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    10 <!DOCTYPE concept

    11   PUBLIC "-//OASIS//DTD DITA Concept//EN" "concept.dtd">

    12 <concept id="GUID-5580195F-3DE7-55FA-B2C1-91A950A39C6E" xml:lang="en"><title>Nodes

    13 in Symbian Platform</title><shortdesc>This topic describes the basic concept of a <i>Node</i> in Symbian

    14 platform. </shortdesc><prolog><metadata><keywords/></metadata></prolog><conbody>

    15 

    16 <p>The Communications Framework is modular and can adapt to changes in the

    17 networks that are available. The Communications Framework can also adapt to

    18 changes in technology. The modular design is described as a <i>Distributed

    19 Object Model</i>. Nodes are the components of a Distributed Object Model. </p>

    20 <p>A Distributed Object Model describes a system of entities or <i>Nodes</i> that

    21 can exist in different run contexts. The Nodes can exchange asynchronous messages.

    22 In Symbian platform, the concept of different run contexts refers to separate

    23 threads and separate processes. The scope of a Node is limited to a device.

    24 A Node cannot exist on a separate device. </p>

    25 <p>Symbian platform provides the Distributed Object Model framework that the

    26 Communications Architecture uses. The Distributed Object Model framework is

    27 a general purpose tool that other software entities can also use. </p>

    28 <p>A Node is an object that has an interface and an address. A Node uses messages

    29 to communicate with other Nodes. Some types of Node can use direct function

    30 calls to communicate if speed is important. Symbian platform defines the interface

    31 to a Node as the sequence of messages that the Node knows and to which the

    32 Node responds. </p>

    33 <p>A Node is an instance of a class derived from <xref href="GUID-3462501E-FDE1-3F3C-B26D-7FF3C826311F.dita"><apiname>ANodeBase</apiname></xref>. </p>

    34 <p>A parent Node is responsible for the destruction of its child Nodes. A

    35 parent Node can pass a reference to a child Node to other Nodes and implements

    36 the concept of containment. </p>

    37 <p>Nodes have <i>Roles</i>. A Role : </p>

    38 <ul>

    39 <li id="GUID-FCAA95EC-73CE-55D6-958F-4489069915D9"><p>identifies a service

    40 that the Node provides </p> </li>

    41 <li id="GUID-D9A10365-54BC-5F28-A081-FBB9963FCA38"><p>describes the series

    42 of messages that a Node sends and receives as part of a service </p> </li>

    43 </ul>

    44 <p>A Node can have more than one role. Examples of roles are as follows: </p>

    45 <ul>

    46 <li id="GUID-76207994-4326-5CB1-BE14-F20037A9B0BE"><p>a Node can accept requests

    47 to connect to another Node. </p> </li>

    48 <li id="GUID-3F4B59F6-12DD-5381-ACE9-DD021F41BF66"><p>a Node can own other

    49 Nodes. This is the concept of the <i>parent</i> Node. </p> </li>

    50 <li id="GUID-1B92A012-72B4-5DAC-9F15-D7FB802E2625"><p>A Node can be owned

    51 by another Node. This is the concept of the <i>child</i> Node. </p> </li>

    52 </ul>

    53 </conbody></concept>