“…The evidence theory and graph models are two of the most representative examples. Based on the evidence theory, for example, reference [6] proposed a network security threat situation assessment method based on unsupervised generation reasoning, which solves the shortcomings of high computational cost, time consuming and low efficiency of the supervised assessment method, and can more intuitively assess the overall situation of network threats; Reference [7] studied a network security situation assessment model based on DS evidence theory, which used principal component analysis (PCA) to preprocess the alarm data, adopted the improved DS evidence theory and combined the credibility of multi-source attack data to improve the alarm recognition rate. Based on the graph model, for example, reference [8] proposed a situation assessment method using the Seeker Optimization Algorithm to improve the hidden Markov model, which can more accurately assess the situation of network security, but there were irrelevant and false positive data in situation VOLUME XX, 2017 elements, which need further research on observation sequence; Reference [9] proposed a network security situation assessment method with Markov game model as the core and combined with four-level data fusion, which considered the interaction between attackers and defenders, so it was closer to reality and can assess the network security situation more accurately.…”