This RFC talks about the various high level directions which are being proposed for Score combination and Normalization techniques to improve Semantic Search/Neural Search Queries in OpenSearch(META ISSUE: #123).
Problem:
BM25 works well in exact match use cases and k-NN score works well in understanding context and getting relevant documents. It is important to get benefits from both of these relevancy mechanisms and one could achieve by combining these scores. One caveat is scores are on different scales and hence some kind of normalization is required.
Please find more details here: [RFC] High Level Approach and Design For Normalization and Score Combination · Issue #126 · opensearch-project/neural-search · GitHub