CN115033780A - Privacy protection cross-domain recommendation system based on federal learning - Google Patents

Privacy protection cross-domain recommendation system based on federal learning Download PDF

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CN115033780A
CN115033780A CN202210484040.2A CN202210484040A CN115033780A CN 115033780 A CN115033780 A CN 115033780A CN 202210484040 A CN202210484040 A CN 202210484040A CN 115033780 A CN115033780 A CN 115033780A
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赵鑫
田长鑫
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Renmin University of China
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Abstract

The invention discloses a privacy protection cross-field recommendation system based on federal learning, which comprises the following steps: s1: private updating in a single domain, namely fusing user global and local preferences through a graph migration module, and locally updating the global and local preferences by a gradient descent algorithm based on data in the domain; s2: after private updating, collaborative learning of global user preferences based on multi-domain data is performed by adopting a federal updating process, and the global preferences are adapted to heterogeneous domain data through personalized aggregation; s3: the use of a periodic synchronization mechanism reduces communication costs. The privacy protection cross-domain recommendation system based on federal learning provided by the application protects user privacy information from multiple layers. In the invention, the original interaction data of each domain is locally stored in the private space of the domain and is not uploaded to other domains, so that the risk of privacy disclosure can be effectively reduced.

Description

Privacy protection cross-domain recommendation system based on federal learning
Technical Field
The invention relates to the field of artificial intelligence natural language processing and the field of recommendation systems, in particular to a privacy protection cross-field recommendation system based on federal learning.
Background
In modern recommendation systems, it has become a technical trend to develop multi-domain recommendation services to meet different user requirements. In order to improve multi-domain services of information systems, cross-domain recommendation is increasingly concerned by research and industry, and the purpose of the problem is to utilize useful information in other domains to improve the recommendation quality in target domains. A typical cross-domain recommendation method is to establish a connection between different domains mainly by overlapping users/items and to transfer useful information between these domains. In this study we are concerned with collaborative cross-domain recommendations without auxiliary interaction data, which tend to apply classical machine learning techniques, either directly share or indirectly map user/item embedding, or capture cross-domain common patterns.
Existing cross-domain recommendation methods, while effective, typically rely on a strong assumption that all or part of the user item interaction data can be accessed between different domains. However, this assumption may not be realistic in practice due to business competition and privacy issues. For example, application data from different domains often belong to different companies or departments, and these data cannot be directly shared. Furthermore, recent data protection legislation, such as GDPR and the like, places severe restrictions on the storage and sharing of privacy-sensitive user data. The above privacy and security issues severely limit the practical application of existing cross-domain recommendation methods. Recently, some studies propose cross-domain recommendation models that consider privacy, but these approaches either ignore the heterogeneity of different domain data or fail to achieve consistent improvements for all users. Aiming at the defects of the existing cross-domain recommendation method, the invention provides a privacy protection cross-domain recommendation system based on federal learning.
The information disclosed in this background section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.
Disclosure of Invention
The invention aims to provide a privacy protection cross-domain recommendation system based on federal learning. Specifically, for each domain, a domain-specific user-item interaction graph (user-entry interaction graph) is constructed according to user interaction data of the domain, global and local user nodes are set to model global and local user preferences, and edges connecting the global and local user nodes are added. Based on the user-project diagram, the invention designs a federal cross-domain recommendation model. In order to learn cross-domain recommendation knowledge in a privacy-protecting manner, each training iteration of the cross-domain recommendation model provided by the invention is composed of a private updating process in a local domain and a federal updating process across multiple domains. In the private updating process, a Graph transfer module (Graph transfer module) is designed for each domain to perform bidirectional message exchange and propagation, so that the global preference and the local preference of a user are fused. Then, during the federal update, each domain applies Local Differential Privacy (LDP) techniques to the learned global user preferences and shares them to other domains. Meanwhile, each domain receives global user preference from other domains, and then the global user preference is updated locally through the personalized aggregation strategy, so that the self-adaption of the user preference in a specific domain is realized. Therefore, the cross-domain recommendation model provided by the invention can effectively approach a multi-domain training process, and the process directly shares local interactive data in a privacy protection mode. In addition, the invention provides a periodic synchronization mechanism to reduce communication cost brought by learning of cross-domain global preference.
In order to achieve the purpose, the invention adopts the following technical scheme:
the invention provides a privacy protection cross-field recommendation system based on federal learning, which comprises the following steps:
s1: private updating in a single domain, namely fusing user global and local preferences through a graph migration module, and locally updating the global and local preferences by a gradient descent algorithm based on data in the domain;
s2: after private updating, collaborative learning of global user preferences based on multi-domain data is performed by adopting a federal updating process, and the global preferences are adapted to heterogeneous domain data through personalized aggregation;
s3: the use of a periodic synchronization mechanism reduces communication costs.
As a further technical solution, the graph migration module in step S1 specifically is:
for each domain, constructing a domain-specific user-item interaction graph (as shown in FIG. 3) according to the user interaction data of the domain, setting global and local user nodes to model global and local user preferences, and adding edges connecting the global and local user nodes; wherein, the global user node and embedding (embedding) of the user u
Figure BDA00036288682700000310
Associated, original user node of user u with embedded e u Is associated with e u And
Figure BDA0003628868270000031
all vectors are vectors with dimension m in real number space; the graph transmission module can be abstracted into L-layer conversion; at the l-th level, a bi-directional embedded transport is first applied to exchange messages between local and global user preferences, which is calculated in the following way:
Figure BDA0003628868270000032
Figure BDA0003628868270000033
wherein,
Figure BDA0003628868270000034
f T (. beta.) is the transfer function, beta 1 And beta 2 Is at [0,1 ]]An over-parameter controlling the retention rate in the transmission in the range,
Figure BDA0003628868270000035
represents the neighbor set of user u in the diagram;
Figure BDA0003628868270000036
and
Figure BDA0003628868270000037
respectively representing a local and global representation of user u before transmission, wherein the local user representation
Figure BDA0003628868270000038
Before being sent to the l +1 layer, the message is further updated in the message propagation, and the specific operation of the message propagation is as follows:
Figure BDA0003628868270000039
wherein,
Figure BDA0003628868270000041
representing the neighbor set of item i in the graph on the user item interaction graph, and item representation
Figure BDA0003628868270000042
By embedding e in learning i ∈R m To initialize; after L-layer transformation in the graph transport module, we concatenate the representations generated by all L layers, resulting in the final user representation and item representation as follows:
Figure BDA0003628868270000043
wherein Concat () represents a join operation; final user representation h u Global and local user preferences have been encoded, as well as high-level information on the user project graph.
As a further technical solution, the step S1 of locally updating global and local preferences by using a gradient descent algorithm based on intra-domain data specifically includes:
given user and item representations, an inner product operation is adopted to generate a score so as to predict the interaction possibility of the user u and the item i from the d domain, and the specific calculation mode is as follows:
Figure BDA0003628868270000044
wherein
Figure BDA0003628868270000045
Predicted scores for user u and item i; then updating local and global user embedding based on single-domain interaction data by adopting Bayes personalized sorting loss, wherein the definition is as follows:
Figure BDA0003628868270000046
where σ () is the Sigmoid function, λ controls the strength of L2 regularization, Θ d Is a model parameter for domain d; a training sample pair is constructed by negative sampling,
Figure BDA0003628868270000047
representing a set of paired training data; in this way, the model learns locally for each domain local user embedding and domain specific item embedding based on the data within the domain.
As a further technical solution, after the private update in step S2, the collaborative learning of the global user preference based on the multi-domain data by using the federal update process specifically includes:
in the private update process, each domain d is a global user
Figure BDA0003628868270000051
Maintenance insert
Figure BDA0003628868270000052
The global user of (2), the user
Figure BDA00036288682700000512
Local updating is carried out by using data in the domain; to characterize more comprehensive user preferences, it is necessary to learn cross-domain knowledge to enhance local user preferences; to this end, decentralized federated learning is employed to cooperatively update global user embedding based on data of multiple domains; these global user embeddings will be multipleSharing among the individual domains; however, these users embed private information that contains the user's behavior and cannot be shared directly outside the domain for privacy reasons; applying a local differential privacy technique to global user embedding prior to shared global user embedding; in particular, for each global user
Figure BDA0003628868270000053
Addition intensity of lambda LDP To obtain cryptographically protected embedding
Figure BDA0003628868270000054
Then, each domain d sends a protected embedding
Figure BDA0003628868270000055
To other domains while accepting shared embedding from other domains
Figure BDA0003628868270000056
As a further technical solution, the adapting, in step S2, the global preferences to the heterogeneous domain data through personalized aggregation specifically includes:
in a cross-domain recommendation scene, in order to consider the domain adaptability of cross-domain knowledge utilization, a personalized preference aggregation strategy is adopted to generate a domain-specific global user embedding for each domain; specifically, personalized preference aggregation is performed in each domain based on an attention mechanism; when domain name d accepts shared embedding from other domains
Figure BDA0003628868270000057
The personalized aggregation layer adopts a learnable transformation matrix W ∈ R 2m And calculating the attention coefficient in a specific calculation mode of:
Figure BDA0003628868270000058
wherein g (-) is LeakyReLU activation function, and softmax function is adopted to couple attention coefficientsCarrying out normalization; attention coefficient alpha d,d′ Representing the importance of the domain knowledge to the domain d; these attention coefficients are used as weights for personalized federated aggregation to generate global embedding of user u in d-domain, in the following way:
Figure BDA0003628868270000059
wherein, beta F Is at [0,1 ]]The over-parameters of the retention rate are controlled within the range, and the second item of the equation is self-adaptive and combines knowledge from different fields; for the user
Figure BDA00036288682700000510
Generated global user inlining
Figure BDA00036288682700000511
Private updates will be made by the graph transmission module in the next round of training.
As a further technical solution, step S3 specifically includes:
when each domain receives a protected global user embedding shared by other domains, applying personalized preference aggregation to generate a domain-specific global user embedding; then, given that these global user embeddings and local user embeddings are maintained locally, the private update process is first performed a number of times to optimize the local BPR penalty function, and then a global update is invoked.
By adopting the technical scheme, the invention has the following beneficial effects:
compared with the existing cross-domain recommendation system, the privacy protection cross-domain recommendation system based on the federal learning provided by the invention protects the user privacy information from multiple layers. Firstly, in the method, the original interaction data of each domain is locally stored in the private space of the domain and is not uploaded to other domains, so that the risk of privacy disclosure can be effectively reduced. Secondly, according to data processing inequality, the only data of inter-domain communication is user global embedding, and the private information contained in the data is much less than the original interactive data; furthermore, the user global embedding encodes the user's global preferences across domains, rather than domain-specific preferences, making upload global embedding more secure. Third, user global embedding is updated based on a set of user interactions rather than a single user interaction, which makes it difficult to recover a particular interaction history. Fourthly, a Local Differential Privacy (LDP) technology is applied to user global embedding, zero-mean Laplacian noise is added to the user global embedding, and the difficulty of deducing privacy information is increased. Therefore, the method provided by the invention can be used for modeling the global preference of the user for recommendation on the premise of not revealing the privacy of the user, and is safer compared with the existing cross-domain recommendation system.
Compared with the existing recommendation system considering privacy, the method provided by the invention learns uniform cross-domain information for all the fields, and the information in different fields is personalized and aggregated by means of an attention mechanism, so that each field can be subjected to field-specific adaptation according to the received global user preference. This domain-specific adaptation is necessary due to the heterogeneity of data across domains in the real world. In addition, the periodic synchronization mechanism provided by the invention reduces the communication cost, and the mechanism executes a cross-domain federal update process after a fixed number of private updates. Compared with the existing cross-domain recommendation system considering privacy, the method provided by the invention is lower in communication cost.
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In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, and it is obvious that the drawings in the following description are some embodiments of the present invention, and other drawings can be obtained by those skilled in the art without creative efforts.
FIG. 1 is an overall architecture diagram of the federated learning-based privacy preserving cross-domain recommendation system of the present invention;
FIG. 2 is a flow chart of the algorithm in an update cycle within a single domain according to the present invention;
FIG. 3 is a domain-specific user-item interaction diagram constructed by the present invention.
Detailed Description
The technical solutions of the present invention will be described clearly and completely with reference to the accompanying drawings, and it should be understood that the described embodiments are some, but not all embodiments of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
The following describes in detail embodiments of the present invention with reference to the drawings. It should be understood that the detailed description and specific examples, while indicating the present invention, are given by way of illustration and explanation only, not limitation.
With reference to fig. 1-2, the present embodiment provides a privacy protection cross-domain recommendation system based on federal learning, including the following steps:
s1: private updating in a single domain, namely fusing user global and local preferences through a graph migration module, and locally updating the global and local preferences by a gradient descent algorithm based on data in the domain; the main purpose of the private update process is to locally fuse the global and local preferences of the user and update them based on the intra-domain data to capture domain-specific knowledge. Specifically, the invention provides a graph migration module to fuse user global and local preferences and locally update the global and local preferences with a gradient descent algorithm based on intra-domain data.
S2: after private updating, collaborative learning of global user preferences based on multi-domain data is performed by adopting a federal updating process, and the global preferences are adapted to heterogeneous domain data through personalized aggregation;
s3: the use of a periodic synchronization mechanism reduces communication costs.
As a further technical solution, the graph migration module in step S1 specifically is:
for each domain, a domain-specific user-item interaction graph (as shown in FIG. 3) is constructed based on the domain's user interaction data, global and local user nodes are set to model global and local user preferences, and links are addedEdges of local and local user nodes; wherein, the global user node and embedding (embedding) of the user u
Figure BDA0003628868270000081
Associated, original user node of user u with embedded e u Is associated with e u And
Figure BDA0003628868270000082
all vectors are vectors with dimension m in real number space; the graph transport module can be abstracted as an L-layer conversion; at the l-th level, a bi-directional embedded transport is first applied to exchange messages between local and global user preferences, which is calculated in the following way:
Figure BDA0003628868270000083
Figure BDA0003628868270000084
wherein,
Figure BDA0003628868270000085
f T (. beta.) is the transfer function, beta 1 And beta 2 Is at [0,1 ]]Model (A) of
Figure BDA0003628868270000086
A hyper-parameter that controls the retention rate in transmission within the enclosure,
Figure BDA0003628868270000087
represents the neighbor set of user u in the diagram;
Figure BDA0003628868270000088
and
Figure BDA0003628868270000089
respectively representing the user u's own book before transmissionGround and global representations, where local user represents
Figure BDA00036288682700000810
Before being sent to the l +1 layer, the message is further updated in the message propagation, and the specific operation of the message propagation is as follows:
wherein,
Figure BDA0003628868270000095
representing the neighbor set of item i in the graph on the user item interaction graph, and item representation
Figure BDA0003628868270000091
By embedding e in learning i ∈R m To initialize; after L-layer transformation in the graph transport module, we concatenate the representations generated by all L layers, resulting in the final user representation and item representation as follows:
Figure BDA0003628868270000092
wherein Concat () represents a join operation; final user representation h u Global and local user preferences have been encoded, as well as high-level information on the user project graph.
As a further technical solution, the step S1 of locally updating global and local preferences by using a gradient descent algorithm based on intra-domain data specifically includes:
given user and item representations, an inner product operation is adopted to generate a score so as to predict the interaction possibility of the user u and the item i from the d domain, and the specific calculation mode is as follows:
Figure BDA0003628868270000093
wherein
Figure BDA0003628868270000096
Predicted scores for user u and item i; then adopts BayesThe si-personalized ranking penalty, updating local and global user embedding based on single domain interaction data, is defined as:
Figure BDA0003628868270000094
where σ () is the Sigmoid function, λ controls the strength of L2 regularization, Θ d Is a model parameter for domain d; a training sample pair is constructed by negative sampling,
Figure BDA0003628868270000097
representing a set of paired training data; in this way, the model learns locally for each domain local user embedding and domain specific item embedding based on the data within the domain.
As a further technical solution, after the private update in step S2, the collaborative learning of the global user preference based on the multi-domain data by using the federal update process specifically includes:
in the private update process, each domain d is a global user
Figure BDA0003628868270000107
Maintenance insert
Figure BDA0003628868270000108
The global user of (2), the user
Figure BDA0003628868270000109
Local updating is carried out by using data in the domain; to characterize more comprehensive user preferences, it is necessary to learn cross-domain knowledge to enhance local user preferences; to this end, decentralized federated learning is employed to cooperatively update global user embedding based on data of multiple domains; these global user embeddings will be shared among multiple domains; however, these users embed private information that contains the user's behavior and cannot be shared directly outside the domain for privacy reasons; applying a local differential privacy technique to global user embedding prior to shared global user embedding; in particular, for each global user
Figure BDA00036288682700001010
The addition strength is lambda LDP To obtain cryptographically protected embedding
Figure BDA0003628868270000101
Then, each domain d sends a protected embedding
Figure BDA0003628868270000102
To other domains while accepting shared embedding from other domains
Figure BDA0003628868270000103
As a further technical solution, the adapting, in step S2, the global preferences to the heterogeneous domain data through personalized aggregation specifically includes:
in a cross-domain recommendation scene, in order to consider the domain adaptability of cross-domain knowledge utilization, a personalized preference aggregation strategy is adopted to generate a domain-specific global user embedding for each domain; specifically, personalized preference aggregation is performed in each domain based on an attention mechanism; when domain name d accepts shared embedding from other domains
Figure BDA0003628868270000104
The personalized aggregation layer adopts a learnable transformation matrix W ∈ R 2m And calculating the attention coefficient in a specific calculation mode of:
Figure BDA0003628868270000105
in the formula, g (-) is an LeakyReLU activation function, and the attention coefficient is normalized by adopting a softmax function; attention coefficient α d,d′ Representing the importance of the domain knowledge to the domain d; these attention coefficients are used as weights for personalized federated aggregation to generate global embedding of user u in d-domain, in the following way:
Figure BDA0003628868270000106
wherein beta is F Is at [0,1 ]]Controlling the over-parameter of the retention rate in the range, and combining the second term of the equation with knowledge from different fields in a self-adaptive manner; for the user
Figure BDA00036288682700001012
Generated global user inlining
Figure BDA00036288682700001011
Private updates will be made by the graph transmission module in the next round of training.
As a further technical solution, step S3 specifically includes:
in order to reduce the communication cost, the invention additionally provides a periodic synchronization mechanism to reduce the communication cost. And (4) periodic synchronization. In decentralized federated learning, communication bandwidth is a major bottleneck, because clients attempt to pass their local update information to other clients, and for this reason the present invention proposes a periodic synchronization mechanism to reduce communication costs, which performs a cross-domain federated update process after a fixed number of private updates. In particular, when each domain receives a protected global user embedding shared by other domains, personalized preference aggregation is applied to generate domain-specific global user embedding. Then, given that these global user embeddings and local user embeddings are maintained locally, the private update process is first performed T times to optimize the local BPR penalty function, and then a global update is invoked.
In summary, the present invention at least includes the following inventions:
1. a graph migration module: on the basis of the user project interaction graph with the global user nodes and the local user nodes, the graph migration module expands the message transmission scheme of the traditional graph neural network, and simultaneously considers the following steps: (1) message exchange between global and local user preferences; (2) message propagation on user-project graphs.
2. Personalized aggregation module of global user preferences: to account for domain adaptability across domain knowledge utilization, a personalized aggregation module performs personalized preference aggregation in each domain based on an attention mechanism, generating domain-specific global user embedding for each domain.
3. A periodic synchronization mechanism: in order to reduce the communication cost, the invention provides a periodic synchronization mechanism to reduce the communication cost, and the mechanism executes a cross-domain federal update process after a fixed number of private updates, thereby reducing the communication frequency and further reducing the communication cost.
Finally, it should be noted that: the above embodiments are only used to illustrate the technical solution of the present invention, and not to limit the same; while the invention has been described in detail and with reference to the foregoing embodiments, it will be understood by those skilled in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some or all of the technical features may be equivalently replaced; and these modifications or substitutions do not depart from the spirit of the corresponding technical solutions of the embodiments of the present invention.

Claims (6)

1. A privacy protection cross-domain recommendation system based on federal learning is characterized by comprising the following steps:
s1: private updating in a single domain, namely fusing user global and local preferences through a graph migration module, and locally updating the global and local preferences by a gradient descent algorithm based on data in the domain;
s2: after private updating, collaborative learning of global user preferences based on multi-domain data is performed by adopting a federal updating process, and the global preferences are adapted to heterogeneous domain data through personalized aggregation;
s3: the use of a periodic synchronization mechanism reduces communication costs.
2. The federated learning-based privacy protection cross-domain recommendation system according to claim 1, wherein the graph migration module in step S1 is specifically:
for each domain, according to the fieldDomain-specific user-project interaction graphs are constructed, global and local user nodes are set to model global and local user preferences, and edges connecting the global and local user nodes are added; wherein, the global user node and the embedding of the user u
Figure FDA0003628868260000011
Associated, original user node of user u with embedded e u Is associated with e u And
Figure FDA0003628868260000012
all vectors are vectors with dimension m in real number space; the graph transmission module can be abstracted into L-layer conversion; at the l-th level, a bi-directional embedded transport is first applied to exchange messages between local and global user preferences, which is calculated in the following way:
Figure FDA0003628868260000013
Figure FDA0003628868260000014
wherein,
Figure FDA0003628868260000021
f T (. beta.) is the transfer function, beta 1 And beta 2 Is at [0,1 ]]Model (A) of
Figure FDA0003628868260000022
A hyper-parameter that controls the retention rate in transmission within the enclosure,
Figure FDA0003628868260000023
represents the neighbor set of user u in the diagram;
Figure FDA0003628868260000024
and
Figure FDA0003628868260000025
respectively representing a local and global representation of user u before transmission, wherein the local user representation
Figure FDA0003628868260000026
Before being sent to the l +1 layer, the message is further updated in the message propagation, and the specific operation of the message propagation is as follows:
wherein,
Figure FDA0003628868260000027
representing the neighbor set of the item i in the graph on the user item interaction graph, the item represents
Figure FDA0003628868260000028
By embedding e in learning i ∈R m To initialize; after L-layer transformation in the graph transport module, we concatenate the representations generated by all L layers, resulting in the final user representation and item representation as follows:
Figure FDA0003628868260000029
wherein Concat () represents a join operation; final user representation h u Global and local user preferences have been encoded, as well as high-level information on the user project graph.
3. The federated learning-based privacy-preserving cross-domain recommendation system according to claim 2, wherein the local updating of global and local preferences with a gradient descent algorithm based on intra-domain data in step S1 is specifically:
given user and item representations, an inner product operation is adopted to generate a score so as to predict the interaction possibility of the user u and the item i from the d domain, and the specific calculation mode is as follows:
Figure FDA00036288682600000210
wherein
Figure FDA00036288682600000211
Predicted scores for user u and item i; then, updating local and global user embedding based on single-domain interactive data by adopting Bayes personalized sorting loss, wherein the updating is defined as follows:
Figure FDA0003628868260000031
where σ (-) is the Sigmoid function, λ controls the strength of L2 regularization, Θ d Is a model parameter for domain d; a training sample pair is constructed by negative sampling,
Figure FDA0003628868260000032
representing a set of paired training data; in this way, the model learns locally per-domain local user embedding and domain-specific item embedding based on intra-domain data.
4. The privacy-preserving cross-domain recommendation system based on federated learning according to claim 1, wherein after the private update in step S2, the collaborative learning of the multi-domain data-based global user preferences using the federated update process is specifically:
in the private update process, each domain d is a global user
Figure FDA0003628868260000033
Maintenance insert
Figure FDA0003628868260000034
The global user of (2), the user
Figure FDA0003628868260000035
Local updating is carried out by using data in the domain; to characterize more comprehensive user preferences, it is necessary to learn cross-domain knowledge to enhance local user preferences; to this end, decentralized federated learning is employed to cooperatively update global user embedding based on data of multiple domains; these global user inlays will be shared among multiple domains; however, these users embed private information that contains the user's behavior and cannot be shared directly outside the domain for privacy reasons; applying a local differential privacy technique to global user embedding prior to shared global user embedding; in particular, for each global user
Figure FDA0003628868260000036
Addition intensity of lambda 3DP To obtain cryptographically protected embedding
Figure FDA0003628868260000037
Then, each domain d sends a protected embedding
Figure FDA0003628868260000038
To other domains while accepting shared embedding from other domains
Figure FDA0003628868260000039
5. The system according to claim 1, wherein the step S2 of adapting the global preferences to the heterogeneous domain data through personalized aggregation is specifically:
in a cross-domain recommendation scene, in order to consider the domain adaptability of cross-domain knowledge utilization, a personalized preference aggregation strategy is adopted to generate domain-specific global user embedding for each domain; specifically, personalized preference aggregation is performed in each domain based on an attention mechanism; when domain name d accepts shared embedding from other domains
Figure FDA00036288682600000310
The personalized aggregation layer adopts a learnable transformation matrix W ∈ R 2m And calculating the attention coefficient in a specific calculation mode of:
Figure FDA0003628868260000041
in the formula, g (-) is an LeakyReLU activation function, and the attention coefficient is normalized by adopting a softmax function; attention coefficient α d,d′ Representing the importance of the domain knowledge to the domain d; these attention coefficients are used as weights for personalized federated aggregation to generate global embedding of user u in d-domain, in the following way:
Figure FDA0003628868260000042
wherein, beta 3 Is at [0,1 ]]Controlling the over-parameter of the retention rate in the range, and combining the second term of the equation with knowledge from different fields in a self-adaptive manner; for the user
Figure FDA0003628868260000043
Generated global user inlining
Figure FDA0003628868260000044
Private updates will be made by the graph transmission module in the next round of training.
6. The federated learning-based privacy protection cross-domain recommendation system according to claim 1, wherein step S3 specifically is:
when each domain receives a protected global user embedding shared by other domains, applying personalized preference aggregation to generate a domain-specific global user embedding; then, given that these global user embeddings and local user embeddings are maintained locally, the private update process is first performed M times to optimize the local BPR penalty function, and then a global update is invoked.
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