DCE: Interoperability and Architectural Views

The OSF DCE approach assumes, at the outset, that heterogeneous network and computing technologies will be used to implement distributed systems. This approach envisions a software abstraction layer, often termed "middleware", to reside between applications programs on host computing systems and the network protocol(s) used to interconnect these host systems. This middleware software thus provides a common inteface from two perspectives: it provides a common interface for host/network and network/host access, and it provides a standardized method for invoking specific services across disparate platforms. Each of these common interface perspectives may require translation to be effective.

The OSF DCE approach specifies services in six (6) major areas. These are:

• DCE Thread Management -- the management of separate execution threads within processes when these processes are distributed over diverese computing platforms and networks.
• DCE Remote Procedure Calls -- the provision of a standardized method for executing remote procedure calls across diverse computing platforms and networks.
• DCE Directory Services -- provides a method for identifying and locating required network computing resources when requested by a calling application.
• DCE Distributed Time Service -- provides a mechanism for time-synchronization of distributed computing assets connected via networks of varying length.
• DCE Security Service -- provides mechanisms for confidentiality, authentication, and account management in a diverse, distributed computing environment.
• DCE Distributed File System -- provides a mechanism for synchronizing and coordinating the file systems of diverse interconnected systems, allowing their collected file systems (or a subset thereof) to be used as a single logical file system by other interconnected systems.

The OSF DCE also specifies a number of architectural views to be considered when designing distributed systems. These architectural views can be categorized into three major areas, each having one or more different views:

The first category of DCE architectural views is the Functional category. This category has a single architectural view, the Functional View. The focus of the Functional View is on what the system is intended to do. It consideres operational aspects of the system and is developed from known system requirements and projected new system requirements.

The second category of DCE architectural views is the Implementation category. This category focuses on issues relating to the implementation of a system whose requirements are know. It has five (5) distinct architectural views:

• The Management View, which considers how to manage the system.
• The Security View, which considers how to protect the information processed by the system.
• The Builder's View, which considers issues relelvant to the development of software for the system.
• The Data Management View, which considers the management of the storage, retrieval, processing, archiving, and security of data within the system.
• The User View, which considers system usability.

The third caetgory of DCE Architectural views is the Physical category. This category focuses on the physical assets to be used within a system, their geographical locations, and the requirements and methods for interconnection. It is has two (2) distinct architectural views:

• The Computing View, which considers the computing environment (both hardware and software) at nodes within the distributed system.
• The Communications View, which considers the requirements for and means of interconnection of distributed computing nodes.

Three of these views: the Security View, the Computing View, and the Communications View, are of particular interest in any NAVSTAR redesign. They will be the focus of redesign analysis during the remainder of this report.

More information on the DCE Architecture may be obtained from ECE678 class notes on the subject (available here, in MicroSoft PowerPoint format), and from the Open Group's WWW site, available here. More information on DCE architectural views can also be obtained from the Open Group WWW site, available here.