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Re: Subsetting data

From: Phil Archer <phila@w3.org>
Date: Fri, 1 Jan 2016 09:30:29 +0000
To: Peter Baumann <p.baumann@jacobs-university.de>, Rob Atkinson <rob@metalinkage.com.au>, Simon.Cox@csiro.au, koubarak@di.uoa.gr, public-sdw-comments@w3.org, amgreiner@lbl.gov, ericphb@gmail.com, jeremy.tandy@metoffice.gov.uk, public-dwbp-comments@w3.org
Message-ID: <56864735.5060504@w3.org>

On 31/12/2015 10:14, Peter Baumann wrote:
> hm, a thought: is it mandatory that a "subset extraction" has an ID?

Not mandatory, but useful in some circumstances.

> will always be applied to some identifiable set, so it could be considered as a
> "modifier" of the set without own identity.

Yes. I see that as a query that works today, which is different from an 
ID for a subset I want to be able to rely on indefinitely.

> Putting semantics into a process might make it difficult to reason about it. A
> query (not in the URL syntax sense, but in the general sense of a declarative
> way to express "gimme that") allows reasoning and server-side optimization.

Yes, but those semantics and optimisation wouldn't be in the URI.

> IMHO you have raised a (the?) key question below:
>> Can you define an ontology for terms like subset, query, response that you all
> agree on?
> - what is the set to be subset?
> - what is a subset?
> - what constraints have to hold on a subset?
> - ...and after that: what are the meaningful operations that fulfil these
> constraints?

For me those questions are interesting and, *if* the DWBP and/or SDW WGs 
want to work on a document talking about this then that kind of 
semantics discussion may well be relevant. But both WGs are working at 
full capacity so we probably need to keep our ambitions modest.


> cheers,
> Peter
> On 2015-12-31 03:07, Rob Atkinson 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 <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 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; 'public-sdw-comments@w3.org
>>      <mailto:public-sdw-comments@w3.org>'; Annette Greiner; Eric Stephan;
>>      Tandy, Jeremy; 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
>>      --
>>      Phil Archer
>>      W3C Data Activity Lead
>>      http://www.w3.org/2013/data/
>>      http://philarcher.org
>>      +44 (0)7887 767755
>>      @philarcher1


Phil Archer
W3C Data Activity Lead

+44 (0)7887 767755
Received on Friday, 1 January 2016 09:29:53 UTC

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