YAZ supports facets in the Solr, SRU 2.0 and Z39.50 protocols.
Like Type-1/RPN, YAZ supports a string notation for specifying
facets. This notataion maps straight to facets.asn.
The notation is parsed by function
yaz_pqf_parse_facet_list defined in header
yaz/pquery.h.
For ZOOM C the facets are specified by option "facets". For yaz-client, the 'facets' command is used.
The grammar of this specification is as follows:
facet-spec ::= facet-list
facet-list ::= facet-list ',' attr-spec | attr-spec
attr-spec ::= attr-spec '@attr' string | '@attr' string
The notation is inspired by PQF. The string following '@attr'
must not include blanks and is of the form
type=value,
where type is an integer and
value is a string or an integer.
There is no formal facets attribute set (it is not given in the protocol by the facets, although it could). The following types apply:
Table 7.4. Facet attributes
| Type | Description |
|---|---|
| 1 | Field-name. This is often a string, e.g. "Author", "Year", etc. |
| 2 | Sort order. Value should be an integer. Value 0: count descending (frequency). Value 1: alpha ascending. |
| 3 | Number of terms requested. |
| 4 | Start offset (starting from 1) |