Property-graph schemas often contain descriptive properties that recur across heterogeneous nodes and edges. Some are ordinary local attributes, while others behave as reusable metadata that may be externalized as shared structures. However, property-graph schema design lacks an explicit 5GNF-oriented method for deciding when a repeated property should become a reusable metadata candidate.

This paper proposes a rule-based design method for identifying such candidates before trait-node externalization. The method evaluates five criteria: cross-element occurrence, conceptual independence, lossless externalization, reuse potential, and governance relevance. Based on these criteria, properties are classified as trait candidates, embedded properties, or borderline cases.

The method is illustrated using a library-domain example and evaluated across two schema contexts. The validation combines eight human and four LLM-based responses and examines classification distributions, agreement, and comparison with a recurrence-based baseline. Results indicate that repetition alone is insufficient for externalization. Clear embedded properties and reusable descriptors achieve stronger agreement, whereas semantically ambiguous properties remain context-dependent. The method therefore provides an explainable basis for identifying reusable metadata candidates before 5GNF-oriented normalization.