R 2 A - TLS : Reflective Retrieval-Augmented Timeline Summarization with Causal-Semantic Integration (2025)

Abstract: Open-domain timeline summarization (TLS) faces challenges from information overload and data sparsity when processing large-scale textual streams. Existing methods struggle to capture coherent event narratives due to fragmented descriptions and often accumulate noise through iterative retrieval strategies that lack effective relevance evaluation. This paper proposes: Reflective Retrieval-Augmented Timeline Summarization with Causal-Semantic Intergration, which offers a novel perspective for open-domain TLS by time point completion and event element completion. R2A-TLS establishes an initial retrieval, reflection, and deep retrieval system that reduces noise through a double filtering mechanism that iteratively generates a timeline for each text which passes the filtering. Then, the system reflects on the initial timeline with the aim of identifying information gaps through causal chain analysis and FrameNet based element validation. These gaps are reformulated into targeted queries to trigger deep retrieval for refining timeline coherence and density. Empirical evaluation on Open-TLS dataset reveals that our approach outperforms the best prior published approaches.

## introduction condensing a vast collection of texts into comprehensible summaries is a crucial and challenging task. timeline summarization (tls) aims to distill large-scale text collections into structured summaries by extracting and chronologically organizing key events @xcite . current tls research is generally divided into open-domain and closed-domain paradigms @xcite . opendomain tls refers to the process of generating * these authors contribute equally to this work. to address these challenges, we consider reducing noise to tackle information overload, and optimizing the iterative questioning method to deal with data sparsity. regarding noise reduction and reducing inference demands, we can filter articles, generate timeline fragments for each useful article, and finally merge and deduplicate. humans can infer missing time points or identify incomplete event descriptions in timelines through commonsense reasoning, causal logic, and domain knowledge. in recent researches, the generic llm has been trained on extensive corpora and has mastered common sense and causal logic @xcite , as for domain knowledge, it can be enhanced by fine-tuning the model or introducing an external knowledge base @xcite . inspired by this sight, we can use the generic llm and fine-tune a domain-adapted model to jointly identify the missing time point, which involves causal chains analysis and domain-informed pattern matching, and use framenet @xcite to guide the llm to discover incomplete descriptions. motivated by the above, we propose r2a-tls: reflective retrieval-augmented timeline summarization with causal-semantic integration, which introduces a novel perspective for modeling event relationships in open-domain tls by performing time point completion and event element completion through reflection and deep retrieval. r2a-tls establishes an initial retrieval, reflection, and deep retrieval system, adding a dual-filtering mechanism that applies topical relevance judgment and information gain assessment to process retrieved texts. we use llms to generate timeline fragments for each texts that passed the filter and merge them to get an initial timeline. then, by synergizing llm-powered causal reasoning with framenetbased element validation, the system performs reflection to detect information gaps from the initial timeline. these gaps are then reformulated into targeted queries to trigger deep retrieval to complete the timeline. our contributions can be summarized as follows: ## experiments baselines our baselines are consistent with chronos @xcite , which is the sota approach, and an additional method, filter, is proposed as the baseline. ## conclusion in conclusion, this paper presents r2a-tls, a novel framework for tls that leverages llms through reflections for timeline completion and retrieval-based process. this framework establishes a closed-loop system of "retrieval reflection deep retrieval", to solve the redundant interference caused by information overload in traditional methods. and we address the problem of missing time points or missing event elements due to discrete open-domain information through collaborative reflection, leveraging causal chain analysis and framenet-based validation. experiments demonstrates that r2a-tls achieves sota results on open-tls dataset. next, an interesting and useful topic would be to explore the future trend of events target news: islamic state questions for time point completion reference timeline: 2013-04-08: abu bakr al-baghdadi, the leader of al-qaida's branch in iraq, announces the merger of his group with al-qaida's franchise in syria, forming the islamic state in iraq and the levant. 2014-01-04: al-baghdadi's forces seize control of the city of fallujah in western iraq and parts of the nearby provincial capital of ramadi. 2014-02-03: al-qaida leader ayman al-zawahri disavows al-baghdadi after the iraqi militant ignores his demands that is leave syria. 2014-06-10: is captures mosul, iraqi's second-largest city, and pushes south as iraqi forces crumble, eventually capturing saddam hussein's hometown of tikrit and reaching the outskirts of baghdad.", "when they threaten shiite holy sites, iraq's top shiite cleric issues a call to arms, and masses of volunteers, largely backed and armed by iran, join militias. 2014-06-29: the group renames itself the islamic state and declares the establishment of a self-styled caliphate, a traditional model of islamic rule, in its territories in iraq and syria.", "al-baghdadi is declared the caliph. 2014-07-04: al-baghdadi makes his first public appearance, delivering a friday sermon in mosul's historic al-nuri mosque. he urges muslims around the world to swear allegiance to the caliphate and obey him as its leader. 2014-08-03: is captures the town of sinjar west of mosul and begins a systematic slaughter of the tiny yazidi religious community. women and girls are kidnapped as sex slaves; hundreds remain missing to this day. 2014-08-08: the u.s. launches its campaign of airstrikes against is in iraq. 2014-09-22: the u.s.-led coalition begins an air campaign against is in syria. rewritten questions: 1. when did baghdadi become caliph? 2. where did baghdadi become caliph? generated timeline: 2013-04-01: abu bakr al-baghdadi, the leader of al-qaida's branch in iraq, announces the merger of his group with al-qaida's franchise in syria, forming the islamic state in iraq and the levant 2014-01-04: baghdadi's forces occupied parts of the area. 2014-02-01: al-qaida leader ayman al-zawahri disavows al-baghdadi after the iraqi militant ignores his demands that is leave syria. 2014-06-01: is captures mosul, iraqi's second-largest city, and pushes south as iraqi forces crumble, eventually capturing saddam hussein's hometown of tikrit and reaching the outskirts of baghdad. when they threaten shiite holy sites, iraq's top shiite cleric issues a call to arms, and masses of volunteers, largely backed and armed by iran, join militias. 2014-06-29: the group renames itself the islamic state and declares the establishment of a self-styled 'caliphate', a traditional model of islamic rule, in its territories in iraq and syria. al-baghdadi is declared the caliph. 2014-07-04: al-baghdadi makes his first public appearance, delivering a friday sermon in mosul's historic al-nuri mosque. he urges muslims around the world to swear allegiance to the caliphate and obey him as its leader. . . . questions for event element completion rewritten questions: from the existing timeline. this research needs to improve temporal reasoning ability for llms, which has not yet received widespread attention.