Metadata is generally referred as data about other data or catalog for a data. It describes, identifies, explains, manages, and uses a data resource. Metadata can be grouped as descriptive, structural and administrative metadata. Descriptive metadata identifies a data resource. Administrative metadata defines the ways of managing a data resource. Structural metadata describes relationships between parts of a composite object. Metadata can generally be stored in various storage structures such as a field of relational database’s table, XML files, RDF models. Therefore, the correct option is D.