Metadata when conceptualized into a shared standard can be said to be part of an ontology. An ontology(12) renders shared vocabulary and taxonomy, which models a domain with the definition of objects and/or concepts and their properties and relations.
By grouping together metadata and defining a standard from it is useful for searching and understanding what a digital object is. It is now common practice for all digital cameras to capture and store metadata about the photo in metadata fields conforming to the EXIF standard. This can include aperture, focal length, brightness, and GPS co-ordinates of the image.
Most metadata is stored in the XML format, which is an easy-to-use and flexible data storage format. The definitions of the metadata within an XML format can be described using the XMP standard, which is also in XML.
The popularity, simplicity, flexibility, and wide-spread use of XML has resulted in nearly all metadata being stored in the XML format. Even older formats...