+ <para>The getter</para>
+ <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://$(user.home)/.matita/xml/matita/
+ </key>
+ <key name="prefix">
+ cic:/Coq/
+ http://mowgli.cs.unibo.it/xml/
+ legacy
+ </key>
+ </section>
+]]>
+ </programlisting>
+ if the same URI has to be written, the former prefix is skipped
+ since it is marked as readonly (<userinput>ro</userinput>).
+ Objects resolved using the third prefix are readonly too, and are
+ retrieved using the network. There is no limit to the number of
+ prefixes the user can define. The distinction between prefixes marked
+ as readonly and legacy is that, legacy ones are really read only, while
+ the ones marked with <userinput>ro</userinput> are considered for
+ writing when &appname; is started in system mode (used to publish user
+ developments in the library space).
+ </para>
+ <para>The db</para>
+ <para>
+ The database subsystem has three fron ends: library, user and
+ legacy. The latter is the only optional one. Every query is done on
+ every frontend, making the duplicate free union of the results.
+ The user front end kepps metadata produced by the user, and is thus
+ heavily accessed in read/write mode, while the library and legacy
+ fron ends are read only. Every front end can be connected to
+ backend, the storage actually.
+ Consider the following snippet.
+ <programlisting>
+<![CDATA[
+ <section name="db">
+ <key name="metadata">mysql://mowgli.cs.unibo.it matita helm none legacy</key>
+ <key name="metadata">file://$(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>