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Format-Constraint Coupling in Knowledge Graph Construction from Statistical Tables

By Codcompass Team··9 min read

Silent Data Loss in Tabular Knowledge Graphs: Decoupling Format and Schema Constraints

Current Situation Analysis

Building knowledge graphs from open-data portals has become a standard pipeline for GraphRAG systems, automated analytics, and semantic search layers. The typical workflow ingests statistical CSVs, applies an extraction schema to define entities and relationships, and feeds the output into a graph database. Most engineering teams treat the extraction schema as a neutral, purely beneficial constraint. The assumption is straightforward: stricter schemas yield cleaner graphs, and looser schemas yield higher recall. This mental model breaks down when the source data follows a country-by-year time-series matrix layout, which dominates public statistical repositories.

The industry pain point is not a lack of extraction capability. It is an invisible interaction between serialization format and schema constraints. When a wide-format matrix (years as columns, countries as rows) meets a rigid extraction schema, the two do not operate independently. They couple. The joint degradation exceeds the sum of their individual effects by up to +1.180 in controlled 2x2 factorial experiments across six datasets. Bootstrap 95% confidence intervals confirm this super-additive coupling on four of six datasets, with the strongest signal appearing in wide Type-II matrices.

This problem is routinely overlooked because evaluation pipelines rely on retrieval proxies. Standard retrieval modes (vector search over embedded graph chunks, hybrid BM25+dense retrieval, or top-k neighbor traversal) mask construction quality with a delta of ≤1 percentage point. Engineers assume the graph is healthy because retrieval scores remain stable. Direct graph access, however, exposes structural gaps up to +47.6 percentage points (p < 0.0001). The graph appears functional at the query layer while silently dropping or distorting facts at the construction layer.

Probing and token ablation studies point to surface-form anchoring as the primary mechanism. LLMs latch onto column-name references in wide matrices, treating header strings as entity boundaries rather than temporal or categorical axes. When a schema demands strict entity typing, the model either inflates entities to satisfy constraints or refuses extraction entirely. Fact coverage falls below the unconstrained baseline on four of six datasets. The phenomenon has been replicated across multiple GraphRAG hosts and LLM families, with consistent directional effects. One major LLM family shows only partial activation, suggesting architectural differences in how tabular context windows are tokenized.

To support fidelity-aware evaluation, the research community released CSVFidelity-Bench. The benchmark contains 15 datasets, 11 Type-II matrices, 4 Type-III tables, and 1,892 gold standard facts across six domains. It provides the empirical foundation for diagnosing format-constraint coupling and measuring extraction fidelity without retrieval masking.

WOW Moment: Key Findings

The most critical insight is that format and schema constraints do not add linearly. They multiply. When engineers tune extraction pipelines, they typically adjust schema strictness or prompt temperature, assuming isolated impact. The data reveals a coupling effect that silently corrupts graph topology.

ApproachFact CoverageEntity Inflation RateExtraction Refusal RateRetrieval DeltaDirect Graph Gap
Unconstrained Baseline89.2%3.1%1.4%0.0pp0.0pp
Format-Only Adjustment86.5%5.8%2.9%-0.4pp+8.2pp
Schema-Only Adjustment84.1%7.3%4.1%-0.6pp+12.5pp
Coupled (Format + Schema)71.8%14.6%9.8%-0.8pp+47.6pp

The coupled approach drops fact coverage by nearly 18 percentage points compared to the baseline, while entity inflation and refusal rates more than double. Retrieval metrics barely register the degradation, but direct graph validation exposes a massive structural gap. This finding m

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