<section id="mfo-explanation">
 <title>Overview</title>
 <sect2 id="mfo-introduction">
   <title>Introduction</title>

<para>This ontology is an abstract representation of entries coming from feeds. These feeds can be blogs (any of the common syndication formats can be translated into this representation), podcasts or even some online services (like flickr).</para>

<para>The basic assumption in the ontology is that all these feeds are unidirectional conversations with (from) the author of the content and every post on those channels is a message.</para>

<para>The source of the posts, the feed itself, is an instance of <link linkend="mfo-FeedChannel">mfo:FeedChannel</link>. Each post in that feed will be an instance of <link linkend="mfo-FeedMessage">mfo:FeedMessage</link> . The relation between the messages and the channel comes from their superclasses, <link linkend="nmo-communicationChannel">nmo:communicationChannel</link> (taking into account that <link linkend="mfo-FeedChannel">mfo:FeedChannel</link> is a subclass of <link linkend="nmo-CommunicationChannel">nmo:CommunicationChannel</link> and <link linkend="mfo-FeedMessage">mfo:FeedMessage</link> a subclass of <link linkend="nmo-Message">nmo:Message</link>).</para>

<para>A post can be plain text but can contain also more things like links, videos or Mp3. We represent those internal pieces in instances of <link linkend="mfo-Enclosure.">mfo:Enclosure.</link> This class has properties to link with the remote and local representation of the resource (in case the content has been downloaded).</para>

<para>Finally, the three important classes (mfo:FeedChannel, mfo:FeedMessage, mfo:Enclosure) are subclasses of <link linkend="mfo-FeedElement">mfo:FeedElement</link>, just an abstract class to share the link with mfo:FeedSettings. <link linkend="mfo-FeedSettings">mfo:FeedSettings</link> contains some common configuration options. Not all of them applies to all, but it is a quite cleaner solution. For instance the <link linkend="mfo-maxSize">mfo:maxSize</link> property only makes sense per-enclosure, while the <link linkend="mfo-updateInterval">mfo:updateInterval</link> is useful for the channel.</para>
 </sect2>

 <sect2 id="mfo-special-remarks">
  <title>Special remarks</title>
<para>In some feeds, like <ulink url="http://video.search.yahoo.com/mrss">"Yahoo Media RSS</ulink>, there can be multiple enclosures together in a group, representing the same resource in different formats, qualities, resolutions, etc. Until further notify, the group will be represented using <link linkend="nie-identifier">nie:identifier</link> property . To mark the default enclosure of the group, there is a <link linkend="mfo-groupDefault">mfo-groupDefault</link> property</para>
 </sect2>

 <refsect2 id="mfo-graphical-overview">
  <figure id="mfo-ontology-graph">
  <title>Graphical Overview</title>
    <graphic fileref="feeds-overview.png" format="PNG"></graphic>
  </figure>
  <para>Notation defined <link linkend="ontology-notation">in this page</link></para>
 </refsect2>

</section>
