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Re: Subsetting data

From: Peter Baumann <p.baumann@jacobs-university.de>
Date: Thu, 31 Dec 2015 11:14:15 +0100
To: Rob Atkinson <rob@metalinkage.com.au>, <Simon.Cox@csiro.au>, <phila@w3.org>, <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: <5684FFF7.2000707@jacobs-university.de>
hm, a thought: is it mandatory that a "subset extraction" has an ID? Subsetting
will always be applied to some identifiable set, so it could be considered as a
"modifier" of the set without own identity.

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.

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


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

Dr. Peter Baumann
 - Professor of Computer Science, Jacobs University Bremen
   mail: p.baumann@jacobs-university.de
   tel: +49-421-200-3178, fax: +49-421-200-493178
 - Executive Director, rasdaman GmbH Bremen (HRB 26793)
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Received on Thursday, 31 December 2015 10:14:58 UTC

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