Distributed object: Difference between revisions

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{{Short description|Concept in distributed computing}}

'''Distributed objects''' are [[Computer software | software]] modules that are designed to work together, but reside either in multiple [[Computer | computers]] connected via [[Computer network | network]] or in different [[Process (computing) | processes]] inside the same computer. One object sends a message to another object in a remote machine or process to perform some task. The results are sent back to the calling object.

[[File:Distributed object communication.png|thumb|Image describes communication between distributed objects residing in different machines.]]

In [[distributed computing]], '''distributed objects'''{{citation needed|date=May 2016}} are objects (in the sense of [[object-oriented programming]]) that are distributed across different [[address space]]s, either in different [[Process (computing)|processes]] on the same computer, or even in multiple [[computer]]s connected via a [[Computer network|network]], but which work together by sharing data and invoking methods. This often involves [[___location transparency]], where remote objects appear the same as local objects. The main method of [[distributed object communication]] is with [[remote method invocation]], generally by message-passing: one object sends a message to another object in a remote machine or process to perform some task. The results are sent back to the calling object.

See also [[Internet protocol suite]].

Distributed objects were popular in the late 1990s and early 2000s, but have since fallen out of favor.<ref>[http://martinfowler.com/articles/distributed-objects-microservices.html Microservices and the First Law of Distributed Objects], Martin Fowler, 13 August 2014</ref>

== Local vs Distributed Objects ==

The term may also generally refer to one of the extensions of the basic [[object (computer science)|object]] concept used in the context of distributed computing, such as ''replicated objects'' or ''live distributed objects''.

Local and distributed objects differs in many dimentions<ref>W. Emmerich (2000) Engineering distributed objects, John Wiley & Sons Ltd.</ref> here is some of them:

* ''[[replication (computer science)|Replicated objects]]'' are groups of software components (''replicas'') that run a distributed multi-party protocol to achieve a high degree of consistency between their internal states, and that respond to requests in a coordinated manner. Referring to the group of replicas jointly as an ''object'' reflects the fact that interacting with any of them exposes the same externally visible state and behavior.

# Life cycle : Creation, migration and deletion of distributed objects is different from local objects.

* ''[[Live distributed object]]s'' (or simply ''[[live distributed object|live objects]]'')<ref>Ostrowski, K., Birman, K., Dolev, D., and Ahnn, J. (2008). "Programming with Live Distributed Objects", ''Proceedings of the 22nd European Conference on Object-Oriented Programming'', Paphos, Cyprus, July 07–11, 2008, J. Vitek, Ed., ''Lecture Notes in Computer Science'', vol. 5142, Springer-Verlag, Berlin, Heidelberg, 463-489, http://portal.acm.org/citation.cfm?id=1428508.1428536.</ref> generalize the ''replicated object'' concept to groups of replicas that might internally use any distributed protocol, perhaps resulting in only a weak consistency between their local states. Live distributed objects can also be defined as running instances of distributed multi-party protocols, viewed from the object-oriented perspective as entities that have a distinct identity, and that can encapsulate distributed state and behavior.

# Reference : Objets reference of distributed objetcs are more complex than simple pointer to memory adress.

# Request Latency : A distributed objects request is orders of maginitude slower than local method invocation.

# Object Activation : Distributed objects may not always be advailable to serve and object request at any point in time.

# Parallelism : Distributed object may be executed in parallel.

# Communication : there are different communication primitive available for distributed objects requests.

# Failure : Distributed object have a lot more point of failure than typical local objects

# Security : Distribution make it vulnarable for security attacks and so on.

See also [[Internet protocol suite]].

== Local vs. Distributeddistributed Objectsobjects ==

Local and distributed objects differsdiffer in many dimentionsrespects.<ref>W. Emmerich (2000) Engineering distributed objects, John Wiley & Sons Ltd.</ref><ref>Samuel C. Kendall, [[Jim Waldo]], Ann Wollrath, and Geoff Wyant. 1994. A Note on Distributed Computing. Technical Report. Sun Microsystems, Inc., Mountain View, CA, USA.</ref> hereHere isare some of them:

# Life cycle : Creation, migration and deletion of distributed objects is different from local objects.

# Reference : ObjetsRemote referencereferences ofto distributed objetcsobjects are more complex than simple pointerpointers to memory adress.addresses

# Request Latency : A distributed objectsobject request is orders of maginitudemagnitude slower than local method invocation.

# Object Activation : Distributed objects may not always be advailableavailable to serve andan object request at any point in time.

# Parallelism : Distributed objectobjects may be executed in parallel.

# Communication : thereThere are different communication primitiveprimitives available for distributed objects requests.

# Failure : Distributed objectobjects have a lotfar more pointpoints of failure than typical local objects.

# Security : Distribution makes them vulnerable to attack.

== Examples ==

The RPC facilities of the cross platform serialization protocol, [[Cap'n Proto]] amount to a distributed object protocol. Distributed object method calls can be executed (chained, in a single network request, if needs be) through interface references/[[Capability-based security|capabilities]].<ref>{{Cite web|url=https://kentonv.github.io/capnproto/rpc.html|title = Cap'n Proto: RPC Protocol}}</ref>

Distributed objects are implemented in [[Objective-C]] using the [[Cocoa (API) | Cocoa API]] with the NSConnection class and supporting objects.

Distributed objects are implemented in [[Objective-C]] using the [[Cocoa (API) | Cocoa API]] with the NSConnection class and supporting objects.

Distributed objects are used in [[Java RMI]].

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[[CORBA]] lets one build distributed mixed object systems.

[[Component_Object_ModelDistributed Component Object Model|DCOM]] is a framework for distributed objects on the Microsoft platform.

[[DDObjects]] is a framework for distributed objects using Borland Delphi.

[[Pyro]]Jt is a framework for distributed objectscomponents using the [[Python (programming language)|Pythona programmingmessaging language]]paradigm.

[[JavaSpaces]] is a Sun specification for a distributed, shared memory (space based)

[[PYthon Remote Objects|Pyro]] is a framework for distributed objects using the [[Python (programming language)|Python programming language]].

[[dRuby]]Distributed Ruby (DRb) is a framework for distributed objects using the [[Ruby programming language]].

==See also==

[http://www.replicanet.com/about.html Distributed Objects using C++]

*[[Fragmented object]]

*[[Distributed object communication]]

*[[Object request broker]]

==References==

{{Comp-sci-stub}}

{{reflist}}

[[Category:Distributed computing architecture]]