Workbook on Digital Private Papers > Administrative and preservation metadata > Using METS for the preservation and dissemination of digital archives
Using METS for the preservation and dissemination of digital archives
Structure of a METS file
Structural map <structMap> The <structMap> sits at the heart of a METS document; it organises the digital content represented by the <file> elements in the METS <fileSec> into a coherent hierarchical structure. More than one <structMap> can be included in a METS document, so more than one method of organisation is possible - e.g. physical, logical or a mixture of the two. The structural divisions in the map are represented by division (<div>) elements, which can be nested to any depth to allow for very complex hierarchies.
As well as organising content, the <structMap> provides a mechanism for linking content at any hierarchical level with the relevant descriptive or administrative metadata sections in the same METS document.
Nested divisions within the <structMap> can be used to reflect the hierarchy of folders, subfolders and files in a digital accession in an accession-level METS document. The <structMap> for digital objects, such as that representing the single email at AIP stage will be a very straightforward one, containing only one division.
Example:
In the example below, the type of the <structMap> is given as a "single digital file"; METS does not prescribe values for the TYPE attribute, and "physical" or "logical" are the usual examples given; preferred attribute values for this could be established in METS profiles.
The <structMap> only contains one <div> element because the METS document represents a single file. Its type has been set to "email" (again a value not prescribed by METS) and a comprehensive label supplied for the user; labels may differ according to the type of <structMap> which is being presented.
The <div> element contains a file pointer, or <fptr>, element. This is used to link the division to the file content it represents (the email), as recorded in the File Section of the same METS document; the link is made by means of the unique ID (em01) which was allocated to the
The structural map can also deal with much more complex objects. For example, the <area> element within <fptr> can be used to point to just one portion or area of a file representing as a <file> element in the <fileSec>. In addition, the sequence of files (<seq>) and parallel files (<par>) elements aggregate pointers to files, parts of files, or sequences or sections of files, that must be played or displayed either sequentially or simultaneously to manifest a block of digital content.
The <structMap> is not the final section of a METS document, but often only the five sections covered to this point are all that is needed to represent even fairly complex objects. The final two sections - <structLink> and <behaviourSec> - are not therefore covered in any detail here.
