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<chapter>
  <header>
    <copyright>
      <year>1999</year><year>2016</year>
      <holder>Ericsson AB. All Rights Reserved.</holder>
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      Licensed under the Apache License, Version 2.0 (the "License");
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    <title>Introduction to Orber</title>
    <prepared>Megan Lynch</prepared>
    <docno></docno>
    <date>1998-09-21</date>
    <rev></rev>
    <file>ch_introduction.xml</file>
  </header>

  <section>
    <title>Overview</title>
    <p>The Orber application is a CORBA compliant Object Request Brokers
      (ORB), which provides CORBA functionality in an Erlang
      environment. Essentially, the ORB channels communication or
      transactions between nodes in a
      heterogeneous environment.
      </p>
    <p><term id="CORBA"><termdef>Common Object Request Broker Architecture is a common communication standard developed by the OMG (Object Management Group)</termdef></term>(Common Object Request Broker
      Architecture) provides an interface definition language  allowing
      efficient system integration and also supplies standard
      specifications for some services.
      </p>
    <p>The Orber application contains the following parts:</p>
    <list type="bulleted">
      <item>
        <p>ORB kernel and IIOP support</p>
      </item>
      <item>
        <p>Interface Repository</p>
      </item>
      <item>
        <p>Interface Definition Language Mapping for Erlang</p>
      </item>
      <item>
        <p>CosNaming Service</p>
      </item>
    </list>

    <section>
      <title>Benefits</title>
      <p>Orber provides CORBA functionality in an Erlang environment that enables:
        </p>
      <list type="bulleted">
        <item>
          <p><em>Platform interoperability and transparency</em></p>
          <p>Orber enables communication between
            OTP applications or Erlang environment applications and
            other platforms; for example,  Windows NT, Solaris
            etc, allowing platform  transparency. This is especially helpful in situations where there
            are many users with  different platforms.  For example,
            booking airline tickets would require the airline database
            and hundreds of travel agents (who may not have the same
            platform) to book seats on flights. </p>
        </item>
        <item>
          <p><em>Application level interoperability and transparency</em></p>
          <p>As Orber is a CORBA compliant application, its purpose is
            to provide interoperability and transparency on the application
            level. 
            Orber simplifies the distributed system software  by defining the
            environment as  objects, which in effect, views
            everything as identical regardless of programming
            languages.            <br></br>
 Previously, time-consuming programming was
            required to facilitate communication between different languages.
            However, with CORBA compliant Orber the Application
            Programmer is relieved of this task. This makes 
            communication on an application level relatively transparent to the user.</p>
        </item>
      </list>
    </section>

    <section>
      <title>Purpose and Dependencies</title>
      <p>The system architecture and OTP dependencies of Orber are illustrated in figure 1 below:</p>
      <marker id="dependent"></marker>
      <image file="dependent.gif">
        <icaption>
Figure 1: Orber Dependencies and Structure.</icaption>
      </image>
      <p>Orber  is dependent on  Mnesia (see the Mnesia
        documentation) - an Erlang database management application
        used to store object information.</p>
      <note>
        <p>Although Orber does not have a  run-time
          application dependency to IC (an <term id="IDL"><termdef>Interface Definition Language - IDL is the OMG specified interface definition language, used to define the CORBA object interfaces.</termdef></term>compiler for
          Erlang), it is necessary when building
          services and applications.  See the IC documentation for
          further details.</p>
      </note>
      <marker id="orbs"></marker>
      <image file="orbs.gif">
        <icaption>
Figure 2: ORB interface between Java and Erlang Environment Nodes.</icaption>
      </image>
      <p>This simplified illustration in figure 2 demonstrates how Orber can facilitate communication in a heterogeneous environment. The Erlang Nodes running 
        OTP and the other Node running applications written in Java  can
        communicate via an <term id="ORB"><termdef>Object Request Broker - ORB open software bus architecture specified by the OMG which allows object components to communicate in a heterogeneous environment.</termdef></term>(Object Request Broker). Using
        Orber means that CORBA functions can be used to achieve this
        communication.
        </p>
      <p>For example, if one of the above nodes requests an object, it does not
        need to know if that object is located on the same, or 
        different, Erlang or Java nodes. The ORB will channel the
        information creating platform and application transparency for
        the user.
        </p>
    </section>

    <section>
      <title>Prerequisites</title>
      <p>To fully understand the concepts presented in the
        documentation, it is recommended that the user is familiar
        with distributed programming and CORBA (Common Object Request
        Broker Architecture).  
        </p>
      <p>Recommended reading includes <em>Open Telecom Platform Documentation Set</em> and <em>Concurrent Programming in Erlang</em>.
        </p>
    </section>
  </section>
</chapter>

