- <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>
-
- </para>
-
- <sect1 id="local-representation">
- <title>Local Representation</title>
-
- <para>
- As mentioned earlier, Zebra places few restrictions on the type of
- data that you can index and manage. Generally, whatever the form of
- the data, it is parsed by an input filter specific to that format, and
- turned into an internal structure that Zebra knows how to handle. This
- process takes place whenever the record is accessed - for indexing and
- retrieval.
- </para>
-
- <para>
- The RecordType parameter in the <literal>zebra.cfg</literal> file, or
- the <literal>-t</literal> option to the indexer tells Zebra how to
- process input records.
- Two basic types of processing are available - raw text and structured
- data. Raw text is just that, and it is selected by providing the
- argument <emphasis>text</emphasis> to Zebra. Structured records are
- all handled internally using the basic mechanisms described in the
- subsequent sections.
- Zebra can read structured records in many different formats.
- How this is done is governed by additional parameters after the
- "grs" keyword, separated by "." characters.
- </para>