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Re: [QB] ISSUE-31 (Aggregation hierarchies) Discussion and proposal

From: Sarven Capadisli <sarven.capadisli@deri.org>
Date: Fri, 01 Mar 2013 10:18:45 +0100
Message-ID: <51307275.50404@deri.org>
To: public-gld-wg@w3.org
Hi Dave, thanks for putting this together.

On 02/28/2013 12:30 PM, Dave Reynolds wrote:
> ISSUE 31 [1] concerns support for hierarchies other than SKOS. I know
> this one is controversial ...
>
> In Data Cube as it stands then a cube component (qb:ComponentProperty,
> especially a dimension) can be coded using codes from a
> skos:ConceptScheme. This roughly corresponds to the SDMX notion of a
> Concept Scheme [2] where codes are arranged in a parent/child hierarchy.
> The normal skos:narrower/skos:broader relationships are used to express
> such parent/child relationships.
>
> Often in statistical publishing values will be given for different
> levels in such a concept scheme - e.g. the population statistics for the
> UK as a whole as well as those for each region. Though the value for the
> parent may not simply be the sum of those for its children.
>
> Especially when dealing with geographic hierarchies some limitations of
> the current approach that have come up in practice, e.g. see [3].
>
> There are 3 problems here and a non-problem.
>
> The non-problem is that it is perfectly reasonable to create a
> skos:Concept to represent an geographic region and to use
> skos:narrower[4] to represent a relevant containment hierarchy. That's
> not why ISSUE-31 is on the list.
>
> The problems are:
>
> (a) Publishers would like to reuse existing geographic hierarchies
> already published as linked data (e.g. [5]) but where that data uses
> different predicates to represent the hierarchy than skos:narrower.
>
> (b) The same geographic regions can participate in multiple hierarchies.
> As well as spatial containment there is also administrative containment.
> We can only use skos:narrower for one of these.
>
> (c) In cases like [3] people also wish to state when the child concepts
> are disjoint so that aggregation might be possible (so long as the
> measures themselves can be aggregated), or more strongly that the parent
> concepts are a disjoint union of the child concepts.
>
> It is possible to work around (a) by publishing your own skos:narrower
> assertions about the existing published linked data. However, that is
> problematic to keep up to date, may conflict with someone who wants to
> use skos:narrower in a different sense over the same concepts (see b)
> and can be socially/politically problematic.
>
> Problems like (b) are handled in SDMX through the use of hierarchical
> code schemes [6] which can be used to create multiple different
> generalized hierarchies over the same code list.
>
> PROPOSAL.  Proposed approach is a vocabulary extension:

I for one would welcome these type of extensions because they are much 
clear than re-purposing or fitting the requirements into existing 
relations out there.

I will first mention how I tried to deal with SDMX-ML to RDF/XML mapping 
by using SKOS and XKOS. To simplify:

#An SDMX structure:HierarchicalCodelist
:foo
   a skos:Collection ;
   skos:member :bar ;

#An SDMX structure:Hierarchy
:bar a skos:Collection, xkos:ClassificationLevel ;
   skos:member :baz .

#Hierarchy for the SDMX structure:Codes
:baz
   a skos:Concept ;
   xkos:hasPart :bbq .

:bbq
   a skos:Concept ;
   xkos:isPartOf :baz .

I'm not completely sure if that's accurate but it seems close enough. 
But, it took me awhile to get my mind wrapped around it, in order to 
reuse what's out there. It is probably insufficient and would probably 
create undesirable relations - to be reviewed. So, again, I welcome the 
proposal.

Some comments on the following.

> qb:hierarchy (domain: qb:CodedProperty, range: qb:Hierarchy)
>     Indicates a specification of the hierarchy used for coding this
> property (typically a DimensionProperty). Where a skos:ConceptScheme
> exists with appropriate broader/narrower relations then that should be
> used and should be specified using qb:codeList. The qb:hierarchy
> declaration is only need for situations where a suitable
> skos:ConceptScheme is not available.

I don't think I fully understand this. Is this supposed to handle 
situations in absence of @codelist in <structure:Dimension>?

Aside: my first impression of qb:hierarchy was for 
domain:HierarchicalCodelist, range:Hierarchy

> qb:Hierarchy (owl:Class)
>     Specifies a hierarchy which can be used for coding. The same
> concepts may be members of multiple hierarchies provided that different
> qb:[narrowing/broadening]Property values are using for each hierarchy.

Clear.

> qb:AggregatableHierarchy (sub class of: qb:Hierarchy)
>      Indicates a hierarchy in which each parent concept is a disjoint
> union of its child concepts. So that measures such as simple counts
> *may* be aggregated up the hierarchy.

Would you mind elaborating on this or point at what it corresponds to in 
SDMX Structure 2.0/1?

> qb:hierarchyRoot (domain: qb:Hierarchy, range: skos:Concept)
>     Specifies a root of the hierarchy. A hierarchy may have multiple
> roots but must have at least one.[7]
>
> qb:narrowingProperty (domain: qb:Hierarchy, range: rdf:Property)
>     Specifies a property which relates a parent concept in the hierarchy
> to a child concept. One of qb:narrowingProperty or qb:broadeningProperty
> must be given but it is not necessary to have both. Note that a child
> may have more than one parent.
>
> qb:broadeningProperty (domain: qb:Hierarchy, range: rdf:Property)
>     Specifies a property which relates a child concept in the hierarchy
> to a parent concept. One of qb:narrowingProperty or
> qb:broadeningProperty must be given but it is not necessary to have
> both. Note that a child may have more than one parent.

Clear.

> Dave
>
> [1] http://www.w3.org/2011/gld/track/issues/31
>
> [2] http://sdmx.org/docs/2_0/SDMX_2_0%20SECTION_02_InformationModel.pdf
> p.39
>
> [3]
> https://groups.google.com/forum/#!topic/publishing-statistical-data/3I1-Ix1Hk14/discussion
>
>
> [4] I'm using skos:narrower as a shorthand for
> skos:narrower/skos:broader, no slight intended to skos:broader
>
> [5] http://data.ordnancesurvey.co.uk/.html
>
> [6] http://sdmx.org/docs/2_0/SDMX_2_0%20SECTION_02_InformationModel.pdf
> p.96
>
> [7] This is to match SDMX 2.0 [6] which also supports multiple roots.
>


Really cool. Looking forward to this.

-Sarven
Received on Friday, 1 March 2013 09:19:17 UTC

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