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Desktop Support

Fundamental to DCE is its ability to support distributed networked application segments. DCE RPCs allow application segments on low-end client machines to access other application segments on other architectures and share applications with other systems on the network. Applications running on PCs, Macintosh, UNIX-based systems, and proprietary systems can interoperate seamlessly.

Vendor Support for DCE

DCE is supported on most UNIX platforms and many non-UNIX platforms. Most vendors support at least the “secure core,” which means that all the DCE services except the distributed file system and X.500 interface to the global directory service are supported.

Some products are client-only, which means that the actual servers for the DCE services are not provided. Servers not provided are directory service, security service, and time service. Although client machines can use these services, they cannot run the server programs. Another machine in the cell must provide the server programs. Application programs can be built and run the application servers on these client-only systems.

OPEN MANAGEMENT ARCHITECTURE

The Object Management Architecture from the Object Management Group (OMG) combines distributed and object-oriented computing. OMA provides a standard methodology for the creation, persistence,a nd location of objects coupled with communication between objects. Objects can be entire applications or application segments. Combining objects facilitates cooperative processing in a heterogeneous hardware and software environment. OMA is embodied within the common object request broker architecture (CORBA) specification. CORBA provides for object-based systems with DCE provides for procedural systems.

The OMG is an international software industry consortium whose aim is the promotion of the object-oriented approach to software engineering in general, the development of command models and a common interface for development, and also the use of large-scale distributed applications (i.e., open distributed processing) using object-oriented methodology. Although the OMG is not a recognized standards group like the ISO, IEEE, or national bodies such as ANSI, it is developing standards in the form of wholesale consensus agreements between member companies, leading to a single architecture and interface specification for application and enterprise integration on both a small and a large scale.

In 1990, the OMG published its Object Management Architecture (OMA) Guide. This guide outlines a single terminology for object-oriented languages, systems, data bases, and application frameworks; an abstract framework for object-oriented systems; a set of both technical and architectural goals; and an architecture—the OMG object reference model—for distributed applications using object-oriented techniques.

Need for Object Technology

The need for object-based technologies is closely related to the requirement to manage software complexity, the capabilities provided by distributed computing platforms, and the backlog in the applications development within many organizations. An object encapsulates data and behavior and is accessible through methods (or predefined interfaces) that are published for that object. Some key advantages to objects are that they can be reused, and as long as their interfaces remain unchanged, they can be enhanced without affecting other objects that have already been designed to use their capabilities. An object mirrors a real-world item in several ways:

  It has a name (by which it is referenced).
  It performs functions (its methods).
  It queries other objects (sends request).
  It may contain variable information (data).
  It may contain other objects.

Objects are used to hide complexity by encapsulating both data and behavior. In procedural systems, data and behavior are thought of separately, kept separately, and therefore managed separately. Object orientation facilitates modularity as objects themselves are usually kept fairly small, by their very nature must define specific “things,” and have clearly defined interfaces.

Distributed object systems, like distributed computing environments, provide a mechanism for integration of applications and services across heterogeneous systems. The object request broker (ORB) of CORBA provides a means by which objects within an environment can tell other objects what they can and cannot do. Such direction helps reduce the complexity of building distributed applications, as the information is freely “published” within the environment and allows other objects to be built to use the capability provided by a defined object, without having to worry about future changes to the defined object’s interface. Just as DCE allows applications to be segmented into procedural components across heterogeneous platforms using RPC mechanisms, distributed object systems allow applications to be segmented as multiple objects across heterogeneous platforms using such architectures as OMG’s CORBA specification.

Distributed object systems facilitate the integration of different hardware and software systems and help leverage the self-defining nature of objects. They also allow objects to be easily combined in new ways to create applications and to distribute the intelligence throughout the network.

CORBA Version 1.0

In 1992, the CORBA Version 1.0 (CORBA1) specification became available and was adopted by more than 50 computer manufacturers and software developers. Hewlett-Packard (HP), in conjunction with Parc Place Systems, became the first to market a CORBA1-compliant environment, Distributed Smalltalk.

Other CORBA1-compliant systems have been available on a limited basis, but objects created in one CORBA1 environment would not necessarily be able to interoperate with objects created in another CORBA1-based environment. Some implementations used DCE as the underlying communications core (e.g., HP), whereas others used ONC+ (a distributed computing environment proposed by Sun Microsystems but not accepted by OSF). In addition, there was no agreed-on standard for C++ bindings in CORBA1.


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