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

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

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

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

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

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

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

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

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

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

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

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

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

Communications Architecture uses. The Distributed Object Model framework is

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

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

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

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

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

Node responds. </p>

<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>

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

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

the concept of containment. </p>

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

<ul>

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

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

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

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

</ul>

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

<ul>

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

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

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

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

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

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

</ul>