A Theory of Distributed Objects

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Distributed and communicating objects are becoming ubiquitous. In global, Grid and peer-to-peer computing environments, extensive use is made of objects interacting through method calls. So far, no general formalism has been proposed for the foundation of such systems. Caromel and Henrio are the first to define a calculus for distributed objects interacting using asynchronous method calls with generalized futures - a must in large-scale systems, providing both high structuring and low coupling, and thus scalability.

The authors provide very generic results on expressiveness and determinism, and the potential of their approach is further demonstrated by its capacity to cope with advanced issues such as mobility and components. Researchers and graduate students will find here an extensive review of concurrent languages and calculi, with comprehensive figures and summaries. Developers of distributed systems can adopt the many implementation strategies that are presented and analyzed in detail.

Also, in remote method calling, the programmer must handle exceptions. Another difference from HORB is that super class is determined in remote objects.

A Theory of Distributed Objects

If asked which is currently the best solution, we would have to answer, the network seamless concept of HORB. But we can answer based only on personal preference; we are not able to make an objective evaluation. Instead of deciding which is good and which is bad at this time, we recommend that readers compare HORB and RMI from a more objective viewpoint. By doing so, you will be able to understand the intentions of the creator of the distributed object technology that is to be used.

You also will be able to understand the software while compensating for any defects. And, you may be able to gain insight into the form that distributed objects should take in the future.


In sum, the best solution is something that is determined by the trends of the time and timing. Deciding which items to set as remote objects is an important point. Distributed objects are single-memory objects that have been expanded to the network. When designing remote objects, programmers should consider the overhead involved.

Specifically, programmers must consider points such as minimizing the network transfer volume in remote processing and making the client and remote object interface as small as possible. In choosing to build a system, in order to create a balanced design, requirements for including distributed objects in the network must be considered. Another important point is to use object passing and remote objects properly.

Remote objects represent a method of referring to server objects through proxies. For example, in the music object example that was introduced earlier, the processing can be implemented by mounting the music objects as remote objects instead of by using object passing. Object passing allows the programmer to reduce the network communication overhead because the object is copied to the client.

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Remote objects are better suited for cases in which objects need to access server CPU resources or server data resources directly. From the viewpoint of data consistency, remote objects are preferred when the client only requires some object attributes and all server objects do not have to be copied. Remote objects also are preferred for models in which the server object attributes constantly are changed by server processes.

Designs in which the distribution targets are clearly indicated should be implemented seamlessly from the object-orientation analysis. In the future, the network distributed object model probably will have to be incorporated as a development process link of the object-orientation methodology. The reuse base model is a category classification method that classifies objects from the request analysis stage into roles such as View views , Process processes , and Data data management , and clarifies the reuse scope, such as Generic general use , AppParts system common , and App application specific.

The essence of COM is a language-neutral way of implementing objects that can be used in environments different from the one in which they were created, even across machine boundaries. For well-authored components, COM allows reuse of objects with no knowledge of their internal implementation, as it forces component implementers to provide well-defined interfaces that are separated from the implementation. The different allocation semantics of languages are accommodated by making objects responsible for their own creation and destruction through reference-counting.

Type conversion casting. DDM was initially designed to support record-oriented files; it was extended to support hierarchical directories, stream-oriented files, queues, and system command processing; it was further extended to be the base of IBM's Distributed Relational Database Architecture DRDA ; and finally, it was extended to support data description and conversion. Defined in the period from to , DDM specifies necessary components, messages, and protocols, all based on the principles of object-orientation. DDM is not, in itself, a piece of software; the implementation of DDM takes the form of client and server products.

As an open architecture, products can implement subsets of DDM architecture and products can extend DDM to meet additional requirements. Taken together, DDM products implement a distributed file system. DDM Architecture in the media. Protocol is a term used by particular object-oriented programming languages with a variety of specific meanings, which other languages may term interface or trait.

Protocol when used otherwise is akin to a Communication protocol, indicating the chain of interactions between the caller and the object. Languages which use the term Protocol include: Clojure Elixir Java 8 Kotlin Logtalk Objective-C[1] Swift Python[2] In these languages, a protocol is a common means for discrete objects to communicate with each other.

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These are definitions of methods and values which the objects agree upon, in order to co-operate, as part of an API. The arguments that these messages may be supplied with. The types of results that these messages return. The invariants that are preserved despite modifications to the state of an object. The exceptional situations that will be required to be handled by clients to the. A distributed operating system is a software over a collection of independent, networked, communicating, and physically separate computational nodes. They handle jobs which are serviced by multiple CPUs.

Each subset is a composite of two distinct service provisioners. Second is a higher-level collection of system management components that coordinate the node's individual and collaborative activities. These components abstract microkernel functions and support user applications. They support the system's goal of integrating multiple resources and processing functionality into an efficient and stable system. Fragmented objects are truly distributed objects. It is a novel design principle extending the traditional concept of stub based distribution.

In contrast to distributed objects, they are physically distributed and encapsulate the distribution in the object itself. Parts of the object - named fragments - may exist on different nodes and provide the object's interface. Each client accessing a fragmented object by its unique object identity presumes a local fragment. Fragmented objects may act like a RPC-based infrastructure or a caching smart proxy as well.

Therefore, clients cannot distinguish between the access of a local object, a local stub or a local fragment. Full transparency is gained by the following characteristics of fragmented objects. Fragmented object Arbitrary internal communication Arbitrary protocols may be chosen for the internal communication between the fragments. For instance, this allows to hide real-time protocols e. In computer programming, the proxy pattern is a software design pattern. A proxy, in its most general form, is a class functioning as an interface to something else.

The proxy could interface to anything: a network connection, a large object in memory, a file, or some other resource that is expensive or impossible to duplicate. In short, a proxy is a wrapper or agent object that is being called by the client to access the real serving object behind the scenes.

Use of the proxy can simply be forwarding to the real object, or can provide additional logic. In the proxy, extra functionality can be provided, for example caching when operations on the real object are resource intensive, or checking preconditions before operations on the real object are invoked. For the client, usage of a proxy object is similar to using the real object, because both implement the same interface. Overview The Proxy [1] design pattern is one of the twenty-three well-known GoF design patterns that describe how to solve recurring des.

An illustration of a shared memory system of three processors. In computer science, shared memory is memory that may be simultaneously accessed by multiple programs with an intent to provide communication among them or avoid redundant copies. Shared memory is an efficient means of passing data between programs.

Depending on context, programs may run on a single processor or on multiple separate processors. Using memory for communication inside a single program, e. In computer hardware, shared memory refers to a typically large block of random access memory RAM that can be accessed by several different central processing units CPUs in a multiprocessor computer system.

Inter-process communication

Shared memory systems may use:[1] uniform memory access UMA : all the processors share the physical mem. A distributed control system DCS is a computerised control system for a process or plant usually with a large number of control loops, in which autonomous controllers are distributed throughout the system, but there is central operator supervisory control.

Distributed computing architecture

This is in contrast to systems that use centralized controllers; either discrete controllers located at a central control room or within a central computer. The DCS concept increases reliability and reduces installation costs by localising control functions near the process plant, with remote monitoring and supervision. Distributed control systems first emerged in large, high value, safety critical process industries, and were attractive because the DCS manufacturer would supply both the local control level and central supervisory equipment as an integrated package, thus reducing design integration risk.

In software engineering, the mediator pattern defines an object that encapsulates how a set of objects interact. This pattern is considered to be a behavioral pattern due to the way it can alter the program's running behavior. Usually a program is made up of many classes. Logic and computation are distributed among these classes. This makes the program harder to read and maintain.

Furthermore, it can become difficult to change the program, since any change may affect code in several other classes. With the mediator pattern, communication between objects is encapsulated within a mediator object. Objects no longer communicate directly with each other, but instead communicate through the mediator.

This reduces the dependencies between communicating objects, thereby reducing coupling. Overview The Mediator[1] design pattern is one of the. In distributed programming, a portable object is an object which can be accessed through a normal method call while possibly residing in memory on another computer. It is portable in the sense that it moves from machine to machine, irrespective of operating system or computer architecture.

This mobility is the end goal of many remote procedure call systems. The advantage of portable objects is that they are easy to use and very expressive, allowing programmers to be completely unaware that objects reside in other locations. It provides a repository of tuples that can be accessed concurrently. As an illustrative example, consider that there are a group of processors that produce pieces of data and a group of processors that use the data.

Producers post their data as tuples in the space, and the consumers then retrieve data from the space that match a certain pattern. This is also known as the blackboard metaphor. Tuple space may be thought as a form of distributed shared memory. Tuple spaces were the theoretical underpinning of the Linda language developed by David Gelernter and Nicholas Carriero at Yale University in NET framework. Object Spaces Object Spaces is a paradigm for development of distributed computing applications.

It is characterized by the existence of logical entit. Schmidt during his graduate work at the University of California, Irvine. Development followed him to the Washington University, St. Louis, where he was employed. It provides common data types and methods[3] to access the powerful but complex features of modern operating systems. These include: inter-process communication, thread management, efficient memory management, etc.

It was designed to be. A distributed hash table DHT is a class of a decentralized distributed system that provides a lookup service similar to a hash table: key, value pairs are stored in a DHT, and any participating node can efficiently retrieve the value associated with a given key. Keys are unique identifiers which map to particular values, which in turn can be anything from addresses, to documents, to arbitrary data.

This allows a DHT to scale to extremely large numbers of nodes and to handle continual node arrivals, departures, and failures. DHTs form an infrastructure that can be used to build more complex services, such as anycast, cooperative Web caching, distributed file systems, domain name services, instant messaging, multicast, and also peer-to-peer file sharing and content distribution systems.

Notable distributed networks th. Visual infographic showing plant cell types. Image showing the visual communication process Visual communication is the conveyance of ideas and information in forms that can be seen. Visual communication in part or whole relies on eyesight. Besides two dimensional images, there are other ways to express information visually - gestures and body language, animation digital or analogue , and film.

Visual communication by e-mail, a textual medium, is commonly expressed with ASCII art, emoticons, and embedded digital images. Visual communication has become one of the most impo. Anything between the kernel and user applications is considered middleware. Middleware is computer software that provides services to software applications beyond those available from the operating system. It can be described as "software glue". It gained popularity in the s as a solution to the problem of how to link newer applications to older legacy systems, although the term had been in use since An IETF workshop in defined middleware as "those services found above the transport i.

The Unified Modeling Language UML is a general-purpose, developmental, modeling language in the field of software engineering that is intended to provide a standard way to visualize the design of a system. It was developed by Grady Booch, Ivar Jacobson and James Rumbaugh at Rational Software in —, with further development led by them through Domain-driven design DDD is an approach to software development for complex needs by connecting the implementation to an evolving model.

The term was coined by Eric Evans in his book of the same title. The subject area to which the user applies a program is the domain of the software; Model A system of abstractions that describes selected aspects of a domain and can be used to solve problems related to that domain; Ubiquitous Language A language structured around the doma. Graphic communication as the name suggests is communication using graphic elements. These elements include symbols such as glyphs and icons, images such as drawings and photographs, and can include the passive contributions of substrate, color and surroundings.

It is the process of creating, producing, and distributing material incorporating words and images to convey data, concepts, and emotions. The drawings of plans and refinements and a rough map sketched to show the way could be considered graphical communication. Any medium that uses a graphics to aid in conveying a message, instruction, o.

Distributed Interactive Simulation DIS is an IEEE standard for conducting real-time platform-level wargaming across multiple host computers and is used worldwide, especially by military organizations but also by other agencies such as those involved in space exploration and medicine. BBN introduced the concept of dead reckoning to efficiently transmit the state of battle field entities. The platform is Java-based, but can broker interactions between other platforms such as.

NET using web services or sockets. The architecture is a scalable,[2] distributable object broker that can handle interactions across legacy systems, in-house applications, and almost all modern transports and protocols. It consists of two types of editors for development: Visual editor and XML editor. Anypoint Enterprise Security: A suite of security-related features for secure access and transactions to Mule applications. Management Tools Mule M. In distributed computing, a remote procedure call RPC is when a computer program causes a procedure subroutine to execute in a different address space commonly on another computer on a shared network , which is coded as if it were a normal local procedure call, without the programmer explicitly coding the details for the remote interaction.

That is, the programmer writes essentially the same code whether the subroutine is local to the executing program, or remote. The RPC model implies a level of location transparency, namely that calling procedures is largely the same whether it is local or remote, but usually they are not identical, so local calls can be distinguished from remote calls.

Remote calls are usually orders of magnitude slower and l. NET Framework.