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<TITLE>A CORBA Primer</TITLE>

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<p class=ColumnTitle>Distributed

CBuilder </p>



<p class=ColumnSubtitle>CORBA

/ VisiBroker / ORB / C++Builder 4, 5</p>



<p class=BodyText> &nbsp; </p>



<p class=Byline>By Rabi    

Satter</p>    

    

<p class=BodyText> &nbsp; </p>    

    

<p class=StoryTitle><b>A CORBA    

Primer</b></p>    

    

<p class=StorySubtitle>Building    

Cross-platform Distributed Applications</p>    

    

<p class=BodyText> &nbsp; </p>    

    

<p class=BodyText> Common    

Object Request Broker Architecture (CORBA) is a technology standard developed    

by the Object Management Group (OMG), a non-profit group, to allow objects to    

communicate with each other and develop the architecture to support remote    

objects. This article shows how to use C++Builder 4/5 Enterprise and VisiBroker    

to build distributed object applications. The article covers what CORBA is, how    

it works, and the steps for building a CORBA-based application. </p>    

    

<p class=BodyText> &nbsp; </p>    

    

<p class=BodyText> CORBA    

consists of standards for an Object Request Broker (ORB) and the services and    

facilities for supporting a distributed application. The ORB defines a mechanism    

for objects to communicate with each other. A common way for people to view ORB    

is as an object bus that one can plug objects into to communicate, regardless    

of the location and language in which the object was written. In addition, the    

mechanism for communication is transparent to the programmer. The programmer    

uses the remote object the same way one would use a regular object. The client    

object views the remote object as local and the remote object views the client    

object as local. </p>    

    

<p class=BodyText> &nbsp; </p>    

    

<p class=BodyText> The    

CORBA services represent services that distributed object systems may need.    

These services are used by the remote and local objects to work with the ORB    

and other objects (see Figure 1). </p>    

    

<p class=BodyText> &nbsp; </p>    

    

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  <p class=BodyText> <b>Service</b></p>    

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  <p class=BodyText> <b>Description</b></p>    

  </td>    

 </tr>    

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  <p class=BodyText> Naming</p>    

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  <p class=BodyText> Used    

  to locate other objects by a name. </p>    

  </td>    

 </tr>    

 <tr>    

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  <p class=BodyText> Externalization    

  </p>    

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  <p class=BodyText> Standard    

  way for retrieving and saving information using streams. </p>    

  </td>    

 </tr>    

 <tr>    

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  <p class=BodyText> Persistence</p>    

  </td>    

  <td width=247 valign=top style='width:185.0pt;border-top:none;border-left:    

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  <p class=BodyText> Standard    

  way for storing objects. </p>    

  </td>    

 </tr>    

 <tr>    

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  border-top:none;mso-border-top-alt:solid windowtext .5pt;padding:0in 5.4pt 0in 5.4pt'>    

  <p class=BodyText> Events</p>    

  </td>    

  <td width=247 valign=top style='width:185.0pt;border-top:none;border-left:    

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  <p class=BodyText> Standard    

  way for registering and un-registering objects interested in an event. The    

  event object is responsible for notifying event recipients. </p>    

  </td>    

 </tr>    

 <tr>    

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  <p class=BodyText> Life    

  Cycle</p>    

  </td>    

  <td width=247 valign=top style='width:185.0pt;border-top:none;border-left:    

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  <p class=BodyText> Defines    

  the life cycle of objects on the object bus. </p>    

  </td>    

 </tr>    

 <tr>    

  <td width=87 valign=top style='width:65.4pt;border:solid windowtext .5pt;    

  border-top:none;mso-border-top-alt:solid windowtext .5pt;padding:0in 5.4pt 0in 5.4pt'>    

  <p class=BodyText> Transactions</p>    

  </td>    

  <td width=247 valign=top style='width:185.0pt;border-top:none;border-left:    

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  <p class=BodyText> Defines    

  a two-phase commit mechanism for objects. </p>    

  </td>    

 </tr>    

 <tr>    

  <td width=87 valign=top style='width:65.4pt;border:solid windowtext .5pt;    

  border-top:none;mso-border-top-alt:solid windowtext .5pt;padding:0in 5.4pt 0in 5.4pt'>    

  <p class=BodyText> Properties</p>    

  </td>    

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  <p class=BodyText> Service    

  for associating properties with an object. </p>    

  </td>    

 </tr>    

 <tr>    

  <td width=87 valign=top style='width:65.4pt;border:solid windowtext .5pt;    

  border-top:none;mso-border-top-alt:solid windowtext .5pt;padding:0in 5.4pt 0in 5.4pt'>    

  <p class=BodyText> Query</p>    

  </td>    

  <td width=247 valign=top style='width:185.0pt;border-top:none;border-left:    

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  <p class=BodyText> Standard    

  for querying objects using a scripting language. Similar to SQL and based on    

  SQL 3 specification and Object Database Management Group Object Query    

  Language. </p>    

  </td>    

 </tr>    

 <tr>    

  <td width=87 valign=top style='width:65.4pt;border:solid windowtext .5pt;    

  border-top:none;mso-border-top-alt:solid windowtext .5pt;padding:0in 5.4pt 0in 5.4pt'>    

  <p class=BodyText> Concurrency    

  Control</p>    

  </td>    

  <td width=247 valign=top style='width:185.0pt;border-top:none;border-left:    

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  <p class=BodyText> Provides    

  a locking mechanism for objects. </p>    

  </td>    

 </tr>    

 <tr>    

  <td width=87 valign=top style='width:65.4pt;border:solid windowtext .5pt;    

  border-top:none;mso-border-top-alt:solid windowtext .5pt;padding:0in 5.4pt 0in 5.4pt'>    

  <p class=BodyText> Relationships</p>    

  </td>    

  <td width=247 valign=top style='width:185.0pt;border-top:none;border-left:    

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  <p class=BodyText> Allows    

  for creating links between objects that have no direct knowledge of each    

  other. </p>    

  </td>    

 </tr>    

 <tr>    

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  border-top:none;mso-border-top-alt:solid windowtext .5pt;padding:0in 5.4pt 0in 5.4pt'>    

  <p class=BodyText> Collection</p>    

  </td>    

  <td width=247 valign=top style='width:185.0pt;border-top:none;border-left:    

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  <p class=BodyText> Standard    

  for creating and manipulating collections of objects. </p>    

  </td>    

 </tr>    

 <tr>    

  <td width=87 valign=top style='width:65.4pt;border:solid windowtext .5pt;    

  border-top:none;mso-border-top-alt:solid windowtext .5pt;padding:0in 5.4pt 0in 5.4pt'>    

  <p class=BodyText> Time</p>    

  </td>    

  <td width=247 valign=top style='width:185.0pt;border-top:none;border-left:    

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  <p class=BodyText> Standard    

  for providing synchronizing time in a distributed environment. </p>    

  </td>    

 </tr>    

 <tr>    

  <td width=87 valign=top style='width:65.4pt;border:solid windowtext .5pt;    

  border-top:none;mso-border-top-alt:solid windowtext .5pt;padding:0in 5.4pt 0in 5.4pt'>    

  <p class=BodyText> Security</p>    

  </td>    

  <td width=247 valign=top style='width:185.0pt;border-top:none;border-left:    

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  <p class=BodyText> Framework    

  for security on an object. </p>    

  </td>    

 </tr>    

 <tr>    

  <td width=87 valign=top style='width:65.4pt;border:solid windowtext .5pt;    

  border-top:none;mso-border-top-alt:solid windowtext .5pt;padding:0in 5.4pt 0in 5.4pt'>    

  <p class=BodyText> Startup</p>    

  </td>    

  <td width=247 valign=top style='width:185.0pt;border-top:none;border-left:    

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  <p class=BodyText> Automatic    

  activation service to start objects not yet started. </p>    

  </td>    

 </tr>    

 <tr>    

  <td width=87 valign=top style='width:65.4pt;border:solid windowtext .5pt;    

  border-top:none;mso-border-top-alt:solid windowtext .5pt;padding:0in 5.4pt 0in 5.4pt'>    

  <p class=BodyText> Trader</p>    

  </td>    

  <td width=247 valign=top style='width:185.0pt;border-top:none;border-left:    

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  <p class=BodyText> Directory    

  of available objects as services. </p>    

  </td>    

 </tr>    

 <tr>    

  <td width=87 valign=top style='width:65.4pt;border:solid windowtext .5pt;    

  border-top:none;mso-border-top-alt:solid windowtext .5pt;padding:0in 5.4pt 0in 5.4pt'>    

  <p class=BodyText> Licensing</p>    

  </td>
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