REVIEW 4 major objections 6 minor 1 cited by
XRAG: Cross-lingual Retrieval-Augmented Generation
T0 review · 4 major / 6 minor · reviewed 2026-08-15 · deepseek-v4-flash
Pith's one-line read XRAG, a new benchmark for cross-lingual retrieval-augmented generation, shows that LLMs' main difficulty is reasoning across languages rather than generating non-English text.
desk verdict A useful new cross-lingual RAG benchmark with two plausible findings; needs verification that questions truly require both documents before the central claim is accepted. read the letter →
The pith
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
The reading
What carries the argument
The construction pipeline is the central mechanism: from News Crawl articles dated after the models' knowledge cutoffs, the authors (1) pair related articles by shared entities or by multilingual retrieval over international events, (2) prompt an LLM to summarize each article and generate simple single-step Q&A pairs, (3) prompt it to connect those pairs into cross-document questions of four types—aggregation, comparison, multi-hop, and set—such that at least one piece of evidence comes from each article, and (4) have professional annotators verify facts and translate the questions. The controlled analysis in the multilingual setting then isolates the source of difficulty by successively replacing the question, supporting articles, and distractors with English equivalents, attributing the largest accuracy gain to translating the supporting articles.
What would settle it
Run the no-retrieval and single-supporting-article conditions on the German, Spanish, Chinese, and Arabic versions of XRAG: if any evaluated model scores near its two-article retrieval accuracy without outside documents, or if one supporting article alone suffices for a large share of questions, the claim that XRAG requires external knowledge and cross-document reasoning would be falsified.
Extended reading notes
Core claim
XRAG claims that cross-lingual RAG should be evaluated as two distinct scenarios—monolingual retrieval, where a non-English query is answered from English documents, and multilingual retrieval, where evidence comes in both the query language and English—and that existing cross-lingual QA datasets are too simple and too English-centric to expose the real failure modes. Using questions that require combining information from two supporting articles while ignoring distractors, the paper finds that all five evaluated LLMs suffer from response language correctness problems in the monolingual setting, and that in the multilingual setting replacing non-English supporting articles with English translations improves accuracy more than replacing the question language. That pattern indicates that cross-lingual reasoning over retrieved evidence, not non-English generation, is the core difficulty.
Load-bearing premise
The benchmark rests on the assumption that each question's two supporting articles are individually necessary and jointly sufficient, so that a correct answer really requires reading both; if many questions can be answered from one article or from the model's own knowledge, the cross-document reasoning measurement fails.
Editorial extensions
If this is right
- Deploying a RAG system with an English-only knowledge base for non-English users requires explicit response-language enforcement; current models silently switch to English.
- Adding native-language retrieval alongside English retrieval changes the failure profile: the bottleneck becomes fusing evidence across languages, not generating the answer language.
- Benchmarks for multilingual QA that do not force external-knowledge use may overstate cross-lingual RAG ability; XRAG-style questions separate retrieval need from reasoning ability.
- The four-question taxonomy (aggregation, comparison, multi-hop, set) gives evaluation designers a reusable template for cross-document reasoning questions.
- Cross-document reasoning over mixed-language evidence is a distinct capability worth measuring separately from language generation.
Reading between the lines
- A testable extension is to feed the model machine-translated versions of the non-English supporting articles: if accuracy then approaches the English-monolingual baseline, the deficit is evidence access, not inference per se.
- The response-language-correctness finding suggests that constrained decoding with a language identifier, or an explicit language tag in the prompt, may close much of the monolingual-retrieval gap without retraining.
- The two-scenario split implies that retrieval quality should be evaluated separately in each language: a retriever serving one shared English index and one native index may need different relevance criteria.
- If XRAG-style questions continue to be generated from recent news, the benchmark can be refreshed over time, keeping it a moving target against parametric-knowledge memorization.
Signed reviews
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The paper introduces XRAG, a benchmark for evaluating LLMs in cross-lingual retrieval-augmented generation (RAG). XRAG consists of two settings: monolingual retrieval, where four non-English query languages are answered using English supporting and distracting documents, and multilingual retrieval, where documents in both the query language and English are provided. Questions are generated from recent News Crawl articles via a GPT-4o workflow that first creates simple QA pairs from each of two related articles and then combines them into cross-document questions (aggregation, comparison, multi-hop, set), followed by human quality control, human translation into German, Spanish, Chinese, and Arabic, and automatic selection of topically related distractors. The authors evaluate five LLMs and report two findings: (1) in monolingual retrieval, models frequently answer in English instead of the query language, and (2) in multilingual retrieval, translating supporting articles into English yields larger accuracy gains than translating the question, suggesting the main challenge is cross-lingual reasoning rather than non-English generation. The paper also includes no-retrieval and oracle-retrieval bounds, a human upper bound of 85%, and an LLM-judge panel validated against human annotations with Cohen's kappa of 0.71.
Significance. If the benchmark's design assumptions hold, XRAG fills a real gap: existing cross-lingual QA benchmarks (XQA, XOR QA) are largely English-document and span-extraction oriented, whereas XRAG provides controlled monolingual and multilingual retrieval settings with distractors, recency-based external-knowledge requirements, and human quality control. The reported human-LLM gap (85% vs. 55.5% for GPT-4o) and the low no-retrieval scores (below 16%) support the benchmark's difficulty and its potential as a reasoning testbed. The two empirical findings—response language correctness failures and the dominant effect of translating supporting articles—are plausible and would be useful for system developers. The paper also deserves credit for shipping a comparatively complete evaluation stack: a three-judge panel with majority vote, a language detector, a human-judge agreement check, and a controlled decomposition of the multilingual retrieval setting across five models (Tables 6, 9–11).
major comments (4)
- [Section 3 and Section 4.2 Step 3] The central claim that every XRAG question requires cross-document reasoning rests on the assumption that the two supporting articles are individually necessary and jointly sufficient. The construction pipeline (Section 4.2, Step 3) only enforces that at least one sub-QA pair is selected from each source; it does not check whether the final question can be answered from a single article alone (e.g., because one article incidentally contains all needed facts or the question phrasing gives away the answer). The human QA guideline (Figure 17, item 4) asks annotators to label each article as Sufficient/Some/None, but the paper neither reports this distribution nor states that examples labeled 'Sufficient' were discarded. Without this information, a nontrivial fraction of instances could be answerable from one supporting article, which would overstate the benchmark's cross-document reasoning claim and make the +ES improvement in Section 5.4 ambiguous (it could reflect better single-document comprehension rather than integration of evidence across two documents). Please report the annotation distribution and either discard or re-verify all instances where either article is labeled 'Sufficient', or provide direct evidence that such instances are negligible.
- [Section 5.4, Table 6 and Appendix D.1] The controlled analysis that supports the paper's second main conclusion is not statistically grounded. The differences between conditions, e.g., GPT-4o's average improvement from +EQ to +EQ,+ES is 2.91 points (58.25 to 61.16, Table 6), and per-language improvements vary (En+Es improves by only 1.33 points; En+Ar by 3.67), are computed over 300-item subsets per language without confidence intervals, significance tests, or effect sizes. Across Tables 6 and 9–11, some 'improvements' are within 1–2 points and could be noise. Please report per-condition accuracy with confidence intervals (e.g., bootstrap) and apply a paired significance test (e.g., McNemar's test) across the full 1,200-item multilingual set and per language. Without this, the claim that 'the main challenge lies in reasoning over retrieved information across languages' is not yet empirically supported.
- [Section 5.2, Table 3] The no-retrieval check is run only on English questions from the monolingual retrieval setting (as stated in the text and Figure 21). The translated German, Spanish, Chinese, and Arabic versions of these questions are not directly tested for answerability from parametric knowledge. Since the benchmark's stated property is that questions require external knowledge to answer, and since translation can alter lexical cues or expose answers differently across languages, the cross-lingual validity of this property is not established. Please run the no-retrieval experiment on the translated non-English questions (or, if a retriever is needed, at least on a representative sample per language) and report the resulting accuracies. If the no-retrieval check cannot be run for all languages, explicitly acknowledge this limitation and discuss the risk it poses to the cross-lingual conclusions.
- [Figure 5] The Response Language Correctness (RLC) finding is presented only for German and Chinese in Figure 5, even though the monolingual retrieval setting includes Spanish and Arabic. The paper states that 'all evaluated models struggle with response language correctness' but provides no RLC numbers for Spanish and Arabic. Without these, it is unclear whether the phenomenon is universal or language-dependent. Please provide RLC rates for all four languages (e.g., a table with percentages per model and language), or explicitly state that only German and Chinese were analyzed and why.
minor comments (6)
- [Section 2] The sentence 'Vu et al. (2024) construct a a dynamic QA benchmark' contains a duplicated article 'a a'; please fix.
- [Abstract and Section 1] The hyphen in 'design-ed-' in the abstract appears to be a linebreak artifact; please ensure the final PDF renders cleanly.
- [Section 5.4] The controlled analysis uses a single order of interventions (EQ then ES then ED). A less assumption-laden analysis would also test the reverse order or a factorial design, since the marginal effect of ES may depend on whether EQ is already applied.
- [Section 4.4] The selection of distracting articles uses a multilingual dense retriever and a two-week publication gap, but the paper does not describe how the number of distractors (six) was chosen or whether the retrieved distractors were filtered for redundancy or near-duplicate content. A brief clarification would improve reproducibility.
- [Appendix C.2] The Cohen's kappa of 0.71 is reported for the LLM judge panel versus human evaluators, but the paper does not report the raw agreement rate or per-judge agreement. Adding these would help readers assess the reliability of the evaluation.
- [Appendix A] The retrieval quality investigation in Appendix A relies on proprietary data (SimilarWeb traffic) and a proprietary evaluation by Claude 3.5 Sonnet; the results are not reproducible from the paper. Please clearly label this as preliminary evidence and, if possible, provide an anonymized description of the query set or a reproducible proxy.
Circularity Check
No circular derivation found: XRAG's cross-lingual findings are empirical outputs, and the GPT-4o generation/judging overlap is an acknowledged bias caveat, not a construction-level reduction.
full rationale
The paper's derivation chain is not circular. The benchmark is constructed from news articles and an explicit LLM-based pipeline whose outputs (questions, gold answers, supporting and distracting articles) are then used to evaluate five LLMs; none of the reported findings—response-language correctness in the monolingual setting or the relative difficulty of cross-lingual reasoning in the multilingual setting—is a fitted parameter or a renamed input. The controlled analysis in Section 5.4 successively replaces questions, supporting articles, and distracting articles by English counterparts; this is a measurement protocol, not a reduction of the conclusion to the data-generation procedure. The GPT-4o overlap (generator and judge) is explicitly flagged in footnote 5 ('QA pairs are generated by GPT-4o, and evaluation may be biased in its favor'); this is a legitimate bias caveat, but it is not load-bearing for the main cross-model findings, which hold across five systems and are checked against human judgments with Cohen's kappa 0.71. The Section 3 claim that supporting articles are individually necessary and jointly sufficient is a design property rather than a circular derivation; while the paper does not report the human 'Sufficient/Some/None' distribution from Figure 17, this is a benchmark-validity gap, not a case where the benchmark's definition forces its conclusions. No self-citation chain or imported uniqueness theorem is used as a load-bearing premise.
Assumptions & free parameters
free parameters (7)
- num_supporting_articles =
2
- num_distracting_articles =
6 (3 per language in multilingual retrieval)
- distractor_publication_gap =
at least two weeks before supporting articles
- article_min_tokens =
1200
- title_entity_overlap =
2
- max_pair_time_gap =
2 weeks
- questions_per_language =
1000 monolingual; 300 per language multilingual
assumptions (6)
- domain assumption News Crawl articles are factually reliable
- domain assumption Evaluated models lack parametric knowledge of the article facts
- domain assumption LLM judge panel majority is a valid proxy for human judgement
- domain assumption lingua language detector correctly classifies response language
- domain assumption Google Translate output is acceptable for baselines and controls
- domain assumption Professional human translation preserves question meaning
Cite this review
Pith. "Pith review of XRAG: Cross-lingual Retrieval-Augmented Generation." pith.science (2026). https://pith.science/paper/RSAMJXQZ
@misc{pith2026250510089,
author = {Pith},
title = {Pith review of: XRAG: Cross-lingual Retrieval-Augmented Generation},
year = {2026},
howpublished = {\url{https://pith.science/paper/RSAMJXQZ}},
note = {Machine review of arXiv:2505.10089}
}
read the original abstract
We propose XRAG, a novel benchmark designed to evaluate the generation abilities of LLMs in cross-lingual Retrieval-Augmented Generation (RAG) settings where the user language does not match the retrieval results. XRAG is constructed from recent news articles to ensure that its questions require external knowledge to be answered. It covers the real-world scenarios of monolingual and multilingual retrieval, and provides relevancy annotations for each retrieved document. Our novel dataset construction pipeline results in questions that require complex reasoning, as evidenced by the significant gap between human and LLM performance. Consequently, XRAG serves as a valuable benchmark for studying LLM reasoning abilities, even before considering the additional cross-lingual complexity. Experimental results on five LLMs uncover two previously unreported challenges in cross-lingual RAG: 1) in the monolingual retrieval setting, all evaluated models struggle with response language correctness; 2) in the multilingual retrieval setting, the main challenge lies in reasoning over retrieved information across languages rather than generation of non-English text.
Figures
Figures from the paper (16 more)
Forward citations
Cited by 1 Pith paper
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Linguistic Nepotism: Trading-off Quality for Language Preference in Multilingual RAG
In multilingual retrieval-augmented generation, models cite English evidence more accurately than translated evidence, and this language preference can outweigh document relevance.
Reference graph
Works this paper leans on
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[2]
Compare whether the two texts are about related entities
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[3]
Compare whether the high level topics of the two texts are related (e.g., both describe stock price, sport, film, a country, a party, or the same event)
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[4]
LLM evaluators recognize and favor their own generations. In The Thirty-eighth Annual Conference on Neural Information Processing Systems. Peng Qi, Yuhao Zhang, Yuhui Zhang, Jason Bolton, and Christopher D. Manning. 2020. Stanza: A python natural language processing toolkit for many human languages. In Proceedings of the 58th Annual Meet- ing of the Assoc...
arXiv 2020
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[5]
Create your response. Here are the two given texts: <text1> {{ text1 }} </text1> <text2> {{ text2 }} </text2> If they are topically related, format your response as: <answer>yes</answer> otherwise, output: <answer>no</answer> Figure 9: Prompt for topic relevance verification. Summary generation You are an AI assistant tasked with generating a summary for ...
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[6]
ing only those confirmed to be truly related to the next step
Not exceed 180 words Here is the given article: <article> {{ article }} <\article> Format your response as: <summary>[your generated summary]</summary> Figure 10: Prompt for summary generation, as described in Step 1 of Section 4.2. ing only those confirmed to be truly related to the next step. Figure 9 shows the prompt we used to instruct GPT-4o for rele...
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Do not pay much attention to details but high level topics!
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Have the same language as the article
Show all 57 references
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Be ACCURATE, clear, specific, and concise
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Cover the key information of the given article, such as names, places, time strings, events, results, and ect
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Be abstract and have little lexicon overlap with the article
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[15]
Joe Biden
Not use pronouns or partial names to refer something in your summary. Use its actual name or full name (e.g., “Joe Biden” instead of “Biden”, “Olympics 2024” instead of “Olympics”)
2024
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[17]
how many Oscar awards did Meryl Streep win?
The prompt used for generating an answers to the created cross-document question is presented in Figure 16. Quesiton typeDefinition AggregationQuestions that require the aggregation of information across articles to answer (e.g., “how many Oscar awards did Meryl Streep win?”) ...
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Be clear and unambiguous
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Joe Biden
Not use pronouns or partial names to refer something in your question. Use its actual name or full name (e.g., "Joe Biden" instead of "Biden", "Olympics 2024" instead of "Olympics")
2024
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[20]
Not exceed 20 words The corresponding answers should:
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Be accurate and supported by facts in the given text
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Be concise and NOT exceed 12 words
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Use its actual name or full name
Not use pronouns or partial names to refer something in your answer. Use its actual name or full name
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Be in English The number of question-answer pairs can range from 1 to 6, depending on the amount of information (facts) in the given text. Here is the given text: <text> {{ text }} </text> Format your response as: <list> <question>[your first question]</question> <answer>[answ...
2021
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Based on high-level topics, generate aggregation questions that require aggregating multi-pieces of information from selected sub-question-answer pairs to obtain answers from the selected pairs
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[30]
Don't make the generated questions too long! Generate no more than two questions, and present your results as: <output> <question>[Your first question]</question>
The questions should NOT have more than 25 words and must be succinct. Don't make the generated questions too long! Generate no more than two questions, and present your results as: <output> <question>[Your first question]</question> ... </output> Example of generated elaborat...
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Look for common themes or connections between two sets of sub- question-answer pairs
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Based on high-level topics, generate comparison questions that require comparing multi-pieces of information from selected sub-question-answer pairs to obtain answers
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Don't make the generated questions too long! Generate no more than two questions, and present your results as: <output> <question>[Your first question]</question>
The questions should NOT have more than 25 words and must be succinct. Don't make the generated questions too long! Generate no more than two questions, and present your results as: <output> <question>[Your first question]</question> ... </output> Example of generated elaborat...
2016
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Look for common themes or connections between two sets of sub-question- answer pairs
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Select A T LEAST ONE sub-question-answer pair from each set
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Based on high-level topics, generate multi-hop questions which need reasoning over multi-pieces of information from selected sub-question-answer to obtain answers
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Avoid creating questions that can be answered by simply combining or concating answers of sub-questions
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Don't make the generated questions too long! Generate no more than two questions, and present your results as: <output> <question>[Your first question]</question>
The questions should NOT have more than 25 words and must be succinct. Don't make the generated questions too long! Generate no more than two questions, and present your results as: <output> <question>[Your first question]</question> ... </output> Example of generated elaborat...
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Look for common themes or connections between two sets of sub-question-answer pairs
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Select AT LEAST ONE sub-question-answer pair from each set
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Based on high-level topics, generate "set" questions which need entities or objects of same category from selected sub-question-answer pairs to obtain answers
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Avoid creating questions by simply connecting two sub-questions with a conjunction
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Use its actual name or full name
Not use pronouns or partial names to refer something in your question. Use its actual name or full name
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[48]
Microsoft updated the Copilot
The questions should NOT have more than 25 words and must be succinct. Don't make the generated questions too long! Generate no more than two questions, and present your results as: <output> <question>[Your first question]</question> ... </output> Example of generated elaborat...
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Look for connections between the given questions and sub-questions
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Read answers of sub-questions and the two reference texts
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DO NOT generate answers use information OUTSIDE of sub-question-answer pairs and two reference texts, such as your own knowledge
Generate an ENGLISH answer based solely on those information. DO NOT generate answers use information OUTSIDE of sub-question-answer pairs and two reference texts, such as your own knowledge
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GPT-4o-2024-08-06, Claude 3.5 Sonnet (2024-06- 20), Mistral-Large-Instruct-2407, Command-r+, and Nova-pro
Format your response as: <answer>[your answer]</answer> Figure 16: Prompt for creating an answer for a gener- ated cross-document question, as described in Step 3 of Section 4.2. GPT-4o-2024-08-06, Claude 3.5 Sonnet (2024-06- 20), Mistral-Large-Instruct-2407, Command-r+, and N...
2024
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Don’t take more than ten seconds to decide
Read the question and make sure it is intelligible and natural. Don’t take more than ten seconds to decide. If it is not clear what the question is asking for, mark it as not intelligible. Unnatural questions are questions that sound forced and unlikely to be asked by a human,...
2024
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Search within the two provided articles for the entities in the question to speed up the process
Determine if the question is answerable based on the information in the articles alone: a. Search within the two provided articles for the entities in the question to speed up the process. b. You can look up background knowledge in an encyclopaedia to get context if you are no...
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Determine if the provided answer is correct. a. If the answer is incorrect, please provide the correct answer based on the information in the articles
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Sufficient: The information in the article is sufficient to answer the question
For each of the two articles, mark what information they contain: a. Sufficient: The information in the article is sufficient to answer the question. b. Some: The article contains necessary information to answer the question but is not sufficient. c. None: The article does not...
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Fully answer the question
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Be brief and concise
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Use the SAME LANGUAGE as the given question
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No Retrieval
Be supported by the articles. Here are the given question and articles: <question> {{ question }} </question> <articles> {% for (idx, text, date) in articles %} <text_{{ idx }}> {{ text }} </text_{{ idx }}> <date_{{ idx }}> {{ date }} </date_{{ idx }}> {% endfor %} </articles>...
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Analyze the question type and conditions in the question
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Who" questions and numbers for
Identify the key information in the golden answer that can completely solve the question (e.g., names for "Who" questions and numbers for "how many" questions)
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Check whether the key information exists in the generated answer
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It is OK if the generated answer contains more information than the golden answer, as long as it does not contain any conflicting statements
Ignore differences in punctuation and phrasing between the golden answer and the generated answer. It is OK if the generated answer contains more information than the golden answer, as long as it does not contain any conflicting statements
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justification
If the generated answer is in a different language than the golden answer, it should be considered as wrong. Your response should be in json format as follows: { "justification": [Explain why you think the GENERA TED ANSWER is Correct or Incorrect. Use one or two sentences at ...
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[2018]
bridge entity
Constructing datasets for multi-hop reading comprehension across documents. Transactions of the Association for Computational Linguistics, 6:287– 302. Jian Yang, Shaohan Huang, Shuming Ma, Yuwei Yin, Li Dong, Dongdong Zhang, Hongcheng Guo, Zhou- jun Li, and Furu Wei. 2022. CRO...
2018
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[2019]
In Proceedings of the 57th An- nual Meeting of the Association for Computational Linguistics, pages 2358–2368, Florence, Italy
XQA: A cross-lingual open-domain question answering dataset. In Proceedings of the 57th An- nual Meeting of the Association for Computational Linguistics, pages 2358–2368, Florence, Italy. Asso- ciation for Computational Linguistics. Dominik Macko, Robert Moro, Adaku Uchendu, ...
2023
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In Proceedings of the 1st Work- shop on Towards Knowledgeable Language Models (KnowLLM 2024), pages 177–188, Bangkok, Thai- land
Retrieval-augmented generation in multi- lingual settings. In Proceedings of the 1st Work- shop on Towards Knowledgeable Language Models (KnowLLM 2024), pages 177–188, Bangkok, Thai- land. Association for Computational Linguistics. Cohere. 2024. Introducing command-r+: Advance...
2024 arXiv
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[9474]
Tian Liang, Xing Wang, Mingming Yang, Yujiu Yang, Shuming Shi, and Zhaopeng Tu
Curran Associates, Inc. Tian Liang, Xing Wang, Mingming Yang, Yujiu Yang, Shuming Shi, and Zhaopeng Tu. 2024. Addressing entity translation problem via translation difficulty and context diversity. In Findings of the Associa- tion for Computational Linguistics ACL 2024, pages ...
2024
Reviewed August 15, 2026 · model on record in the stance chip above.
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