- <sect3 id="querymodel-zebra-attr-limit">
- <title>Zebra Extension Approximative Limit Attribute (type 9)</title>
- </sect3>
- <para>
- Newer Zebra versions normally estimate hit count for every APT
- (leaf) in the query tree. These hit counts are returned as part of
- the searchResult-1 facility in the binary encoded Z39.50 search
- response packages.
- </para>
- <para>
- By setting a limit for the APT we can make Zebra turn into
- approximate hit count when a certain hit count limit is
- reached. A value of zero means exact hit count.
- </para>
- <para>
- For example, we might be interested in exact hit count for a, but
- for b we allow hit count estimates for 1000 and higher.
- <screen>
- Z> find @and a @attr 9=1000 b
- </screen>
- </para>
- <note>
- The estimated hit count facility makes searches faster, as one
- only needs to process large hit lists partially.
- </note>
- <warning>
- This facility clashes with rank weight, because there all
- documents in the hit lists need to be examined for scoring and
- re-sorting.
- It is an experimental
- extension. Do not use in production code.
- </warning>
+ <section id="querymodel-zebra-attr-weight">
+ <title>Zebra Extension Rank Weight Attribute (type 9)</title>
+ <para>
+ Rank weight is a way to pass a value to a ranking algorithm - so
+ that one APT has one value - while another as a different one.
+ See also <xref linkend="administration-ranking"/>.
+ </para>
+ <para>
+ For example, searching for utah in title with weight 30 as well
+ as any with weight 20:
+ <screen>
+ Z> find @attr 2=102 @or @attr 9=30 @attr 1=4 utah @attr 9=20 utah
+ </screen>
+ </para>
+ </section>
+
+ <section id="querymodel-zebra-attr-limit">
+ <title>Zebra Extension Approximative Limit Attribute (type 11)</title>
+ <para>
+ Zebra computes - unless otherwise configured -
+ the exact hit count for every APT
+ (leaf) in the query tree. These hit counts are returned as part of
+ the searchResult-1 facility in the binary encoded Z39.50 search
+ response packages.
+ </para>
+ <para>
+ By setting an estimation limit size of the resultset of the APT
+ leaves, Zebra stoppes processing the result set when the limit
+ length is reached.
+ Hit counts under this limit are still precise, but hit counts over it
+ are estimated using the statistics gathered from the chopped
+ result set.
+ </para>
+ <para>
+ Specifying a limit of <literal>0</literal> resuts in exact hit counts.
+ </para>
+ <para>
+ For example, we might be interested in exact hit count for a, but
+ for b we allow hit count estimates for 1000 and higher.
+ <screen>
+ Z> find @and a @attr 11=1000 b
+ </screen>
+ </para>
+ <note>
+ <para>
+ The estimated hit count facility makes searches faster, as one
+ only needs to process large hit lists partially.
+ It is mostly used in huge databases, where you you want trade
+ exactness of hit counts against speed of execution.
+ </para>
+ </note>
+ <warning>
+ <para>
+ Do not use approximative hit count limits
+ in conjunction with relevance ranking, as re-sorting of the
+ result set obviosly only works when the entire result set has
+ been processed.
+ </para>
+ </warning>
+ <warning>
+ <para>
+ This facility clashes with rank weight, because there all
+ documents in the hit lists need to be examined for scoring and
+ re-sorting.
+ It is an experimental
+ extension. Do not use in production code.
+ </para>
+ </warning>
+ </section>