added doc for db and getter sections

diff --git a/matita/help/C/sec_install.xml b/matita/help/C/sec_install.xml
index 9dd240daf1435e395932d84bed10307796bec794..4d50db4e64907fd9e48989a4073cc9aaba6c79e2 100644 (file)
--- a/matita/help/C/sec_install.xml
+++ b/matita/help/C/sec_install.xml
@@ -247,10 +247,11 @@
     </sect2>
 
     <sect2 id="database_setup">
-      <title>Database setup</title>
+      <title>(optional) &MYSQL; setup</title>
 
-      <para> To fully exploit &appname; indexing and search capabilities you
-       will need a working &MYSQL; database. Detalied instructions on how to do
+      <para> To fully exploit &appname; indexing and search capabilities 
+       on a huge metadata set you may
+       need a working &MYSQL; database. Detalied instructions on how to do
        it can be found in the <ulink type="http"
          url="http://dev.mysql.com/doc/">MySQL documentation</ulink>. Here you
        can find a quick howto. </para>
@@ -386,11 +387,25 @@
   </sect1>
 
   <sect1 id="matita.conf.xml">
-    <title>Configuring Matita</title>
+    <title>Configuring &appname;</title>
     <para>
     The file <emphasis>matita.conf.xml</emphasis>...
     &TODO;
     </para>
+  <sect2>
+   <title>The db and the getter sections</title>
+   <para>
+          &appname; needs to store/fetch data and metadata. Data is essentially
+          composed of XML files, metadata is a set of tuples for a relational
+          model. Data and metadata can produced by the user or be already
+          available. Both kind of data/metadata can be local and/or remote.
+   </para>
+   <para>
+          The db section tells &appname; where to store and retrieve metadata,
+          while the getter section describes where XML files have to be
+          found. The following picture describes the suggested configuration.
+          Dashed arrows are determined by the configuration file.
+   </para>
    <figure><title>Configuring the Databases</title>
      <mediaobject>
        <imageobject>
@@ -399,6 +414,79 @@
        <textobject><phrase>How to configure the databases.</phrase></textobject>
      </mediaobject>
    </figure>
+  <sect3>
+   <title>The getter</title>
+   <para>
+          Consider the following snippet and the URI
+          <userinput>cic:/matita/foo/bar.con</userinput>. If &appname;
+          is asked to read that object it will resolve the object trough
+          the getter. Since the first two entries are equally specific
+          (longest match rule applies) first the path
+          <userinput>file://$(matita.rt_base_dir)/xml/standard-library/foo/bar.con</userinput>
+          and then <userinput>file://$(user.home)/.matita/xml/matita/foo/bar.con</userinput>
+          are inspected.
+          <programlisting>
+<![CDATA[
+  <section name="getter">
+    <key name="cache_dir">$(user.home)/.matita/getter/cache</key>
+    <key name="prefix">
+      cic:/matita/
+      file://$(matita.rt_base_dir)/xml/standard-library/
+      ro
+    </key>
+    <key name="prefix">
+      cic:/matita/
+      file://$(user.home)/.matita/xml/matita/
+    </key>
+    <key name="prefix">
+      cic:/Coq/
+      http://mowgli.cs.unibo.it/xml/
+      legacy
+    </key>
+  </section>
+]]>    
+       </programlisting> 
+       if the same URI has to be written, the former prefix is skipped
+       since it is marked as readonly (<userinput>ro</userinput>).
+       Objects resolved using the third prefix are readonly too, and are
+       retrieved using the network. There is no limit to the number of
+       prefixes the user can define. The distinction between prefixes marked
+       as readonly and legacy is that, legacy ones are really read only, while
+       the ones marked with <userinput>ro</userinput> are considered for
+       writing when &appname; is started in system mode (used to publish user
+       developments in the library space).
+   </para>
+  </sect3>
+  <sect3>
+         <title>The db</title>
+       <para>
+          The database subsystem has three fron ends: library, user and
+          legacy.  The latter is the only optional one. Every query is done on
+          every frontend, making the duplicate free union of the results.
+          The user front end kepps metadata produced by the user, and is thus
+          heavily accessed in read/write mode, while the library and legacy
+          fron ends are read only. Every front end can be connected to
+          backend, the storage actually. 
+          Consider the following snippet.
+          <programlisting>
+<![CDATA[
+  <section name="db">
+    <key name="metadata">mysql://mowgli.cs.unibo.it matita helm none legacy</key>
+    <key name="metadata">file://$(matita.rt_base_dir) metadata.db helm helm library</key>
+    <key name="metadata">file://$(matita.basedir) user.db helm helm user</key>
+  </section>
+]]>    
+       </programlisting> 
+       Here the usr database is a file (thus locally accessed trough the
+       Sqlite library) placed in the user's home directory. The library one is
+       placed in the &appname; runtime directory. The legacy fron end is
+       connected to a remote &MYSQL; based storage. Every metadata key 
+       takes a path to the storage, the name of the database, the user name,
+       a password (or <userinput>none</userinput>) and the name of the front 
+       end to which it is attached.
+   </para>
+  </sect3>
+  </sect2>
   </sect1>
 
 </chapter>