Distributed object computing forms the basis for nextgeneration application middleware. At the heart of distributed object computing are Object Request Brokers (ORBs), which automate many tedious and error-prone distributed programming tasks. This article presents a case study of key design patterns needed to develop ORBs that can be dynamically configured and evolved for specific application requirements and system characteristics.

This paper describes the object-oriented scripting language XOTcl (Extended OTcl), which is a value added replacement of OTcl. OTcl implements dynamic and introspective language support for objectorientation on top of Tcl. XOTcl includes the functionality of OTcl but focuses on the construction, management, and adaptation of complex systems. In order to

Often a project is faced with non-object-oriented languages or with object systems that are not powerful enough for the project’s purposes. But nevertheless we want to apply advanced object-oriented techniques in these languages. Therefore, build or use an object system as a language extension in the target language, and then implement the design on top of this OBJECT SYSTEM LAYER.

communication types are used as rst-class objects that represent abstractions over the interaction of objects. They encapsulate and enforce invariant behavior in object communications, can achieve the reduction of complexity of object interactions, and can achieve reusability of object interaction types. Besides being a variant of Before/After Interceptor, the abstract communicate types are Component Wrappers and implement a form of Explicit Export/Import.

Component-orientation is an emerging paradigm that promises components that are usable as prefabricated black-boxes. But components

xoComm is a communication infrastructure for web applications based on the HTTP protocol. It provides an HTTP server and client access. Furthermore it is the basic communication service for the ActiWeb web object and mobile code system. The HTTP server component of xoComm is used to implement ActiWeb places. The places use the HTTP client access to provide the communication means for their agents. We present the design and architecture of xoComm on several crucial excerpts of the design. These are closely related to their implementation in the object-oriented scripting language XOTcl. We discuss how a dynamic and reective environment, high-level language constructs, and concepts like design patterns inuence the design and architecture. Keywords: HTTP server/client, web object system, design patterns, dynamics, reection, interception techniques. ii 1 INTRODUCTION In the current practice the WWW is mostly used by exchanging HTML pages and associated les with the HTTP protocol and...

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Many types of applications can benefit from flexible and open middleware. CORBA is an emerging middleware standard for Object Request Brokers (ORBs) that simplifies the development of distributed applications and services. Experience with CORBA demonstrates that it is suitable for traditional RPC-style applications. However, the lack of performance optimizations and quality of service (QoS) features in conventional CORBA implementations make them unsuited for highperformance and real-time applications. This paper makes four contributions to the design of CORBA ORBs for applications with high-performance and real-time requirements. First, it describes the design of TAO, which is our high-performance, real-time CORBA-compliant ORB. Second, it presents TAO's Real-time Scheduling Service, which provides QoS guarantees for deterministic realtime CORBA applications. Third, empirically evaluates the effects of priority inversion and non-determinism in conventional ORBs and shows how these ha...

Large applications that have evolved over the years, are often well-functioning and reliable, but have severe problems regarding flexibility and reuse. It is hard to migrate such systems to a more flexible architecture or to new technologies. The document archive/retrieval system discussed in this paper is an example system, that has these problems. We will present a reengineering case study based to component technology based on an architectural pattern language. The patterns aim at the introduction of flexibility into blackbox component architectures in a piecemeal way. 1 Document Archive/Retrieval System The document archive/retrieval system in focus of this work, is a large C application that has evolved over the years. The system has a suitable large-scale architecture for

Software patterns have been widely promoted as a means of conveying practical design knowledge in a reusable fashion. Several approaches for providing better implementation variants of certain patterns have been presented. These approaches promise great advantages for flexibility, traceability, and reusability of pattern implementations. However, there are only a few larger practical case studies of these concepts available. In this paper we will present a case study of a component framework for flexible processing of markup languages in the objectoriented scripting language XOTcl. The language offers high-level means and architectural support for component integration ("component glueing"), introspection, language dynamics, and message interception techniques. These language constructs enable developers to extend the language with pattern implementations, and so to provide language support for certain pattern fragments. As a case study domain we discuss an extensible and flexible framework for XML/RDF parsing and interpretation that was developed and evolved over a period of three years and is now in use in numerous applications.