- <xref linkend="record-types"/>.
- <!--
- FIXME - Need to describe the simple string-tag model, or at least
- refer to it here. -H
- -->
- </para>
-
- <para>
- Records pass through three different states during processing in the
- system.
- </para>
-
- <para>
-
- <itemizedlist>
- <listitem>
-
- <para>
- When records are accessed by the system, they are represented
- in their local, or native format. This might be SGML or HTML files,
- News or Mail archives, MARC records. If the system doesn't already
- know how to read the type of data you need to store, you can set up an
- input filter by preparing conversion rules based on regular
- expressions and possibly augmented by a flexible scripting language
- (Tcl).
- The input filter produces as output an internal representation,
- a tree structure.
-
- </para>
- </listitem>
- <listitem>
-
- <para>
- When records are processed by the system, they are represented
- in a tree-structure, constructed by tagged data elements hanging off a
- root node. The tagged elements may contain data or yet more tagged
- elements in a recursive structure. The system performs various
- actions on this tree structure (indexing, element selection, schema
- mapping, etc.),
-
- </para>
- </listitem>
- <listitem>
-
- <para>
- Before transmitting records to the client, they are first
- converted from the internal structure to a form suitable for exchange
- over the network - according to the Z39.50 standard.
- </para>
- </listitem>
-
- </itemizedlist>
-