Enum NegativeStrategy 

pub enum NegativeStrategy {
    WrongPublicationDate,
    WrongArticle,
    QuestionAnswerMismatch,
}

Strategy for picking the negative record in a triplet.

Each variant defines the candidate pool from which the negative record is drawn. By default all variants scope candidates to the same source as the anchor, so negatives are hard relative to the source domain rather than trivially cross-domain. A same-split fallback engages automatically when the in-source pool is too small (for example a source with only one record in the split).

When the bm25-mining feature is enabled, BM25 lexical re-ranking is applied on top of the strategy-filtered pool — BM25 re-orders candidates by keyword overlap with the anchor, but does not widen or replace the strategy pool. BM25 is a first-pass lexical ranker, not a semantic one; it is well-suited for lifting average negative quality without an encoder at data-generation time. Semantic or embedding-based re-ranking (iterative hard-negative mining with the trained encoder, cross-encoder scoring, dense retrieval) is out of scope for the data pipeline and can be integrated by pre-ranking negatives before ingestion or by reweighting source batches in the training loop.

Variants

WrongPublicationDate

Choose a record with a different publication date from record metadata.

This refers to metadata/taxonomy publication-date values (for example META_FIELD_DATE), not filesystem timestamps like mtime/ctime/atime.

WrongArticle

Choose a different record from the same source.

Negatives are drawn from within the same source, making them hard relative to the source domain. This is appropriate when each source represents a coherent domain (a collection of finance articles, a physics paper set, etc.) where same-source records are already confusable. If your sources are not meaningful domain boundaries, the fallback path (same split, any source) is the relevant escape hatch.

QuestionAnswerMismatch

Choose a mismatched Q/A pair.

Trait Implementations

impl Clone for NegativeStrategy

fn clone(&self) -> NegativeStrategy

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for NegativeStrategy

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.