ISO/IEC 11179-4:2004 specifies requirements and recommendations for constructing definitions for data and metadata. Only semantic aspects of definitions are addressed; specifications for formatting the definitions are deemed unnecessary for the purposes of this standard. While especially applicable to the content of metadata registries as specified in ISO/IEC 11179-3, ISO/IEC 11179-4:2004 is useful broadly for developing definitions for data and metadata. These definitional requirements and recommendations pertain to formulating definitions for data elements and other types of data constructs such as entity types, entities, relationships, attributes, object types (or classes), objects, composites, code entries, metadata items, and the data referred to by XML tags.