RE: Subsetting data

+1

Simon J D Cox

Research Scientist

Environmental Information Infrastructures

Land and Water

CSIRO



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________________________________
From: Annette Greiner
Sent: Tuesday, 5 January 2016 10:40:13 PM
To: Peter Baumann; Rob Atkinson; janowicz@ucsb.edu; Dan Brickley; Clemens Portele
Cc: Phil Archer; Cox, Simon (L&W, Clayton); ericphb@gmail.com; jeremy.tandy@metoffice.gov.uk; koubarak@di.uoa.gr; public-dwbp-comments@w3.org; public-sdw-comments@w3.org
Subject: Re: Subsetting data

I would stop at saying URIs for subsets are a Good Thing, and maybe mention in the implementation section that they will naturally be assigned URIs if you use a REST-based architecture. What those URIs look like will depend on the implementation. (There's a difference between nobody knowing how to use them and the fact that different contexts call for different implementations, which I think is the case here.)
-Annette

On 1/5/16 1:43 PM, Peter Baumann wrote:
+1
-Peter

On 2016-01-05 22:18, Rob Atkinson wrote:

given stable URIs for subsets (which I don think there is any disagreement about) AFACIT there are two unresolved issues - both concerned with the scope of the BP:
1) What is the BP for describing how subsets relate to each other and the master data set (avoiding implementation details)
2) what is the relationship between identifiable subsets, query endpoints and the subsets returned - do they all have identifiers, and what is the BP for a common vocabulary to relate these different aspects

Maybe a valid result is to say that there really isnt a BP in term of these requirements - and stop at saying URI idenfiers for subsets is a Good Thing  Nobody Knows How To Use and throw out a challenge

Rob


On Wed, 6 Jan 2016 at 05:13 Krzysztof Janowicz <janowicz@ucsb.edu<mailto:janowicz@ucsb.edu>> wrote:
Hi Dan,


Isn't a "subset" just a query result, or which there are effectively an unlimited number?

I would say so.


Storing a query so it can be re-run against evolving data has value. Having a URI for that, perhaps less so.

There are many cases, particularly if dealing with streams of data, e.g., form sensors, where having URIs for subsets is very useful, and, in fact, there are many ways to do so. Some years ago we implemented one such solution at 52North where we developed a transparent (i.e., invisible) proxy on top of an endpoint that translates a URI minted in a specific way to return specific query results.  For instance, the URI <http://my.authority.org/observations/samplingtimes/ont:time:relation:between,2008-01-10T14:00,2008-01-12T16:00/sensors/thermometer1/observedproperties/temperature> http://my.authority.org/observations/samplingtimes/ont:time:relation:between,2008-01-10T14:00,2008-01-12T16:00/sensors/thermometer1/observedproperties/temperature points to the observation collection with all temperature observations from January 10th 2008 at 2pm until January 12th at 4pm made by thermometer1. Having such URIs (and proxies) is one way of mitigating the problem that the content  referenced by URIs should be as stable as possible which is (often) not the case for sensor data. In our case we worked on transparently mapping between SPARQL and OGC's Sensor Observation Services but the idea can (and has been) used in many other settings.

Happy new year.
Krzysztof


On 12/31/2015 03:09 AM, Dan Brickley wrote:

Isn't a "subset" just a query result, or which there are effectively an unlimited number?

Storing a query so it can be re-run against evolving data has value. Having a URI for that, perhaps less so.

Dan

On Thu, 31 Dec 2015, 08:14 Clemens Portele <portele@interactive-instruments.de<mailto:portele@interactive-instruments.de>> wrote:
Rob,

what you describe seems to apply to the dataset (resource) the same way it would apply to any subset resource. I.e. are you discussing a more general question, not the subsetting question?

Phil,

a (probably often unproblematic) restriction to the temperature/uk/london or stations/manchester approach is that there is only one path, so you end up with limitations on the subsets. If you want to support multiple subsets, e.g. also stations where high speed trains stop, stations that have a ticket shop, etc. then there are several issues with a /{dataset}/{subset}/…/{subset}/{object} approach. These include an unclear URI scheme ("manchester" and "eurostar" would be on the same path level), potential name collisions of subset names of different subsetting categories, and multiple URIs for the same feature/object.

Best regards,
Clemens


On 31 Dec 2015, at 03:07, Rob Atkinson <rob@metalinkage.com.au<mailto:rob@metalinkage.com.au>> wrote:

I'm not a strong set-theoretician - but it strikes me there are some tensions here:

Does the identifier of a set mean that the members of that set are constant, known in advance and always retrievable?   Is a query endpoint a resource (does either URI or URL have meaning against a query that delivers real time data - including the use case of "at this point in time we think these things are members of this set?" )

If the subset is the result of a query - and you care that it is the same subset another time you look at it - are you actually assigning an identifier to the artefact - which is the query response, whose properties include the original query, where it was made, and the time it was made?

Can you define an ontology for terms like subset, query, response that you all agree on?

I share Phil's implicit concern that subsetting by type with URI patterns may not be universally applicable - IMHO that equates to a "sub-register" pattern, where a set has its members defined by some identifiable process (indepent of any query functions available) - which may include explicit subsets - for example by object type, or delegated registration processes. That probably fits the UK implementation better than a query-defined subset.

If subsets have some prior meaning - and a query is used to access then from a service endpint - then the query is a URL that needs to be bound to the object URI. AFAICT thats a very different thing to saying an arbitrary query result defines a subset of data.

I think you may, in general, assign an ID to the artefact which is the result of a query at a given time, and if you want to make that into something with more semantics then you need make it into a new type of object which can be described in terms of what it means. I think currently the conversation is conflating these two perspectives of "subset".

Cheers, and farewell to 2015.
Rob Atkinson.




On Thu, 31 Dec 2015 at 08:26 <<mailto:Simon.Cox@csiro.au>Simon.Cox@csiro.au<mailto:Simon.Cox@csiro.au>> wrote:
Another way of looking at it is that a query, encoded as a URI pattern, defines an implicit set of potential URIs, each of which denotes a subset.

Simon J D Cox
Environmental Informatics
CSIRO Land and Water

E simon.cox@csiro.au<mailto:simon.cox@csiro.au> T +61 3 9545 2365 M +61 403 302 672
Physical: Central Reception, Bayview Avenue, Clayton, Vic 3168
Deliveries: Gate 3, Normanby Road, Clayton, Vic 3168
Postal: Private Bag 10, Clayton South, Vic 3169
http://people.csiro.au/Simon-Cox
http://orcid.org/0000-0002-3884-3420
http://researchgate.net/profile/Simon_Cox3

________________________________
From: Phil Archer
Sent: Wednesday, 30 December 2015 6:31:16 PM
To: Manolis Koubarakis; '<mailto:public-sdw-comments@w3.org>public-sdw-comments@w3.org<mailto:public-sdw-comments@w3.org>'; Annette Greiner; Eric Stephan; Tandy, Jeremy; <mailto:public-dwbp-comments@w3.org> public-dwbp-comments@w3.org<mailto:public-dwbp-comments@w3.org>
Subject: Subsetting data

At various times in recent months I have promised to look into the topic
of persistent identifiers for subsets of data. This came up at the SDW
F2F in Sapporo but has also been raised by Annette in DWBP. In between
festive activities I've been giving this some thought and have tried to
begin to commit some ideas to a page [1].

During the CEO-LD meeting, Jeremy pointed to OpenSearch as a possible
way forward, including its geo-temporal extensions defined by the OGC.
There is also the Linked Data API as a means of doing this, and what
they both have in common is that they offer an intermediate layer that
turns a URL into a query.

How do you define a persistent identifier for a subset of a dataset? IMO
you mint a URI and say "this identifies a subset of a dataset" - and
then provide a means of programmatically going from the URI to a query
that returns the subset. As long as you can replace the intermediate
layer with another one that also returns the same subset, we're done.

The UK Government Linked Data examples tend to be along the lines of:

http://transport.data.gov.uk/id/stations
returns a list of all stations in Britain.

http://transport.data.gov.uk/id/stations/Manchester
returns a list of stations in Manchester

http://transport.data.gov.uk/id/stations/Manchester/Piccadilly
identifies Manchester Piccadilly station.

All of that data of course comes from a single dataset.

Does this work in the real worlds of meteorology and UBL/PNNL?

Phil.




[1] <https://github.com/w3c/sdw/blob/gh-pages/subsetting/index.md> https://github.com/w3c/sdw/blob/gh-pages/subsetting/index.md




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