Abstract
Influence Maximization (IM), an NP-hard central issue for social network research, aims to recognize the influential nodes in a network so that the message can spread faster and more effectively. A large number of existing studies mainly focus on the heuristic methods, which generally lead to sub-optimal solutions and suffer time-consuming and inapplicability for large-scale networks. Furthermore, the present community-aware random walk to analyze IM using network representation learning considers only the node’s influence or network community structures. No research has been found that surveyed both of them. Hence, the present study is designed to solve the IM problem by introducing a novel influence network embedding (NINE) approach and a novel influence maximization algorithm, namely NineIM, based on network representation learning. First, a mechanism that can capture the diffusion behavior proximity between network nodes is constructed. Second, we consider a more realistic social behavior assumption. The probability of information dissemination between network nodes (users) is different from other random walk based network representation learning. Third, the node influence is used to define the rules of random walk and then get the embedding representation of a social network. Experiments on four real-world networks indicate that our proposed NINE method outperforms four state-of-the-art network embedding baselines. Finally, the superiority of the proposed NineIM algorithm is reported by comparing four traditional IM algorithms. The code is available at https://github.com/baiyazi/NineIM.
Introduction
Social media platforms, e.g., Facebook and Weibo, have been playing an increasingly critical role in helping people get knowledge and information [1]. People join multiple platforms, e.g., Facebook and Weibo, to enjoy services, express opinions, and share their own stories, simultaneously. Social networks abstracted from the platform users and their relations are essential for analyzing and predicting network information propagation dynamics.
The Influence Maximization (IM) problem, which aims to recognize the influential users in a social network, has recently attracted substantial research attention due to its practical value in information propagation issues. Perfect examples can be found in such well-recognized small sets of highly influential users as the government Weibo, and opinion leaders in product marketing [2], both of which have provided faster and more effective message propagation power. These specific user sets usually maintain an orderly social network evolution, acting as the suns or moons distributed in a social network.
The goal of IM strategies is to capture the optimal seed set with maximize activated nodes around the set. The primary issue framework of IM can be depicted in a slightly formal way as follows. An initial node-set, denoted by
The first serious discussions and analyses of IM problems have emerged in [3], which proves that the optimization problem of IM is NP-hard. Furthermore, a greedy approximation algorithm is introduced to guarantee the optimal influence spread (
The improved greedy algorithm has good performance for the IM problem. Yet this updated method has given rise to a lot of heated debate. Researchers are more concerned about its disadvantages for propagation probability and large-scale social networks. Therefore, much work pays attention to heuristic algorithms. A StaticGreedy heuristic algorithm is proposed by [6], which applies the sub-modularity properties of the IM objective function to select the most influential node, reducing the time cost in candidate nodes selection. Much of the research on heuristic IM solutions has been exploratory by the topology of communities and nodes. e.g., the hybrid heuristic model TBH [7] and the structural-based heuristic algorithms CDH-Kcut and CDH-SHRINK [8]. The community structural features are adopted to avoid information overlap and reduce the number of candidate seed nodes. The excellent technique, usually called Technique for Order of Preference by Similarity to Ideal Solution (TOPSIS) [9], considers the minimum overlap and maximum coverage to select the node-set. Some challenges still exist about the data processing with large-scale and structural complexity social networks.
Recent developments in network representation learning have led to a renewed interest in IM studies by deep learning. DeepIM [10] is the first algorithm of employing deep learning techniques for IM problems, which uses the Community Aware Random walk for network Embedding (CARE) [11] to learning the node embedding of a network. A predefined cosine similarity function is offered to measure the similarity between any two nodes. Then, a group of
This paper provides an innovative network representation approach, named
The main contributions of our work are as follow:
Most previous studies have not considered the use of deep learning techniques to solve the IM problem. This paper has provided a deeper insight into applying network representation learning technology in IM issues. Then, a network embedding method NINE and a seed node selection strategy based on deep learning are introduced to fill this gap. One of the main obstacles of existing IM solutions using deep learning is that only network structures or attributes are tacked without considering the node influence and community features. A complete understanding of combining the above multi-dimensional information to handle the IM problem is reported. The model performance of NineIM is extensively evaluated in four real-world data sets (DBLP, FootBall, NetScience, and Ca-GrQc) with different fields. Experimental results demonstrate the effectiveness of our proposed algorithm.
The rest of the paper is organized as follows. Section 2 briefly reviews related work on IM issues and network representation learning. Section 3 introduces the proposed approach NINE and the subsequent IM model NineIM. Section 4 outlines the experimental results of the proposed method on different datasets. Finally, Section 5 presents the conclusion of this work.
Influence maximization
Influence maximization (IM) problem was first studied by Domingos and Richardson [2, 15]. As noted by their pioneering work, IM is concerned with probability problems. On top of that, Kempe et al. [16] found that IM can be simulated as a class of discrete optimization problems. Most existing IM algorithms are based on simple greedy computing, traversing the influence range of each node in a network and adding the nodes with greater influence to the seed set. The process is formalized as follows.
The final seed set
Some heuristic algorithms have gradually entered people’s field of vision on node selections, such as degree analysis [17], PageRank [18], and Distance Centrality [19]. Kimura et al. [20] consider the shortest path between two nodes for measuring the influence degree of each user. Gong et al. [21] designed the IM algorithm PTMA based on the probability transition matrix, which primarily uses the greedy idea to find the first
Recently heuristic algorithms have examined the effects of community structure on solving IM issues. Bozorgi et al. [22] exploit the community structures to find the influential communities in a network. They combine local and global influences of a node to capture the influence nodes in the communities. The method FSIM [23] chooses a limited number of communities as important ones containing the candidate seeds by a measure of betweenness centrality. Wang et al. [24] presented Weighted LeaderRank with Neighbors (WLRN) to rank users in a single community. An Optimal Budget Allocation (OBA) strategy is applied for multiple communities. Heuristic factors found to be influencing IM problems have also been explored in the three studies [25, 26, 27].
Some of the recent IM research has focused on identifying and evaluating the user influences of a social network by using deep learning techniques. Classical examples include DeepIM [10], NE-IM [12], and reinforcement learning-based IM model [28]. The common process of these models is transforming the structure or attribute features of a social network into a low-dimensional vector representation. Using the vector representation of nodes can obtain the final node-set through a predefined seed selection strategy or a vector-specific location tag update strategy.
Community structure is one of the important characteristics of social networks. Community discovery algorithms have been widely used in many fields such as personalized interest recommendation [29] and social network analysis [30]. Notable applications of community discovery include finding user groups with similar interests and detecting academic groups with similar research interests, etc.
Louvain community discovery algorithm [31] has become popular with social network analysis for its simplicity and excellent accuracy. This study set out to use the Louvain algorithm to deal with the IM issues. The primary creative concept of the algorithm is the modularity that can be used to estimate the modularity gain of each node joining other communities. We can determine the community to which the node belongs. Modularity can be formalized as:
where,
Network representation learning, also known as network embedding [32, 33], has attracted great attention in recent years. The central to the entire discipline of social network analysis using deep learning is the technologies of network representation learning. The purpose of the learning is to transform network characteristics into a low-dimensional continuous representation matrix that serves as the algorithm input of machine learning approaches. The learning intention is to preserve network structure and inherent properties to the greatest extent.
Some social network studies are devoted to applying deep learning techniques to learn node embeddings, including DeepWalk [34], LINE [35], and node2vec [36], etc. Sampling random walk makes an important contribution to preserve the features of network structure. The sampling sequences of a social network can be generated through a predefined random walk strategy to obtain a corpus that represents the network structural relationships. Then, the SkipGram model [37] is used for the corpus to learn the node vector representation of the network. Finally, a low-dimensional embedding representation of the nodes in a network is obtained. Although these random walk methods have been proven to achieve better performance in network embedding, these methods neglect the global structure information and the properties of nodes. Therefore, some researchers have begun to combine network exploration strategies with other node properties.
Some scholars have begun to combine node community factors in the process of random walk. Keikha et al. [11], introduced a network embedding algorithm named CARE, trying to preserve the node’s local neighborhood and community information of a network. They apply the SkipGram model to learn the representation vector of network nodes in the corpus obtained by random walks. Gao et al. in [38] proposed a community-oriented attributed network embedding method, which designed a margin-based random walk procedure coupled with flexible margins among communities to limit the scope of random walks. However, they only recognize community information to preserve the global network structure and do not utilize the critical feature, i.e., node structure influence bias. Furthermore, these methods are unstable when the sampling frequency or the number of node sequences changes.
Some scholars consider the process of random walk and information diffusion in social networks. Shi et al. [39] used a diffusion-driven process to capture both depth and breadth information in networks. They stochastic sampling in the process of information cascades diffusion procedure to get an approximation of a network structure information. Zhang et al. [40] achieve a network representation according to a degree-biased random walk method that can well extract network information with much less redundancy. This new type of walk strategy with a high-degree biased backtracking mechanism has given rise to better capture the local and global network structure. The research has tended to focus only on the immediate neighborhood of nodes rather than community information. In addition, no study has been reported that both global network structure and node structure influence bias are preserved in a social network.
Node influence and community factor will be two critical interactive supplements to the network representation learning. Inspired by the above research, this paper establishes a novel random walk algorithm, combining node influence and community factor to obtain the node context corpus. Community structures will be applied, which also play a significant role in random walk processes. The recommended method can preserve both micro-structure and community characteristics to learn more meaningful and differentiated network representations.
Methodology
Measurement of node influence
The studies of IM issue have benefited a lot from a systematic measurement of node influence in a social network. This paper recommends to obtain the influence of an arbitrary node
where notation
where,
The calculation of global information
People tend to communicate with others who have direct connections. These connected users often referred to as direct neighbors or 1-hop neighbors; People tend to share with people who have common friends.
Some literature regards 2-hop neighbors of nodes as the global information, which are limited to small-scale social networks. The global information of a node should contain full structural features from the node to other ones. This paper believes that both 1-hop and 2-hop neighbors should be recognized as the local information of a node. The novel local information connotation can be exemplified in work undertaken by the example shown in Fig. 1.
Case network.
Node 10 can be considered as a real role, i.e., a big
where,
The local influence
This study integrates the global and local structure information to get the influence
Mathematical symbols
where
We select the degree centrality (DC), closeness centrality (CC), betweenness centrality (BC), and eigenvector centrality (EC) to evaluate the comparative values of our influences by the example shown in Fig. 1. Table 1 shows the results with
A case study of comparison of calculation results of node influence
To combine the node influences with network representation learning, this paper redefines the random-walk sampling strategy for network nodes and then learns the vectorized representation of the network.
As previously stated, the global information of a node
Inspired by the PageRank model, we use a similar method to capture the global structure information of the graph. Let
Matrix
where,
Having discussed how to optimize
This paper combines node influence with a random sampling strategy. If a random walk starts from a node
It is now well established of a novel backtracking mechanism [40] to simplify the biased sampling strategy of the random walk. First, the approach randomly selects a neighbor
[h] : NodeInfRW(G,
Another critical factor associated with the node influence may be focused on the communities of a social network since users’ interests are different in distinctive communities. The objective is to associate the user’s community information in the process of network embedding. First of all, a random walk sampling based on the node influence is performed. On top of that, the resulting sampling sequences will be input into the SkipGram model for training. Finally, we can obtain the embedding representation of the network structure. The community solution of user influence is already represented in Alg. 3.3.
Node embedding based on random walk
Algorithm 3.3 generates the training corpus of network nodes by using the biased random walk recommenced in this paper. SkipGram model is applied to learn a representation of nodes, which can predict the co-occurrence conditional probability of the remaining words in a predefined window size. The vector representation of words in the corpus can be obtained by maximizing the probability. Specifically, given a sequence of training words
where win indicates a predefined window size. A greater value of win results in more additional training examples and thus can lead to a higher accuracy. Softmax function is used to approximate the probability distribution of
where
[h] : NINE(
As explained in Algs 3.3 and 3.4, it is clear that the vector representation, i.e.,
where
Finally, the influence of each nodes in the network can be achieved and denoted by
[h] : NineIM(
The connection between the three algorithms proposed in this paper is illustrated as follows. First, the influence matrix Inf of a network should be calculated. Its subscript representation
Aiming to verify the feasibility and effectiveness of the proposed NINE approach, this section mainly conducts the performance comparison experiments with the current state-of-the-art approaches, including DeepWalk [34], node2vec [36], LINE [35], and GraRep [41]. Four public real-world datasets are applied to evaluate our proposed NINE method. This section also conducts extensive evaluations on the proposed seed node selection algorithm. We use the SIR model to simulate the information propagation process and then compare it with the existing evaluations of Degree, Connected Components Heuristic (CCHeuristic) [3], Betweenness Centrality [42], and PageRank [43].
Dataset description
The following is a brief introduction to the dataset used in this article:
NetScience [46].
Before proceeding to experiments, it is necessary to data pre-processing. First, the size of DBLP is enormous, which is reduced by discovering network communities and repeatedly deleting leaf nodes. The result data set is labeled with DBLP-S that also enjoy the characteristics of the power-law distribution and the high aggregation coefficient. Second, NetScience has many isolated nodes or communities. This work has combined these isolated elements. The largest connected subgraphs are captured. On top of that, we randomly add an edge between any remaining isolated element and its largest connected subgraph to form the final dataset. Third, we extract the maximum interconnection subgraph of Ca-GrQc directly as the final experimental data set. To make the structure of the network closer to the real network structure, the experiment needs first to remove the abnormal value of high node degree in the network. The network structure has typical social network characteristics such as power-law distribution and high aggregation coefficient. The statistics of these data sets are displayed in Table 2.
Statistics of datasets used in the experimental, showing the number of nodes #Node, the number of edges #Edge, modularity of graph #Modularity, and the number of community #Com
As mentioned in the previous section, this paper proposes a biased random walk sampling strategy based on node influence. Then the SkipGram algorithm is used to learn the embedding representation of a network. This section will evaluate the performance of the NINE embedding algorithm.
Baseline methods
The following baseline methods are introduced to evaluate the comparative performance of the proposed NINE model.
DeepWalk [34]. DeepWalk is a representative embedding method to learn the low-dimensional vector representation of social network structure. The algorithm inputs the sequence into the SkipGram model and applies the truncated random walks to learn the vector representation of words through the word co-occurrence relationship. LINE [35]. LINE is the abbreviation of Large-scale information network embedding. The network’s local and global structure information are preserved by using the first-order similarity and the second-order similarity, respectively. The final low-dimensional vector is obtained by simply splicing the representations learned by the two similarities. node2vec [36]. Node2vec is a derivative model of Deepwalk. Through random walk sampling, node2vec combines Depth-First Search (DFS) and Breadth-First Search (BFS) to calculate the transfer probability of nodes to their neighbors. Then, the sequence is also input into the SkipGram model to learn a low-dimensional vector representation for network nodes. GraRep [41]. GraRep is the abbreviation of Learning Graph Representations with Global Structural Information, which uses the idea of matrix factorization to solve the network embedding problem. The procedure applies sparse truncated SVD to learn embeddings for the powers of the PMI matrix that are computed from powers of the normalized adjacency matrix.
To validate the performance of NINE, its learned low-dimensional representations of nodes are used to solve a node classification problem. The node label is the same as the tag of the community to which it belongs. The validity of the model can be verified by predicting these node labels. In this section, a popular community discovery algorithm Louvain [31] is performed to calculate the community tags. We consider the following performance metrics: Micro-F1 and Macro-F1 and compare NINE with the four baselines on the node classification task. The proportion of the training set to the data sets varies from 5% to 80%, and the rest of the data is used as a test set. Their values of baseline evaluation metrics on four data sets DBLP-S, FootBall, NetScience, and Ca-GrQc are recorded in Tables 3–6, respectively.
The experiment of node classification result on DBLP-S
The experiment of node classification result on DBLP-S
The experiment of node classification results on Football
The experiment of node classification results on NetScience
The experiment of node classification results on CA-GrQc
First of all, the results in Table 3 show that NINE outperforms other baseline algorithms in all data divisions at the Micro-F1 and Macro-F1 metrics, which illustrate the effectiveness of our model. On top of that, as can be seen from Table 4, the approaches of DeepWalk and node2vec perform well on the dataset Football. However, when the dataset is divided into 60%, 70%, and 80%, NINE offers excellent performance in the node classification task. All the methods have reliable performance improvements with increased proportions of the training set. Among them, DeepWalk and NINE are more prominent.
Tables 5 and 6 show the results of classification experiments on datasets NetScience and CA-GrQc, respectively. The most striking result from the tables is that adding node influences to the network embedding can achieve optimal performance compared with the state-of-art methods in the node classification task.
This section outlines the experimental parameter setting. Specifically, the node global and local influence parameters are
The benefits of node influences are clearly supported by the proposed seed set selection algorithm based on NINE. As discussed above, we can get the vector representation of each node’s predefined dimensions through the random walk sampling and the SkipGram model. The final score of the nodes in a network can be calculated by vector correlation computing. The predefined number of seed nodes can be placidly selected by Alg. 3.5. This section chooses the Degree, CC-Heuristic, Betweenness Centrality, and PageRank Centrality algorithms as the baselines to evaluate the propagation influence capacity of the final seed set obtained by Alg. 3.5.
The number of node influence on seed set under different datasets.
The number of influence propagation of seed set in different datasets.
Degree. Degree method sorts the nodes based on the node’s degree in a graph and returns the top CC-Heuristic [3]. CC-Heuristic is a heuristic-based algorithm to obtain connected components for an undirected graph. The main idea of the CC-Heuristic is to remove an edge from the original graph with a certain probability and calculate the connected components of the graph. Then, the method updates the node weight values with the reciprocal 1/2 power of the component size. The update process is repeated Betweenness Centrality [42]. Betweenness centrality is one of the essential measurement parameters of network centrality in social networks. The betweenness centrality of a particular node is the statistics of shortest paths between all node pairs in a network through the node. A higher betweenness centrality value indicates a further quantity of the shortest paths through the node. PageRank Centrality [43]. PageRank centrality measures the features of a network structure, which is initially developed to evaluate the importance of web pages by their link structures. Subsequently, various study fields such as social network analysis, link prediction, and recommendation benefit from the technology of PageRank.
NineIM algorithm (Alg. 3.5) achieves the correlation degree calculations between node pairs and an immeasurable selection of a seed set. This part evaluates the performances of the NineIM algorithm concerning the choice of a seed set. SIR model and the well-established seed set are applied to illustrate the algorithm performance with respect to the simulation of information propagation processes.
The number of influence propagation of seed set in NetScience dataset under different parameters of the SIR model.
In a SIR model, the initial state of the seed nodes and the rest nodes of a network in the influence maximization problem is denoted by the capital
We select Degree, CC-Heuristic, Betweenness Centrality, and PageRank Centrality on four date sets, including DBLP-S, FootBall, NetScience, and Ca-GrQc as baseline methods to assess the comparative performance of the proposed NineIM. Figure 2 depicts the number of node influences on seed set under different datasets. The proposed NineIM achieves the optimal performance at the datasets DBLP and FootBall, which possesses the sub-optimal performance compared with the traditional IM algorithm in the datasets NetScience and CA-GrQc.
This section also uses Alg. 3.5 to capture the seed set in the baseline network embedding methods. The infection and recovery coefficients of the SIR simulation propagation process are set to 0.07 and 0.136, respectively. The experimental results shown in Fig. 3 illustrate that the network representation learning algorithm proposed in this paper has a broader influence propagation in the final SIR simulation and has achieved excellent results.
Moreover, we compare the network coverage of seed sets which are obtained by NineIM under different infection and recovery coefficients of the SIR model in NetScience dataset. In the experiment, the number of seed nodes is set at 50, and the influence propagation under different infection and recovery coefficients is tested. As shown in Fig. 4, the influence spread of NineIM algorithms has risen with the growth of infection coefficient or decrease of recovery coefficient. In the lower infection coefficient or higher recovery coefficient, there is less opportunities to diffuse influence because each edge has small chances to an active destination node, whereas, in higher lower recovery coefficient or higher infection coefficient, a considerable number of users can be affected by the seed set which is chosen by NineIM.
Finding a group of users with a significant influence in a social network has been playing an increasingly important role in helping people transfer particular information or promote specific products. A growing number of prestigious sociologists and artificial intelligence scholars around the world have started to post their excellent ideas on the IM problem. The present study was designed to solve the IM problem by introducing a novel influence maximization algorithm NineIM based on network representation learning. NineIM applies network representation learning technologies to obtain the low-dimensional vector representations of nodes in a social network. Local and global influences of network nodes are combined, and the community structure information is also added and tackled to enrich the embedding features of the nodes. As a result, a seed set selection algorithm with good performance can be deduced according to the idea of the proposed NINE. Extensive experiments conducted on four real-world networks show that NINE and NineIM have an excellent performance on both tasks. The Macro-F1 and Micro-F1 scores of NINE in the data sets increase by at least 3% or equal at the complete data sets compared with existing state-of-the-art NE baselines. As the result, the influence spread score of NineIM is better than or similar to the baseline method in the article.
This study still has some limitations worthy of future research. First, NINE is designed to capture the structural characteristics of nodes. We will extend this research to attribute networks in the future because users usually have rich attribute characteristics in social networks. Second, NINE is designed for static network settings. However, social networks in real life are constantly changing, and we will consider the support of dynamic networks in the future. Finally, In the NineIM algorithm ignores the competition problems in reality. In the end, we will consider using the feature of node attributes to enhance NINE performance and study how to apply NineIM to consider competitors.
Footnotes
Acknowledgments
This work is supported by the National Natural Science Foundation (Nos. 61902324, 11426179, and 61872298), the Social Science Planning Project of Sichuan Province (No. SC20TJ020), the Xihua University Graduate Innovation Fund 2020 (Grant Nos. ycjj2020098, YCJJ2020023), the Science and Technology Program of Sichuan Province (nos. 2021YFQ0008, 2020JDRC0067, 2019GFW131), the Foundation of Cyberspace Security Key Laboratory of Sichuan Higher Education Institutions (no. sjzz2016-73), the Scientific Research Fund of Sichuan Provincial Education Committee (nos. 15ZB0134 and 17ZA0360), and the Open Fund Project of Xihua University (Nos. 20170410143123, szjj2015-059).
