Ashley Plank

Background for association rules and cost estimate of selected mining algorithms

Association rules may be used to represent regular patterns in databases for the purpose of decision suppori applications. Fast algorithms for mining association rules have been proposed and studied experimentally in the literature. A key to the algorithms is to find large itemsets, i.e., sets of items that are well supported in the database. In this paper, we study association rules from a statistical viewpoint. Assuming statistical independence, we obtain the expected support of an itemset, which we regard as the background. Fluctuation of support of an itemset is noise unless it differs significantly from the background. We introduce the concept of clusters, which are the largest large itemsets. From clusters in a database, we may estimate the number of large itemsets and candidate itemsets (intermediate results), which are important to the space complexity. We consider computation costs of Aprioti, AprioriTid, AprioriHybrid, OCD, SETM and DHP algorithms and study their scalability. Our study suggeststhat the key to costs and scalability is the space complexity of large itemsets and candidate itemsets. If the size of candidate k-itemsets is less than main memory, then the above algorithms scale up well. If the size of candidate k-itemsets is larger than main memory, however, the costs increase very rapidly.

Advanced Permission-Role Relationship in Role-Based Access Control

Permission-role assignment is an important issue in role-based access control (RBAC). There are two types of problems that may arise in permission-role assignment. One is related to authorization granting process. Conflicting permissions may be granted to a role, and as a result, users with the role may have or derive a high level of authority. The other is related to authorization revocation. When a permission is revoked from a role, the role may still have the permission from other roles. In this paper, we discuss granting and revocation models related to mobile and immobile memberships between permissions and roles, then provide proposed authorization granting algorithm to check conflicts and help allocate the permissions without compromising the security. To our best knowledge, the new revocation models, local and global revocation, have not been studied before. The local and global revocation algorithms based on relational algebra and operations provide a rich variety. We also apply the new algorithms to an anonymity scalable payment scheme.