14376672
Report on the 1995 international workshop on temporal databases
This paper provides an overview of the 1995 International Workshop on Temporal Databases. It summarizes the technical papers and related discussions, and three panels: “Wither TSQL3?”, “Temporal Data Management in Financial Applications,” and “Temporal Data Management Infrastructure & Beyond.”
616587
Querying the trajectories of on-line mobile objects
Position data is expected to play a central role in a wide range of mobile computing applications, including advertising, leisure, safety, security, tourist, and traffic applications. Applications such as these are characterized by large quantities of wirelessly Internet-worked, position-aware mobile objects that receive services where the objects' position is essential. The movement of an object is captured via sampling, resulting in a trajectory consisting of a sequence of connected line segments for each moving object. This paper presents a technique for querying these trajectories. The technique uses indices for the processing of spatiotemporal range queries on trajectories. If object movement is constrained by the presence of infrastructure, e.g., lakes, park areas, etc., the technique is capable of exploiting this to reduce the range query, the purpose being to obtain better query performance. Specifically, an algorithm is proposed that segments the original range query based on the infrastructure contained in its range. The applicability and limitations of the proposal are assessed via empirical performance studies with varying datasets and parameter settings.
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>>
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).
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.
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.
2014239
Process modeling across the web information infrastructure
Web-based open source software development (OSSD) project communities provide interesting and unique opportunities for software process modeling and simulation. While most studies focus on analyzing processes in a single organization, we focus on modeling software development processes both within and across three distinct but related OSSD project communities: Mozilla, a Web artifact consumer; the Apache HTTP server that handles the transactions of Web artifacts to consumers such as the Mozilla browser; and NetBeans, a Java-based integrated development environment (IDE) for creating Web artifacts and application systems. In this article, we look at the process relationships within and between these communities as components of a Web information infrastructure. We employ expressive and comparative techniques for modeling such processes that facilitate and enhance understanding of the software development techniques utilized by their respective communities and the collective infrastructure in creating them. Copyright © 2005 John Wiley & Sons, Ltd.
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).
14098973
CryptoCache: a secure sharable file cache for roaming users
Small mobile computers are now sufficiently powerful to run many applications, but storage capacity remains limited so working files cannot be cached or stored locally. Even if files can be stored locally, the mobile device is not powerful enough to act as server in collaborations with other users. Conventional distributed file systems cache everything locally or not at all; there is no possibility to cache files on nearby nodes.In this paper we present the design of a secure cache system called CryptoCache that allows roaming users to cache files on untrusted file hosting servers. The system allows flexible sharing of cached files among unauthenticated users, i.e. unlike most distributed file systems CryptoCache does not require a global authentication framework.Files are encrypted when they are transferred over the network and while stored on untrusted servers. The system uses public key cryptography, which allows roaming users to selectively grant read and write access to others by entrusting them with respectively the public key or the private key.
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.
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.