Security critical AI applications require a standardized and interoperable data and metadata documentation that makes the source data explainable-AI ready (XAIR). Within the domain of materials modelling and characterization, European initiatives have proposed a series of metadata standards and procedural recommendations that were accepted as CEN workshop agreements (CWAs): CWA 17284 MODA, CWA 17815 CHADA, and CWA 17960 ModGra. It is discussed how these standards have been ontologized, and gaps are identified as regards the epistemic grounding metadata, i.e., an annotation of data and claims by something that substantiates whether, why, and to what extent they are indeed knowledge and can be relied upon.