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{{Short description|Standard to facilitate communication between systems on diverse platforms}}
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{{Use dmy dates|date=December 2019}}
{{Infobox
| title = Common Object Request Broker Architecture
| status = Published
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| website = {{URL|https://www.corba.org/}}
}}
The
While briefly popular in the mid to late 1990s, CORBA's complexity, inconsistency, and high licensing costs have relegated it to being a niche technology.<ref>[https://cacm.acm.org/practice/the-rise-and-fall-of-corba/ The Rise and Fall of CORBA]</ref>
==
CORBA enables communication between software written in different languages and running on different computers. Implementation details from specific operating systems, programming languages, and hardware platforms are all removed from the responsibility of developers who use CORBA. CORBA normalizes the method-call semantics between application objects residing either in the same address-space (application) or in remote address-spaces (same host, or remote host on a network). Version 1.0 was released in October 1991.
CORBA uses an [[interface definition language]] (IDL) to specify the interfaces that objects present to the outer world. CORBA then specifies a ''mapping'' from IDL to a specific implementation language like [[C++]] or [[Java (programming language)|Java]]. Standard mappings exist for [[Ada (programming language)|Ada]], [[C (programming language)|C]], [[C++]], [[C++11]], [[COBOL]], [[Java (programming language)|Java]], [[Lisp (programming language)|Lisp]], [[PL/I]], [[Object Pascal]], [[Python (programming language)|Python]], [[Ruby (programming language)|Ruby]], and [[Smalltalk]]. Non-standard mappings exist for [[C Sharp (programming language)|C#]], [[Erlang (programming language)|Erlang]], [[Perl]], [[Tcl]], and [[Visual Basic]] implemented by [[object request broker]]s (ORBs) written for those languages. Versions of IDL have changed significantly with annotations replacing some pragmas.
The CORBA specification dictates there shall be an ORB through which an application would interact with other objects. This is how it is implemented in practice:
# The application initializes the ORB, and accesses an internal ''Object Adapter'', which maintains things like [[reference counting]], object (and reference) instantiation policies, and object lifetime policies.
# The Object Adapter is used to register instances of the ''generated code classes''. Generated code classes are the result of compiling the user IDL code, which translates the high-level interface definition into an OS- and language-specific class base for use by the user application. This step is necessary in order to enforce CORBA semantics and provide a clean user process for interfacing with the CORBA infrastructure.
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In order to build a system that uses or implements a CORBA-based distributed object interface, a developer must either obtain or write the IDL code that defines the object-oriented interface to the logic the system will use or implement. Typically, an ORB implementation includes a tool called an IDL compiler that translates the IDL interface into the target language for use in that part of the system. A traditional compiler then compiles the generated code to create the linkable-object files for use in the application. This diagram illustrates how the generated code is used within the CORBA infrastructure:
[[
This figure illustrates the high-level paradigm for remote interprocess communications using CORBA. The CORBA specification further addresses data typing, exceptions, network protocols, communication timeouts, etc. For example: Normally the server side has the [[Portable Object Adapter]] (POA) that redirects calls either to the local [[
In addition to providing users with a language and a platform-neutral [[remote procedure call]] (RPC) specification, CORBA defines commonly needed services such as transactions and security, events, time, and other ___domain-specific interface models.
==
This table presents the history of CORBA standard versions.<ref>{{cite web
| url=http://www.omg.org/gettingstarted/history_of_corba.htm▼
▲| title=History of CORBA
▲| publisher=[[Object Management Group]]
|
| url=http://www.corba.org/history_of_corba.htm▼
▲| title=History of CORBA
▲| publisher=[[Object Management Group]]
|
<ref>{{cite web
| url=https://www.omg.org/spec/IDL/ISO/19516/PDF▼
▲| title=OMG IDL Corba Version
▲| publisher=[[Object Management Group]]
|
{| class="wikitable"
|-
!width=60 | Version
!width=110 | Version Date
!width=400 | Highlights
!width=60 | Corba IDL Version
|-
|1.0||October 1991||First version, C mapping || -
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Note that IDL changes have progressed with annotations (e.g. @unit, @topic) replacing some pragmas.
==
A '''servant''' is the invocation target containing methods for handling the [[remote method invocation]]s. In the newer CORBA versions, the remote object (on the server side) is split into the '''object''' ''(that is exposed to remote invocations)'' and '''servant''' ''(to which the former part [[
''Incarnation'' is the act of associating a servant with a CORBA object so that it may service requests.
The ''{{visible anchor|Portable Object Adapter}}'' (POA) is the CORBA object responsible for splitting the server side remote invocation handler into the remote ''object'' and its ''servant''. The object is exposed for the remote invocations, while the servant contains the methods that are actually handling the requests. The servant for each object can be chosen either statically (once) or dynamically (for each remote invocation), in both cases allowing the call forwarding to another server.
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On the server side, the POAs form a tree-like structure, where each POA is responsible for one or more objects being served. The branches of this tree can be independently activated/deactivated, have the different code for the servant ___location or activation and the different request handling policies.
==
The following describes some of the most significant ways that CORBA can be used to facilitate communication among distributed objects.
===
This reference is either acquired through a stringified [[Uniform Resource Locator]] (URL), NameService lookup (similar to [[Domain Name System]] (DNS)), or passed-in as a method parameter during a call.
Object references are lightweight objects matching the interface of the real object (remote or local). Method calls on the reference result in subsequent calls to the ORB and blocking on the thread while waiting for a reply, success, or failure. The parameters, return data (if any), and exception data are marshaled internally by the ORB according to the local language and OS mapping.
===
The CORBA Interface Definition Language provides the language- and OS-neutral inter-object communication definition. CORBA Objects are passed by reference, while data (integers, doubles, structs, enums, etc.) are passed by value. The combination of Objects-by-reference and data-by-value provides the means to enforce great data typing while compiling clients and servers, yet preserve the flexibility inherent in the CORBA problem-space.
===Objects By Value (OBV)===
Apart from remote objects, the CORBA and [[RMI-IIOP]] define the concept of the OBV and Valuetypes. The code inside the methods of Valuetype objects is executed locally by default. If the OBV has been received from the remote side, the needed code must be either ''[[
===CORBA Component Model (CCM)===
CORBA Component Model (CCM) is an addition to the family of CORBA definitions.<ref>{{cite web
| url=http://www.drdobbs.com/the-corba-component-model/184403888▼
▲| title=The CORBA Component Model
▲| publisher=[[Dr. Dobb's Journal]]
▲| date=1 September 2004
|
The CCM has a component container, where software components can be deployed. The container offers a set of services that the components can use. These services include (but are not limited to) [[
===
Portable interceptors are the "hooks", used by CORBA and [[RMI-IIOP]] to mediate the most important functions of the CORBA system. The CORBA standard defines the following types of interceptors:
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Minor codes for the standard exceptions are prefaced by the VMCID assigned to OMG, defined as the unsigned long constant CORBA::OMGVMCID, which has the VMCID allocated to OMG occupying the high order 20 bits. The minor exception codes associated with the standard exceptions that are found in Table 3–13 on page 3-58 are or-ed with OMGVMCID to get the minor code value that is returned in the ex_body structure (see Section 3.17.1, "Standard Exception Definitions", on page 3-52 and Section 3.17.2, "Standard Minor Exception Codes", on page 3-58).
Within a vendor assigned space, the assignment of values to minor codes is left to the vendor. Vendors may request allocation of VMCIDs by sending email to <code>tagrequest@omg.org</code>. A list of currently assigned VMCIDs can be found on the OMG website at:
The VMCID 0 and 0xfffff are reserved for experimental use. The VMCID OMGVMCID (Section 3.17.1, "Standard Exception Definitions", on page 3-52) and 1 through 0xf are reserved for OMG use.
[
===Corba Location (CorbaLoc)===
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: {{mono|corbaloc::160.45.110.41:38693/StandardNS/NameServer-POA/_root}}
A CORBA product may optionally support the "{{mono|http:}}", "{{mono|ftp:}}", and "{{mono|file:}}" formats. The semantics of these is that they provide details of how to download a stringified IOR (or, recursively, download another URL that will eventually provide a stringified IOR). Some ORBs do deliver additional formats which are proprietary for that ORB.
==
CORBA's benefits include language- and OS-independence, freedom from technology-linked implementations, strong data-typing, high level of tunability, and freedom from the details of distributed data transfers.
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; Data-typing: CORBA provides flexible data typing, for example an "ANY" datatype. CORBA also enforces tightly coupled data typing, reducing human errors. In a situation where Name-Value pairs are passed around, it is conceivable that a server provides a number where a string was expected. CORBA Interface Definition Language provides the mechanism to ensure that user-code conforms to method-names, return-, parameter-types, and exceptions.
; High tunability: Many implementations (e.g.
; Freedom from data-transfer details: When handling low-level connection and threading, CORBA provides a high level of detail in error conditions. This is defined in the CORBA-defined standard exception set and the implementation-specific extended exception set. Through the exceptions, the application can determine if a call failed for reasons such as "Small problem, so try again", "The server is dead", or "The reference does not make sense." The general rule is: Not receiving an exception means that the method call completed successfully. This is a very powerful design feature.
; Compression: CORBA marshals its data in a binary form and supports compression. IONA, Remedy IT, and [[Telefonica|Telefónica]] have worked on an extension to the CORBA standard that delivers compression. This extension is called ZIOP and this is now a formal OMG standard.
==
While CORBA delivered much in the way code was written and software constructed, it has been the subject of criticism.<ref name="CORBA_trouble">{{cite web |title=Trouble with CORBA |last=Chappel |first=David |date=May 1998 |publisher=davidchappel.com |url=
Much of the criticism of CORBA stems from poor implementations of the standard and not deficiencies of the standard itself. Some of the failures of the standard itself were due to the process by which the CORBA specification was created and the compromises inherent in the politics and business of writing a common standard sourced by many competing implementors.
; Initial implementation incompatibilities
: The initial specifications of CORBA defined only the IDL, not the on-the-wire format. This meant that source-code compatibility was the best that was available for several years. With CORBA 2 and later this issue was resolved.
; Location transparency
: CORBA's notion of ___location transparency has been criticized; that is, that objects residing in the same [[address space]] and accessible with a simple [[function call]] are treated the same as objects residing elsewhere (different processes on the same machine, or different machines). This is a fundamental design flaw,<ref>{{cite journal |last=Waldo |first=Jim |author2=Geoff Wyant |author3=Ann Wollrath |author4=Sam Kendall |title=A Note on Distributed Computing |journal=Sun Microsystem Laboratories |date=November 1994 |url=
; Design and process deficiencies
: The creation of the CORBA standard is also often cited for its process of [[design by committee]]. There was no process to arbitrate between conflicting proposals or to decide on the hierarchy of problems to tackle. Thus the standard was created by taking a union of the features in all proposals with no regard to their coherence.<ref name="ACM_fall"/> This made the specification complex, expensive to implement entirely, and often ambiguous.
: A design committee composed of a mixture of implementation vendors and customers created a diverse set of interests. This diversity made difficult a cohesive standard. Standards and interoperability increased competition and eased customers' movement between alternative implementations. This led to much political fighting within the committee and frequent releases of revisions of the CORBA standard that some ORB implementors ensured were difficult to use without proprietary extensions.<ref name="CORBA_trouble"/> Less ethical CORBA vendors encouraged customer lock-in and achieved strong short-term results. Over time the ORB vendors that encourage portability took over market share. {{Citation needed|date=November 2017}}
; Problems with implementations
: Through its history, CORBA has been plagued by shortcomings in poor ORB implementations. Unfortunately many of the papers criticizing CORBA as a standard are simply criticisms of a particularly bad CORBA ORB implementation.
: CORBA is a comprehensive standard with many features. Few implementations attempt to implement all of the specifications,<ref name="ACM_fall">{{cite journal |
: Robust implementations of CORBA have been very difficult to acquire in the past, but are now much easier to find. The SUN Java SDK comes with CORBA built-in. Some poorly designed implementations have been found to be complex, slow, incompatible, and incomplete. Robust commercial versions began to appear but for significant cost. As good quality free implementations became available the bad commercial implementations died quickly.
; Firewalls
: CORBA (more precisely, [[General Inter-ORB Protocol|GIOP]]) is not tied to any particular communications transport. A specialization of GIOP is the Internet Inter-ORB Protocol or IIOP. IIOP uses raw [[TCP/IP]] connections in order to transmit data.
: If the client is behind a very restrictive firewall or [[transparent proxy]] server environment that only allows [[HTTP]] connections to the outside through port 80, communication may be impossible, unless the proxy server in question allows the [[
==
===Software engineering===
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===Component-based software technologies===
* [[
* [[GNOME]] [[Bonobo (GNOME)|Bonobo]] – deprecated GNOME cross-language object model▼
* [[KDE]] [[Desktop communication protocol|DCOP]] – deprecated KDE interprocess and software componentry communication system▼
* [[KDE]] [[KDE Platform#KParts|KParts]] – KDE component framework▼
* [[Component Object Model]] (COM) – Microsoft Windows-only cross-language object model
* [[Distributed Component Object Model|DCOM]] (Distributed COM) – extension making COM able to work in networks
* [[
▲* [[GNOME]] [[Bonobo (GNOME)|Bonobo]] – deprecated GNOME cross-language object model
* [[XPCOM]] (Cross Platform Component Object Model) – developed by Mozilla for applications based on it (e.g. [[Mozilla Application Suite]], [[SeaMonkey]] 1.x)▼
* [[IBM System Object Model]] SOM and DSOM – component systems from IBM used in [[OS/2]] and [[AIX]]
* [[Internet Communications Engine]] (ICE)
* [[Java remote method invocation]] (Java RMI)▼
* [[Java Platform, Enterprise Edition]] (Java EE)
▲* [[Java remote method invocation]] (Java RMI)
* [[JavaBean]]
▲* [[KDE]] [[Desktop communication protocol|DCOP]] – deprecated KDE interprocess and software componentry communication system
▲* [[KDE]] [[KDE Platform#KParts|KParts]] – KDE component framework
* [[OpenAIR]]
* [[Remote procedure call]] (RPC)
* [[Windows Communication Foundation]] (WCF)▼
* [[Software Communications Architecture]] (SCA) – components for embedded systems, cross-language, cross-transport, cross-platform
▲* [[Windows Communication Foundation]] (WCF)
▲* [[XPCOM]] (Cross Platform Component Object Model) – developed by Mozilla for applications based on it (e.g. [[Mozilla Application Suite]], [[SeaMonkey]] 1.x)
===Language bindings===
* [[Application binary interface]] - ABI▼
* [[Language binding]]▼
* [[
* [[Calling convention]]
* [[Comparison of application virtual machines]]▼
* [[Dynamic Invocation Interface]]
* [[Foreign function interface]]
▲* [[Language binding]]
* [[Name mangling]]
▲* [[Application binary interface]] - ABI
▲* [[Comparison of application virtual machines]]
* [[SWIG]] opensource automatic interfaces bindings generator from many languages to many languages
==
{{Reflist}}
==
* {{cite web
* {{cite book |
* {{cite book |last1=Brose |first1=
* {{cite book |last1=Harmon |first1=
* {{cite book |last1=Hartman |first1=
* {{cite book
* {{cite book
* {{cite book |
* {{cite book |
* {{cite book |
* {{cite book
* {{cite book |last1=Orfali |first1=
* {{cite book |
* {{cite book |
* {{cite book |
* {{cite book |
* {{cite book |
* {{cite book |
* {{cite book |last1=Slama |first1=
* {{cite book |
==
{{
* [http://www.omg.org/spec/CCM/ Official OMG CORBA Components page]
* [
* [https://www.taox11.org/documents/presentations.html Comparing IDL to C++ with IDL to C++11]
* [
* [http://www.omg.org/spec/CORBA/ OMG XMI Specification]
{{ISO standards}}
{{Authority control}}▼
▲{{Authority control}}
[[Category:Common Object Request Broker Architecture| ]]
[[Category:Component-based software engineering]]
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