Why create “a separate property for every combination of tag, two indicators, and subfield”, as I mentioned in Low-hanging MARC fruit?
As Karen says in her comment on Getting to higher MARC branches, in the case of the Target audience data element there is no need for the RDF properties defined for each MARC21 “resource type” when the Target audience value vocabulary can be linked directly to the property defined at the higher level of the MARC21 resource.
The data element is one of several in the MARC 21 format for bibliographic data that are “defined the same in the specifications for more than one type of material” and share the same value vocabulary; this requires inspection of the vocabulary for each type, as there seems to be no explicit indication in the text. We have used the prefix “common” in the vocabulary URIs to reflect this, as in the value URI of the object of the ex:1 data triple (“commonaud#j”). Examples include commonaud (MARC21-008: Target audience) itself, as well as commonfor (MARC21-008: Form of item) and commonnat (MARC21-008: Nature of contents).
Despite this, I think it is worth including the 006 equivalents of the Target audience element in the RDF graph, as they represent “special aspects of the item being cataloged that cannot be coded in field 008”. This ensures that any semantic relationship between the 006 and 008 fixed-length data elements is preserved in the data. The semantic relationship between “type” and “form” of material in the 006/008 relationship table is not specified, so I assume that it will be incorporated, along with usage guidelines, etc., in one or more application profiles. Application profiles can also ensure that values from the common Vocabulary Encoding Scheme are preserved in data triples entailed during dumb-up to the level of the resource as a whole.
This illustrates one of the intended benefits of the level 0 properties:
- Maximum flexibility for inclusion in application profiles and mappings to external namespaces, of which m21plus is just an example.
Other benefits include:
- Support of very simple algorithms for the production of data triples from existing MARC21 records. There is only a single decision point, based on the data in Leader 06 of the record.
- Support for round-tripping data triples back to MARC21 encoded records.
Disadvantages of the level 0 properties include:
- The need to create super-properties to support data triples at the level of the whole resource and for aggregated statements.
- The need to add mappings between level 0 and super-properties.
We have developed a full set of m21plus super-properties for the fixed-length data fields, with rdfs:subPropertyOf mappings from the level 0 properties, and hope to load them into the OMR real soon now for use by applications.
We also expect to find more benefits and disadvantages in using the level 0 properties as we continue to investigate the MARC21 variable data fields.