Data catalogues will advertise the existence of shared data and will contain information about all data assets contained in the associated shared data space (including databases, system output files, web pages, documents, and access services). At a minimum, the mandatory metadata elements in the Discovery Services must be represented within data catalogues for any data asset posted to a shared space. NATO Communities of Interest (COIs) should establish and maintain catalogues in their respective interest areas. Each catalogue may be organized according to a community-defined ontology (the classes, properties of and relationships among items of interest to a community). An Alliance wide data catalogue will have to be established that links to catalogues of communities and data spaces, effectively creating a “catalogue of catalogues.” The Alliance wide catalogue will also contain metadata for data posted by users and applications without a specific functional area service affiliation. Catalogues will be searchable by humans through web-based user interfaces and for machines through application programming interfaces. All metadata catalogues will adhere to NATO agreed standards to allow federated searches across multiple catalogues.