On 10/14/13 10:03 AM, Frans Knibbe | Geodan wrote:
On 9-10-2013 14:07, Hugh Glaser wrote:On 9 Oct 2013, at 12:46, Barry Norton<[email protected]> wrote:On Wed, Oct 9, 2013 at 12:15 PM, Hugh Glaser<[email protected]> 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.
Yes of course.Maybe its just better to think of "data" instead of "dataset" i.e., you have data accessible via a variety of data access services.
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?
datasets and endpoints are disjoint.
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) :-)
It can have a description of the services it provides. It can also be associated with data describing the data for which it provides data access services.
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 mirrorsYes, 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?
This is basically the task at hand i.e., add some descriptions oriented towards the data access services esp., as Linked Data is all about Data Connectivity as opposed to Database Connectivity.
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.
As indicated above, we need cater to the needs of data access services (what the endpoint offers) and actual data (the collection of statements partitioned using named graph IRIs).
Links:1. http://bit.ly/1biJTBZ -- Illustrating Data Access Pathways (note: ODBC, JDBC, ADO.NET etc. have long established metadata patterns for data access services) .
Regards, Frans
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