+ <para>
+ This is bad not just because it requires a lot of typing, but more
+ significantly because it ties searching semantics to the physical
+ structure of the searched records. You can't use the same search
+ specification to search two databases if their internal
+ representations are different. Consider an alternative dinosaur
+ database in which the records have author names specified
+ inside an <literal><authorName></literal> element directly
+ inside a top-level <literal><taxon></literal> element: then
+ you'd need to search for them using
+ <literal>1=/taxon/authorName</literal>
+ </para>
+ <para>
+ How, then, can we build broadcasting Information Retrieval
+ applications that look for records in many different databases?
+ The Z39.50 protocol offers a powerful and general solution to this:
+ abstract ``access points''. In the Z39.50 model, an access point
+ is simply a point at which searches can be directed. Nothing is
+ said about implementation: in a given database, an access point
+ might be implemented as an index, a path into physical records, an
+ algorithm for interrogating relational tables or whatever works.
+ The key point is that the semantics of an access point are fixed
+ and well defined.
+ </para>
+ <para>
+ For convenience, access points are gathered into <firstterm>attribute
+ sets</firstterm>. For example, the BIB-1 attribute set is supposed to
+ contain bibliographic access points such as author, title, subject
+ and ISBN; the GEO attribute set contains access points pertaining
+ to geospatial information (bounding box, ###, etc.); the CIMI
+ attribute set contains access points to do with museum collections
+ (provenance, inscriptions, etc.)
+ </para>
+ <para>
+ In practice, the BIB-1 attribute set has tended to be a dumping
+ ground for all sorts of access points, so that, for example, it
+ includes some geospatial access points as well as strictly
+ bibliographic ones. Nevertheless, the key point is that this model
+ allows a layer of abstraction over the physical representation of
+ records in databases.
+ </para>
+ <para>
+ In the BIB-1 attribute set, an author search is represented by
+ access point 1003. (See
+ <ulink url="###bib1-semantics"/>)
+ So we need to configure our dinosaur database so that searches for
+ BIB-1 access point 1003 look the
+ <literal>name</literal> attribute of the
+ <literal><AUTHOR></literal> element,
+ inside the
+ <literal><SPECIES></literal> element,
+ inside the top-level
+ <literal><GENUS></literal> element.
+ </para>
+ <para>
+ This is a two-step process. First, we need to tell Zebra that we
+ want to support the BIB-1 attribute set. Then we need to tell it
+ which elements of its record pertain to access point 1003.
+ </para>
+ <para>
+ We need to create an <link linkend="abs-file">Abstract Syntax
+ file</link> named after the document element of the records we're
+ working with, plus a <literal>.abs</literal> suffix - in this case,
+ <literal>GENUS.abs</literal> - as follows:
+ </para>
+ <itemizedlist>