In RDF(Resource Description Framework) graph query

accurately estimating the size of the query result is a crucial step to the query optimizer.The previous work

which ignores both the uncertainty of RDF graph itself and the correlations between subqueries

is difficult to obtain accurate estimations.To solve this problem

this paper proposes an estimation method based on Bayesian probability model.Our method introduces Bayesian network model for subqueries to dig out the dependencies between properties in subqueries.At the meanwhile

based on these dependencies we propose a connection approach of subnets to compute the impact factors between subqueries.Finally

we exploit the above information to accurately estimate the cardinality of the result about an arbitrary query.The experiments indicate that the accuracy of our estimation results is improved by over 15% and that the query run-time is not increased significantly in comparison with the previous art.