Graph-based Document Structure Analysis

Authors: Yufan Chen, Ruiping Liu, Junwei Zheng, Di Wen, Kunyu Peng, Jiaming Zhang, Rainer Stiefelhagen
Primary area: datasets and benchmarks
Keywords: Document Structure Analysis, Document Layout Analysis, Document Relational Graph

Abstract:
When reading a document, glancing at the spatial layout of a document is an initial step to understand it roughly. Traditional document layout analysis (DLA) methods, however, offer only a superficial parsing of documents, focusing on basic instance detection and often failing to capture the nuanced spatial and logical relationships between instances. These limitations hinder DLA-based models from achieving a gradually deeper comprehension akin to human reading. In this work, we propose a novel graph-based Document Structure Analysis (gDSA) task. This task requires that model not only detects document elements but also generates spatial and logical relations in form of a graph structure, allowing to understand documents in a holistic and intuitive manner. For this new task, we construct a relation graph-based document structure analysis dataset(GraphDoc) with 80K document images and 4.13M relation annotations, enabling training models to complete multiple tasks like reading order, hierarchical structures analysis, and complex inter-element relationship inference. Furthermore, a document relation graph generator (DRGG) is proposed to address the gDSA task, which achieves performance with 57.6% at $mAP_g$@$0.5$ for a strong benchmark baseline on this novel task and dataset. We hope this graphical representation of document structure can mark an innovative advancement in document structure analysis and understanding. The new dataset and code will be made publicly available.

Decision: accept (poster)
Reviewer scores: 6, 8, 6, 8

Reviews and discussion:
<thread>
creation date:
1729998092904

thread_type:
official_review

<thread_object>
creator: reviewer_g241

<content>
summary:
In this paper, the authors introduced an approach to analyzing document structures using graph theory, which offers a unique perspective on understanding the complex relationships and patterns within documents. The primary contribution of this paper lies in its methodology that transforms textual content into graphical representations, enabling researchers and practitioners to visualize and analyze the hierarchical and relational aspects of documents more effectively.

strengths:
1. The authors propose a method that represents documents as graphs, where nodes could represent sentences or paragraphs and edges could capture relationships between these elements based on semantic similarity or other linguistic features. This original perspective offers a fresh way of understanding the hierarchical organization within texts.

2. The authors provide a clear and systematic approach to converting textual documents into graph structures, followed by an analysis that leverages graph algorithms. They also discuss the advantages of their method over traditional text-based approaches, such as improved handling of complex document structures and enhanced interpretability through visual representations. 

3.  The clarity of the paper is good. The authors have structured the content logically, starting with an introduction to graph theory and its relevance to document analysis, followed by a detailed explanation of their method, implementation details, and results.

weaknesses:
1. The paper could benefit from a more explicit discussion on potential weaknesses or limitations of the proposed method. This includes considerations such as scalability with large datasets, robustness to noise, and applicability across different types of documents.  

2. There are lack of comparison with MLLM based methods. The results of GPT4 should be reported for readers to compare.

questions:
1. A higher IoU score suggests a better alignment between the predicted and actual bounding boxes.What is the IoU score when it falls between 0.7 - 0.95  and  0.8 - 0.95?
</content>
</thread_object>

</thread>
<thread>
creation date:
1730207070147

thread_type:
official_review

<thread_object>
creator: reviewer_zrck

<content>
summary:
The paper defines a graph-based Document Structure Analysis task (gDSA) and builds a new Document Structure Analysis dataset, GraphDoc, based on existing datasets. By constructing a document layout graph structure that includes spatial and logical relationships, it enhances the depth of document structure understanding. Additionally, the paper presents a new end-to-end Document Relation Extraction model, DRGG, designed to extract features from the document layout and generate a relation graph that includes spatial and logical relationships among document elements.

strengths:
The author compares the proposed DRGG framework with several existing document layout analysis and graph structure analysis methods, demonstrating through experiments that this model exhibits outstanding performance on the gDSA task, particularly in handling complex document structures, which is significant for achieving deeper document understanding.

weaknesses:
1. Most document instances exhibit multiple relationships. The paper should provide additional experiments to evaluate the precision and recall of DRGG in capturing instances that have both spatial and logical relationships, compared to those with only one type of relationship.
2. In the dataset, the number of samples in the position relationship category is significantly higher than that in the logical relationship category. It would be better to consider adding experiments to demonstrate how to select the relationship confidence threshold to ensure evaluation accuracy in the context of imbalanced sample sizes among relationship categories.

questions:
1. A performance bottleneck has been observed in detecting reference relationships in the experiments. Given the importance of reference relationships in document structure understanding, could you supplement with an analysis of the error cases in reference relationship detection, discussing the reasons for these errors and suggesting improvements.
2. It is suggested that the author can elaborate on the utility of the proposed dataset, evaluation tasks, and evaluation metrics in understanding complex document interactions. Is it possible to provide specific examples of how the GraphDoc dataset and DRGG model can be applied in real-world document understanding tasks? Highlighting of these advantages, such as Reading Order Prediction and Document Hierarchical Structure Analysis tasks mentioned in the paper.
</content>
</thread_object>

</thread>
<thread>
creation date:
1730610102489

thread_type:
official_review

<thread_object>
creator: reviewer_hrlr

<content>
summary:
This paper introduces the **GraphDoc dataset**, a new dataset for document layout and structure analysis derived from the DocLayNet dataset by adding relation annotations. The authors propose a new task called **graph-based Document Structure Analysis (gDSA)** that involves not only detecting document elements, but also generating **spatial and logical relations** in the form of a graph. To address this new task, the authors also propose a model called the **Document Relation Graph Generator (DRGG)** that can generate relation graphs from document layouts, achieving 57.6% mAPg@0.5 on the GraphDoc dataset.  The authors hope that this graphical representation of document structure will be an innovative advancement in document structure analysis and understanding.

strengths:
This is a large new dataset (80,000 single-page document images ; 1.10 million instances across 11 categories: Caption, Footnote, Formula, Listitem, Page-footer, Page-header, Picture, Section-header, Table, Text, and Title.) that extends DocLayNet Pfitzmann et al. (2022), and the relative location of the document elements is key to document understanding

weaknesses:
This paper doesn't really have any major weaknesses. it is mostly a dataset paper and the dataset is strong. The authors also introduce a new model, which is rather straightforward but still interesting.

questions:
Line 284: "most of the results have been manually verified and refined". What percentage of results have been manually verified and what percentage of results have been manually refined?
</content>
</thread_object>

</thread>
<thread>
creation date:
1730698331536

thread_type:
official_review

<thread_object>
creator: reviewer_jdza

<content>
summary:
This paper introduces a dataset which is built on top of the DocLayNet dataset to provide detailed annotation of both spatial and logical relation annotations for understanding the structure of single-page documents. As well as, a new framework, Document Relation Graph Generator, is proposed as a baseline for conducting layout and structure understanding in an end-to-end manner.

strengths:
1. The research problem is interesting and novel which is the less explored in this area.
2. The dataset generation and the evaluation metrics look reasonable.
3. Some analyses are conducted to show the insight of the datasets such as the correlations and co-occurrence of different relation pairs.

weaknesses:
1. Some key concepts are not clearly defined: e.g. why spatial relations are important, why only four spatial relation types are defined, Is proper all documents from different domains to adopt the same rule to define the relations between semantic entities.
2. Lack of analysis about rule-based generated relation and human refining details which is essential for demonstrating the high quality of the dataset.
3. It would be clearer if the detailed categorisation of parent, child, and reference relation types could be provided with examples (visualised would be much better) to enable the reader to understand definitions and tasks clearly.
4. The description of Document Relation Graph Generator is not clearly described to me. The overall workflow with the corresponding aim is relatively hard to understand. I have gone through it several times but still hard to understand including input to the framework, why the encoder and encoder structure, and how the decoder works during training and inferencing. 
5. The experimental section is underexplored. Analysis of different document domains, fine-grained relation type analysis (section->subsection, section->paragraph). 
6. Similar to quantitative analysis, more qualitative analyses are expected. 
I really like the idea of the paper, but more in-depth analysis is essential to maximising the contributions of the author desired.

questions:
1. Why do you think spatial relation should be considered as one of the relation types of this dataset which might be directly acquired by leveraging the predicted bbox coordinated?
2. Could you provide more statistics details before and after human checking?
3. Do you think the rules might be updated based on different document domains?
4. For the relation prediction dataset, is there any reason you choose single-page datasets? It is more natural to use multipage-scenarios to establish the entire document's logical structure.
</content>
</thread_object>

</thread>
<thread>
creation date:
1732656624974

thread_type:
official_comment

<thread_object>
creator: authors

<content>
title:
Summary of Revision

comment:
We sincerely thank all reviewers for their valuable feedback and constructive comments. Your suggestions significantly help us to improve the quality of our manuscript. We are a bit late in responding, as we have been actively organizing additional analyses of our previous experiments and conducting new ones. 

Thanks to the reviewers' suggestions, we have carefully addressed each concern or question individually and revised our paper accordingly, with **the changed content marked in red** and **the added text marked in orange**. Below, we summarize the key updates:

- In Sec. 3.2 DRGG, we have updated the explanation of the DRGG structure and workflow.
- In Supplementary Sec. A.1, we have added a detailed explanation of the human verification and refinement process.
- In Supplementary Sec. A.2, we have revised the explanation of spatial relations to clearly justify our decision to use four types of spatial relations.
- In Supplementary Sec. C, we have included a detailed figure illustrating the DRGG structure.
- In Supplementary Sec. D, we have added additional experimental results of DRGG across different document domains and relation types.
- In Supplementary Sec. E, we have clarified the analysis section of the previous ablation study and included new ablation study results along with the corresponding analysis.
- In Supplementary Sec. G, we have enhanced and expanded the detailed analysis of the qualitative results of DRGG and provided suggestions for potential improvements.

We hope the revised version can address all concerns of reviewers. Thank you again for your time and consideration.
</content>
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</thread>


Metareview:
metareview:
This paper introduces a novel task called Graph-based Document Structure Analysis, which extends traditional document layout analysis by not only detecting document elements but also modeling their spatial and logical relationships as a graph structure. Additionally, the authors present GraphDoc, a comprehensive dataset that includes relational annotations across diverse categories.

The reviewers recognized the significance and originality of this contribution, particularly highlighting the introduction of the proposed task and the extensive dataset. While some concerns were initially raised regarding the clarity of key concepts and the need for more detailed analyses, the authors thoroughly addressed these issues in their revisions. They provided additional explanations, experimental results, and qualitative analyses, which further strengthened the paper. Considering the novelty of the work, its potential impact on the field, and the satisfactory responses to the reviewers' feedback, I recommend this paper for acceptance.