Made to Measure: Ranking Evaluation using Elasticsearch
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The document describes ranking evaluation in Elasticsearch using its rank_eval API. Ranking evaluation allows measuring search quality through repeatable testing across different user needs. It defines typical search queries and rates documents to calculate metrics like precision, reciprocal rank, and discounted cumulative gain. This provides a way to quickly iterate on search and optimize for more user needs compared to methods like A/B testing. The demo uses Wikipedia data to illustrate the ranking evaluation process and API.
![!14
Ranking Evaluation API
GET /my_index/_rank_eval
{
"metric": {
"mean_reciprocal_rank": {
[...]
}
},
"templates": [{
[...]
}],
"requests": [{
"template_id": “my_query_template”,
"ratings": [...],
"params": {
"query_string": “hotel amsterdam",
"field": "text"
}
[...]
}]
}
• introduced in 6.2 (still experimental API)
• joint work between
• Christoph Büscher (@dalatangi)
• Isabel Drost-Fromm (@MaineC)
• Inputs:
• a set of search requests (“information needs”)
• document ratings for each request
• a metrics definition; currently available
• Precision@K
• Discounted Cumulative Gain / (N)DCG
• Expected Reciprocal Rank / ERR
• MRR, …](https://image.slidesharecdn.com/meetuprankingevaluationzurich-190416101204/85/Made-to-Measure-Ranking-Evaluation-using-Elasticsearch-14-320.jpg)
![!15
Ranking Evaluation API Details
"metric": {
"precision": {
"relevant_rating_threshold": "2",
"k": 5
}
}
metric
"requests": [{
"id": "JFK_query",
"request": {
“query”: { […] }
},
"ratings": […]
},
… other use cases …]
requests
"ratings": [ {
"_id": "3054546",
"rating": 3
}, {
"_id": "5119376",
"rating": 1
}, […]
]
ratings](https://image.slidesharecdn.com/meetuprankingevaluationzurich-190416101204/85/Made-to-Measure-Ranking-Evaluation-using-Elasticsearch-15-320.jpg)
![{
"rank_eval": {
"metric_score": 0.431,
"details": {
"my_query_id1": {
"metric_score": 0.6,
"unrated_docs": [
{
"_index": "idx",
"_id": "1960795"
}, [...]
],
"hits": [...],
"metric_details": {
“precision" : {
“relevant_docs_retrieved": 6,
"docs_retrieved": 10
}
}
},
"my_query_id2" : { [...] }
}
}
}
!16
_rank_eval response
overall score
details per query
maybe rate those?
details about metric](https://image.slidesharecdn.com/meetuprankingevaluationzurich-190416101204/85/Made-to-Measure-Ranking-Evaluation-using-Elasticsearch-16-320.jpg)
Made to Measure: Ranking Evaluation using Elasticsearch
- 1. Daniel Schneiter Elastic{Meetup} #41, Zürich, April 9, 2019 Original author: Christoph Büscher Made to Measure: Ranking Evaluation using Elasticsearch
- 2. !2 If you can not measure it, you cannot improve it! AlmostAnActualQuoteTM by Lord Kelvin https://commons.wikimedia.org/wiki/File:Portrait_of_William_Thomson,_Baron_Kelvin.jpg
- 4. !4 Image by Muff Wiggler https://www.flickr.com/photos/muffwiggler/5605240619 (CC BY 2.0)
- 5. !5 Ranking Evaluation A repeatable way to quickly measure the quality of search results over a wide range of user needs
- 6. !6 • Automate - don’t make people look at screens • no gut-feeling / “management- driven” ad-hoc search ranking REPEATABILITY
- 7. !7 • fast iterations instead of long waits (e.g. in A/B testing) SPEED
- 8. !8 • numeric output • support of different metrics • define “quality“ in your domain QUALITY MEASURE
- 9. !9 • optimize across wider range of use case (aka “information needs”) • think about what the majority of your users want • collect data to discover what is important for your use case USER NEEDS
- 10. !10 Prerequisites for Ranking Evaluation 1. Define a set of typical information needs 2. For each search case, rate your documents for those information needs (either binary relevant/non-relevant or on some graded scale) 3. If full labelling is not feasible, choose a small subset instead (often the case because document set is too large) 4. Choose a metric to calculate. Some good metrics already defined in Information Retrieval research: • Precision@K, (N)DCG, ERR, Reciprocal Rank etc… Source: Gray Arial 10pt
- 11. !11 Search Evaluation Continuum speed preparation time people looking at screens Some sort of unit test QA assisted by scripts user studies A/B testing Ranking Evaluation slow fast little lots
- 12. !12 Where Ranking Evaluation can help Development Production Communication Tool • guiding design decisions • enabling quick iteration • helps defining “search quality” clearer • forces stakeholders to “get real” about their expectations • monitor changes • spot degradations
- 14. !14 Ranking Evaluation API GET /my_index/_rank_eval { "metric": { "mean_reciprocal_rank": { [...] } }, "templates": [{ [...] }], "requests": [{ "template_id": “my_query_template”, "ratings": [...], "params": { "query_string": “hotel amsterdam", "field": "text" } [...] }] } • introduced in 6.2 (still experimental API) • joint work between • Christoph Büscher (@dalatangi) • Isabel Drost-Fromm (@MaineC) • Inputs: • a set of search requests (“information needs”) • document ratings for each request • a metrics definition; currently available • Precision@K • Discounted Cumulative Gain / (N)DCG • Expected Reciprocal Rank / ERR • MRR, …
- 15. !15 Ranking Evaluation API Details "metric": { "precision": { "relevant_rating_threshold": "2", "k": 5 } } metric "requests": [{ "id": "JFK_query", "request": { “query”: { […] } }, "ratings": […] }, … other use cases …] requests "ratings": [ { "_id": "3054546", "rating": 3 }, { "_id": "5119376", "rating": 1 }, […] ] ratings
- 16. { "rank_eval": { "metric_score": 0.431, "details": { "my_query_id1": { "metric_score": 0.6, "unrated_docs": [ { "_index": "idx", "_id": "1960795" }, [...] ], "hits": [...], "metric_details": { “precision" : { “relevant_docs_retrieved": 6, "docs_retrieved": 10 } } }, "my_query_id2" : { [...] } } } } !16 _rank_eval response overall score details per query maybe rate those? details about metric
- 17. !17 How to get document ratings? 1. Define a set of typical information needs of user (e.g. analyze logs, ask product management / customer etc…) 2. For each case, get small set of candidate documents (e.g. by very broad query) 3. Rate those documents with respect to the underlying information need • can initially be done by you or other stakeholders; later maybe outsource e.g. via Mechanical Turk 4. Iterate! Source: Gray Arial 10pt
- 18. !18 Metrics currently available Metric Description Ratings Precision At K Set-based metric; ratio of relevant doc in top K results binary Reciprocal Rank (RR) Positional metric; inverse of the first relevant document binary Discounted Cumulative Gain (DCG) takes order into account; highly relevant docs score more if they appear earlier in result list graded Expected Reciprocal Rank (ERR) motivated by “cascade model” of search; models dependency of results with respect to their predecessors graded
- 19. !19 Precision At K • In short: “How many good results appear in the first K results” (e.g. first few pages in UI) • supports only boolean relevance judgements • PROS: easy to understand & communicate • CONS: least stable across different user needs, e.g. total number of relevant documents for a query influences precision at k Source: Gray Arial 10pt prec@k = # relevant docs{ } # all results at k{ }
- 20. !20 Reciprocal Rank • supports only boolean relevance judgements • PROS: easy to understand & communicate • CONS: limited to cases where amount of good results doesn’t matter • If averaged over a sample of queries Q often called MRR (mean reciprocal rank): Source: Gray Arial 10pt RR = 1 position of first relevant document MRR = 1 Q 1 rankii Q ∑
- 21. !21 Discounted Cumulative Gain (DCG) • Predecessor: Cumulative Gain (CG) • sums relevance judgement over top k results Source: Gray Arial 10pt CG = relk i=1 k ∑ DCG = reli log2 (i +1)i=1 k ∑ • DCG takes position into account • divides by log2 at each position • NDCG (Normalized DCG) • divides by “ideal” DCG for a query (IDCG) NDCG = DCG IDCG
- 22. !22 Expected Reciprocal Rank (ERR) • cascade based metric • supports graded relevance judgements • model assumes user goes through result list in order and is satisfied with the first relevant document • R_i probability that user stops at position i • ERR is high when relevant document appear early Source: Gray Arial 10pt ERR = 1 r (1− Ri )Rr i=1 r−1 ∏r=1 k ∑ Ri = 2 reli −1 2 relmax reli ! relevance at pos. i relmax ! maximal relevance grade
- 23. !23 DEMO TIME
- 24. !24 Demo project and Data • Demo uses aprox. 1800 documents from the english Wikipedia • Wikipedias Discovery department collects and publishes relevance judgements with their Discernatron project • Bulk data and all query examples available at https://github.com/cbuescher/rankEvalDemo Source: Gray Arial 10pt
- 25. !25 Q&A
- 26. !26 Some questions I have for you… • How do you measure search relevance currently? • Did you find anything useful about the ranking evaluation approach? • Feedback about usability of the API (ping be on Github or our Discuss Forum @cbuescher) Source: Gray Arial 10pt
- 27. !27 Further reading • Manning, Raghavan & Schütze: Introduction to Information Retrieval, Cambridge University Press. 2008. • Metlzer, D., Zhang, Y., & Grinspan, P. (2009). Expected reciprocal rank for graded relevance. Proceeding of the 18th ACM Conference on Information and Knowledge Management - CIKM ’09, 621. • Blog: https://www.elastic.co/blog/made-to-measure-how-to- use-the-ranking-evaluation-api-in-elasticsearch • Docs: https://www.elastic.co/guide/en/elasticsearch/reference/ current/search-rank-eval.html • Discuss: https://discuss.elastic.co/c/elasticsearch (cbuescher) • Github: :Search/Ranking Label (cbuescher) Source: Gray Arial 10pt