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<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>
</conbody></concept>