29911898
Incremental Implementation Model for Relational Databases with Transaction Time
An implementation model for the standard relational data model extended with transaction time is presented. The implementation model integrates techniques of view materialization, differential computation, and deferred update into a coherent whole. It is capable of storing any view (reflecting past or present states) and subsequently using stored views as outsets for incremental and decremental computations of requested views, making it more flexible than previously proposed partitioned storage models. The working and the expressiveness of the model are demonstrated by sample queries that show how historical data are retrieved. >
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.
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.
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.
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.
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.
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.
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.
2348538
Combating Spam with TEA
— It has been observed that the underlying reasons for the continuing growth of the " spam " problem are a lack of reliable sender authentication and the near-zero cost of sending huge volumes of marketing material worldwide, via email. Previous attempts to address these problems either change the fundamental properties of email, reducing its usefulness to legitimate senders, or require an infeasible move to new system architectures. In this paper we present two new techniques for increasing the level of sender authentication for legacy-system plain text email addresses. We then show how these Trustworthy Email Addresses (TEA) can be used in conjunction with a trust and risk-based security framework as an effective anti-spam tool. Our prototype Java implementation is then evaluated in the context of a spammer threat model with an economic analysis of the viability of each threat.