206519638
PEM/sup 3/ - the policy enhanced memory management model
Over the past decade, clusters of workstations have become widely accepted as a cost efficient way of obtaining computational power. Moreover, clusters have increasingly been used to support multi-application environment, such as web servers and application servers, and to concurrently support a number of different services. In such an environment, resources become difficult to manage, e.g., it is difficult to adequately support the varying memory usage requirements of each application with a single strategy. In this paper we propose a policy-based model that provides applications with an interface to the underlying system in order to adapt the behavior of system services at runtime. The use of policies is illustrated by presenting the design of a memory management model for distributed shared memory systems, which allows different memory placement policies, while providing the ability to change consistency and coherency protocols at runtime.
18687186
Trading Privacy for Trust
Both privacy and trust relate to knowledge about an entity. However, there is an inherent conflict between trust and privacy: the more knowledge a first entity knows about a second entity, the more accurate should be the trustworthiness assessment; the more knowledge is known about this second entity, the less privacy is left to this entity. This conflict needs to be addressed because both trust and privacy are essential elements for a smart working world. The solution should allow the benefit of adjunct trust when entities interact without too much privacy loss. We propose to achieve the right trade-off between trust and privacy by ensuring minimal trade of privacy for the required trust. We demonstrate how transactions made under different pseudonyms can be linked and careful disclosure of such links fulfils this right trade-off.
14146996
Cryptographic access control in a distributed file system
Traditional access control mechanisms rely on a reference monitor to mediate access to protected resources. Reference monitors are inherently centralized and existing attempts to distribute the functionality of the reference monitor suffer from problems of scalability.Cryptographic access control is a new distributed access control paradigm designed for a global federation of information systems. It defines an implicit access control mechanism, which relies exclusively on cryptography to provide confidentiality and integrity of data managed by the system. It is particularly designed to operate in untrusted environments where the lack of global knowledge and control are defining characteristics.The proposed mechanism has been implemented in a distributed file system, which is presented in this paper along with a preliminary evaluation of the proposed mechanism.
7607582
Trust enhanced ubiquitous payment without too much privacy loss
Computational models of trust have been proposed for use in ubicomp environments for deciding whether to allow customers to pay with an e-purse or not. In order to build trust in a customer, a means to link transactions using the same e-purse is required. Roughly, trust is a result of knowledge. As the number of transactions increases, the resulting increase in knowledge about the user of the e-purse threatens privacy due to global profiling. We present a scheme (and its prototype) that mitigates this loss of privacy without forbidding the use of trust for smoothing payment by giving the opportunity to the user to divide trust (i.e. transactions) according to context (e.g. location, user's current activity or subset of shops).
2275333
Risk probability estimating based on clustering
Ubiquitous computing environments are highly dynamic, with new unforeseen circumstances and constantly changing environments, which introduces new risks that cannot be assessed through traditional means of risk analysis. Mobile entities in a ubiquitous computing environment require the ability to perform an autonomous assessment of the risk incurred by a specific interaction with another entity in a given context. This assessment will allow a mobile entity to decide whether sufficient evidence exists to mitigate the risk and allow the interaction to proceed. Such evidence might include records of prior experiences, recommendations from a trusted entity or the reputation of the other entity. We propose a dynamic mechanism for estimating the risk probability of a certain interaction in a given environment using hybrid neural networks. We argue that traditional risk assessment models from the insurance industry do not directly apply to ubiquitous computing environments. Instead, we propose a dynamic mechanism for risk assessment, which is based on pattern matching, classification and prediction procedures. This mechanism uses an estimator of risk probability, which is based on the automatic clustering of defining features of the environment and the other entity, which helps avoid subjective judgments as much as possible.
34386518
Privacy Recovery with Disposable Email Addresses
Disposable e-mail address (DEA) services are a privacy recovery mechanism for the growing spam problem. However, this problem is clearly more complex than simply closing DEA; as the rolling e-mail address protocols (REAP) system demonstrates, recovery approaches must accommodate different normal states.
6090199
Modeling part-whole relationships for spatial data
Spatial applications must manage partwhole (PW) relationships between spatial objects, for example, the division of an administrative region into zones based on land use. Support for conceptual modeling of relationships between parts and whole, such as aggregation and membership, has been well researched in the object oriented (OO) community; however, spatial data has generally not been considered. We propose here a practical approach to integrating support for spatial PW relationships into conceptual modeling languages. Three different types of relationships—spatial part, spatial membership, and spatial inclusion—that are of general utility in spatial applications are identified and formally defined using a consistent classification framework based on spatial derivation and constraint relationships. An extension of the Unified Modeling Language (UML) for spatiotemporal data, namely Extended Spatiotemporal UML, is used to demonstrate the feasibility of using such an approach to define modeling constructs supporting spatial PW relationships.
111397
Point-versus interval-based temporal data models
The association of timestamps with various data items such as tuples or attribute values is fundamental to the management of time varying information. Using intervals in timestamps, as do most data models, leaves a data model with a variety of choices for giving a meaning to timestamps. Specifically, some such data models claim to be point based while other data models claim to be interval based. The meaning chosen for timestamps is important it has a pervasive effect on most aspects of a data model, including database design, a variety of query language properties, and query processing techniques, e.g., the availability of query optimization opportunities. The paper precisely defines the notions of point based and interval based temporal data models, thus providing a new formal basis for characterizing temporal data models and obtaining new insights into the properties of their query languages. Queries in point based models treat snapshot equivalent argument relations identically. This renders point based models insensitive to coalescing. In contrast, queries in interval based models give significance to the actual intervals used in the timestamps, thus generally treating non identical, but possibly snapshot equivalent relations differently. The paper identifies the notion of time fragment preservation as the essential defining property of an interval based data model.
8086987
Multidimensional data modeling for complex data
Online Analytical Processing (OLAP) systems considerably ease the process of analyzing business data and have become widely used in industry. Such systems primarily employ multidimensional data models to structure their data. However current multidimensional data models fall short in their abilities to model the complex data found in some real world application domains. The paper presents nine requirements to multidimensional data models, each of which is exemplified by a real world, clinical case study. A survey of the existing models reveals that the requirements not currently met include support for many-to-many relationships between facts and dimensions, built-in support for handling chance and time, and support for uncertainty as well as different levels of granularity in the data. The paper defines an extended multidimensional data model, and an associated algebra, which address all nine requirements.
34647773
Conceptual Data Modeling for Spatiotemporal Applications
Many exciting potential application areas for database technology manage time-varying, spatial information. In contrast, existing database techniques, languages, and associated tools provide little built-in support for the management of such information. The focus of this paper is on enhancing existing conceptual data models with new constructs, improving their ability to conveniently model spatiotemporal aspects of information. The goal is to speed up the data modeling process and to make diagrams easier to comprehend and maintain. Based on explicitly formulated ontological foundations, the paper presents a small set of new, generic modeling constructs that may be introduced into different conceptual data models. The ER model is used as the concrete context for presenting the constructs. The semantics of the resulting spatiotemporal ER model, STER, is given in terms of the underlying ER model. STER is accompanied by a textual counterpart, and a CASE tool based on STER is currently being implemented, using the textual counterpart as its internal representation.
1232131
When the Internet Hits the Road
The Internet has recovered from the dot-com crash of the early 2000’s and now features an abundance of new, innovative technologies and services. We are also witnessing the emergence of a communication and computing infrastructure that encompasses millions of people with mobile devices, such as mobile phones, with Internet connectivity. This infrastructure will soon enable the Internet to go mobile. This paper describes the background and aspirations of a new research project that is concerned with data management aspects of innovative mobile Internet services. It is argued that mobile services will be context aware, and the project devotes particular attention to geographical context awareness. The project will adopt a prototyping approach where services are built and exposed to users, and where data management challenges are identified and addressed. The paper describes the evolving service platform that supports the approach chosen, it describes some of the data management techniques being integrated into the service platform, and it describes research guidelines that the project aims to follow.