3937672
Evaluating the Completeness of TSQL2
The question of what is a well-designed temporal data model and query language is a difficult, but also an important one. The consensus temporal query language TSQL2 attempts to take advantage of the accumulated knowledge gained from designing and studying many of the earlier models and languages. In this sense, TSQL2 represents a constructive answer to this question. Others have provided analytical answers by developing criteria, formulated as completeness properties, for what is a good model and language.
44396365
Specification-based data reduction in dimensional data warehouses
Presents a powerful and easy-to-use technique for aggregation-based data reduction that enables the gradual change of the data from being detailed to being increasingly aggregated. The technique enables huge storage gains while retaining the data that is essential to the users, and it preserves the ability to query original and reduced data in an integrated manner.
1348801
Using differential technlques to efficiently support transaction time
We present an architecture for query processing in the relational model extended with transaction time. The architecture integrates standard query optimization and computation techniques with new differential computation techniques. Differential computation computes a query incrementally or decrementally from the cahced and indexed results of previous computations. The use of differential computation techniques is essential in order to provide efficient processing of queries that access very large temporal relations. Alternative query plans are integrated into a state transition network, where the state space includes backlogs of base relations, cached results from previous computations, a cache index, and intermediate results; the transitions include standard relational algebra operators, operators for constructing differential files, operators for differential computation, and combined operators. A rule set is presented to prune away parts of state transition networks that are not promising, and dynamic programming techniques are used to identify the optimal plans from the remaining state transition networks. An extended logical access path serves as a “structuring” index on the cached results and contains, in addition, vital statistics for the query optimization process (including statistics about base relations, backlogs, and queries-previously computed and cached, previously computed, or just previously estimated).
1723263
Multidimensional data modeling for location-based services
Abstract.With the recent and continuing advances in areas such as wireless communications and positioning technologies, mobile, location-based services are becoming possible.Such services deliver location-dependent content to their users. More specifically, these services may capture the movements and requests of their users in multidimensional databases, i.e., data warehouses, and content delivery may be based on the results of complex queries on these data warehouses. Such queries aggregate detailed data in order to find useful patterns, e.g., in the interaction of a particular user with the services.The application of multidimensional technology in this context poses a range of new challenges. The specific challenge addressed here concerns the provision of an appropriate multidimensional data model. In particular, the paper extends an existing multidimensional data model and algebraic query language to accommodate spatial values that exhibit partial containment relationships instead of the total containment relationships normally assumed in multidimensional data models. Partial containment introduces imprecision in aggregation paths. The paper proposes a method for evaluating the imprecision of such paths. The paper also offers transformations of dimension hierarchies with partial containment relationships to simple hierarchies, to which existing precomputation techniques are applicable.
45102117
Temporal specialization
The authors explore a variety of temporal relations with specialized relationships between transaction and valid time. An example is a retroactive temporal event relation, where the event must have occurred before it was stored, i.e., the valid time-stamp is restricted to be less than the transaction time-stamp. The authors discuss many useful restrictions, defining a large number of specialized types of temporal relations, and indicate some of their applications. A detailed taxonomy of specialized temporal relations is presented. This taxonomy may be used during database design to specify the particular time semantics of temporal relations.<<ETX>>
1655888
Supporting imprecision in multidimensional databases using granularities
Online analytical processing (OLAP) technologies are being used widely, but the lack of effective means of handling data imprecision, which occurs when exact values are not known precisely or are entirely missing, represents a major obstacle in applying these technologies in many domains. The paper develops techniques for handling imprecision that aim to maximally reuse existing OLAP modeling constructs such as dimension hierarchies and granularities. With imprecise data available in the database, queries are tested to determine whether or not they may be answered precisely given the available data; if not, alternative queries unaffected by the imprecision are suggested. When processing queries affected by imprecision, techniques are proposed that take into account the imprecision in the grouping of the data, in the subsequent aggregate computation, and in the presentation of the imprecise result to the user. The approach is capable of exploiting existing OLAP query processing techniques such as pre-aggregation, yielding an effective approach with low computational overhead and that may be implemented using current technology.
5451193
ECOOP Workshop on Distributed Object Security
The purpose of this workshop was to provide a forum for discussion of security problems relating to distributed object-oriented programming environments. As object-oriented technology is becoming more widely deployed, security has become a pressing issue. Object-Oriented programming languages and object-based systems generally offer a convenient set of abstractions for security, such as strong typing, well-defined interfaces and encapsulation of data. However, they also introduce a number of new problems, such as deciding on the granularity of protection in fine-grained object systems and the possible ambiguities arising from polymorphism and dynamic binding, e.g., can a compromised class be substituted for a valid one.
26363914
Trust-Based Route Selection in Dynamic Source Routing
Unlike traditional mobile wireless networks, ad hoc networks do not rely on any fixed infrastructure. Nodes rely on each other to route packets to other mobile nodes or toward stationary nodes that may act as a gateway to a fixed network. Mobile nodes are generally assumed to participate as routers in the mobile wireless network. However, blindly trusting all other nodes to respect the routing protocol exposes the local node to a wide variety of vulnerabilities. Traditional security mechanisms rely on either the authenticated identity of the requesting principal or some form of credentials that authorise the client to perform certain actions. Generally, these mechanisms require some underlying infrastructure, e.g., a public key infrastructure (PKI). However, we cannot assume such infrastructures to be in place in an ad hoc network. In this paper we propose an extension to an existing ad hoc routing protocols, which selects the route based on a local evaluation of the trustworthiness of all known intermediary nodes (routers) on the route to the destination. We have implemented this mechanism in an existing ad hoc routing protocol, and we show how trust can be built from previous experience and how trust can be used to avoid routing packets through unreliable nodes.
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.
7815359
Trust Transfer: Encouraging Self-recommendations Without Sybil Attack
Trading privacy for trust thanks to the linkage of pseudonyms has been proposed to mitigate the inherent conflict between trust and privacy. This necessitates fusionym, that is, the calculation of a unique trust value supposed to reflect the overall trustworthiness brought by the set of linked pseudonyms. In fact, some pieces of evidence may overlap and be overcounted, leading to an incorrect trust value. In this approach, self-recommendations are possible during the privacy/trust trade. However, this means that Sybil attacks, where thousands of virtual identities belonging to the same real-world entity recommend each other, are potentially easier to carry out, as self-recommendations are an integral part of the attack. In this paper, trust transfer is used to achieve safe fusionym and protect against Sybil attacks when pieces of evidence are limited to direct observations and recommendations based on the count of event outcomes. Trust transfer implies that recommendations move some of the trustworthiness of the recommending entity to the trustworthiness of the trustee. It is demonstrated and tailored to email anti-spam settings.
11578916
Adaptability in CORBA: the mobile proxy approach
Adaptability is one of the most important challenges in modern distributed systems. It may be defined as the ease with which a software application satisfies the different system constraints and the requirements of users and other applications. Adaptability is needed because distributed systems are inherently open, heterogeneous, and dynamic environments integrating a wide range of platforms, operating systems and applications from a number of different sources. We propose to use mobile proxies to provide adaptability in distributed applications integrated using the CORBA technology. Downloading stubs and skeletons at runtime allows the adaptation of either client or server interfaces as well as the protocol linking the two.