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+<body>
+<div id="header">
+<h1>How to provide context properties</h1>
+<div id="toc">
+ <div id="toctitle">Table of Contents</div>
+ <noscript><p><b>JavaScript must be enabled in your browser to display the table of contents.</b></p></noscript>
+</div>
+</div>
+<div id="preamble">
+<div class="sectionbody">
+<div class="paragraph"><p>Any component can provide its own key/value pairs and make them appear
+as a <tt>ContextProperty</tt> for C++ (and in other forms for other
+languages).</p></div>
+<div class="paragraph"><p>As a provider of context properties, you need to drop one or more
+<em>property declaration</em> files into <tt>/usr/share/contextkit/providers/</tt>
+to register your properties with the context framework. This file
+follows a format described below and is used by <tt>libcontextsubscriber</tt>
+and others to find you when someone subscribes to your properties.
+The file is also used by the Context Commander to show descriptions of
+your properties and to learn about the possible values that a property
+can legally have.</p></div>
+<div class="paragraph"><p>The property declaration files also inform the context framework how
+you want to be contacted. Right now, you have to implement the
+<tt>org.freedesktop.ContextKit</tt> D-Bus interface, and register yourself on
+either the system or the session D-Bus with a suitable bus name. The
+choice of system or session bus and your bus name go into the property
+declaration file.</p></div>
+<div class="paragraph"><p>The only supported way right now to implement the
+<tt>org.freedesktop.ContextKit</tt> interface is to use the
+<a href="libcontextprovider"><tt>libcontextprovider</tt></a> library.</p></div>
+<div class="paragraph"><p>The name of the property declaration file must be
+"<em>bus-name</em><tt>.context</tt>".</p></div>
+</div>
+</div>
+<h2 id="_the_property_declaration_file">The property declaration file</h2>
+<div class="sectionbody">
+<div class="paragraph"><p>The property declaration file contains XML and must follow
+<a href="context-provider-schema.html">this XML schema</a>. A simple example
+for the <tt>Example.Random</tt> property looks like this:</p></div>
+<div class="listingblock">
+<div class="content">
+<pre><tt><?xml version="1.0"?>
+<provider bus="session"
+ service="com.example.RandomProvider">
+ <key name="com.example.Random">
+ <type>double</type>
+ <doc>
+ A random number between 0 and 1 that changes every now and then.
+ </doc>
+ </key>
+</provider></tt></pre>
+</div></div>
+<div class="paragraph"><p>This file declares the single property <tt>com.example.Random</tt> and
+instructs the Content Framework to connect to the
+<tt>com.example.RandomProvider</tt> bus name on the session D-Bus. It would
+be stored as
+<tt>/usr/share/contextkit/providers/com.example.RandomProvider.context</tt></p></div>
+<div class="paragraph"><p>You need to be careful when choosing property name; see the
+"Guidelines for property providers" section for how to avoid
+conflicts.</p></div>
+<div class="paragraph"><p>When providing properties from the <a href="context-properties.html">core
+list</a>, you need to follow additional rules to make sure that your
+property declarations and the centrally maintained core list do not
+fall out of synch. See the "Providing core properties" section for
+more about them.</p></div>
+<div class="paragraph"><p>After installing a property declaration file into a directory <tt>$dir</tt>,
+you should usually execute <tt>update-contextkit-providers</tt>. This will
+update the various caches that clients like the <tt>libcontextsubscriber</tt>
+library use.</p></div>
+<div class="paragraph"><p>But, if a property declaration file is installed via a Debian package,
+you should not call <tt>update-contextkit-providers</tt> in your maintainer
+scripts. Triggers in the relevant packages take care of running
+update-contextkit-providers at the right time and only as often as
+necessary.</p></div>
+<div class="paragraph"><p>The XML element tree in the property declaration file simply consists
+of a list of <tt>key</tt> elements.</p></div>
+<div class="paragraph"><p>A <tt>key</tt> element in the property declaration tree can have a <tt>doc</tt>
+child element. The contents of this element should be plain text
+without any additional markup.</p></div>
+<h3 id="_types">Types</h3><div style="clear:left"></div>
+<div class="paragraph"><p><strong>NOTE:</strong> This is preview of things that might come, or not. For now,
+just use a <tt>type</tt> attribute in your <tt>key</tt> elements with one of
+<tt>"TRUTH"</tt>, <tt>"STRING"</tt>, <tt>"INT"</tt>, or <tt>"DOUBLE"</tt> as the value.</p></div>
+<div class="paragraph"><p>ContextKit uses the experimental <a href="context-types.html">Desktop Type
+System</a>. A property declaration should have a <tt>type</tt> element that
+conforms to the Desktop Type System.</p></div>
+<div class="paragraph"><p>For example, a property that is a enumeration would be declared like
+this:</p></div>
+<div class="listingblock">
+<div class="content">
+<pre><tt><key name="Economy">
+ <type>
+ <int-enum>
+ <up val="1" doc="Getting better"/>
+ <down val="2" doc="Getting worse"/>
+ <even val="3" doc="Getting boring"/>
+ </int-enum>
+ </type>
+ <doc>
+ The current economic trend, as an enumerated value.
+ </doc>
+</key></tt></pre>
+</div></div>
+</div>
+<h2 id="_guidelines_for_property_providers">Guidelines for property providers</h2>
+<div class="sectionbody">
+<h3 id="_names">Names</h3><div style="clear:left"></div>
+<div class="paragraph"><p>Context property names can contain any character except "/".</p></div>
+<div class="paragraph"><p>Only core property names are allowed to start with a capital ASCII
+letter ("A" to "Z").</p></div>
+<div class="paragraph"><p>When defining a new non-core property, you need to choose a unique
+prefix. Start with a reversed fully qualified domainname that you
+control, such as "com.nokia." or "org.gnome.". Then, if the first
+component is "org" and the second component is not a top-level domain,
+drop "org". Then convert the first character of the prefix to
+lower-case if it is one of "A" to "Z".</p></div>
+<div class="paragraph"><p>For example, the GNOME project can use "gnome." as their prefix, KDE
+can use "kde.", and Nokia can use "com.nokia.".</p></div>
+</div>
+<h2 id="_providing_core_properties">Providing core properties</h2>
+<div class="sectionbody">
+<div class="paragraph"><p>The Context Framework project maintains a list of <em>core properties</em>.
+These core properties are intended to cover the needs of most
+applications and be meaningful for many different devices.</p></div>
+<div class="paragraph"><p>When you are implementing a provider for some of the core properties,
+you must of course make sure that you follow the specification of that
+property. You can not redefine its type or description in your
+property declaration file, obviously.</p></div>
+<div class="paragraph"><p>Thus, for core properties, you should not include any <tt>type</tt> or <tt>doc</tt>
+elements in your key declarations, just a <tt>name</tt> element. The list of
+core properties is also known to context subcribers at run-time and
+will be used to fill in the missing details.</p></div>
+<div class="paragraph"><p>For example, a property declaration file for core properties could
+look like this:</p></div>
+<div class="listingblock">
+<div class="content">
+<pre><tt><?xml version="1.0"?>
+<provider bus="session"
+ service="com.example.RandomProvider">
+ <key name="Example.Random"/>
+</provider></tt></pre>
+</div></div>
+<div class="paragraph"><p>This just declares that the <tt>Example.Random</tt> property can be
+subscribed to by contacting <tt>com.example.RandomProvider</tt> on the
+session bus. It’s type and documentation are found elsewhere.</p></div>
+</div>
+<div id="footer">
+<div id="footer-text">
+Last updated 2009-11-26 11:20:27 EEST
+</div>
+</div>
+</body>
+</html>
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