Managing complexity: middleware explained

Describes the initial design work of the New Zealand Distributed Information Systems (NZDIS) research project, which seeks to develop an architecture for building distributed information systems from existing information resources, based on software agent and distributed object technologies. An agent-based architecture is used, with messages exchanged via the FIPA (Foundation for Intelligent Physical Agents) agent communication language (ACL). Novel features of this system include the use of standards from the object-oriented programming community, such as the Common Object Request Broker Architecture (CORBA) as a communications infrastructure, the Unified Modeling Language (UML), which is used as an ontology representation language, the Object Data Management Group's Object Query Language (OQL), which is used for queries, and the Object Management Group's Meta Object Facility (MOF), which is used as the basis for an ontology repository agent. 'Stringified' object references may be returned as the content of ACL messages, allowing query results to be made available via a variety of CORBA interfaces.

DIMMA - A Distributed Interactive Multi-Media Architecture - is an open distributed processing (ODP) platform that facilitates the production of distributed applications. It has particular support for those applications that have soft real-time constraints, and those that make use of multi-media. DIMMA consists of a portable layer of distribution engineering (middleware), together with tools to interface applications to this engineering. The most popular commercial ODP platform is the Common Object Request Broker Architecture (CORBA) whose definition is managed by the Object Management Group (OMG). In recognition of this popularity, DIMMA supports a CORBA compliant API so that CORBA applications may be easily ported to or from the DIMMA platform. This paper describes the example implementation of DIMMA. It gives an overview of the motivations behind the design of DIMMA and then highlights some key features of the DIMMA implementation. It concludes with a brief analysis of DIMMA's performance

There is a growing international interest in using coupled, multidisciplinary computer simulations for a variety of purposes, including nuclear reactor safety analysis. Reactor behaviour can be modeled using a suite of computer programs simulating phenomena or predicting parameters that can be categorized into disciplines such as Thermalhydraulics, Neutronics, Fuel, Fuel Channels, Fission Product Release and Transport, Containment and Atmospheric Dispersion, and Severe Accident Analysis. Traditionally, simulations used for safety analysis individually addressed only the behaviour within a single discipline, based upon static input data from other simulation programs. The limitation of using a suite of stand-alone simulations is that phenomenological interdependencies or temporal feedback between the parameters calculated within individual simulations cannot be adequately captured. To remove this shortcoming, multiple computer simulations for different disciplines must exchange data during runtime to address these interdependencies. This article describes the concept of a new framework, which we refer to as the “Backbone,” to provide the necessary runtime exchange of data. The Backbone, currently under development at AECL for a preliminary feasibility study, is a hybrid design using features taken from the Common Object Request Broker Architecture (CORBA), a standard defined by the Object Management Group, and the Message Passing Interface (MPI), a standard developed by a group of researchers from academia and industry. Both have well-tested and efficient implementations, including some that are freely available under the GNU public licenses. The CORBA component enables individual programs written in different languages and running on different platforms within a network to exchange data with each other, thus behaving like a single application. MPI provides the process-to-process intercommunication between these programs. This paper outlines the different CORBA and MPI configurations examined to date, as well as the preliminary configuration selected for coupling 2 existing safety analysis programs used for modeling thermal–mechanical fuel behavior and fission product behavior respectively. In addition, preliminary work in hosting both the Backbone and the associated safety analysis programs in a cluster environment are discussed.

Today, more and more distributed computer applications are being modeled and constructed using real‐time principles and concepts. In 1989, the Object Management Group (OMG) formed a Real‐Time Special Interest Group (RT SIG) with the goal of extending the Common Object Request Broker Architecture (CORBA) standard to include real‐time specifications. This group's most recent efforts have focused on the requirements of dynamic distributed real‐time systems.One open problem in this area is resource access synchronization for tasks employing dynamic priority scheduling. This paper presents two resource synchronization protocols that the authors have developed which meet the requirements of dynamic distributed real‐time systems as specified by Dynamic Scheduling Real‐Time CORBA (DSRT CORBA). The proposed protocols can be applied to both Earliest Deadline First (EDF) and Least Laxity First (LLF) dynamic scheduling algorithms, allow distributed nested critical sections, and avoid unnecessary runtime overhead. In order to evaluate the performance of the proposed protocols, we analyzed each protocol's schedulability. Since the schedulability of the system is affected by numerous system configuration parameters, we have designed simulation experiments to isolate and illustrate the impact of each individual system parameter. Simulation experiments show the proposed protocols have better performance than one would realize by applying a schema that utilizes dynamic priority ceiling update. Copyright © 2004 John Wiley & Sons, Ltd.

One of the most attractive aspects of the Common Object Request Broker Architecture (CORBA) lies in its open standard nature. Code that is based only on constructs described in the CORBA specification is portable between object request brokers (ORBs) without depending on any single ORB implementation. However, this portability feature is not completely achieved in real-world applications. This paper discusses CORBA portability issues through our experience in implementing a CORBA object group service (OGS) and porting it on different ORBs. In particular, we discuss some implementation choices we made with Orbix and VisiBroker, and we point out the impact of these choices on the service portability and interoperability. This sheds some light on whether the current CORBA specification is mature enough to be deployed in industrial systems that have requirements regarding portability and interoperability. We also present how new CORBA specifications solve part of the shortcomings mentioned in this paper.

This chapter introduces a programming environment for SCI clusters that takes advantage of both parallel and distributed programming paradigms. It aims at helping programmers to design high performance applications based on the assembling of generic software components. This environment is based on CORBA (Common Object Request Broker Architecture), with our own extensions to support parallelism across several cluster nodes within a distributed system. Our contribution concerns extensions to support a new kind of object, which we call a parallel CORBA object (or parallel object), as well as the integration of message-passing paradigms, mainly MPI, within a parallel object. These extensions exploit as much as possible the functionality offered by CORBA and require few modifications to an available CORBA implementation. This paper reports on these extensions and the description of a runtime system, called Cobra, which provides resource allocation services for the execution of parallel objects.

Distributed computing applications rely on transmissions of messages between processes. However, as workstations are not intended to manage this kind of communications, it is necessary to use some communication tools known as message passing libraries. Currently, MPI (Message Passing Interface) and PVM (Parallel Virtual Machine) are the most used. In addition, the need for interoperability among the rapidly proliferating amount of hardware and software led to the definition of CORBA (Common Object Request Broker Architecture), which standardizes the execution support of distributed object applications. This architecture offers good interoperability and encapsulation support. Moreover, its method invocation mechanism, offers several features and can be used as a good communication model. Consequently, the use of such an architecture for distributed and grid computing applications seems interesting and promising. However, CORBA is always criticized on the performance level. By taking account of all these elements, a performance evaluation of CORBA seems necessary. The aim of the paper is to present benchmark results of some CORBA implementations (ORBacus and TAO) and to compare them with those of the two message passing libraries MPI (MPICH and LAM) and PVM, by using a Network of WorkStations (NOW).

A mobile service robot is a complex distributed system integrating various technologies and having large heterogeneity. In order to facilitate component development and system integration of the mobile service robots, a middleware-based simulation and control framework for system integration and application development, as well as the robotic functional component (RFC) framework with a simplified structure and an efficient transmission scheme, is proposed for mobile service robot systems. Designed to implement a distributed modular mechanism for a mobile service robot, the middleware-based framework for simulation and control is comprised of four layers: low-level abstraction layer, communication layer, high-level abstraction layer, and application layer. Common Object Request Broker Architecture (CORBA) and Robot Technology Middleware (RTM) are employed as middleware for the development of RFCs and for system integration. Communication between the components and the graphical programming tool is done by the communication layer (CORBA ORB). The conducted experiments validated the proposed framework in terms of ideal performance of reusability, interoperability, and extensibility, as well as indicated that the proposed RFC framework is simplified and easy enough to perform well in data transmission, which will reduce the costs and the threshold of robot development.

To develop a conventional CORBA(Common Object Request Broker Architecture)-based distributed object system, first the system’s requirements must be analyzed in requirements analysis step and system’s overall interface and details must be specified and built using IDL(Interface Definition Language) in design step. However, there are not too many models available that can be used as a benchmark in specifying the requirements and details of the CDO(CORBA-based distributed object) system. Conversion to IDL from requirements analysis step or preliminary design stage is a difficult task and an effective method for verification of IDL is not currently available. In the light of unique features of distributed object system, IDL errors that occur in the beginning of software development become the main causes of errors for the system as a whole. This paper suggests SACC (Software Architecture-based CORBA Component) model as a solution to the problems mentioned above m specifying details and verifying CDO system. SACC model uses SCI (SACC Converted IDL) algorithms to be converted to IDL. SACC model utilizes software architecture approach. SACC modeling method uses CTL (Computational Tree Logic) to verify CORBA system that is specified by SACC model. In conclusion, SACC modeling method is proven effective in specifying details and verifying the CDO system. Furthermore, it helps programmers to effectively convert to IDL, which is highly reliable.

The U.S. Army Medical Command, lead by the Brooke Army Medical Center, has embarked on a futuristic project which will revolutionize the practice of radiology in the DoD. The U.S. Army Virtual Radiology Environment (USAVRE) is a CONUS-based network that connects all the Army's major medical centers and Regional Medical Commands (RMC). The purpose of the USAVRE is to improve the quality, access, and cost of radiology services in the Army via the use of state-of-the-art medical imaging, computer, and networking technologies. The USAVRE contains multimedia-viewing workstations for static and dynamic modality cases. The storage and archiving systems are based on a distributed computing environment using Common Object Request Broker Architecture (CORBA) middleware protocols. Collaboration between archive centers and viewing workstations are managed by CORBA functions and multimedia object streams. The underlying Telecommunications network is an ATM based backbone network that connects to the RMC regional networks and PACS local networks at medical centers and RMC clinics. The U.S. Army Information Systems Engineering Command (USAISEC) at Ft. Huachuca, AZ is responsible for the ATM backbone network to the RMC sites. The virtual Radiology services in a USAVRE must be applied to several radiology modalities in a virtual network environment. In this discussion, we assume the existence of several PACS networks within a USAVRE environment that have a need to exchange multimedia images and patient information. We define a multimedia collaborative distributed computing environment (DCE) in medical imaging and radiology as a collection of collaborating PACS networks with workstations and image archive systems for the purposes of acquiring and exchanging patient static and video sequence images; storage, retrieval, and archival of those images; performing image analysis and multimedia consultation on patient cases; operation and management of the network to optimize its resources; and to improve the quality and access of the radiology services to the patients. This paper describes the open systems architecture for the USAVRE, including the PACS and Global PACS user equipment. This project is a collaborative effort between military, university, and industry centers with expertise in Teleradiology and Global PACS applications.

In this paper, we present the management of mobile switching center (MSC) trunks and trunk groups in cellular and personal communications systems (PCS) networks. We discuss platform-centered network management approaches based on simple network management protocol (SNMP) and common management information protocol (CMIP). We also describe the Common Object Request Broker Architecture (CORBA <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">∗</sup> ) solution for distributed computing and implementation of distributed objects based on Object Management Group (OMG) Interface Definition Language. <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">∗</sup> CORBA appears to provide a better backbone for manager and agent applications than CMIP. In higher-level designs, the manager and agent applications can be adapted to a CMIP-style interface.

A growing class of real-time systems require end-to-end support for various quality-of-service (QoS) aspects, including bandwidth, latency, jitter and dependability. Applications include command and control, manufacturing process control, videoconferencing, large-scale distributed interactive simulation, and testbeam data acquisition. These systems require support for stringent QoS requirements. To meet this challenge, developers are turning to distributed object computing middleware, such as the Common Object Request Broker Architecture, an Object Management Group (OMG) industry standard. In complex real-time systems, DOC middleware resides between applications and the underlying operating systems, protocol stacks and hardware. CORBA helps decrease the cycle time and effort required to develop high-quality systems by composing applications using reusable software component services rather than building them entirely from scratch. The Real-Time CORBA specification includes features to manage CPU, network and memory resources. The authors describe the key Real-Time CORBA features that they feel are the most relevant to researchers and developers of distributed real-time and embedded systems.

This tutorial addresses how both the Object Management Group (OMG) specifications and the implementation choices made by middleware providers and application developers affect Common Object Request Broker Architecture (CORBA) application scalability. We will cover a range of scalability issues, starting with Object Request Broker (ORB) internals and working outward to full-scale applications, addressing issues such as connection management, Portable Object Adapter (POA) scalability features, multithreading, object lifecycle issues, object location, system configuration, maintenance, and management, and common application architectures. This tutorial is not language-centric and is useful to developers using Java, C++, or any other language to develop CORBA-based applications.

The integration of heterogeneous networks and systems is one of the more urgent requirements expressed by networks and computer users. ISO and ITU-T normalisation bodies have contributed in a significant manner to the definition of a global management framework called TMN (Telecommunication Management Network). TMN is an agreed framework that permitted to a number of public and private network operators to build their management system. However, these existing systems are confronted to the heterogeneity of emerging technologies. In fact, new equipment is built with specific management interfaces, which are not conforming, to the TMN one. The heterogeneity considered in this paper is the one that emerges from the OMG (Object Management Group) CORBA (Common Object Request Broker Architecture). In fact, a lot of CORBA based systems are emerging in the field of management. In this context, telecommunication operators are willing in the short term to use their existing management systems to control them in a uniform way. The aim of this paper is to propose solutions to these problems through the use of Q Adapter that permits to integrate CORBA based equipment into the global management framework based on TMN.KeywordsManagementCORBAOSIAdaptationObjectProtocolService

This tutorial addresses how both the Object Management Group (OMG) specifications and the implementation choices made by middleware providers and application developers affect Common Object Request Broker Architecture (CORBA) application scalability. We will cover a range of scalability issues, starting with Object Request Broker (ORB) internals and working outward to full-scale applications, addressing issues such as connection management, Portable Object Adapter (POA) scalability features, multithreading, object lifecycle issues, object location, system configuration, maintenance, and management, and common application architectures. This tutorial is not language-centric and is useful to developers using Java, C++, or any other language to develop CORBA-based applications.