[LUCENE-4799] Enable extraction of originating term for ICU collation keys

• Type: Improvement
• Status: Open
• Priority: Minor
• Resolution: Unresolved
• Affects Version/s: 4.1
• Component/s: core/other
• Labels: collator facet
• Lucene Fields: New, Patch Available
• Assignee: Unassigned
• Reporter: Toke Eskildsen
• Created: 26/Feb/13 09:41
• Updated: 28/Aug/22 13:40

Description

By concatenating generated ICU collation keys bytes with the originating term, it is possible to extract the originating term at a later time. This makes it possible to build a collator sorted facet field and similar multi-value/document structures.

ICU collation keys are guaranteed to be terminated by a 0 (https://ssl.icu-project.org/apiref/icu4j48rc1/com/ibm/icu/text/CollationKey.html) and since comparison of keys stop when a 0 is encountered, the addition of the originating term does not affect sort order. As 0 are only used for termination in the key bytes, the extraction of the originating term is unambiguous.