<?xml version="1.0" encoding="utf-8"?>

<!-- Copyright (c) 2007-2010 Nokia Corporation and/or its subsidiary(-ies) All rights reserved. -->

<!-- This component and the accompanying materials are made available under the terms of the License 

"Eclipse Public License v1.0" which accompanies this distribution, 

and is available at the URL "http://www.eclipse.org/legal/epl-v10.html". -->

<!-- Initial Contributors:

    Nokia Corporation - initial contribution.

Contributors: 

-->

<!DOCTYPE concept

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

<concept id="GUID-8255A186-C1AC-44DA-844C-1FEA029C73BC" xml:lang="en"><title>Publish and Subscribe</title><prolog><metadata><keywords/></metadata></prolog><conbody>

<p><i>Publish and Subscribe</i> has replaced System Agent and the

usage of temporary Shared Data keys.</p>

<p>Publish and Subscribe allows the setting, retrieving and monitoring

of system-wide variables and provides a new inter process communication

(IPC) mechanism for peer to peer communication between threads. Threads

may have the role of the publisher or of the subscriber, while any

thread can define the property to be published. The process that defines

a property can specify access rights for both reading and writing.

Rights can be defined in terms of either requiring a particular <xref href="GUID-6971B0A2-F79B-4E05-8AF3-BB1FC1932A22.dita">capability</xref>, by a process <xref href="GUID-3B6E25F7-C1A8-461F-97F7-421DB559BC98.dita#GUID-3B6E25F7-C1A8-461F-97F7-421DB559BC98/GUID-EEC50FC0-46D5-4ED7-AD95-67430D5EC652">Secure Identifier</xref>, or by a process <xref href="GUID-3B6E25F7-C1A8-461F-97F7-421DB559BC98.dita#GUID-3B6E25F7-C1A8-461F-97F7-421DB559BC98/GUID-EEC50FC0-46D5-4ED7-AD95-67430D5EC654">VID</xref>. </p>

<p>Publish and Subscribe should be considered under any of the

following conditions:</p>

<ul>

<li><p>An event should be sent simultaneously to multiple

places over the system.</p></li>

<li><p>Only the last value of the property is significant,

not the intermediate values.</p></li>

<li><p>The source of the value is not significant. The value

may have been set by any publisher with proper rights.</p>

</li>

</ul>

<p>For more information about the use of Publish and Subscribe,

see <xref href="GUID-FE910347-7CC1-5241-B443-88AD3F5A96EF.dita">Using Publish

and Subscribe</xref>.</p>