[NLP2RDF] NIF ontology modifications for dependency relations and ambigious OLiA properties

[Martin Brümmer]

Hi there,

while converting the TIGER corpus and its dependency trees to NIF, I 
bumped against some limitations of the NIF ontology:

At the moment, the only dedicated property for dependency structures is 
"nif:dependency", pointing from the head to the dependant. However, I 
think an inverse property to that would also be nice to have. So I 
propose "nif:phraseHead", pointing in the other direction.

A completely missing property is "nif:dependencyRelationType", 
annotating the type of the dependency relation as a literal, just like 
"nif:posTag" does for POS tags.

It would also be nice to have some property that annotates the root node 
of a sentence that could be used to traverse the dependency tree of the 
sentence just like "nif:firstWord" and "nif:nextWord" enable traversing 
surface structure of the sentence.

I think these additions to the ontology are not controversial and rather 
useful. Do you agree?


On a different node, the OLiA tags may need some changes:

At the moment, there is nif:oliaLink and nif:oliaCategory used to link 
annotated words to respective OLiA resources. However, these resources 
can either be mophological or syntactic annotations. The properties 
themselves don't make it sufficiently clear if the oliaLink is used to 
link to a POS tag category or a syntactic category, like "NounPhrase". I 
think this is semantically ambigious. If OLiA is used for different 
classes of annotation, the properties should reflect this. So the tags 
should rather be "nif:oliaPosLink" and "nif:oliaSyntaxLink" or something 
like that.

Another point in question is that NIF is rather dependent on OLiA 
categories. Now some tagsets used to annotate corpora are not mapped by 
OLiA. Users might also not agree with the OLiA categories themselves and 
might like to define own categories. There is no way to support such 
additions. Of course we could speak to Christian Chiarcos about 
additions to OLiA, but I don't know how open he will be to collaborative 
additions and changes to his model. My vague proposal (just an idea at 
this point) would be:

A new ontology, "nif-annotation" and some additions to the core ontology 
that define classes that are superclasses of OLiA categories and 
properties that are superproperties of nif:oliaLink and nif:oliaCategory 
(like "nif:posLink/posCategory" and "nif:syntaxLink/syntaxCategory") 
essentially setting an ontology on top of the existing OLiA model, 
allowing users to define fitting categories for tags not included in 
OLiA without breaking existing NIF applications.

So what do you think?

regards,
Martin