Oliver Günther

Multidimensional access methods

Search operations in databases require special support at the physical level. This is true for conventional databases as well as spatial databases, where typical search operations include the point query (find all objects that contain a given search point) and the region query (find all objects that overlap a given search region). More than ten years of spatial database research have resulted in a great variety of multidimensional access methods to support such operations. We give an overview of that work. After a brief survey of spatial data management in general, we first present the class of point access methods, which are used to search sets of points in two or more dimensions. The second part of the paper is devoted to spatial access methods to handle extended objects, such as rectangles or polyhedra. We conclude with a discussion of theoretical and experimental results concerning the relative performance of various approaches.

RFID and the perception of control: the consumer's view

This publication contains reprint articles for which IEEE does not hold copyright. Full text is not available on IEEE Xplore for these articles.

Efficient computation of spatial joins

Spatial joins are join operations that involve spatial data types and operators. Due to basic properties of spatial data, many conventional join strategies suffer serious performance penalties or are not applicable at all. The join strategies known from conventional databases that can be applied to spatial joins and the ways in which some of these techniques can be modified to be more efficient in the context of spatial data are discussed. A class of tree structures, called generalization trees, that can be applied efficiently to compute spatial joins in a hierarchical manner are described. The performances of the most promising strategies are analytically modeled and compared.<<ETX>>Spatial joins are join operations that involve spatial data types and operators. Due to basic properties of spatial data, many conventional join strategies suffer serious performance penalties or are not applicable at all. The join strategies known from conventional databases that can be applied to spatial joins and the ways in which some of these techniques can be modified to be more efficient in the context of spatial data are discussed. A class of tree structures, called generalization trees, that can be applied efficiently to compute spatial joins in a hierarchical manner are described. The performances of the most promising strategies are analytically modeled and compared. >

Efficient structures for geometric data management

Operators and representation schemes for geometric data.- Polyhedral chains.- A dual approach to detect polyhedral intersections in arbitrary dimensions.- The cell tree: An index for geometric databases.- The arc tree: An approximation scheme to represent arbitrary curved shapes.- Conclusions.

Self-disclosure and Privacy Calculus on Social Networking Sites: The Role of Culture

Social Network Sites (SNSs) rely exclusively on user-generated content to offer engaging and rewarding experience to its members. As a result, stimulating user communication and self-disclosure is vital for the sustainability of SNSs. However, considering that the SNS users are increasingly culturally diverse, motivating this audience to self-disclose requires understanding of their cultural intricacies. Yet existing research offers only limited insights into the role of culture behind the motivation of SNS users to self-disclose. Building on the privacy calculus framework, this study explores the role of two cultural dimensions – individualism and uncertainty avoidance – in self-disclosure decisions of SNS users. Survey responses of US and German Facebook members are used as the basis for our analysis. Structural equation modeling and multi-group analysis results reveal the distinct role of culture in the cognitive patterns of SNS users. The authors find that trusting beliefs play a key role in the self-disclosure decisions of users from individualistic cultures. At the same time, uncertainty avoidance determines the impact of privacy concerns. This paper contributes to the theory by rejecting the universal nature of privacy calculus processes. The findings provide for an array of managerial implications for SNS providers as they strive to encourage content creation and sharing by their heterogeneous members.

MMM: a Web-based system for sharing statistical computing modules

This prototype method management system (MMM), implemented with Web technologies, supports distributed authoring and execution of computational software modules among an interdisciplinary group of developers and users. Heterogeneous data formats, programming languages, and computing platforms pose various challenges whenever researchers are sharing and combining software modules, especially when the collaboration occurs across different traditions of scientific computing. To meet these challenges, we designed and implemented MMM. MMM is a collection of middleware services to support the interaction between software users and developers, and to facilitate the sharing of software modules across heterogeneous networks. The system design follows the World Wide Web paradigm: developers (providers) install their modules on the network in a way that allows users (consumers) to access and execute them. A prototype is available on the Web.

Progress in computational methods for representing geographical concepts

Over the past ten years, a subfield of GIScience has been recognized that addresses the linkage between human thought regarding geographical space, and the mechanisms for implementing these concepts in computational models. This research area has developed an identity through a series of successful international conferences and the establishment of a journal. It has also been complemented through community activities such as international standardization efforts and GIS interoperability. Historically, much of the advancement in computational methods has occurred at or close to the implementation level, as exemplified by attention to the development of spatial access methods. Significant progress has been made at the levels of spatial data models and spatial query languages, although we note the lack of a comprehensive theoretical framework comparable to the relational data model in database management systems. The difficult problems that need future research efforts are at the highly abstract level of cap...

Event-based monitoring of process execution violations

Process-aware information systems support business operations as they are typically defined in a normative process model. Often these systems do not directly execute the process model, but provide the flexibility to deviate from the normative model. This paper proposes amethod for monitoring control-flow deviations during process execution. Our contribution is a formal technique to derive monitoring queries from a process model, such that they can be directly used in a complex event processing environment. Furthermore, we also introduce an approach to filter and aggregate query results to provide compact feedback on deviations. Our techniques is applied in a case study within the IT service industry.

Distributed ONS and its Impact on Privacy

The EPC Network is an industry proposal to build a global information architecture for objects carrying RFID tags with electronic product codes (EPC). A so-called object naming service (ONS) is used to locate information sources for these objects in the EPC Network. But ONS is based on DNS, which suffers from well-studied weaknesses in robustness, configuration complexity and security. There are promising approaches to enhance the performance and robustness of DNS by using structured P2P systems based on distributed hash tables (DHT) that have a high potential as a replacement for ONS as well. We investigate if and how a decentralized alternative to ONS based on DHT could additionally offer data access control and enhance the privacy of its clients. As it turns out, the strength of privacy protection will slightly increase by using DHT compared to DNS, but strong protection will depend on the feasibility of secure out- of-band key distribution mechanisms.

Tree-based access methods for spatial databases: implementation and performance evaluation

Experiences with the implementation of the cell tree dynamic access method for spatial databases are reported, and the results of an experimental performance comparison with the R-tree of A. Guttman (1984) and with the R-tree of T. Sellis et al. (1987) are given. Cell tree design and implementation are discussed. Although the cell tree often requires more storage space and more CPU time to answer a search query, it usually obtains the results with a lower number of disk accesses than the two rival structures. >