Standards, de facto standards and specifications
Jenn Riley’s Visualization of the Metadata Universe[8]has been around for a while, but still gives the best overview of standardsused in the cultural sector, archives, libraries and museums. In the image there are numerous standards are displayed in the context of their function and where they are used.
The visualization of the Metadata Universe by Jenn Riley. (The recommendation is to look on-line)
Almost all standards on the metadata map created by Jenn Riley have an XML format available described with an DTD or an XML-schema. For the XML-schemas both the ISO standard RelaxNG as well as W3C XML-schema formats are used. The choice depends solely on the skills of the creator of the schema and at the same time it’s also common to ensure that all different type of schemas are available so transformations from RelaxNG to XML-schema and vice versa is often used. DTD are still around due to the fact that old software is still in use and they are based upon using a DTD.
The most common way to use the standards is to write a specification which describes a profile for our use case of the standard which then in its turn are implemented in the setting you are operating. The best way of describing the use of profiles is the standard METS (more about that later) which requires the user to write a profile describing how it is used.