The ontology Metadata4Ing is developed within the NFDI Consortium NFDI4Ing with the aim of providing a thorough framework for the semantic description of research data, with a particular focus on engineering sciences and neighbouring disciplines. This ontology allows a thorough description of the whole data generation process (experiment, observation, simulation), embracing the object of investigation, all sample and data manipulation procedures, a summary of the data files and the information contained, and all personal and institutional roles. The subordinate classes and relations can be built according to the two principles of inheritance and modularity. Inheritance means that a subclass inherits all properties of its superordinate class, possibly adding some new ones. Modularity means that all expansions are independent of each other; this makes possible for instance to generate expanded ontologies for any possible combinations of method × object of research. The new version 1.3.0 introduces several changes and improvement: Ontology: reorganizes classes (si:Real, pims-ii:QuantityValue --> m4i:NumericalVariable) to simplify the modeling of numerical variables ( #245, #258, #262) includes Croissant classes and properties to model data files as input or output of processing steps in the research process ( #111) distincts between published datasets with their metadata (dcat:Dataset) and their data files ( #235) adds mapping and additional context file to use m4i files in RO-Crates ( #199) flexibilises the relationship between processing steps and actors to make it compatible with PROV-O ( #246) Documentation: expands introduction ( #265) adds funding acknowledgement and additional references ( #251, #266) color-codes figures and provides them with links ( #260) references DataCite metadata scheme version 4.5 ( #266/ !229) Training material: adds RO-Crate example ( #199) corrects errors ( #169) adds license and citing information ( #268) improves visibility of first-steps guide ( #263, #261) Continuous integration: updates script for documentation generation to consider new Widoco version and to access sibling folders ( #148, #264/ !232, !233, !234) Others: adds ontology logo ( #148) minor changes in the README ( #251)

The authors (Metadata4Ing Workgroup) would like to thank the Federal Government and the Heads of Government of the Länder, as well as the Joint Science Conference (GWK), for their funding and support within the framework of the NFDI4Ing consortium. Funded by the German Research Foundation (DFG) - project number 442146713.