9. A method for evaluating data access statements with respect to database security, comprising: evaluating criticality of multiple Structured Query Language (SQL) statements contained in multiple sessions accessing, from a first computing system, a database implemented on a data server; generating, on the data server, a critical item set from the multiple sessions, each element in the critical item set indicating one or more SQL statements contained in a session of the multiple sessions; extracting at least one association rule from the critical item set, each of the at least association rule indicating, a sequence of SQL statements; calculating criticality of each of the at least one association rule; evaluating a session based upon a criticality of at least one association rule; terminating, by the data server, the session based upon a result of the evaluating; ranking, by the data server, at least two association rules by the criticality of each of the at least two association rules; and specifying, by the data server, a security policy corresponding to each of the at least two association rules according to the ranking.
12. The method according to claim 9 , wherein the generating a critical item set from the multiple sessions comprises: generating a critical 1-item set of the at least a portion of sessions, wherein each element in the critical 1-item set comprises one SQL statement; in at least one round, in response to a critical (n−1)-item set of the at least a portion of sessions being, non-mill, generating a critical n-item set of the at least a portion of sessions, wherein n≧2 and each element in the critical n-item set comprises n SQL statements that are arranged in order.