Re: A draft outline for the CSV2RDF document

On 20 May 2014, at 12:16 , Andy Seaborne <andy@apache.org> wrote:

> On 20/05/14 05:52, Ivan Herman wrote:
>> But also... If my application needs (forgive me:-) RDF/XML, but the
>> author of the metadata has put in the row-level template using
>> JSON-LD as a base syntax, then I need a JSON-LD parser to make any
>> sense of it, right? In other words, the field-level template approach
>> is RDF syntax independent. That seems to be another major difference,
>> too...
>> 
> 
> We're defining the correct output of a conversion process when the input is the metadata (without any user templates).  We aren't
> requiring the processor does exactly and only those steps.  It outputs whatever format(s) it supports.
> 
> Adding user templates is 'advanced' and if we want to allow control of
> the shape of the RDF emitted (c.f. Jeremy's example) we do need to have
> a language for describing shape. However, that's not the required mechanism for implementation of metadata\templates to RDF.
> 

I am still trying to turn my head around it; sorry if I am slow... Is this so that (at least conceptually for the user):

- The 'field level templates', essentially as I described and used in [1] can be used essentially as described there (what templates exactly do is something that we still have to define, but I guess we have an idea about a simple mechanism, like the one in R2RML)
- There is, _additionally_, the possibility to define a 'shape', ie, a row level template; if present, that replaces the mechanism described in [1]

(Specification-wise, one can of course turn things upside down, describe the 'shape' template mechanism and, if, for a specific data, no shape is defined, one could virtually generate such a shape from the metadata. But that is for specification writers and, possibly, for implementers.)

I think that this, technically, works indeed. But I am not sold on it...

- I have the impression that the generic shape mechanism is more complicated to understand for a user and more complex to implement
- Although I forgot to add this to [1] (and we were not sure whether that should go into the metadata spec in the first place) we did say that we can assign, say, an XSLT script for XML, or a SPARQL CONSTRUCT pattern for RDF that would be executed on the result of the RDF generation; such an extra step could take care of Jeremy's example, right? It is, of course, a bit more complex to do this than with shapes, but how frequently do I have to do this?
- I still do not see how you can get around the fact that the shape is very language specific, ie, I am not sure how you would define metadata that RDF serialization syntax independent and, even more, independent on whether the target is RDF, JSON, or XML (which works much more easily with the scheme in [1])

Cheers

Ivan

[1] http://htmlpreview.github.io/?https://github.com/w3c/csvw/blob/rdfconversion-ivan/csv2rdf/index.html


> 	Andy
> 
>> Ivan


----
Ivan Herman, W3C 
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