17104606
Distributed Query Scheduling Service: An Architecture and Its Implementation
We present the systematic design and development of a distributed query scheduling service (DQS) in the context of DIOM, a distributed and interoperable query mediation system.26 DQS consists of an extensible architecture for distributed query processing, a three-phase optimization algorithm for generating efficient query execution schedules, and a prototype implementation. Functionally, two important execution models of distributed queries, namely moving query to data or moving data to query, are supported and combined into a unified framework, allowing the data sources with limited search and filtering capabilities to be incorporated through wrappers into the distributed query scheduling process. Algorithmically, conventional optimization factors (such as join order) are considered separately from and refined by distributed system factors (such as data distribution, execution location, heterogeneous host capabilities), allowing for stepwise refinement through three optimization phases: Compilation, parallelization, site selection and execution. A subset of DQS algorithms has been implemented in Java to demonstrate the practicality of the architecture and the usefulness of the distributed query scheduling algorithm in optimizing execution schedules for inter-site queries.
13069643
The Role of Polymorphic Reuse Mechanisms in Schema Evolution in an Object-Oriented Database
A seamless approach to the incremental design and reuse of object oriented methods and query specifications is presented. We argue for avoiding or minimizing the effort required for manually reprogramming methods and queries due to schema modifications, and demonstrate how the role of polymorphic reuse mechanisms is exploited for enhancing the adaptiveness of database programs against schema evolution in an object oriented database. The salient features of our approach are the use of propagation patterns and a mechanism for propagation pattern refinement. Propagation patterns are employed as an interesting specification formalism for modeling operational requirements. They encourage the reuse of operational specifications against the structural modification of an object oriented schema. Propagation pattern refinement is suited for the specification of reusable operational modules. It promotes the reusability of propagation patterns toward the operational requirement changes. This approach has a formal basis and emphasizes structural derivation of specifications. The main innovations are in raising the level of abstraction for behavioral schema design, and for making possible the derivation of operational semantics from structural specifications. As a result, both the modularity and reusability of object oriented schemas are increased.
3582970
Building a Semantic Web System for Scientific Applications: An Engineering Approach
This paper presents an engineering experience for building a Semantic Web compliant system for a scientific application – agricultural zoning. First, we define the concept of ontological cover and a set of relationships between such covers. These definitions, based on domain ontologies, can be used, for example, to support the discovery of services on the Web. Second, we propose a semantic acyclic restriction on ontologies which enables the efficient comparison of ontological covers. Third, we present different engineering solutions to build ontology views satisfying the acyclic restriction in a prototype. Our experimental results unveil some limitations of the current Semantic Web technology to handle large data volumes, and show that the combination of such technology with traditional data management techniques is an effective way to achieve highly functional and scalable solutions.
6609876
MobiEyes: A Distributed Location Monitoring Service Using Moving Location Queries
With the growing popularity and availability of mobile communications, our ability to stay connected while on the move is becoming a reality instead of science fiction as it was just a decade ago. An important research challenge for modern location-based services is the scalable processing of location monitoring requests on a large collection of mobile objects. The centralized architecture, though studied extensively in literature, would create intolerable performance problems as the number of mobile objects grows significantly. This paper presents a distributed architecture and a suite of optimization techniques for scalable processing of continuously moving location queries. Moving location queries can be viewed as standing location tracking requests that continuously monitor the locations of mobile objects of interest and return a subset of mobile objects when certain conditions are met. We describe the design of MobiEyes, a distributed real time location monitoring system in a mobile environment. The main idea behind the MobiEyes' distributed architecture is to promote a careful partition of a real time location monitoring task into an optimal coordination of server-side processing and client-side processing. Such a partition allows evaluating moving location queries with a high degree of precision using a small number of location updates, thus providing highly scalable location monitoring services. A set of optimization techniques are used to limit the amount of computation to be handled by the mobile objects and enhance the overall performance and system utilization of MobiEyes. Important metrics to validate the proposed architecture and optimizations include messaging cost, server load, and amount of computation at individual mobile objects. We evaluate the scalability of the MobiEyes location monitoring approach using a simulation model based on a mobile setup. Our experimental results show that MobiEyes can lead to significant savings in terms of server load and messaging cost when compared to solutions relying on central processing of location information
12929111
Type Safety in the Context of Method Updates
This paper presents a framework for checking and maintaining type safety in the presence of method evolution. A method update often affects all components of the method, including the inter face and the implementation. The type safety problem is addressed as two levels of type consistency. The first level relates to the type checking of methods in the context of the class inheritance hierarchy, and concerns the semantics of the polymorphism of methods. The second level considers the implementation parts of methods by capturing and preserving the semantics of the chain of calling relationships among relevant methods. A graph-based approach is used to achieve this two-level type consistency required at the level of class inheritance hierarchy and the level of method invocation. We demonstrate that the two levels of type consistency checking combined provide a better control of the run-time type error problems.
13182282
InfoFilter: Supporting quality of service for fresh information delivery
With the explosive growth of the Internet and World Wide Web comes a dramatic increase in the number of users that compete for the shared resources of distributed system environments. Most implementations of application servers and distributed search software do not distinguish among requests to different web pages. This has the implication that the behavior of application servers is quite unpredictable. Applications that require timely delivery of fresh information consequently suffer the most in such competitive environments. This paper presents a model of quality of service (QoS) and the design of a QoS-enabled information delivery system that implements such a QoS model. The goal of this development is two-fold. On one hand, we want to enable users or applications to specify the desired quality of service requirements for their requests so that application-aware QoS adaptation is supported throughout the Web query and search processing. On the other hand, we want to enable an application server to customize how it should respond to external requests by setting priorities among query requests and allocating server resources using adaptive QoS control mechanisms. We introduce the Infopipe approach as the systems support architecture and underlying technology for building a QoS-enabled distributed system for fresh information delivery.
17453773
Automatic 3D to 2D registration for the photorealistic rendering of urban scenes
This paper presents a novel and efficient algorithm for the 3D range to 2D image registration problem in urban scene settings. Our input is a set of unregistered 3D range scans and a set of unregistered and uncalibrated 2D images of the scene. The 3D range scans and 2D images capture real scenes in extremely high detail. A new automated algorithm calibrates each 2D image and computes an optimized transformation between the 2D images and 3D range scans. This transformation is based on a match of 3D with 2D features that maximizes an overlap criterion. Our algorithm attacks the hard 3D range to 2D image registration problem in a systematic, efficient, and automatic way. Images captured by a high-resolution 2D camera, that moves and adjusts freely, are mapped on a centimeter-accurate 3D model of the scene providing photorealistic renderings of high quality. We present results from experiments in three different urban settings.
5150850
Formalizing UML Models with Object-Z
The Unified Modeling Language (UML) has been developed as a standard language for object-oriented designs. Through its graphical and intuitive diagrams, software analysis and design process become easy. However, this graphical notation lacks precisely defined semantics. It is difficult to determine whether the design is consistent, unambiguous and complete. This paper provides a method of formalizing UML models. It gives the transforming rules from UML models to Object-Z constructs. With this method, the semantics of UML models are directly expressed in formal language Object-Z. The UML class, sequence and statechart diagrams are formalized using this method. A tool OZRose is developed to automate the transforming process.
28219085
Reducing Parametric Automata: A Multimedia Protocol Service Case Study
The Capability Exchange Signalling (CES) protocol is a control protocol for multimedia communications developed by the International Telecommunication Union (ITU) [3]. Our goal is to verify this protocol against the set of allowable sequences of service primitives (i.e. user observable events), known as the service language. Thus the first step to verify the CES protocol is to obtain the CES service language. By using automata reduction techniques [2], our approach is to extract the service language from the Occurrence Graph (OG) of the Coloured Petri Net (CPN) model [4] for the protocol’s service definition. The OG of a CPN model is a directed graph comprising all reachable states (nodes) and state changes (edges) of the model.
3525523
Modelling Trust for System Design Using the i* Strategic Actors Framework
The i*framework was developed to support requirement analysis and high-level design in an agent-oriented system development paradigm. It models intentional dependency relationships among strategic actors and their rationales. As actors depend on each other for goals to be achieved, tasks to be performed, and resources to be furnished, the trust relationships among these actors need to be considered to reason about the opportunities and vulnerabilities these dependencies bring. The concept of softgoal is used to model quality attributes for which there are no a priori, clear-cut criteria for satisfaction, but are judged by actors as being sufficiently met (≪satisficed≫) on a case-by-case basis. In this paper, trustworthiness is treated as a softgoal to be satisficed from the viewpoint of each stakeholder. Contributions to trustworthiness are considered using a qualitative reasoning approach. Examples from the smart card domain are used to illustrate.
42350068
Tackling the Infinite State Space of a Multimedia Control Protocol Service Specification
Coloured Petri Nets (CPNs) are used to model the service provided by an International Standard for the control of multimedia communications over telecommunication networks including the Internet, known as the Capability Exchange Signalling (CES) protocol. The state space of the CPN model includes all of the possible sequences of user observable events, known as the service language, which is a useful baseline against which the protocol can be verified. However, the CES service CPN possesses an infinite state space, due to unbounded communication channels. We parameterize the CPN with the channel capacity, propose and prove a recursive formula for its state space and provide an algorithm for its construction. The algorithm generates the state space for capacity l, from the state space for capacity l - 1, providing incremental state space generation rather than generating a new state space for each value of l. The state space is linear in the size of the channel.