3. Result sets

The result set object is a container for records returned from a target.

     ZOOM_resultset ZOOM_connection_search(ZOOM_connection, ZOOM_query q);

     ZOOM_resultset ZOOM_connection_search_pqf(ZOOM_connection c,
                                               const char *q);
     void ZOOM_resultset_destroy(ZOOM_resultset r);

Function ZOOM_connection_search creates a result set, given a connection and query. Destroy a result set by calling ZOOM_resultset_destroy. Simple clients using PQF only, may use the function ZOOM_connection_search_pqf in which case creating query objects is not necessary.

     void ZOOM_resultset_option_set(ZOOM_resultset r,
                                    const char *key, const char *val);

     const char *ZOOM_resultset_option_get(ZOOM_resultset r, const char *key);

     size_t ZOOM_resultset_size(ZOOM_resultset r);

Functions ZOOM_resultset_options_set and ZOOM_resultset_get sets and gets an option for a result set similar to ZOOM_connection_option_get and ZOOM_connection_option_set.

The number of hits, also called result-count, is returned by function ZOOM_resultset_size.

Table 3.3. ZOOM Result set Options

startOffset of first record to be retrieved from target. First record has offset 0 unlike the protocol specifications where first record has position 1. This option affects ZOOM_resultset_search and ZOOM_resultset_search_pqf and must be set before any of these functions are invoked. If a range of records must be fetched manually after search, function ZOOM_resultset_records should be used. 0
countNumber of records to be retrieved. This option affects ZOOM_resultset_search and ZOOM_resultset_search_pqf and must be set before any of these functions are invoked. 0
presentChunkThe number of records to be requested from the server in each chunk (present request). The value 0 means to request all the records in a single chunk. (The old step option is also supported for the benefit of old applications.) 0
elementSetNameElement-Set name of records. Most targets should honor element set name B and F for brief and full respectively. none
preferredRecordSyntaxPreferred Syntax, such as USMARC, SUTRS, etc. none
schemaSchema for retrieval, such as Gils-schema, Geo-schema, etc. none
setnameName of Result Set (Result Set ID). If this option isn't set, the ZOOM module will automatically allocate a result set name. default
rpnCharsetCharacter set for RPN terms. If this is set, ZOOM C will assume that the ZOOM application is running UTF-8. Terms in RPN queries are then converted to the rpnCharset. If this is unset, ZOOM C will not assume any encoding of RPN terms and no conversion is performed. none

For servers that support Search Info report, the following options may be read using ZOOM_resultset_get. This detailed information is read after a successful search has completed.

This information is a list of of items, where each item is information about a term or subquery. All items in the list are prefixed by SearchResult.no where no presents the item number (0=first, 1=second). Read searchresult.size to determine the number of items.

Table 3.4. Search Info Report Options

searchresult.size number of search result entries. This option is non-existent if no entries are returned by the server.
searchresult.no.idsub query ID
searchresult.no.countresult count for item (number of hits)
searchresult.no.subquery.termsubquery term
searchresult.no.interpretation.term interpretation term
searchresult.no.recommendation.term recommendation term

3.1. Z39.50 Result-set Sort

     void ZOOM_resultset_sort(ZOOM_resultset r,
                              const char *sort_type, const char *sort_spec);

     int ZOOM_resultset_sort1(ZOOM_resultset r,
                              const char *sort_type, const char *sort_spec);

ZOOM_resultset_sort and ZOOM_resultset_sort1 both sort an existing result-set. The sort_type parameter is not used. Set it to "yaz". The sort_spec is same notation as ZOOM_query_sortby and identical to that offered by yaz-client's sort command.

These functions only work for Z39.50. Use the more generic utility ZOOM_query_sortby2 for other protocols (and even Z39.50).

3.2. Z39.50 Protocol behavior

The creation of a result set involves at least a SearchRequest - SearchResponse protocol handshake. Following that, if a sort criteria was specified as part of the query, a SortRequest - SortResponse handshake takes place. Note that it is necessary to perform sorting before any retrieval takes place, so no records will be returned from the target as part of the SearchResponse because these would be unsorted. Hence, piggyback is disabled when sort criteria are set. Following Search - and a possible sort - Retrieval takes place - as one or more Present Requests/Response pairs being transferred.

The API allows for two different modes for retrieval. A high level mode which is somewhat more powerful and a low level one. The low level is enabled when searching on a Connection object for which the settings smallSetUpperBound, mediumSetPresentNumber and largeSetLowerBound are set. The low level mode thus allows you to precisely set how records are returned as part of a search response as offered by the Z39.50 protocol. Since the client may be retrieving records as part of the search response, this mode doesn't work well if sorting is used.

The high-level mode allows you to fetch a range of records from the result set with a given start offset. When you use this mode the client will automatically use piggyback if that is possible with the target, and perform one or more present requests as needed. Even if the target returns fewer records as part of a present response because of a record size limit, etc. the client will repeat sending present requests. As an example, if option start is 0 (default) and count is 4, and piggyback is 1 (default) and no sorting criteria is specified, then the client will attempt to retrieve the 4 records as part the search response (using piggyback). On the other hand, if either start is positive or if a sorting criteria is set, or if piggyback is 0, then the client will not perform piggyback but send Present Requests instead.

If either of the options mediumSetElementSetName and smallSetElementSetName are unset, the value of option elementSetName is used for piggyback searches. This means that for the high-level mode you only have to specify one elementSetName option rather than three.

3.3. SRU Protocol behavior

Current version of YAZ does not take advantage of a result set id returned by the SRU server. Future versions might do, however. Since the ZOOM driver does not save result set IDs, any present (retrieval) is transformed to a SRU SearchRetrieveRequest with same query but, possibly, different offsets.

Option schema specifies SRU schema for retrieval. However, options elementSetName and preferredRecordSyntax are ignored.

Options start and count are supported by SRU. The remaining options piggyback, smallSetUpperBound, largeSetLowerBound, mediumSetPresentNumber, mediumSetElementSetName, smallSetElementSetName are unsupported.

SRU supports CQL queries, not PQF. If PQF is used, however, the PQF query is transferred anyway using non-standard element pQuery in SRU SearchRetrieveRequest.

Solr queries need to be done in Solr query format.

Unfortunately, SRU and Solr do not define a database setting. Hence, databaseName is unsupported and ignored. However, the path part in host parameter for functions ZOOM_connecton_new and ZOOM_connection_connect acts as a database (at least for the YAZ SRU server).