommendation model;
and S8, inputting the new user data into the trained local recommendation model to obtain the recommendation content of the user.
In conclusion, the beneficial effects of the invention are as follows:
(1) the traditional recommendation system is combined with federal learning which has great effect on user privacy protection, and the recommendation system using context sensing is built under a federal learning framework, so that personal data of a user can be stored locally, a recommendation model provider does not need to upload the personal data to complete a training process, and a result with the same recommendation accuracy as that of the traditional method or even better can be obtained.
(2) The user-defined data collaboration protocol module can combine various context information of the user with data of the user, and usability of the user data is enhanced to the great extent. The user can control the specific degree of combination of personal data and the recommendation model through the user-defined data cooperation protocol module, so that the personal privacy of the user is protected, the initiative of the user on the use of the personal data is enhanced, and the use of the personal data in the recommendation process is clearer and more reasonable.
Drawings
FIG. 1 is a system block diagram of a context-aware recommendation system based on federated learning;
FIG. 2 is a connection diagram of a user-defined data collaboration protocol module;
FIG. 3 is a flow chart of a context-aware recommendation method based on federated learning;
FIG. 4(a) is a comparison graph of the mean absolute error MAE obtained by the experiment using the data set Ml-100K;
FIG. 4(b) is a comparison graph of the mean absolute error MAE obtained by the data set Ml-latest-small experiment;
FIG. 4(c) is a comparison of the root mean square error RMSE obtained using the Ml-100K data set experiment;
FIG. 4(d) is a graph comparing the root mean square error RMSE obtained from the data set Ml-latest-small experiment;
FIG. 4(e) is a comparison graph of nDCG indexes obtained by the experiment using the data set Ml-100K;
FIG. 4(f) is a comparison graph of nDCG indexes obtained by the data set Ml-latest-small experiment.
Detailed Description
The following description of the embodiments of the present invention is provided to facilitate the understanding of the present invention by those skilled in the art, but it should be understood that the present invention is not limited to the scope of the embodiments, and it will be apparent to those skilled in the art that various changes may be made without departing from the spirit and scope of the invention as defined and defined in the appended claims, and all matters produced by the invention using the inventive concept are protected.
1-2, a context-aware recommendation system based on federated learning includes: a central server and a plurality of clients;
the central server is respectively connected with a plurality of clients; the central server comprises: a global recommendation model; each of the clients includes thereon: a local recommendation model and a user-defined data cooperation protocol module;
the local recommendation model is used for performing federal learning training by using user data output by a user defined protocol (UDCP) and model weight parameters sent by the global recommendation model to obtain a trained local recommendation model; and the trained local recommendation model is used for processing new user data to obtain the recommendation content of the user.
The user-defined data cooperation protocol module is used for splicing the user context information, the article context information, the grading history and the time records of the grading history to obtain user data containing the context information, a user can freely select whether the spliced data contains the user context information or the article context information in the process, and then the module sends the user data to each client side during each iteration; each client is used for training a local recommendation model according to the user data and the server model weight parameters sent by the global recommendation model of the central server, completing one-time training of the local recommendation model, and sending the obtained local model weight parameters to the central server; the global recommendation model of the central server is used for aggregating the local model weight parameters sent by all the clients to obtain new server model weight parameters, sending the new server model weight parameters to the local recommendation model, performing secondary training on the local recommendation model, and training the local recommendation model for multiple times until the local recommendation model converges to obtain a trained local recommendation model; and the trained local recommendation model is used for processing new user data to obtain the recommendation content of the user.
The user-defined data cooperation protocol module effectively utilizes various context information, and associates the context information with the historical scoring behavior data of the user, so that the availability of the user data is greatly enhanced. Meanwhile, the most important point is that the user can control the specific degree of combination of personal data and the recommendation model through the user-defined data cooperation protocol module, so that the personal privacy of the user is protected.
The penalty function for the local recommendation model is:
Figure BDA0002945858840000091
wherein L isi(θ) is the average loss function of the ith local recommendation model over all samples of the ith user, DiRepresenting items scored by a user
Figure BDA0002945858840000092
The total number of (a) and (b),
Figure BDA0002945858840000093
to input the local recommendation model during the training process,
Figure BDA0002945858840000094
j is the number of the local data,
Figure BDA0002945858840000095
the local model weight parameter for the t-th iteration,
Figure BDA0002945858840000096
is the MSE Loss function.
Local model weight parameters
Figure BDA0002945858840000097
The calculation formula at each client is:
Figure BDA0002945858840000098
Figure BDA0002945858840000099
wherein,
Figure BDA00029458588400000910
is the directional weight parameter for the t-1 th iteration, alpha is the learning rate,
Figure BDA00029458588400000911
is a gradient factor, beta is a learning rate,
Figure BDA00029458588400000912
for a test set containing context-embedded information,
Figure BDA00029458588400000913
a training set containing context embedded information.
The calculation formula of the server-side model weight parameter is as follows:
Figure BDA00029458588400000914
Figure BDA00029458588400000915
wherein,
Figure BDA0002945858840000101
a server model weight parameter for the t-th iteration, N is the number of clients, WiThe weight occupied by each client is large.
As shown in fig. 3, a context-aware recommendation method based on federal learning includes the following steps:
s1, constructing a user-defined data cooperation protocol module between the local data and the local recommendation model of each client;
s2, splicing user context information, article context information, scoring history and time records of the scoring history in the local data by adopting a user-defined data cooperation protocol module to obtain user data;
s3, distributing the initial value of the server model weight parameter to each client through the central server;
s4, inputting the initial values of the user data and the server model weight parameters into a local recommendation model of the client, and training the local recommendation model;
s5, sending the local model weight parameters obtained by training on the local recommendation model back to the central server;
s6, receiving the local model weight parameters sent back by all the clients through the central server, carrying out aggregation processing on all the local model weight parameters through a weighting method based on the global recommendation model to obtain cached server model weight parameters, and taking the cached server model weight parameters as new server model weight parameter initial values;
s7, jumping to the step S3, and circularly executing the step S3 to the step S6 until the local recommendation model converges, and ending the federal learning process to obtain a trained local recommendation model;
and S8, inputting the new user data into the trained local recommendation model to obtain the recommendation content of the user.
Experiment:
the effect of the invention is verified on two public data sets Ml-100K and Ml-latest-small.
Ml-latest-small dataset: the data set contains 670 users' scores for 9742 movies, ranging from 0.5 to 5, with a score interval of 0.5.
The Ml-100K data set contained 100000 scores provided by 943 users for 1682 different movies. Each user rated at least 20 movies on a scale of 1 to 5. In addition, user information (such as age, gender, occupation) and item information (such as genre, release date, and IMDb URL) for the movie are provided.
In order to illustrate the superiority of the method (Feded learning based Context-Aware Recommendar System, hereinafter referred to as Fed-CARS) provided by the invention in comparison with the prediction accuracy and ranking performance of other common recommendation System technologies, the method is evaluated by using open source software CaseRecommendar. The application mainly adopts the following recommendation system technologies as comparison baselines:
BPR: bayes personalized ranking is an algorithm designed for implicit feedback, and a potential factor model is optimized by adopting pairwise ranking loss.
POP: the most popular recommendation algorithms are recommendation techniques that are very common in the e-commerce field and medium-scale recommendation engines. It predicts the ranking of users based on their popularity and the items.
UserKNN: a well-known collaborative filtering technique based on user similarity is used to find nearest neighbor users whose favorite items are recommended to the users.
ItemKNN: a well-known collaborative filtering technique based on item similarity is used to find nearest neighbor items to recommend to a user.
PaCo: a recommendation algorithm based on joint clustering has high expandability and anti-noise capability. It is an extension of k-means and agglomerative hierarchical clustering methods.
For the evaluation index of the algorithm, the application decides to adopt the average absolute error (MAE) and the Root Mean Square Error (RMSE) which are widely applied. In addition, in order to more accurately measure the performance of the algorithm in the aspect of ranking evaluation, normalized discounted cumulative gain (nDCG), a performance evaluation method widely used in a recommendation system, is used. The equations for Mean Absolute Error (MAE) and Root Mean Square Error (RMSE) are as follows:
Figure BDA0002945858840000121
Figure BDA0002945858840000122
MAE estimates the distance between the predicted ranking PR and the actual ranking AR of each user item pairAverage absolute deviation of (d). Here, PRuiRepresenting a predicted ranking, AR, of user u for item iuiThe actual ranking is represented. RMSE reflects the degree of deviation between the estimated and actual rankings. The error is squared before it is summed, thus penalizing more for large deviations. The lower these two metrics reflect the higher the prediction accuracy of the recommendation algorithm.
Figure BDA0002945858840000123
The nDCG index is obtained by calculating the ranking of the articles i on n positions and then adding the ranking to the reciprocal of the articles i. Here, N is the number of instances of the ranking that each user in the query set considers as top-N, and N is the number of users in the test data set. The factor mi is 1 if the item is present in the appropriate position in the predicted top n list, and 0 otherwise. R is based on a truly ordered list of recommended items, which means that all truly recommended or purchased items have a smaller index value than non-purchased items. The divided IDCG is ideally the maximum DCG value, which is calculated as follows:
Figure BDA0002945858840000124
the final experimental results are shown in table 1 below:
Figure BDA0002945858840000131
TABLE 1
The bold type indicates that each item works best, and the underlined value indicates that each item works second best. Compared with some traditional or widely-used methods at present, the method provided by the invention has good performance on the precision of the recommendation result. Furthermore, it is also emphasized that the present invention is implemented in a manner that preserves user privacy.
Meanwhile, the utility of the user-defined data cooperation protocol module is verified. This experiment included 3 cases: the first is the invention (symbol: Fed-CARS), the second is the invention which adopts user context information, article context information, time record of scoring history and scoring history, the third is the invention which adopts single user context information (symbol: Fed-CARS-user), and the third is the invention which adopts single article context information (symbol: Fed-CARS-user). The curve trends in fig. 4(a) -4 (f) show that the Fed-CARS with both user context and commodity context achieves lower error rates on both MAE and RMSE indices in all training rounds of model update. In terms of ranking performance, Fed-CARS has slightly improved nDCG values compared to the version without context information.

Claims (6)

1. A federated learning-based context-aware recommendation system, comprising: a central server and a plurality of clients;
the central server is respectively connected with a plurality of clients; the central server comprises: a global recommendation model; each of the clients includes thereon: a local recommendation model and a user-defined data cooperation protocol module;
the local recommendation model is used for performing federal learning training by using user data output by the user-defined data cooperation protocol module and the server model weight parameters sent by the global recommendation model to obtain a trained local recommendation model; and the trained local recommendation model is used for processing new user data to obtain the recommendation content of the user.
2. The context-aware recommendation system based on federated learning of claim 1, wherein the user-defined data collaboration protocol module is configured to splice user context information, item context information, score history and time records of the score history to obtain user data containing the context information, a user can freely select whether the spliced data contains the user context information or the item context information during the process, and then the module sends the user data to each client during each iteration; each client is used for training a local recommendation model according to the user data and the server model weight parameters sent by the global recommendation model of the central server, completing one-time training of the local recommendation model, and sending the obtained local model weight parameters to the central server; the global recommendation model of the central server is used for aggregating the local model weight parameters sent by all the clients to obtain new server model weight parameters, sending the new server model weight parameters to the local recommendation model, performing secondary training on the local recommendation model, and training the local recommendation model for multiple times until the local recommendation model converges to obtain a trained local recommendation model; and the trained local recommendation model is used for processing new user data to obtain the recommendation content of the user.
3. The federated learning-based context-aware recommendation system of claim 2, wherein the loss function of the local recommendation model is:
Figure FDA0002945858830000021
wherein L isi(θ) is the average loss function of the ith local recommendation model over all samples of the ith user, DiRepresenting items scored by a user
Figure FDA0002945858830000022
The total number of (a) and (b),
Figure FDA0002945858830000023
to input the local recommendation model during the training process,
Figure FDA0002945858830000024
j is the number of the local data,
Figure FDA0002945858830000025
the local model weight parameter for the t-th iteration,
Figure FDA0002945858830000026
is the MSE Loss function.
4. The federated learning-based context-aware recommendation system of claim 3, wherein the local model weight parameter
Figure FDA0002945858830000027
The calculation formula at each client is:
Figure FDA0002945858830000028
Figure FDA0002945858830000029
wherein,
Figure FDA00029458588300000210
is the directional weight parameter for the t-1 th iteration, alpha is the learning rate,
Figure FDA00029458588300000211
is a gradient factor, beta is a learning rate,
Figure FDA00029458588300000212
for a test set containing context-embedded information,
Figure FDA00029458588300000213
a training set containing context embedded information.
5. The context-aware recommendation system based on federated learning according to claim 4, wherein the calculation formula of the server-side model weight parameter is:
Figure FDA00029458588300000214
Figure FDA00029458588300000215
wherein,
Figure FDA0002945858830000031
a server model weight parameter for the t-th iteration, N is the number of clients, WiThe weight occupied by each client is large.
6. A context-aware recommendation method based on federated learning is characterized by comprising the following steps:
s1, constructing a user-defined data cooperation protocol module between the local data and the local recommendation model of each client;
s2, splicing user context information, article context information, scoring history and time records of the scoring history in the local data by adopting a user-defined data cooperation protocol module to obtain user data;
s3, distributing the initial value of the server model weight parameter to each client through the central server;
s4, inputting the initial values of the user data and the server model weight parameters into a local recommendation model of the client, and training the local recommendation model;
s5, sending the local model weight parameters obtained by training on the local recommendation model back to the central server;
s6, receiving the local model weight parameters sent back by all the clients through the central server, carrying out aggregation processing on all the local model weight parameters through a weighting method based on the global recommendation model to obtain cached server model weight parameters, and taking the cached server model weight parameters as new server model weight parameter initial values;
s7, jumping to the step S3, and circularly executing the step S3 to the step S6 until the local recommendation model converges, and ending the federal learning process to obtain a trained local recommendation model;
and S8, inputting the new user data into the trained local recommendation model to obtain the recommendation content of the user.
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