After a diversion relating to library systems expectations, I would like to get back to the question of how to handle types, in re titles.
There are significant differences between the functionality of properties (and sub-properties) vs. that of classes (sub-classes). Right now, bf:workTitle is a property with a domain of bf:Work. Therefore, any resource described with a bf:workTitle property can be inferred to be a bf:Work. bf:instanceTitle is a property with domain of bf:Instance, so ditto.
Therefore, in these examples:
1. <http://id.loc.gov/resources/bibs/15798171> ;
bf:workTitle[ a bf:Title ;
bf:titleValue"Heart of Midlothian" ] .
2. <http://id.loc.gov/resources/bibs/15798171> ;
bf:instanceTitle[ a bf:Title ;
bf:titleValue"The heart of Midlothian" ] .
... you can infer the class of your bib resource from the bf:xTitle property used. If all titles become subclasses of bf:Title, then I believe you lose this ability to infer bf:Work and bf:Instance from these properties. *IF* the work and instance titles are good indications of the nature of the resource being described, it would be a shame to lose this ability. There are other properties with bf:Work and bf:Instance as domains, such as bf:creator and bf:publicationDate, but my non-cataloger gut feeling is that these two title properties are key *deciders* of the nature of the entity being described.
There are other title properties that may be less significant for this inference function: keyTitle; originPlace; originDate. Not to mention that may of the title properties refer to parts of a title (which I find a bit confusing in terms of how they would be bound "correctly" in an RDF graph, but a few examples might clear that up).
All that to say that I see some problems with re-casting all types as sub-classes, at least for some key properties where I see some useful inferencing possibilities. However, I do not see anything in the BIBFRAME documentation about intended inferencing, so do not know if my inferencing assumptions are shared.
On 10/27/14 12:17 PM, Robert Sanderson wrote:
Hi Ray, all,
Regarding the Titles and Types issues, I think there's another option as well, Type as Class. Or, if I may, Type as Type :)
_:x a bf:Work ;
bf:title _:y .
_:y a bf:KeyTitle ;
rdf:value "..." .
I believe this is desirable for the following reasons:
* Type as String Value just isn't good linked data. The type should be uniquely distinguishable, and clearly duplicate strings could be used by multiple communities independently. This includes all the *Scheme predicates.
* Type as URI Value is better, but seems pointless when the URI could be more efficiently used as a class. All of the bf:*Type predicates and bf:*Scheme predicates can just be rdf:type instead.
* It makes it easier to express domain and range.
* It's more readable in the RDF/XML serialization and makes any object mapping significantly easier.
* It reduces the number of properties, thereby making it easier to see what's going on in the model. The subclasses are there below the main class for when they're needed rather than cluttering up the top level.
* It's easy to create new types without needing to worry about domain and range of properties, just by subClassing the main class. Otherwise, if you want to have additional predicates associated with your new instance, the domain has to be the main class rather than a subClass, which is very poor modeling.
* It simplifies many other the predicates as the main class isn't necessary in the predicate name, that's just the class of the object that the predicate is being used with. If the predicate should have its value constrained then it shouldn't have Literal as its range. For example no need for identifierValue, instead it can be just value.
* It prevents the possible inconsistency of using a predicate that implies one type on its object, but the object has a different one (eg Work issn x ; x scheme "doi").
So I think Example 2 is the closest, but a proposed Example 5:
a bf:IssnIdentifier ;
rdf:value "12345678" .
Where bf:IssnIdentifier is rdfs:subClassOf bf:Identifier, which is the range of bf:identifier.
The same pattern holds for all of the classes/predicates under consideration.
a bf:KeyTitle ;
rdf:value "Lord of the Rings" .
a bf:AdminHistNote ;
rdf:value "Administrative history note" .
a bf:DdcClassification ;
rdf:value "234.5" .
a bf:MediaCategory ;
rdf:value "something" .
a bf:DdcShelfmark ;
rdf:value "12345678" .
Relators aren't needed as objects, and relationships between Works and Instances are just relationships and thus don't need fixing.
Roles are not types, and thus Provider doesn't fit any of the patterns proposed. Roles are closer to relationships, and thus providerRole should be dropped. If the role is printing, then Work printer Provider, just like Work creator Person. If the role is associated with the Provider object, then it ties it exclusively to that Work so it could never be reused.
And thus to answer the three questions:
1. Please don't do this at all :) The model should not allow multiple, incompatible ways to say the same thing at the same time.
2. Punning properties that can be either literal or a URI break tools and make many things, such as JSON-LD, much harder. Please don't do that either.
3. Good documentation, with contributions from the community accepted in a timely fashion, plus encouragement in the specification to be an active participant in the work.
Hope that helps,
Technology Collaboration Facilitator
Digital Library Systems and Services
Stanford, CA 94305
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