(I had wrist surgery Friday morning, so this post will be shorter than normal.)
When harvesting an unqualified <dc:subject> field:
<dct:audience>Learner</dct:audience>
you can’t tell if the digital library is using a particular subject scheme, random user-entered keywords, or something else.
Enter qualified metadata fields which allow one to specify the range of values that may appear in a particular metadata field.
For instance, here is the NSDL’s qualification for the Audience field (from the Metadata Guidelines).
- Administrator
- Educator
- General Public
- Learner
- Parent/Guardian
- Professional/Practitioner
- Researcher
The fact that a field uses this vocabulary would appear in the XML as:
<dct:audience xsi:type=” nsdl_dc:NSDLAudience”>Learner</dct:audience>
Notice that the only difference is the xsi:type designation (although additional changes would appear in the header of the file).
By having a prearranged agreement on what different metadata fields hold in terms of controlled vocabulary, you can get more meaningful data exchange between libraries. And if you can agree on what fields and vocabularies should be used in assignment, then you can get very meaningful data exchange.
But even if you don’t agree on a particular controlled vocabulary, by designating which vocabularies you are using with qualified metadata fields, you enable partners to create valid crosswalks to their own vocabularies.
Next time, I will talk about crosswalks again, but this time between metadata formats.