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>>
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.
11394430
Unification of temporal data models
A conceptual temporal data model that captures the time-dependent semantics of data while permitting multiple data models at the representation level is described. A conceptual notion of a bitemporal relation in which tuples are stamped with sets of two-dimensional chronons in transaction-time/valid-time space is defined. A tuple-timestamped first normal form representation is introduced to show how the conceptual bitemporal data model is related, by means of snapshot equivalence, with representational models. Querying within the two-level framework is discussed. An algebra is defined at the conceptual level and mapped to the sample representational model in such a way that new operators compute equivalent results for different representations of the same conceptual bitemporal relation.<<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).
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.
14786371
Join operations in temporal databases
Abstract.Joins are arguably the most important relational operators. Poor implementations are tantamount to computing the Cartesian product of the input relations. In a temporal database, the problem is more acute for two reasons. First, conventional techniques are designed for the evaluation of joins with equality predicates rather than the inequality predicates prevalent in valid-time queries. Second, the presence of temporally varying data dramatically increases the size of a database. These factors indicate that specialized techniques are needed to efficiently evaluate temporal joins.We address this need for efficient join evaluation in temporal databases. Our purpose is twofold. We first survey all previously proposed temporal join operators. While many temporal join operators have been defined in previous work, this work has been done largely in isolation from competing proposals, with little, if any, comparison of the various operators. We then address evaluation algorithms, comparing the applicability of various algorithms to the temporal join operators and describing a performance study involving algorithms for one important operator, the temporal equijoin. Our focus, with respect to implementation, is on non-index-based join algorithms. Such algorithms do not rely on auxiliary access paths but may exploit sort orderings to achieve efficiency.
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.
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.
604106
Protection reconfiguration for reusable software
Secure distributed applications often include code to authenticate users, verify access rights, and establish secure communication channels between software components (e.g., clients and servers). This code is often specific to the application and to the context in which the application is used. Embedding protection definitions in the application code makes it difficult to reuse because different applications often have very different protection constraints. We argue that protection definitions should be specified separately from application code in order to facilitate protection reconfiguration and software reuse. This separation may be achieved by specifying protection definitions in a Protection Interface Definition Language, and is implemented by proxies installed between software components that are executing in different protection contexts (e.g., between client and server). Mechanisms for creation and dynamic installation of protection proxies have been implemented in a distributed shared memory system, and the viability of our solution is demonstrated by a simple name server, which is currently being reused in three different protection contexts.
15628651
Experience in Discovering , Modeling , and Reenacting Open Source Software Development Processes
Process discovery has been shown to be a challenging problem offering limited results. This paper describes a new approach to process discovery that examines the Internet information spaces of open source software development projects. In particular, we examine challenges, strengths, weaknesses and findings when seeking to discover, model, and reenact processes associated with large, global OSSD projects like NetBeans.org. The longer-term goal of this approach is to determine the requirements and design of more fully integrated process discovery and modeling mechanisms that can be applied to Web-based, open source software development projects.