BZKO: An Ontology for the Card Index of German Post-War Compensation Records

This poster presents BZKO, an ontology for representing the Central Federal Card Index (Bundeszentralkartei, BZK), a collection of approximately 1.9 million index cards documenting German compensation proceedings for victims of National Socialist persecution. The cards contain biographical information about applicants and persecuted persons and identify the responsible compensation authorities, connecting researchers to related case files. BZKO addresses the challenge of combining ontologically grounded domain semantics with the flexibility and interoperability required for archival data. Its two-layer architecture separates a knowledge layer, grounded in BFO and NFDIcore, from an extension layer incorporating resources such as RiC-O, PROV-O, PiCo, and Schema.org. This design supports semantic precision, provenance, interoperability, independent reuse, and maintainability. The ontology remains under development and is being evaluated through competency questions formulated with archivists.