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Concept rather than Document: Context Compression via AMR-based Conceptual Entropy

Paper · 2026 · Kaize Shi, Xueyao Sun, Xiaohui Tao et al.

Summary

RAG systems often pass LLMs long retrieved documents full of material unrelated to the question, which can hurt reasoning and slow inference. Existing compression methods filter on lexical or token-level signals and can break apart meaningful units. Kaize Shi and colleagues instead compress context at the level of concepts using Abstract Meaning Representation (AMR), with no supervision. Each retrieved document is parsed into sentence-level AMR graphs, and the relation edges are dropped. Each concept node gets an entropy score derived from the parser's own prediction uncertainty, combined across subword tokens. A significance test keeps only concepts with reliably high scores, and these are mapped back to their original wording in the source text. The method was tested on PopQA and EntityQuestions with ten LLM backbones, against vanilla RAG and several compression baselines. It achieved higher accuracy than these alternatives while cutting context to roughly half its original length and lowering latency. The authors present it as the first use of AMR-based conceptual entropy for context engineering.

Key points

  • Parser: AMR graphs come from an mBart-based multilingual parser (BramVanroy's multilingual-text-to-amr) trained on the AMR 3.0 corpus (LDC2020T02). The multilingual parser was chosen because web-retrieved text may contain non-English characters.
  • Controlled evaluation: only retrieved documents that contain a correct answer are kept. This isolates the effect of compression but leaves noisy, real-world retrieval untested.
  • Baselines: TF-IDF, SelCon (Selective-Context), Lingua, Keywords and Summary.
  • Backbones: ten models, labelled G-1.3, G-2.7, O-1.3, O-2.7, b-560, b-7b1, L-13, L3.1-8, DS-V2 and Q3-32.
  • Results:
    • Compressed contexts average about 50% of vanilla length with stable accuracy.
    • Keywords and Summary produce shorter contexts but lose factual cues and accuracy.
    • On long-context instances, gains are smaller but variance across backbones is notably lower.
  • Limitations: the method depends on AMR parser quality and ignores document-level structure. It also adds offline preprocessing cost for parsing and entropy scoring.

Our summary of the paper, in our own words — not its text. The work belongs to its authors; read it at the links above.

 Institutions

Also on the byline: Education University of Hong Kong.

 Fields, topics and concepts

Cite

Cite as Kaize Shi, Xueyao Sun, Xiaohui Tao, Lin Li, Qika Lin and Guandong Xu. 2026. Concept rather than Document: Context Compression via AMR-based Conceptual Entropy. Findings of the Association for Computational Linguistics: ACL 2026.

The paper itself, not this page. BibTeX from the library's record of the work. DOI 10.18653/v1/2026.findings-acl.590

@inproceedings{shi2026concept,
  title = {{Concept rather than Document: Context Compression via AMR-based Conceptual Entropy}},
  author = {Kaize Shi, Xueyao Sun, Xiaohui Tao, Lin Li, Qika Lin and Guandong Xu},
  booktitle = {Findings of the Association for Computational Linguistics: ACL 2026},
  year = {2026},
  doi = {10.18653/v1/2026.findings-acl.590},
  url = {https://doi.org/10.18653/v1/2026.findings-acl.590}
}

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