Catálogo de publicaciones - libros

Maintaining frequency counts for items over data stream has a wide range of applications such as web advertisement fraud detection. Study of this problem has attracted great attention from both researchers and practitioners. Many algorithms have been proposed. In this paper, we propose a new method, pruning method, to maintain frequency more accurately. We also propose a method called to record time information together with the frequency information. Using these two methods, we design three algorithms for finding frequent items and top- frequent items. Experimental results show these methods are effective in terms of improving the maintenance accuracy.

This paper addresses the efficient processing of distributed top- monitoring, which is continuously reporting the largest values according to a user-specified ranking function over distributed data streams. To minimize communication requirements, the necessary data transmitting must be selected carefully. We study the optimization problem of which objects are necessary to be transmitted and present a new distributed top- monitoring algorithm to reduce communication cost. In our approach, few objects are transmitted for maintaining the top-k set and communication cost is independent of . We verify the effectiveness of our approach empirically using both real-world and synthetic data sets. We show that our approach reduces overall communication cost by a factor ranging from 2 to over an order of magnitude compared with the previous approach when is no lees than 10.

XML has emerged as the standard for representing, exchanging and integrating data on the Web. To guarantee the quality of XML documents, the design of quality XML Schemas becomes essentially important. In this paper, we look into this problem by designing quality XML Schemas from given E-R diagrams. We first discuss several criteria in designing a good XML Schema. Following these criteria, transformation rules are then devised that take all constructs of an E-R diagram into account. Finally, a recursive algorithm is developed to transform an E-R diagram to a corresponding quality XML Schema.

Semistructured data has become prevalent in both web applications and database systems. This rapid growth in use makes the design of good semistructured data essential. Formal semantics and automated reasoning tools enable us to reveal the inconsistencies in a semistructured data model and its instances. The Object Relationship Attribute model for Semistructured data (ORA-SS) is a graphical notation for designing and representing semistructured data. This paper presents a methodology of encoding the semantics of ORA-SS in the Web Ontology Language (OWL) and automatically validating the semistructured data design using the OWL reasoning tool – RACER. Our methodology provides automated consistency checking of an ORA-SS data model at both the schema and instance levels.

To ensure the efficiency of data exchange between simulation members via multicast groups in the simulation system based on High Level Architecture (HLA), this paper proposes a novel method of dynamic data distribution based on publication and subscription tree (PS-Tree). The main contributions of this paper include: (1) Proposing the structure of PS-Tree which can manifest the relationship of data exchange between simulation members. (2) Describing the method of dynamic data distribution based on PS-Tree by mining association rule and (3) Analyzing the performance. Experiment shows that this dynamic data distribution method can implement data distribution efficiently and effectively.

The problem of sharing data in peer-to-peer environment has received considerable attention in recent years. However, knowledge sharing in peer architectures has received very little attention. This paper proposes a framework for query reformulation in peer architectures. We first consider a mapping language based on a particular description logic that includes class connectors. Then a set of rules are proposed for building graphs. Because the axioms in a knowledge base have different properties, our graph generation algorithm classifies the generated graphs into four sets (Ugraph, Bgraph, Cgraph and Dgraph). Furthermore, based on the properties of the unification nodes, our algorithms can reformulate each kind of atom in a special way. Finally we do extensive simulation experiments and simulation results show that the proposed method has better performance than those of Mork’s [8].

The computation of a data cube is one of the most essential but challenging issues in data warehousing and OLAP. Partition based algorithm is one of the efficient methods to compute data cubes on high dimensionality, low cardinality, and moderate size datasets, which exist in real applications like bioinformatics, statistics, and text processing. To deal with such high dimensional data cubes, we propose an efficient indexing technique consisting of a compressed bitmap index and two algorithms for cube constructing and querying. Experimental results show that our method saves at least 25% on storage space and about 30% on computation time compared with the Frag-Cubing algorithm.

There is a critical need to automatically manage large volumes of scientific data and applications in scientific workflows. Database technologies seem to be well suited to handle highly complex data managements. However, most of the workflow management systems (WFMSs) only utilize database technologies to a limited extent. In this paper, we present a DB-integrated scientific workflow framework which adopts the object deputy model to describe the execution of a series of scientific tasks. This framework allows WFMS management operations to be performed in a way analogous to traditional data management operations. Most important of all, data provenance method of this framework can provide much higher performance than other methods. Three kinds of schemas for data provenance are proposed and performance for each schema is analyzed in this paper.

Compensation is a widely used concept for maintaining atomicity in both the advanced transaction models and transactional workflow systems. Some Web service protocols also adopt the compensation mechanism for failure recovery when providing transaction management. However, the compensation mechanisms used in these models or protocols are too fixed and cannot satisfy the various requirements of different applications. In this paper, a multiple-compensation mechanism is proposed and defined explicitly in a business process model. An algorithm on how to implement this multiple-compensation mechanism for backward recovery is designed and its computation complexity is analysed.

In this paper, we propose an effective delegation administration model using the organizational structure. From a user-level delegation point of view, previous delegation models built on the (Administrative) Role-Based Access Control model cannot present the best solution to security problems such as the leakage of information and the abuse of delegation in a decentralized enterprise environment. Thus, we propose a new integrated management model of administration role-based access control model and delegation policy, which is called the OS-DRAM. This defines the authority range in an organizational structure that is separated from role hierarchy and supports a clear criterion for user-level delegation administration. Consequently, the OS-DRAM supports a decentralized user-level delegation policy in which a regular user can freely delegate his/her authority to other users within a security officer’s authority range with-out the security officer’s intervention.