The use of metadata is an essential part of any digital preservation strategy. Subsuming descriptive, administrative, as well as structural traits, it has the purpose to support and facilitate the digital preservation process and, ultimately, to ensure access to an archived object over time [oPM01].
The long-term retention of digital data is typically exerted in the setting of a digital archiving system. Descriptive metadata is required for resource discovery, which embodies functions ranging from the ingest of an object into the archive to the provision of access. This is, of course, a core functionality in archival systems. Yet, concerning purely the preservation of the collection items, this type is accredited rather minor importance.
Serving a structural function, preservation metadata details the relationships between multiple objects residing in an archival repository. This refers to tying multiple components of a single complex object together. Alternatively, multiple versions of a single object must be registered and referenced to. This is the case if multiple formats of a document are available, or adapted versions aside from the original object exist, for example, as a result of a Conversion circle. This also includes dynamic documents that have been acquired at different points in time and have changed in the meantime.
The focus of preservation metadata, however, lies in managing the processes the task calls for and, hence, administrative metadata. Foremost, it has to be assured that the digital records remain 'inviolate', 'coherent', and 'auditable'. Collection items have to be 'inviolate', in that they are not damaged, destroyed, or modified. In the future, it must be possible to reconstruct a documents logic relations, executable connections and references, as they existed in the original environment to obtain a 'coherent' document. Preserving an 'auditable' document over time involves the documentation of all actions taken to a record during the course of its life.
Any strategy ensuring that a digital document is retained over time following the requirements above depends on administrative metadata. Considering the Conversion-method (cf. Section 2.4.3), for instance, such a strategy will depend upon metadata being created to record the conversion history of a digital object. Also, it is necessary to record contextual information so that a future user can understand the technological environment in which a particular digital object was created [Day98]. Furthermore, in the Emulation-approach (cf. Section 2.4.4) the 'annotation metadata' being part of an encapsulation is essentially administrative metadata.