Using distributed objects for digital library interoperability

Information repositories are just one of many services tomorrow's digital libraries might offer. Other services include automated news summarization, trend analysis across news repositories, and copyright-related facilities. This distributed collection of services has the potential to be enormously helpful in performing information-intensive tasks. It could also turn such tasks into confusing, frustrating annoyances by forcing programmers and users to learn many interfaces and by confronting users with the bewildering details of fee-based services that were previously only accessible to professional librarians. The Stanford Digital Library project is addressing the problem of interoperability, which is particularly important because standardization efforts are lagging behind the development of digital library services. The authors used CORBA to implement information-access and payment protocols. These protocols provide the interface uniformity necessary for interoperability, while leaving implementers a large amount of leeway to optimize performance and to provide choices in service performance profiles. The authors' initial experience indicates that a distributed object framework does give clients and servers the flexibility to manage their communication and processing resources effectively     

Using augmented reality to build digital twin for reconfigurable additive manufacturing system

The extrusion-based additive manufacturing (AM) processes are those where one or multiple tools (usually nozzles) are driven along predefined paths to deposit fabrication materials. They are usually inherently slow because solid contours have to be filled with mere single deposition lines of material. An intuitive way to improve the fabrication speed is to introduce multiple independent actuators for concurrent deposition of materials without collision among them. In this paper, a methodology of using augmented reality (AR) technique is presented to conveniently communicate the layout information between a reconfigurable AM system made of robotic arms and its corresponding digital twin for toolpath planning and simulation. A prototype system made of two desktops AM robotic arms is developed, and transformation matrices are derived to determine the spatial relation between different items in the system, including camera, markers, robotic arms and part substrate. Case studies are conducted to demonstrate the capability of this methodology in automatically retrieving layout information and assisting users to deploy pre-determined layout. The results show that the developed methodology enables rapid retrieval of position information from the physical system layout into the digital twin simulation and optimization and facilitates convenient deployment of an optimized layout determined in the digital twin into the physical system.     

Recovering distributed objects

Distributed multithreaded applications operating in shared-nothing environments present challenges to classical fault tolerance mechanisms. The piecewise determinism assumption is lost (due to multithreading), and data must be replicated (because of the shared-nothing environment). In this paper, we explore a systematic approach to providing fault tolerance, by considering data-race-free programs that have the benefits of piecewise determinism and yet allow multithreading. We base our logging and recovery algorithm on a logical ring structure that allows the underlying distributed system to migrate threads, migrate and replicate objects, and perform multi-object transactions.     

On the performance of distributed objects

Early distributed shared memory systems used the shared virtual memory approach with fixed-size pages, usually 1–8 KB. As this does not match the variable granularity of sharing of most programs, recently the emphasis has shifted to distributed object-oriented systems. With small object sizes, the overhead of inter-process communication could be large enough to make a distributed program too inefficient for practical use. To support research in this area, we have implemented a user-level distributed programming testbed, DIPC, that provides shared memory, semaphores and barriers. We develop a computationally-efficient model of distributed shared memory using approximate queueing network techniques. The model can accommodate several algorithms including central server, migration and read-replication. These models have been carefully validated against measurements on our distributed shared memory testbed. Results indicate that for large granularities of sharing and small access bursts, central server performs better than both migration and read-replication algorithms. Read-replication performs better than migration for small and moderate object sizes for applications with high degree of read-sharing and migration performs better than read-replication for large object sizes for applications having moderate degree of read-sharing.     

Evolutionary acquisition of behavior to build structural objects by virtual creatures

One of our purposes is to develop virtual creatures which can acquire behaviors such as building structural objects in a 3D physical simulation. In this article, we show the influences of behavior on structural objects which are built by virtual creatures. Many creatures can change their environment for the better by building structural objects, for example, spiders’ nests. In the field of artificial life, there are many studies of virtual creatures which change their bodies and behavior to suit their environments. In contrast, there are few studies about virtual creatures which build structural objects. As for natural creatures, virtual creatures need a physical interaction between their body and their environment. Therefore, our purpose is to develop a framework for the autonomous acquisition of behaviors which build structural objects in a 3D physical simulation. In order to do this, we first studied the evolutionary acquisition of behavior for building structural objects, e.g., a nest for predation, by the simple behavior of throwing blocks. As a result, we show the possibility that virtual creatures can acquire building behavior evolutionarily.     

分布式对象中间件技术研究

中间件是处于操作系统和应用层之间的一个软件层,由于它可以简化基于分布式系统的开发应用,成为目前软件工程中的热点。在对中间件简单概述基础上,讨论了分布式对象中间件的层次结构和发展现状,最后通过对目前主流分布式对象中间件技术的分析和比较,从4个方面给出了中间件技术的发展趋势,它们是接口的标准化、体系结构的构件化、开放化和可配置化以及使用的简单化。     

Real-Time digital libraries based on widely distributed, high performance management of large data objects

Received: 2 April 1997 / Revised: 30 June 1997 / Accepted: 5 August 1997     

An ECA object service to support active distributed objects

Existing Object Management Group (OMG) standards (such as the Common Object Request Broker Architecture specification) provide specific details on how to model distributed objects through the use of an object request broker. However, the specification provided by OMG is not sufficient. For example, it does not specify how active, distributed objects can perform certain functions in response to certain events. It also does not provide any details on how to implement an object service to support active, distributed objects. Such an object service can provide facilities for applications to define events and rules. In view of this, this paper identifies, explores, and provides an approach to model applications as active, distributed objects. The research specifically involves the design, development, and experimental demonstration of an object service based on an active, distributed object model. This object service allows applications to define events and rules. When an event occurs, the object service locates the rule objects and triggers them. It also provides transparency for the objects which generate events. To provide a specific context for the approach, an object service using the specifications provided by the OMG is designed and implemented. The class of application environments for which this approach is suitable and useful includes time-dependent applications and systems that require some form of action such as medical and geographic information systems, distributed work-flow management, distributed expert systems, and computer-integrated manufacturing.     

Partitioned data objects in distributed databases

In many distributed databases locality of reference is crucial to achieve acceptable performance. However, the purpose of data distribution is to spread the data among several remote sites. One way to solve this contradiction is to use partitioned data techniques. Instead of accessing the entire data, a site works on a fraction that is made locally available, thereby increasing the site's autonomy. We present a theory of partitioned data that formalizes the concept and establishes the basis to develop a correctness criterion and a concurrency control protocol for partitioned databases. Set-serializability is proposed as a correctness criterion and we suggest an implementation that integrates partitioned and non-partitioned data. To complete this study, the policies required in a real implementation are also analyzed. Recommended by: Hector Garcia-Molina     

Process machine implementation using distributed objects

Manufacturing environments are moving away from stable, high volume environments to more flexible and lean environments. Industries’ objectives included improvement of the manufacturing process and the creation of a next generation computer integrated manufacturing (CIM) system architecture that could exploit new manufacturing technologies. This paper documents the implementation of the machine control and factory management portions of the CIM framework using distributed objects technology and a common objects request broker architecture compliant object request broker.     

Web services are not distributed objects

Web services are frequently described as the latest incarnation of distributed object technology. This misconception, perpetuated by people from both industry and academia, seriously limits broader acceptance of the true Web services architecture. Although the architects of many distributed and Internet systems have been vocal about the differences between Web services and distributed objects, dispelling the myth that they are closely related appears difficult. Many believe that Web services is a distributed systems technology that relies on some form of distributed object technology. Unfortunately, this is not the only common misconception about Web services. We seek to clarify several widely held beliefs about the technology that are partially or completely wrong. Within the distributed technology world, it is probably more appropriate to associate Web services with messaging technologies because they share a common architectural view, although they address different application types. Web services technology will have a dramatic enabling effect on worldwide interoperable distributed computing once everyone recognizes that Web services are about interoperable document-centric computing, not distributed objects.     

Multi-technology distributed objects and their integration

Research on software objects, components, middleware, and component-based applications concerns among others ActiveX controls, JavaBeans (JBs), the Microsoft Transaction Server (MTS), Enterprise JavaBeans (EJBs), and how they can interoperate with each other. Is their interoperation possible? Which elements are responsible for the software objects' incompatibility? Is compatibility a responsibility of the objects or of their underlying architectures? In this article, we discuss object compatibility problems by outlining three basic middleware remoting technologies: the OMG's Common Object Request Broker Architecture (CORBA), Microsoft's Distributed Component Object Model (DCOM), and Sun's Java Remote Method Invocation (RMI), discussing the basic incompatibility points, and overviewing the basic strategies for bridging the gap between CORBA, DCOM, and RMI.     

Using laser defect avoidance to build large-area FPGAs

Wafer-scale techniques of defect avoidance expend the complexity limits of field-programmable gate arrays by routing around flawed blocks to build working systems. Experiments on test FPGAs show that laser defect avoidance produces signal delays half those of active switches     

Using mobile code to build a smart kitchen

Software infrastructures for handheld and ubiquitous computing systems help developers tackle many implementation problems. Sun Microsystems recently introduced an infrastructure called Jini. We report on our experiences of using Jini to build a smart kitchen. We found that the central Jini concept of code mobility proved very beneficial offering a simple mechanism for device interoperability and encouraging developers to better structure the software.     

Using data mining methods to build customer profiles

This paper describes 1:1 Pro system which constructs personal profiles based on customers' transactional histories. The system uses data mining techniques to discover a set of rules describing customers' behavior and supports human experts in validating the rules     

Using standards to build the DIMAG connected mobile applications framework

The development of connected mobile applications is a complex task due to device diversity. Therefore, device-independent approaches are aimed at hiding the differences among the distinct mobile devices in the market. This work proposes DIMAG, a software framework to generate connected mobile applications for multiple software platforms, following a declarative approach. DIMAG provides transparent data and state synchronization between the server and the client side applications. The proposed platform has been designed making use of existing standards, extending them when a required functionality is not provided.     

Copying structured objects in a distributed system

A distributed system is modelled as a set of disjoint naming environments called contexts among which messages flow as the means of communication. A structured object is considered to be a list of the names of its components. Primitive objects contain no other objects as components. This paper presents an algorithm for copying objects across context boundaries. Each object resides within a context and has a locally unique name assigned to it. The components of a structured object may reside in other contexts. Three copy operations are proposed: (1) copy copies the complete structure without copying any component more than once; (2) copy-local copies all of the structure within the context of the object and directly accessible through the object without copying any component more than once, and sending to the receiver the globally unique names of those components not copied; (3) copy-top copies only the top level of the structure, sending to the receiver the globally unique names of all the components of the top level.     

Implementing set objects in dynamic distributed systems

This paper considers a set object, i.e., a shared object allowing users (processes) to add and remove elements to the set, as well as taking consistent snapshots of its content. Specifically, we show that there not exists any protocol implementing a set object, using finite memory, when the underlying distributed system is eventually synchronous and affected by continuous arrivals and departures of processes (phenomenon also known as churn). Then, we analyze the relationship between system model assumptions and object specification in order to design protocols implementing the set object using finite memory. Along one direction (strengthening the system model), we propose a protocol implementing the set object in synchronous distributed systems and, along the other direction (weakening the object specification), we introduce the notion of a k-bounded set object proposing a protocol working on an eventually synchronous system.     

Using interesting sequences to interactively build Hidden Markov Models

The paper presents a method of interactive construction of global Hidden Markov Models (HMMs) based on local sequence patterns discovered in data. The method is based on finding interesting sequences whose frequency in the database differs from that predicted by the model. The patterns are then presented to the user who updates the model using their intelligence and their understanding of the modelled domain. It is demonstrated that such an approach leads to more understandable models than automated approaches. Two variants of the problem are considered: mining patterns occurring only at the beginning of sequences and mining patterns occurring at any position; both practically meaningful. For each variant, algorithms have been developed allowing for efficient discovery of all sequences with given minimum interestingness. Applications to modelling webpage visitors behavior and to modelling protein secondary structure are presented, validating the proposed approach.