Descriptor references have targets that are either in the Descriptor (internal references) or outside of the Descriptor (external references). The target of a Descriptor reference can be a file or content element in an XML file.

Three mechanisms are used for file and content references in a Descriptor:

• Open Packaging Conventions relationships which can be used for internal and external references,
• AutomationML ExternalDataReference interfaces,
• AutomationML External References.