Meeting minutes
DICOM
eric: Anytime you have a null, in programming you have to do a dance to get around it, because if Sally and Bob both have null in the birthdate predicate, you have to use a null guard in your code, to exclude the case when the value is a fhir:null sentinal.
… .But if you use a bnode, SPARQL won't treat them as the same. So that's a benefit of using a bnode for SPARQL in that case.
jim: bnode seems like a good thing, but I don't think you can have a union of a an object type and a datatype.
… We couldn't use a bnode for the null if it's a datatype property.
eric: Because in DL datatype and object properties are disjoint.
… We tend to use lists when we want to round trip, and want to use sentinal types, so the transfer representation becomes something we can't reason over.
… Because we have RDF lists, we're already outside of what works well in OWL.
jim: Could always use a bnode standoff: [ rdf:value 45 ], [ rdf:value fhir:null ].
eric: Maybe we need a transform for OWL, one optimized for query and one for inference.
eric: Already optimized more for SPARQL.
dbooth: Already going down that path.
dbooth: What do you think would be easiest to process, Erich?
erich: Interesting:
https://
(Discussion about CDT)
eric: If we had a dataset with 2 graphs g1 and g2, and they shared a bnode, _:b1 , they could be written out, g1 as RDFXML and g2 as Turtle. When you parse them again, you'd tell the parser to unify the _:b1 to reconstruct the orignal dataset.
eric: There isn't a way to indicate which bnodes should be treated as the same (in the same dataset) and which shold be renamed.
erich: CDT could be used to represent all the DICOM list data. Or do it only when literal lists -- a hybrid approach.
… If this is adopted, does it replace RDF lists?
eric: If it is, it would take years for it to have traction.
erich: Anything done now cannot do CDT, because it's just a proposal. So we still need a null solution.
… Rather work w what we have today. CDT is potential future direction.
… But need something that's supported now, as a standard.
… DICOM literal lists (whcih may have nulls) are the only problem area.
dbooth: This is reminding me that the ladder of RDF lists is really the wrong way to do lists. Numeric indexes is the right way to do them.
… And they should be called arrays, not lists.
… .It's longstanding big hole in RDF.
erich: I have a DCM to RDF converter that I've used for a while. But never handled nulls.
… Plan to release it as open source, but will leave a placeholder for the null issue.
eric: We care about an RDF rather than having a bnode hidden inside a literal.
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