Re: How to publish SPARQL endpoint limits/metadata?

On 9-10-2013 14:07, Hugh Glaser wrote:
> On 9 Oct 2013, at 12:46, Barry Norton <barrynorton@gmail.com>
>   wrote:
>
>> On Wed, Oct 9, 2013 at 12:15 PM, Hugh Glaser <hg@ecs.soton.ac.uk> wrote:
>> [...]
>>
>> So having a separation between SPARQL Service Description and voiD would just be plain wrong.
>> They must embrace each other, so that consumers can easily work out how to use what they think of as a "dataset".
>>
>> I would also add that if I take a REST-like view of the world, which I do for accessing a SPARQL endpoint (I am simply retrieving a document), the distinction between dataset and service becomes very blurred.
>> Even calling it a "SPARQL Service Description" seems rather old-fashioned to me.
>>
>> Hugh, I tend to agree (certainly about calling them 'service descriptions', ugh). From a REST point of view, void:Datasets, named graphs (capable of RESTful interaction via Graph Store Protocol) and SPARQL query/update 'endpoints' (ugh again) are all resources that allow one to find other, more specific, resources.
>>
>> That said if we accept that one needs some up-front guidance on what those resources allow you to get to (a big 'if', if the REST community, but I don't think anyone in ours would be happy with just a media type) then we want them to be self-describing in RDF.
> Always & everything!
>> At the same time, the relationships we want to attach to the query/update endpoints are semi-distinct, no? You'd agree these are different classes of resource?
> Yes, or perhaps I am saying different sub-classes?

That is an interesting perspective. It is probably because I come from 
the world of relational databases that I see a dataset as a collection 
of data and the endpoint as a means of getting those data. In my setup, 
I have made a single SPARQL endpoint that serves many datasets. I hope 
there is nothing wrong with that approach... I can also imagine a single 
dataset having multiple SPARQL endpoints. For example, a free public 
endpoint and an endpoint for paying users with a higher service level.

If datasets and endpoints would be different subclasses of the same 
parent class, what would be properties of the parent class that the two 
could share?

As an aside,  I now notice a mistake in the subject header of the thread 
if I maintain my view on the distinction between datasets and endpoints: 
If a SPARQL endpoint is not a data collection, it can not have metadata 
(data about data) :-)

> Thinking of it that way, I then look at Frans' list of the kind of thing he would like to be able to say about endpoints.
> It seems that at least the following might be common to almost any delivery mechanism for datasets:
>
> 	• The time period of the next scheduled downtime
> 	• (the URI of) a document that contains a human readable SLA or fair use policy for the service
> 	• URIs of mirrors

Yes, I thought about that too. These are properties that ideally should 
be communicated at a higher conceptual level. I briefly looked at HTTP 
headers but I could not find anything there. Perhaps there is a need to 
have a lightweight vocabulary for describing any data access API? Or 
would that be overcomplicating things? The Linked Data API vocabulary 
<http://linked-data-api.googlecode.com/svn/trunk/vocab/api.ttl#> does 
not seem entirely appropriate, because it seems to exclude SPARQL 
endpoints.

Regards,
Frans