a definition of the data schema and value domains for a dataset. The data schema specifies entities (features), properties associated with each entity, the data type used to specify property values, c
ardinality for property values, and if applicable, other logical constraints that determine data validity. Value domains are specified for simple data types—strings or numbers, and may include controlled vocabularies for terminology required to specify some properties
an identifiable collection of data (ISO19115). a collection of data items unified by some criteria (authorship, subject, scope, extent...). A kind of [Collection](https://n2t.net/99152/h1048) that c
ontains data.