45139817
Alternative methods for the reconstruction of trees from their traversals
It is well-known that given the inorder traversal of a binary tree's nodes, along with either one of its preorder or postorder traversals, the original binary tree can be reconstructed using a recursive algorithm. In this short note we provide a short, elegent, iterative solution to this classical problem.
18022126
Construction of Universal Instances for Loop-Free Network Databases Using a Join-Like Operation
In this paper, we give a polynomial-time method to construct effectively the unique universal instance, using as few nulls as possible, from any loop-free network database, via a "minimal information" extension of natural join. Our results can be seen as concretely and quickly implementing the universal relation view for databases which are not pairwise consistent.
30110235
Distributed Policies for Data Management - Making Policies Mobile
This paper presents the challenges facing developers of multi-tier information systems in providing effective consistent data policy enforcement, such as access control in these architectures. It introduces “Mobile Policy”(MoP) as a potential solution and presents a framework for using mobile policy in the business logic tier of multi-tier information systems.
14768987
Distributed timestamp generation in planar lattice networks
Timestamps are considered for distributed environments in which information flow is restricted to one direction through a planar lattice imposed on a network. For applications in such networks, existing timestamping algorithms require extension and modification. For example, in secure environments, typical timestamps provide a potential signaling channel between incomparable levels. In hierarchical databases, typical timestamps cause peripheral sites to unnecessarily affect the behavior at main sites.
Algorithms are presented by which a network node may generate and compare timestamps using timestamp components maintained at dominated nodes in the network. The comparison relation is shown to be acyclic for timestamps produced by the generation algorithm. We discuss ways to safely relax the requirement that the network be a lattice. By example, we show how to modify a simple nonplanar lattice so that the generation algorithm can be applied. Uses of the timestamp generation algorithm in the motivating applications are outlined.
10196984
Propagation of authorizations in distributed database systems
We consider the propagation of authorizations in distributed database systems. If no constraints are imposed on the propagation of authorization changes, then the authorization states at different sites may evolve inconsistently. A standard solution is to suppress the distributed aspect and make all changes appear as if they had occurred in some serial order at a single site, perhaps via an atomic commit protocol. However, rigid insistence on consistency may result in authorization changes being needlessly delayed, a problem exacerbated in the context of site or communication failures. We propose an optimistic authorization propagation algorithm. We specify an authorization table and a set of operations for altering the authorization table. Each site maintains a log of authorization operations. We exploit the semantics of authorization operations to avoid relying on an undo-redo mechanism for processing out of order operations. Instead we give efficient, direct algorithms to scan the log and update the authorization table. Any inconsistencies in replicas of the authorization table are transient and are eliminated by further communication between sites. We discuss pruning the authorization log.
61285095
Discovering calendar-based temporal association rules
We study the problem of mining association rules and related time intervals, where an association rule holds either in all or some of the intervals. To restrict to meaningful time intervals, we use calendar schemas and their calendar-based patterns. A calendar schema example is (year, month, day) and a calendar-based pattern within the schema is (*, 3, 15), which represents the set of time intervals each corresponding to the 15th day of a March. Our focus is finding efficient algorithms for this mining problem by extending the well-known Apriori algorithm with effective pruning techniques. We evaluate our techniques via experiments.
2187643
Enhancing the Controlled Disclosure of Sensitive Information
The so-called “aggregation problem” is addressed, where the issue is how to release only a limited part of an information resource, and foil any attacks by users trying to aggregate information beyond the preset limits. The framework is that of relational databases, where sensitive information can be defined flexibly using view definitions. For each such view, the tuples that have already been disclosed are recorded intensionally rather than extensionally, that is, at each point, sub-view definitions are maintained that describe all the sensitive tuples that have been released to each individual. While our previous work foiled sequences of single-query attacks attempted by individual users, it did not consider multi-query attacks, where a combination of queries is used to invade the sensitive information. In this study we enhance our previous solutions to guard the sensitive information against two kinds of multi-query attacks: join attacks, and complement attacks. We then argue that the enhanced algorithm renders the sensitive information immune to attacks.