Alexander Schill

DC++: distributed object-oriented system support on top of OSF DCE

The OSF Distributed Computing Environment (DCE) is becoming an industry standard for open distributed computing. DCE only supports client/server-style applications based on the remote procedure call (RPC) communication model. The authors describe the design and implementation of an extended distributed object-oriented environment, DC++, on top of DCE. As opposed to RPC, it supports a uniform object model, location independent invocation of fine-grained objects, remote reference parameter passing, dynamic migration of objects between nodes, and C++ language integration. Moreover, the implementation is fully integrated with DCE, using DCE UUIDs for object identification, DCE threads for interobject concurrency, DCE RPC for remote object invocation, and the DCE Cell Directory Service (CDS) for optional retrieval of objects by name. An additional stub compiler enables automatic generation of C++-based object communication interfaces. Low-level parameter encoding is done by DCE RPCs stub generation facility using the C-based DCE interface definition language (IDL).

Distributed Systems, OSF DCE, and Beyond

This introduction paper presents basic foundations of distributed systems and applications and then shows how OSF DCE addresses the requirements imposed by distributed environments. The DCE architecture is illustrated, the basic functionality of the DCE components is explained, and the DCE RPC as the major base for client/server applications is presented in closer detail.

Generic Support for Distributed Processing in Heterogeneous Networks

The apparent complexity of distributed application development, especially in a heterogeneous environment, is the prime motivation for the network operating system kernel described in this paper. The kernel reduces this complexity by separating the distribution related issues from the application related ones. It provides an interface of generic objects and operations, which are able to take away from the application programmer most of the problems of distribution, access protection, resource management, and data representation. This paper develops the basic concepts of the kernel from rather general design objectives and illustrates its use and major properties. A prototype implementation, which is running on three different architectures, demonstrates the feasibility of adding these facilities to a given operating system without affecting existing interfaces or applications. The paper reports about early experience with the implementation and performance of the prototype.

Distributed system and execution model for office execution model for office environments

Abstract An approach for the representation of distributed office server environments and for the management of distributed office procedures in such systems is presented. A new notation to specify the server structure of a distributed office system is introduced. Based on such a description, complex office procedures to be executed within the environment can be specified using a complementary notation. A rich set of supporting runtime mechanisms is provided to enable flexible routing of office procedures, dynamic service binding, and remote execution monitoring. The approach is based on distributed object-oriented systems, and particularly exploits their notions of object mobility and of location independent object invocation. A number of existing distributed systems, office automation approaches, and emerging standardization efforts are also discussed and compared to this work.

Mobility control in distributed object-oriented applications

Object-oriented programming for distributed systems provides support for location-independent remote object invocations while preserving the ability to control object placement explicitly using mobility operations. The author investigates problems with this approach and proposes a higher-level control of object placement for distributed object-oriented applications. This control mechanism is based on a conceptual object-relationship model. Using a priori knowledge about object communication behavior, appropriate mobility decisions can be performed by a runtime control component. The central thesis is that distribution aspects can be separated from application semantics explicitly. An experimental prototype system to study these issues is described.<<ETX>>

A system framework for open distributed processing

Emerging distributed applications increasingly require adequate tools and techniques for system- and application-level management. The integration of both aspects in an overall system framework is an important issue. This paper presents such a framework supporting advanced distributed applications in the context of the evolving Open Distributed Processing reference model. For system-level communication, an efficient subsystem providing advanced service capabilities is presented to cope with the increasing diversity of application service requirements. For application-level processing, a distributed object-based environment is offered. It implements location-independent invocation and object mobility and provides a high level of distribution transparency. The approach is augmented with tools and techniques for managing an overall application configuration.

Language and distributed system support for complex organizational services

This paper presents a distributed approach and system to support complex distributed application services (briefly: complex services). A basic application service is described by a typed operational interface and is implemented by multiple distributed server instances. Complex services consist of sequential and parallel executions of basic services. They are implemented by a specific execution model. This model allows for specification of complex service execution sequences, for management of data objects to be operated upon, and for flexible binding of requested services to associated servers. This flexibility is mainly achieved by the dynamic routing of objects representing a complex service execution. Specific support for this model is provided by a new high-level language to specify a service/server environment and to describe execution sequences, by an associated runtime environment, and by a supplemental monitor approach to supervise distributed service executions. The paper describes these facilities using examples from the office automation area.

Using the Object Paradigm for Distributed Application Development

During the last decade, significant progress has been achieved in the area of distributed systems. At the same time, the need for distributed applications has increased heavily. A large number of distributed programming languages to support those kinds of applications is now available. Most of these approaches, however, still fail in providing appropriate levels of distribution abstraction and in supporting the software design stage. The object paradigm with extensions towards distributed systems is a promising base to overcome these shortcomings.

A software engineering environment for distributed applications

Abstract With the recent development of powerful workstations integrated in local area networks, the need for distributed applications has increased significantly. This way, formerly autonomous applications of areas like computer integrated manufacturing or office automation can be integrated to cooperating entities. However, the development of these kinds of applications is still not well supported. The paper describes an object-oriented software engineering approach for distributed applications. The approach is centered around a wide-spectrum design language used as a common base for a set of workbenches. The associated tools are focusing on problems related to distribution and complexity of applications. Life-cycle spanning development support shall be provided by the environment.

Integrated support for distributed object-oriented applications

Objects and distribution have been combined to provide a sound base for distributed application development. The main characteristics of this approach are distribution-transparent object invocations and object mobility. Existing systems, however, do not support object mobility control and distributed application configuration management. An integrated higher level approach for these areas based on existing approaches is presented. The mobility control support focuses on the goal of colocating communicating objects. The application configuration management support provides means for appropriate structuring of distributed applications. For a high-level specification of their initial object placement, and for performing configuration changes. It is centered around a separate configuration language. The synthesis of both areas has been the base for integrated prototypical implementation, which is also described briefly together with an example application.<<ETX>>