Dublin Core Format WG - Proposed Format Qualifiers

DC Format Working Group

Proposed Format Qualifiers

Date: 1999-10-09

Status: Working Group proposal

This report proposes a set of core qualifiers for the DC Format element.

Note: The appearance of a qualifier in this list should not be taken as an endorsement of its use by the Dublin Core Metadata Initiative at this time.

Media and MIME Type

The WG proposes a 'Media' element qualifier and an 'IMT' value qualifier. Example usage:

DC.Format.Media = CD-ROM
DC.Format.Media (Scheme=IMT) = text/html
DC.Format.Media = charcoal on paper

Issues:

Note that this gives us a scheme for the media types of digital resources but not for the media types of physical resources.
MIME types and sub-types mix up modality (text) and encoding (html) in a way that is undesirable and confusing with respect to the DC Type element. However, given the widespread use of MIME types for Internet resources, the WG sees little alternative than to recommend their use in the Format element.
Implementations may wish to further qualify the 'Media' element qualifier into DC.Format.Media.Support (e.g. paper), DC.Format.Media.SignalRecording (e.g. charcoal) and DC.Format.Media.Encoding (e.g. HTML). The WG currently make no recommendations about how this should be done.

Physical vs. Digital

The WG feels that it is important to indicate whether a resource is physical or digital. We therefore propose a 'DCF1' value qualifier. DCF1 is a DC-specific list of three values: 'Digital', 'Physical' and 'Analog'. Example usage:

DC.Format (Scheme=DCF1) = Physical
DC.Format (Scheme=DCF1) = Digital
DC.Format (Scheme=DCF1) = Analog

Size or duration

The size or duration of a resource is indicated using an 'Extent' element qualifier. Example usage:

DC.Format.Extent = 3419 bytes
DC.Format.Extent = 34 minutes
DC.Format.Extent = 2 x 3.5 inch floppy disks

Issues:

The WG currently make no recommendations for how to formally associate units with the value of DC.Format.Extent. Recommended best practice is to structure free text values a number, followed by a space character, followed by the units. Where possible recognised standard units (e.g. SI) should be used. Where possible the smallest units should be used (e.g. mm rather than cm, seconds rather than minutes).
Implementations may want to further qualify the 'Extent' element qualifier into DC.Format.Extent.Duration and DC.Format.Extent.FileSize (and others). The WG currently make no recommendations about how this should be done.
Where a compressed file is being described, the WG make no recommendations about how to indicate the compression-ratio. Note that, when describing a compressed file, DC.Format.Extent indicates the size of the compressed file, not the size of the uncompressed file.

Nested Formats

Nested formats, e.g. a Zip'ed Postscript file, should be described by simply repeating the Format element, e.g.

DC.Format.Media (Scheme=IMT) = application/postscript
DC.Format.Media (Scheme=IMT) = application/gzip

Physical collections of digital material

Physical collections of digital material, e.g. a CD-ROM, can be described by describing the CD-ROM

DC.Format (Scheme=DCF1) = Physical
DC.Format.Media = CD-ROM

and each digital file

DC.Format (Scheme=DCF1) = Digital
DC.Format.Extent = 3419 bytes
DC.Format.Media (Scheme=IMT) = application/postscript

separately, linking them together using the DC.Relation element.

Issues:

Clearly not all implementations will require this level of detail. Summary information about the contents of a CD-ROM can be included in its DC.Description, e.g.
```
DC.Description = A CD-ROM containing a collection of 300 postscript files,
                 1200 HTML files and 400 GIF images.
```

Examples

DC.Format (Scheme=DCF1) = Physical
DC.Format.Media = Floppy Disk
DC.Format.Extent = 3.5 inch

DC.Format (Scheme=DCF1) = Digital
DC.Format.Media (Scheme=IMT) = text/html
DC.Format.Extent = 37645 bytes

DC.Format (Scheme=DCF1) = Analogue
DC.Format.Media = VHS
DC.Format.Extent = 90 minutes

Summary

To summarise, the WG recommends the following DC Format qualifiers:

                                   -----------Qualifiers--------------
Element Name                        Element                      Value
----------------------------------------------------------------------
Format                                                           IMT
                                                                 DCF1
                                    Media
                                    Extent
----------------------------------------------------------------------

Contact the DC Format Working Group at: http ://purl.org/DC/groups/format.htm

Content by: Andy Powell, UKOLN

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