I have a proposal to add the usage attribute (currently only defined for the MODS location/url element) to more MODS elements:
I also suggest adding another defined value for the usage attribute (currently there is only one, "Primary display")
In many applications that would use MODS records, where there are multiples of a type of element, only one can display. An example is search "results lists" which may display an assortment of different data elements depending on the system, but generally have only one or two lines of data. If there is not another attribute or aspect of the element to select on, the application "picks one", usually the first such element to appear in a record. With the complex processing that may occur with metadata, the order of appearance in a record cannot always be controlled or may be troublesome to change. There are more areas than the location/url where discovery service providers want to have control over which element is selected for display in limited contexts.
An example, that prompted my interest in this addition, was typeOfResource in our MODS records for articles in the online journal Southern Spaces. Our metadata is for the article as a whole, which may be comprised of combinations of text, video, audio, maps, images, etc. We are mapping to Dublin Core to feed these records to our Primo discovery system, but hope soon to be able to ingest MODS directly. Primo only has one ResourceType for each item, so we need a way of designating which typeOfResource is primary for a particular article. We think adjusting the order of typeOfResource elements in the MODS record would fix the problem in Primo (we have some technical issues and aren't able to test that at the moment). But it would be simpler to be able to designate what we want in the MODS so that our particular transform for Primo would only capture one typeOfResource.
In other contexts, say an individual record display, a particular application may display only the first few of a particular element, with a "see more" or plus sign link to allow the user to see the rest. Being able to designate what elements would appear within such limits could also be helpful, hence the suggestion of a "Secondary display" value.
It occurs to me that designation of "primary" could also be useful to some applications that do ranking of results based on things like presence of keywords in subject headings. In such a case, the ability to go beyond "pick one" to also designating a secondary "higher level of preference" could be useful there.
Another way of approaching this would be to change the attribute so that it has a numeric value, e.g. usageRank="1" usageRank="2" etc. This would allow an even finder level of control, but would not be compatible with MODS version 3, whereas adding the attribute would not make invalid any version 3 records.
Finally, the selection of elements to add this attribute to is just my own sense of where it might be needed: others might see usefulness under other elements.
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