关键词: 贝叶斯网络, 结构学习, 等价类, 本质图

Abstract: Learning equivalence class is an important branch in Bayesian network structure learning，and essential graph is a graphical representation and powerful tool for equivalence classes of Bayesian network.Finding the essential graph of a Bayesian network structure is troublesome，a combined algorithm is presented for constructing the essential graph of Bayesian network.The algorithm starts from the initial directed acyclic graph，firstly sorts all the directed edges，and then keeps the edges participating in V-structures unchanged and transforms all the others into undirected edges，finally determines the orientation of all the undirected edges in essential graph with respect to the three rules successively.The correctness of the method is proved and the validity of the algorithm is analyzed in the case at last.

Key words: Bayesian networks, structure learning, equivalence class, essential graph