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Figure 2. Materials knowledge extraction as a PCA framework. Perception parses raw PDF literature; cognition supplies ontology and knowledge-graph grounding; action converts evidence into structured records through schema-based, schema-free, or agentic extraction. Quality control connects all stages through source provenance, ontology constraints, physical checks, and feedback loops. PCA: Perception–Cognition–Action; AI: artificial intelligence; QC: quality control; KG: knowledge graph.