Datalink vocabulary

[Patrick Dowler]

Thanks Norman. I am tweaking the section to explain it this way (as a 
relative URI rather than a "shortcut") and keeping the #.



General question about this field: how should a client interpret a null 
value for the semantics field? Normally this means "unknown" but in this 
particular case it could be taken to mean "self" in the sense that 
Markus has argued for said term to be part of the vocabulary. The null 
would basically mean there is no relationship with the dataset" because 
this is (part of) the dataset. Kind of like not-applicable...

In thinking about a client that wants to "download a dataset" and it 
gets a links table. In my view, the client would have no choice but to 
download all from all the access_url(s) that have null semantics. If 
there is a value like "self" then the client would download those 
(instead) but I expect that in practice clients would still download all 
the links with null semantics (I don't know what this is, so I'll get it 
anyway).

Having null == self would essentially mean that there is no "unknown" 
relationship between a link and a dataset: links are either "the 
dataset" or "related to the dataset".

Anyway, right now the semantics value is allowed to be null and I need 
to say what that means or not allow null. I cannot see a good reason to 
require semantics it and the sensible fall back is for null == self.

Comments?

Pat


On 23/09/14 05:35 AM, Norman Gray wrote:
>
> Pat and all, hello.
>
> On 2014 Sep 23, at 11:01, Norman Gray <norman at astro.gla.ac.uk> wrote:
>
>> I suggest that the 'semantics' term (of 3.2.6) should be defined as follows:
>>
>>   * The 'semantics' term is interpreted as a URI.
>>   * If the term is a relative URI, then it is resolved against the base URI <http://www.ivoa.net/rdf/datalink/core#> using the standard algorithm of RFC3986 Sect. 5.2.
>
> Two afterthoughts:
>
> 1. This is the sort of thing where it would be very useful for the spec to include some test cases (Markus's "DALI examples" syntax might show how the Datalink standard text could be marked up to make the examples in there mechanically extractable).
>
> 2. It is 'good practice', though not technically required, to have such predicates be retrievable on the web, producing some sort of documentation of the meaning of the 'semantics term'.  This is^W will be the case for <http://www.ivoa.net/rdf/datalink/core#foo>.  This might usefully be added as a Datalink requirement: any non-standard URI term included here must be retrievable to give an explanation.
>
> All the best,
>
> Norman
>
>

-- 

Patrick Dowler
Canadian Astronomy Data Centre
National Research Council Canada
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