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<html><head><meta charset="ISO-8859-1"><title>2.GRS-1 Internal Record Representation</title><meta name="generator" content="DocBook XSL Stylesheets Vsnapshot"><link rel="home" href="index.html" title="Zebra - User's Guide and Reference"><link rel="up" href="grs.html" title="Chapter9.GRS-1 Record Model and Filter Modules"><link rel="prev" href="grs.html" title="Chapter9.GRS-1 Record Model and Filter Modules"><link rel="next" href="grs-conf.html" title="3.GRS-1 Record Model Configuration"></head><body><link rel="stylesheet" type="text/css" href="common/style1.css"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">2.<acronym class="acronym">GRS-1</acronym> Internal Record Representation</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="grs.html">Prev</a></td><th width="60%" align="center">Chapter9.<acronym class="acronym">GRS-1</acronym> Record Model and Filter Modules</th><td width="20%" align="right"><a accesskey="n" href="grs-conf.html">Next</a></td></tr></table><hr></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a name="grs-internal-representation"></a>2.<acronym class="acronym">GRS-1</acronym> Internal Record Representation</h2></div></div></div><p>
When records are manipulated by the system, they're represented in a
tree-structure, with data elements at the leaf nodes, and tags or
variant components at the non-leaf nodes. The root-node identifies the
schema that lends context to the tagging and structuring of the
record. Imagine a simple record, consisting of a 'title' element and
an 'author' element:
</p><p>
</p><pre class="screen">
ROOT
TITLE "Zen and the Art of Motorcycle Maintenance"
AUTHOR "Robert Pirsig"
</pre><p>
</p><p>
A slightly more complex record would have the author element consist
of two elements, a surname and a first name:
</p><p>
</p><pre class="screen">
ROOT
TITLE "Zen and the Art of Motorcycle Maintenance"
AUTHOR
FIRST-NAME "Robert"
SURNAME "Pirsig"
</pre><p>
</p><p>
The root of the record will refer to the record schema that describes
the structuring of this particular record. The schema defines the
element tags (TITLE, FIRST-NAME, etc.) that may occur in the record, as
well as the structuring (SURNAME should appear below AUTHOR, etc.). In
addition, the schema establishes element set names that are used by
the client to request a subset of the elements of a given record. The
schema may also establish rules for converting the record to a
different schema, by stating, for each element, a mapping to a
different tag path.
</p><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="grs-tagged-elements"></a>2.1.Tagged Elements</h3></div></div></div><p>
A data element is characterized by its tag, and its position in the
structure of the record. For instance, while the tag "telephone
number" may be used different places in a record, we may need to
distinguish between these occurrences, both for searching and
presentation purposes. For instance, while the phone numbers for the
"customer" and the "service provider" are both
representatives for the same type of resource (a telephone number), it
is essential that they be kept separate. The record schema provides
the structure of the record, and names each data element (defined by
the sequence of tags - the tag path - by which the element can be
reached from the root of the record).
</p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="grs-variant-details"></a>2.2.Variants</h3></div></div></div><p>
The children of a tag node may be either more tag nodes, a data node
(possibly accompanied by tag nodes),
or a tree of variant nodes. The children of variant nodes are either
more variant nodes or a data node (possibly accompanied by more
variant nodes). Each leaf node, which is normally a
data node, corresponds to a <span class="emphasis"><em>variant form</em></span> of the
tagged element identified by the tag which parents the variant tree.
The following title element occurs in two different languages:
</p><p>
</p><pre class="screen">
VARIANT LANG=ENG "War and Peace"
TITLE
VARIANT LANG=DAN "Krig og Fred"
</pre><p>
</p><p>
Which of the two elements are transmitted to the client by the server
depends on the specifications provided by the client, if any.
</p><p>
In practice, each variant node is associated with a triple of class,
type, value, corresponding to the variant mechanism of <acronym class="acronym">Z39.50</acronym>.
</p></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a name="grs-data-elements"></a>2.3.Data Elements</h3></div></div></div><p>
Data nodes have no children (they are always leaf nodes in the record
tree).
</p></div></div><div class="navfooter"><hr><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="grs.html">Prev</a></td><td width="20%" align="center"><a accesskey="u" href="grs.html">Up</a></td><td width="40%" align="right"><a accesskey="n" href="grs-conf.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">Chapter9.<acronym class="acronym">GRS-1</acronym> Record Model and Filter Modules</td><td width="20%" align="center"><a accesskey="h" href="index.html">Home</a></td><td width="40%" align="right" valign="top">3.<acronym class="acronym">GRS-1</acronym> Record Model Configuration</td></tr></table></div></body></html>
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