The stratify relevance ranking module

The stratify relevance ranking module is used to boost or bury records in the result set.

The stratify relevance ranking module ranks records by stratifying them into groups defined by EQL expressions. The module can be used:
  • in record search options, via the Ntx URL query parameter or the ERecSearch class.
  • as a component of a sort specification given as the default sort or in the API via the Ns URL query parameter or the ENEQuery.setNavActiveSortKeys() method.
The stratify module takes an ordered list of one or more EQL expressions that are used for boosting/burying records. The following example shows one EQL expression for the module: 
N=0&Ntx=mode+matchall+rel+stratify(collection()/record[Score>95],*)&Ntk=WineType&Ntt=merlot

This record search example queries for the term merlot in WineType values. Any record that has a Score value of greater than 95 will be boosted in relation to other records.

Note: When used for sort operations, you must prepend the Endeca prefix to the stratify module name for use in the sort specification (i.e., use Endeca.stratify as the name).

EQL expressions and record strata

Each EQL expression used in the stratify statement corresponds to a stratum, as does the set of records which do not match any expression, producing k + 1 strata (where k is the number of EQL expressions). Records are placed in the stratum associated with the first EQL expression they match. The first stratum is the highest ranked, the next stratum is next-highest ranked, and so forth. Note a record will be stratified in the highest strata it matches, so boosting will have priority over burying.

If a record matches none of the specified EQL expressions, it is assigned to the unmatched stratum. By default, the unmatched stratum is ranked below all strata. However, you can change the rank of the unmatched stratum by specifying an asterisk (*) in the list of EQL expressions. In this case, the asterisk stands for the unmatched stratum.

The rules for using an asterisk to specify the unmatched stratum are:
  • If an asterisk is specified instead of an EQL expression, unmatched records are placed in the stratum that corresponds to the asterisk.
  • If no asterisk is specified, unmatched records are placed in a stratum lower than any expression's stratum.
  • Only one asterisk can be used. If more than one asterisk is specified, the first one will be used and the rest ignored.
This Ntx snippet shows the use of an asterisk in the query: 
N=0&Ntx=rel+stratify(collection()/record[Score>90],*,collection()/record[Score<50])
The query will produce three strata of records:
  • The highest-ranked stratum will be records whose Score value is greater than 90.
  • The lowest-ranked stratum will be records whose Score value is less than 50.
  • All other records will be placed in the unmatched stratum (indicated by the asterisk), which is the middle-ranked stratum.
Note that the EQL expressions must be URL-encoded. For example, this query: 
collection()/record[status = 4]
should be issued in this URL-encoded format: 
collection%28%29/record%5Bstatus%20%3D%204%5D
However, the examples in this chapter are not URL-encoded, in order to make them easier to understand.