Metadata describes how data was created and the context in which it exists. It should make the data identifiable and explain who, how and in which context the data was generated, how it was processed and where it has already been published and under which conditions it is accessible and reusable for others.

The following types of metadata exist:

• Technical metadata (e.g. the size of an image file)
• Metadata that describes the content (title, authors, keywords)
• Administrative metadata (rights, licences, publication date, usage, access rights)
• Relational metadata (reference to other data sets or the associated publication)