+ <sect1 id="zoom.facets"><title>Facets</title>
+ <para>
+ Facets operations is not part of the official ZOOM specification, but
+ is an Index Data extension for YAZ-based Z39.50 targets or
+ <ulink url="&url.solr;">Solr</ulink> targets.
+ In case the target can and is requested to return facets, using a
+ result set the ZOOM client can request one or all facet fields.
+ Using a facet field the client can request the term count and then
+ interate over the terms.
+ </para>
+ <synopsis>
+ ZOOM_facet_field *ZOOM_resultset_facets(ZOOM_resultset r);
+
+ const char ** ZOOM_resultset_facets_names(ZOOM_resultset r);
+
+ ZOOM_facet_field ZOOM_resultset_get_facet_field(ZOOM_resultset r,
+ const char *facet_name);
+
+ ZOOM_facet_field ZOOM_resultset_get_facet_field_by_index(ZOOM_resultset r,
+ int pos);
+
+ size_t ZOOM_resultset_facets_size(ZOOM_resultset r);
+
+ const char *ZOOM_facet_field_name(ZOOM_facet_field facet_field);
+
+ size_t ZOOM_facet_field_term_count(ZOOM_facet_field facet_field);
+
+ const char *ZOOM_facet_field_get_term(ZOOM_facet_field facet_field,
+ size_t idx, int *freq);
+ </synopsis>
+ <para>
+ References to temporary structures are returned by all functions.
+ They are only valid as long the Result set is valid.
+ <function>ZOOM_resultset_get_facet_field</function> or
+ <function>ZOOM_resultset_get_facet_field_by_index</function>.
+ <function>ZOOM_resultset_facets</function>.
+ <function>ZOOM_resultset_facets_names</function>.
+ <function>ZOOM_facet_field_name</function>.
+ <function>ZOOM_facet_field_get_term</function>.
+ </para>
+ <para id="zoom.resultset.get_facet_field">
+ A single Facet field is returned by function
+ <function>ZOOM_resultset_get_facet_field</function> or
+ <function>ZOOM_resultset_get_facet_field_by_index</function> that takes
+ a result set and facet name or positive index respectively. First
+ facet has position zero. If no facet could be obtained (invalid name
+ or index out of bounds) <literal>NULL</literal> is returned.
+ </para>
+ <para id="zoom.resultset.facets">
+ An array of facets field can be returned by
+ <function>ZOOM_resultset_facets</function>. The length of the array is
+ given by <function>ZOOM_resultset_facets_size</function>. The array is
+ zero-based and last entry will be at
+ <function>ZOOM_resultset_facets_size(result_set)</function>-1.
+ </para>
+ <para id="zoom.resultset.facets_names">
+ It is possible to interate over facets by name, by calling
+ <function>ZOOM_resultset_facets_names</function>.
+ This will return an const array of char * where each string can be used
+ as parameter for <function>ZOOM_resultset_get_facet_field</function>.
+ </para>
+ <para>
+ Function <function>ZOOM_facet_field_name</function> gets the request
+ facet name from a returned facet field.
+ </para>
+ <para>
+ Function <function>ZOOM_facet_field_get_term</function> returns the
+ idx'th term and term count for a facet field.
+ Idx must between 0 and
+ <function>ZOOM_facet_field_term_count</function>-1, otherwise the
+ returned reference will be <literal>NULL</literal>. On a valid idx, the
+ value of the freq reference will be the term count.
+ The <literal>freq</literal> parameter must be valid pointer to integer.
+ </para>
+ </sect1>